Toole is unwaveringly scientific in his approach. Speculation or hard evidence is accordingly delineated. His methods for experiment or literature review rigorously account for bias and confounding effects. What he proclaims should never be taken lightly, my man!
I hear you. I am not, in any way, trying to refute, but rather trying to understand why my admittedly limited experience is different.

This is indeed the opposite of what Toole claims in his paper, with the exception of imaging, which he claims can change size and position. And when it does happen it is not necessarily bad. The width of the soundstage should actually widen with reflections. One reason I hazard to put forth for your observations is that very few loudspeakers will yield a spectrally similar reflection to its on-axis response. The NHT Xd or Linkwitz's Orion just may be one of a kind. Aczel's review of the Orion (which was way before the Toole paper) corroborates just about everything Toole claims in his paper.
My speakers are M&K S-150s which are THX Ultra2 certified with very controlled dispersion and off-axis response. Is it possible that by removing confusing early reflections, more of the nuance comes through allowing the listener to more complelely experience the soundfield created by the engineer/producer? My main listening position is in the nearfield; before I added the (six) first reflection point absorbers, it was not.

My speakers are M&K S-150s which are THX Ultra2 certified with very controlled dispersion and off-axis response. Is it possible that by removing confusing early reflections, more of the nuance comes through allowing the listener to more complelely experience the soundfield created by the engineer/producer? My main listening position is in the nearfield; before I added the (six) first reflection point absorbers, it was not.

In the vein of aiming for a reduced interaural cross correlation, Toole reports that reflections at 0 degrees and 180 degrees have found to be least beneficial ... both ears are exposed to the same change at the same instant in time. Also most loudspeakers have an uneven off-axis response in the vertical plane. And he says too many reflections can worsen things. So there is no question that broadband absorption (200-300 Hz and above) at the first reflection points on the ceiling, front wall and center portion of back wall can only be a good thing.

Tumara Baap

In the vein of aiming for a reduced interaural cross correlation, Toole reports that reflections at 0 degrees and 180 degrees have found to be least beneficial ... both ears are exposed to the same change at the same instant in time. Also most loudspeakers have an uneven off-axis response in the vertical plane. And he says too many reflections can worsen things. So there is no question that broadband absorption (200-300 Hz and above) at the first reflection points on the ceiling, front wall and center portion of back wall can only be a good thing.

Tumara Baap
Perhaps my experience is not so contradictory after all; the absorber that made the BIGGEST difference was the one on the rear wall. The one on the front ceiling was a close second. The "chamber" behind my false wall had been lined with fiberglass from the gitgo, so I had no opportunity to A/B that absorber.

Just wanted to add my two cents to this thread. I finally found some fiberglas here locally (1.5" thick, Johns Mansville) and made some 2 x 4 panels, beveled edge, with Pearl GOM fabric. Finished about 8 of them (with more to come) in anticipation of placing them around my new theater that will be finished in late April. Could not wait, of course, and placed them around my existing room, which is open at one end. Put on a demo surround DVD, and could not stop smiling!! This really improved the room. I even got out some old SACDs that I had not listened to in a while, and continued the "I can't believe what I am hearing" amazement. Still smiling hours later. So for a few trips to Lowe's for staples and lumber, a trip to a housing insulation contractor, an order on the web for the fabric, and about 20 hours of labor, I am in heaven right now! If you have not treated your room (but you probably have if you are reading this), I highly recommend it!

My speakers are M&K S-150s which are THX Ultra2 certified with very controlled dispersion and off-axis response.

I'm not sure what entails THX Ultra2 certification, but the datasheet graph of the Genelec 8040a (at Genelec's website) is an example of an excellent off-axis response. Not only do you have significant dispersion off-axis, but the signature profile of the response is more or less retained at 15, 30, 45 and 60 degrees off axis, only gradually being attenuated in amplitude with increasing angle. While this has been recognized as a desirable attribute for a while, it's becoming clear how absolutely critical it is to have that sort of performance from an acoustics perspective. It ought to be a cardinal requirement and everything else in acoustics follows.

Tumara Baap

I'm not sure what entails THX Ultra2 certification, but the datasheet graph of the Genelec 8040a (at Genelec's website) is an example of an excellent off-axis response. Not only do you have significant dispersion off-axis, but the signature profile of the response is more or less retained at 15, 30, 45 and 60 degrees off axis, only gradually being attenuated in amplitude with increasing angle. While this has been recognized as a desirable attribute for a while, it's becoming clear how absolutely critical it is to have that sort of performance from an acoustics perspective. It ought to be a cardinal requirement and everything else in acoustics follows.

Tumara Baap
The THX cert mandates pretty much what you've described as your Genelecs' dispersion and off-axis response; a relatively tightly controlled vertical dispersion and smooth off-axis response in the horizontal plane.

I would like to find a source for acoustically transparent fabric panels. Think
of a speaker grill, except that I'm looking for a panel size of approximately 2'x4'.

I would like to find a source for acoustically transparent fabric panels. Think
of a speaker grill, except that I'm looking for a panel size of approximately 2'x4'.
Built them yourself?

Guys I know this in not ideal but it is what I have to work with..cosmetics is a part of it (WAF)

Here is a sketch of my room.

i have a wall that comes into play that goes about 2/3 rds of the way, then an opening, then a small wall (2 foot)

The hallway is about 3 feet wide that goes upstairs.

I have base traps floor to ceiling in black in these corners. I know the small wall corner may not do much but it was the WAF again.

What can I do where the yellow Star is and will it make a difference.

http://home.mchsi.com/~fun_pictures/Layout.JPG


Any takers on this..

thank you in advance..

K

So is that like the end of a hall or a bare wall at the bottom of the stairs or am I missing something?

The first thing I see in that room is that it looks like your seating is centered in the room. Not a good idea.

Bryan

I would like to find a source for acoustically transparent fabric panels. Think
of a speaker grill, except that I'm looking for a panel size of approximately 2'x4'.

For DIY, most recommend Burlap or a loosely woven natural fiber fabric. www.fabric.com hs burlap in a number of colors. I myself went with some $1/yard fabric from walmart.

The width of the soundstage should actually widen with reflections.Sure, because the speaker and its reflection can create a phantom image (almost a phantom speaker) in between them, stretching the soundstage outside the speaker. While it can sound spectacular (at least it has in my experience), there are a couple of problems that I've noticed.

Sounds at the edges of the soundstage tend to become less clear, maybe because they're being reproduced as multiple mono sources (speaker, reflection and phantom image combine). Also, sounds just inside the L/R speakers can get swamped by sounds just outside. So you get this lush, wide soundstage but things get soft as you move inward of the speakers until you get to the centre. It's actually a little easier to hear this with three speakers up front than with the typical two-speaker front soundstage.

Absorbing side wall reflections tends to restore imaging inward of the speakers (or at least makes them easier to hear) at the expense of a wider soundstage. I don't think one is more right or wrong than the other, just a matter of priorities and personal preferences.

Sanjay

So is that like the end of a hall or a bare wall at the bottom of the stairs or am I missing something?

The first thing I see in that room is that it looks like your seating is centered in the room. Not a good idea.

Bryan


bpape,

You come down the stairs and there is a wall on the right side that runs the length of the room. The wall on the left stops about 6 feet from the end of the steps and that is where you enter the theater. Where it says " <---- Wall ----> It is open into the theater area. The short wall was there since the home was built...

The seating is very close to the center at about 10 feet from the front wall and about 7 feet from the back wall...the drawing is not exactly to scale....is that going to give me some problems???

OK. Where the star is, I'm not seeing a lot of benefit to doing much of anything.

That seating distance should be pretty good. You're about 60% back unless my math is really bad this early in the morning.

Bryan

I live in an area with expansive soil. Basements (like mine) are usually built
with "floating floors", and curtain walls hang from the main floor. This provides
for a ~1 inch gap between the bottom of the wall and the floor. As soil moisture
levels vary, the floating floor can move up and down without causing structural
problems.

This creates an acoustic challenge for basement theater builders... the operation
of this 1" gap cannot be interfered with, but most acoustic treatments are based
on application of rigid materials such as wallboard.

Surely, I do not have a unique problem. What's the standard procedure for
acoustically treating the 1" gap between the bottom of a hanging wall, and
a floating concrete slab?

I live in an area with expansive soil. Basements (like mine) are usually built
with "floating floors", and curtain walls hang from the main floor. This provides
for a ~1 inch gap between the bottom of the wall and the floor. As soil moisture
levels vary, the floating floor can move up and down without causing structural
problems.

This creates an acoustic challenge for basement theater builders... the operation
of this 1" gap cannot be interfered with, but most acoustic treatments are based
on application of rigid materials such as wallboard.

Surely, I do not have a unique problem. What's the standard procedure for
acoustically treating the 1" gap between the bottom of a hanging wall, and
a floating concrete slab?
Treat it for what reason? Acoustical isolation from adjoining rooms or acoustical treatment for the room itself? If the former, then it doesn't seem like you can put anything in there. If the latter, I can't see how a 1" area makes any difference.

I live in an area with expansive soil. Basements (like mine) are usually built
with "floating floors", and curtain walls hang from the main floor. This provides
for a ~1 inch gap between the bottom of the wall and the floor. As soil moisture
levels vary, the floating floor can move up and down without causing structural
problems.

This creates an acoustic challenge for basement theater builders... the operation
of this 1" gap cannot be interfered with, but most acoustic treatments are based
on application of rigid materials such as wallboard.

Surely, I do not have a unique problem. What's the standard procedure for
acoustically treating the 1" gap between the bottom of a hanging wall, and
a floating concrete slab?No, you do not have a unique problem. Try treating it like this...

http://home.comcast.net/~scottj0007/theater/float_wall.jpg

This treats it for both sound isolation and for in-room acoustics.

This topic was discussed in depth a while back. Try a search on "floating walls". I tried to find the link for you, but the search engine is disabled right now.

- Scott

Okay, I've been reading up on acoustic treatments for months. I'm taking all next week off, and the in-laws just cancelled on coming out here for Thanksgiving, so I'm hoping to grab the opportunity to get some acoustic treatments into my home theater (5.1, BTW).

The room is 15x18' with the screen along the 18' wall. One side wall is mostly windows, the other has two doors, one in the middle and one in the back corner.

My plans:

-DIY Absorbers on the front wall, as much as possible. I'd really rather not cut rigid fiberglass.

-Bass traps in front corners, floor to ceiling.

-Side walls: Floor to ear height treated with more absorbers.

-Floors are already carpeted.

-Rear wall/floor corner: I'm talking about the corner behind the seating that's made by the rear wall and floor. Since I've got my projector there anyways, no one can walk behind the seating, so I was going to put another corner bass trap there.

-Ceiling: Not planning anything. I'd like to, but I didn't even trust myself with building the shelf for my projector, I'm not going to even try hanging acoustic treatments.

Now, one side wall is mostly windows, which presents a problem. I've heard that I should put *diffusion* opposite the windows. Opinions?

So, any glaring mistakes or omissions?

Hard to make general statements like diffusion opposite windows. As soon as you do, there will be a situation where it's not right. Personally, I prefer to put curtains over the windows and absorbtion on the opposite wall.

If this yields too much HF absorbtion, then consider not doing the whole bottom up to ear level thing to compensate.

Bryan

Hard to make general statements like diffusion opposite windows. As soon as you do, there will be a situation where it's not right. Personally, I prefer to put curtains over the windows and absorption on the opposite wall.

If this yields too much HF absorption, then consider not doing the whole bottom up to ear level thing to compensate.

Bryan

I second Bryans opinion. Cover those early reflection points no matter where (side wall, ceiling, ect.) they occur.

Stupid newbie question here.....I thought the front projection wall was typically painted in a dark flat paint like black or gray for refectivity purposes but reading through this thread, it appears I should be acoustically treating the front wall. Do people just use a dark GOM for their front walls? I seem to remember seeing alot of HT pics where the front wall appeared painted dark????

Stupid newbie question here.....I thought the front projection wall was typically painted in a dark flat paint like black or gray for refectivity purposes but reading through this thread, it appears I should be acoustically treating the front wall. Do people just use a dark GOM for their front walls? I seem to remember seeing alot of HT pics where the front wall appeared painted dark????

Yep, black GOM, Walmart Bedsheets, whatever. You can also shoot for a neutral grey if you prefer that look.

I used 1.5" Knauff for my front wall and from 8' to 3' for my others. I simply DID the front wall because it seemed reasonable, but the rest I installed beadboard below 3' since it wasn't necessary from a primary reflection point (to treat) unless I were sitting on the floor! I actually have my sheetrock screen ON the front studs. I then added a 2x2 frame on top of it to 'establish' the screen. Casing the 2x2's yeilds a 1-1/2" boarder around the screen -- it looks very professional. Oh, and once all these marerials are installed, there is a natural pocket for the treatment to go.

I used Black for the front wall, Deep Burgundy for the rest and Medium Grey 'diamond' accents. So, YES, the front wall appears Black.

Hard to make general statements like diffusion opposite windows. As soon as you do, there will be a situation where it's not right. Personally, I prefer to put curtains over the windows and absorbtion on the opposite wall.

If this yields too much HF absorbtion, then consider not doing the whole bottom up to ear level thing to compensate.

BryanI've already got fairly thick curtains over the windows, so I'll scratch the diffusors.

There actually won't be much bottom-up-to-ear-level absorption on the side walls, probably 6-8' wide at most.

Now, I forgot to ask about the rear wall. Should I put absorption across from the screen or leave it as is? I think that if I had any more absorption than what I've already got planned the room will be way too dead, so I'm inclined to leave it as is, with the exception of the bass trap I mentioned earlier.

Well, on the back wall, you can put up some absorbtion but with an FSK facing on it. That will help tame nulls off the rear wall in the bottom end without sucking up any more of the highs.

Bryan

Well, on the back wall, you can put up some absorbtion but with an FSK facing on it. That will help tame nulls off the rear wall in the bottom end without sucking up any more of the highs.

Bryan

If you are equating "bottom end" absorption to bass management, I don't know if I can agree with that comment. Even 2" thick fiberglass will not provide much "bottom end" absorption. From everything I have read, bass traps need to be thicker and spaced off a wall to provide any significant benefits.

Please correct me if I am wrong as I am always learning things.

If you are equating "bottom end" absorption to bass management, I don't know if I can agree with that comment. Even 2" thick fiberglass will not provide much "bottom end" absorption. From everything I have read, bass traps need to be thicker and spaced off a wall to provide any significant benefits.

Please correct me if I am wrong as I am always learning things.
You are correct.

To a point - yes. However, even 2" thick material provides SOME absorbtion in the lower frequencies. No - it's not going to have a 1.0 coefficient. BUT, enough square footage with even a .25 coefficient will provide a cumulative effect. The trick is to not overdo the rest of the spectrum at the same time.

Compare 2" of unfaced to 2" of FRK:

2" 703 Plain on wall - 0.17 0.86 1.14 1.07 1.02 0.98

2" 703 FRK on wall - 0.63 0.56 0.95 0.79 0.60 0.35

2" 705 FRK on wall - 0.60 0.50 0.63 0.82 0.45 0.34

As you can see, the faced material is significantly better in the bottom end but not going to overdo the top in the grand scheme of things. That many square feet of .6 at 125Hz is not an insignificant amount of absorbtion.

Will it be effective at 40Hz? No. Not much will. Will it still provide SOME additional control in the 50's to 250Hz range where many bottom end issues exist and the ringing masks a lot of the dialog? Absolutely.

Bryan

Compare 2" of unfaced to 2" of FRK:

2" 703 Plain on wall - 0.17 0.86 1.14 1.07 1.02 0.98

2" 703 FRK on wall - 0.63 0.56 0.95 0.79 0.60 0.35

2" 705 FRK on wall - 0.60 0.50 0.63 0.82 0.45 0.34

As you can see, the faced material is significantly better in the bottom end but not going to overdo the top in the grand scheme of things. That many square feet of .6 at 125Hz is not an insignificant amount of absorption.
Membrane effect?

pepar:
[FRK]membrane effect
Yep.
What you look for is a fall, rise, fall pattern -- and that's a tell tale of a membrane effect.
And a low, little higher, little higher, higher, is indicitive of a porous effect (in octave bands).
In this case
2" 705 FRK on wall - 0.60 0.50 0.63 0.82 0.45 0.34
There's a rise at 125hz, a fall at 250hz, a rise rise at 500hz to 1000hz, a fall at 2000hz.
So, no porous effect (the kraft is towards the room), and two resonances (probably).

pepar:

Yep.
What you look for is a fall, rise, fall pattern -- and that's a tell tale of a membrane effect.
Of course, as the room frequencies approach the resonant frequency of the membrane, it begins to vibrate taking that energy out of the room.

If you are equating "bottom end" absorption to bass management, I don't know if I can agree with that comment. Even 2" thick fiberglass will not provide much "bottom end" absorption. From everything I have read, bass traps need to be thicker and spaced off a wall to provide any significant benefits.

Please correct me if I am wrong as I am always learning things.Now, as bpape just mentioned, bass ringing that masks dialog is a problem I'm trying to correct. Would having 7 2x4' panel bass traps straddling three different corners help this? Or should I build two column-type bass traps and place it in two of the corners?

Now, as bpape just mentioned, bass ringing that masks dialog is a problem I'm trying to correct. Would having 7 2x4' panel bass traps straddling three different corners help this? Or should I build two column-type bass traps and place it in two of the corners?
Have you done any acoustical testing? Ethan has a file on his website that burns to a CD that can be used with a Radio Shack meter to roughly graph your room's response.

Have you done any acoustical testing? Ethan has a file on his website that burns to a CD that can be used with a Radio Shack meter to roughly graph your room's response.
I'll do that tonight or tomorrow and report back. I have a Radio Shack meter that I used to calibrate the system.

edit: My laptop's audio IO isn't playing well with RoomEQ Wizard, so I'm going to have to buy a USB soundcard or fiddle with it quite a bit to get it to work. I'll see what I can do but I don't have my hopes up.

I just made my second set of panels, and these came out much better than my first set. My 1st ones were a terrible color, and even though they were only 2'x2x, they were too big.

This time I cut the 2x4 panels into 18"x36"x2", and picked a burlap that better matched the room. I used some Celotex rigid fiberglass from my local menards, 1 roll of quilt batting, and 5 ft. of burlap. Total cost $30. I already had a can of 3M adhesive.

http://i38.photobucket.com/albums/e127/esthomps/Home%20Theater%202/HomeTheater1-2.jpg

http://i38.photobucket.com/albums/e127/esthomps/Home%20Theater%202/HomeTheater1-3.jpg

General bottom end decay time control can help with dialog issues quite effectively.

Bryan

edit: My laptop's audio IO isn't playing well with RoomEQ Wizard, so I'm going to have to buy a USB soundcard or fiddle with it quite a bit to get it to work. I'll see what I can do but I don't have my hopes up.
Rarely do laptops have full duplex onboard audio required by software like REW. Fortunately, they work well with the least expensive Sound Blaster USB "card."

pepar:
Actually, my laptop doesn't work with the soundblaster USB card, although it does have a USB port. And you're right that ETF5 also doesn't work with my laptop's audio (which can be shut off). (My laptop was free from my IT department after my asking the question: "What do you have that you can't give away")

pepar:
Actually, my laptop doesn't work with the soundblaster USB card, although it does have a USB port. And you're right that ETF5 also doesn't work with my laptop's audio (which can be shut off). (My laptop was free from my IT department after my asking the question: "What do you have that you can't give away")
My laptop(s) automatically turn off onboard audio when the SB USB is plugged in. Is your laptop an older model?

pepar:

Is your laptop an older model? Oh yea.
I wanted something to surf the net with (not something I do with my development computers). It has no software installed that didn't come with the operating system, other than a virus checker. It has very little memory, and the CPU is so slow that I can instantly detect when malware starts to run because even the most efficent malware slows down this slow laptop perceptibly. That's not a planned/wanted feature, that's just the way it is. I can type into notepad and watch the TaskManager performance hit 50%. The LCD doesn't work (I'm using a Samsung SyncMaster 970e - very nice). It takes 15 minutes to boot, and another 15 to log on. CPU usage never drops below 5%.

Frankly I probably wouldn't have enjoyed running ETF5 on it anyway, but there was a day I really really tried. (Purchased copy of RplusD is installed on my testing computer)

i was doing some experimenting in my listening room/theater that I just finished trying to get the best setup for the GIK Acoustics panels that I bought. I have the 4" panels in the front corners, 2" panels at the side first reflection points, and used to have 2 2" panels on the front wall reflection points. I currently am running just a stereo setup with Tyler Linbrook Signature monitors. After getting the speakers in the best place in my 13X12 room, I still noticed that the center of the soundstage wasn't articulate enough, especially given imaging and soundstage that the speakers can give. So on a whim I moved the 2 2" panels off the front wall and put them right behind each speaker (actually leaning on them), so that it blocks any path from the speakers to the front wall at all. Now the soundstage and imaging are perfect.

I realize that many damp their entire front wall, but for me that was not an option. I wonder if anyone else actually puts treatments right on or next to their speakers and whether this is actually not a good thing? It sure sounds better, particularly with the Audyssey auto EQ in my Denon receiver.

Rarely do laptops have full duplex onboard audio required by software like REW. Fortunately, they work well with the least expensive Sound Blaster USB "card."I have a old PowerBook, so I'll have to see what works with OSX and REW. I'll check around a bit and see what I can find.

I have a old PowerBook, so I'll have to see what works with OSX and REW. I'll check around a bit and see what I can find.

cubedude,

It's always nice to hear about other Mac users. I'm in the very early construction phase and am lusting to upgrade to a new Intel MacBook :), so I'm pretty sure Windows on Parallels or Boot Camp will be a fallback option for me by the time I'm in that phase. Anyway, I'll be interested to hear what you find.

Mike

cubedude,

It's always nice to hear about other Mac users. I'm in the very early construction phase and am lusting to upgrade to a new Intel MacBook :), so I'm pretty sure Windows on Parallels or Boot Camp will be a fallback option for me by the time I'm in that phase. Anyway, I'll be interested to hear what you find.

MikeI wish I could afford a MacBook right now, but I'm still saving up for an anamorphic lens and video processor. :D

Anyways, I asked just asked about the Griffin iMic (http://www.griffintechnology.com/products/imic/) over in the REW thread, so I'll see if anyone over there knows anything about it.

i was doing some experimenting in my listening room/theater that I just finished trying to get the best setup for the GIK Acoustics panels that I bought. I have the 4" panels in the front corners, 2" panels at the side first reflection points, and used to have 2 2" panels on the front wall reflection points. I currently am running just a stereo setup with Tyler Linbrook Signature monitors. After getting the speakers in the best place in my 13X12 room, I still noticed that the center of the soundstage wasn't articulate enough, especially given imaging and soundstage that the speakers can give. So on a whim I moved the 2 2" panels off the front wall and put them right behind each speaker (actually leaning on them), so that it blocks any path from the speakers to the front wall at all. Now the soundstage and imaging are perfect.
The area on the wall behind the LCR speakers is a first reflection point. So's the ceiling. And many times overlooked - the back wall.

Actually, directly behind and directly beside the speakers deal more with SBIR - which is still a good thing.

Bryan

Actually, directly behind and directly beside the speakers deal more with SBIR - which is still a good thing.

Bryan

Actually, directly behind and directly beside the speakers deal more with SBIR - which is still a good thing.

Bryan
So, being *that* close makes those surfaces boundaries in addition to first reflection points? Within a certain distance based on wavelength?

Not sure I understand the question. Those places directly around the speaker offer the opportunity for the spherical wavefront of the bass frequencies to bounce off and combine with the direct, front moving waves in either a constructive or destructive manner - either creating a peak or dip in response. Treating those surfaces with appropriate materials reduces the intensity of the reflected waves, thereby reducing the effect of the constructive or destructive combining of the waves.

The frequencies which are most affected are those where the distance from the baffle to the surface and back to the baffle are equal to or 1/2 of the length of the wave in question. Those where it is equal will have a peak (coming back in phase with the direct signal), those at 1/2 will have a dip (coming back 180 degrees out of phase with the direct signal, thereby causing a cancellation).

Bryan

Not sure I understand the question. Those places directly around the speaker offer the opportunity for the spherical wavefront of the bass frequencies to bounce off and combine with the direct, front moving waves in either a constructive or destructive manner - either creating a peak or dip in response. Treating those surfaces with appropriate materials reduces the intensity of the reflected waves, thereby reducing the effect of the constructive or destructive combining of the waves.

The frequencies which are most affected are those where the distance from the baffle to the surface and back to the baffle are equal to or 1/2 of the length of the wave in question. Those where it is equal will have a peak (coming back in phase with the direct signal), those at 1/2 will have a dip (coming back 180 degrees out of phase with the direct signal, thereby causing a cancellation).

Bryan
Seems like you understood it just fine. :D

I'm not sure why you perceive a benefit. However, when using professional loudspeakers, broadband absorption behind the speaker can be useful. First you would have to engage the acoustic space switch for placement near a wall. Doing so rolls off the bass for a flat response. The 1/4 wavelength from the loudspeaker face to the wall behind is small enough that the SBIR frequency of relevance will be both more directional, (and therefore will not radiate rearwards to the same extent as deeper bass) and the little that will radiate is within the performance frequency range of the broadband absorber being used.

In order to minimize SBIR with a regular consumer loudspeaker, one can use a sub with the crossover engaged (80 to 90 Hz) and place the loudspeaker 4 feet or more out into the room. The SBIR frequency in question will then be low enough that the processor would have handed over that job from the loudspeaker to the subwoofer.

Tumara Baap

So on a whim I moved the 2 2" panels off the front wall and put them right behind each speaker (actually leaning on them), so that it blocks any path from the speakers to the front wall at all. Now the soundstage and imaging are perfect.

I'm not sure why you perceive a benefit. However, when using professional loudspeakers, broadband absorption behind the speaker can be useful. First you would have to engage the acoustic space switch for placement near a wall. Doing so rolls off the bass for a flat response. The 1/4 wavelength from the loudspeaker face to the wall behind is small enough that the SBIR frequency of relevance will be both more directional, (and therefore will not radiate rearwards to the same extent as deeper bass) and the little that will radiate is within the performance frequency range of the broadband absorber being used.

In order to minimize SBIR with a regular consumer loudspeaker, one can use a sub with the crossover engaged (80 to 90 Hz) and place the loudspeaker 4 feet or more out into the room. The SBIR frequency in question will then be low enough that the processor would have handed over that job from the loudspeaker to the subwoofer.

Tumara Baap
"professional loudspeakers" = "full range" ?

"regular consumer loudspeaker" = "sat/sub" ?

(Got the Toole paper on deck for review. Thanx!)

"professional loudspeakers" = "full range" ?

It may or may not be full range. What I had in mind was an active monitor, with built-in amplifiers and electronic crossover. These will almost always be sonically superior (and hence more amenable to room acoustics) than similar size consumer loudspeakers irrespective of price. They will typically have an acoustic space switch for placement near a wall or corner. Examples of which are Mackie HR624, Genelec 8040a, Dynaudio BM5a ... all of which can make for truly excellent and versatile HT speakers. Some placement options such as near a wall also yield additional benefits such as superior dynamic headroom, lower distortion, minimizing SBIR, permitting more usable room space, and reducing cable clutter on floors. I have a processor with balanced XLR outs such as B&K Reference 50 S2. Outlaw Model 990 is an alternative.

Tumara Baap

TumaraBaap:

Some placement options such as near a wall also yield additional benefits such as superior dynamic headroom, lower distortion, minimizing SBIR, Can you give a few more words on that topic please?

TumaraBaap:

Can you give a few more words on that topic please?

Most people are already aware that a subwoofer will play more efficiently when placed against a wall versus out in the room. The same goes for a loudspeaker. Bass sucks up most power, and when those demands are reduced, the ability of the loudspeaker to play everything else with aplomb improves. However you cannot attenuate the bass on a consumer loudspeaker with the precision of a dedicated acoustic space switch. Turning down bass on the receiver by 2 decibels or blocking speaker ports are crude measures. I would still keep loudspeakers about 3 feet away from the closest lateral surface, as I believe that plays a role in how the mid and upper frequencies "illuminate" the room.

The benefits of this approach are similar to those of "soffit mounting" or "flush mounting" monitors in high-end recording studios or screening rooms designed by top acousticians, though of course not to the same extent. Proper flush mounting also completely eliminates edge diffraction. (though that was never a significant distortion to begin with ... rounding off cabinet edges for example probably has more to do with vagaries of fashion). Genelec's web site at http://www.genelec.com/support/flushmount.php has some good info on the SBIR phenomenon and the advantages of soffit mounting. But soffit mounting correctly is hideously expensive and hampers future changes and upgrades. However, I can get fairly close to reaping at least some of the benefits with careful positioning and setting up of my Mackie HR624's.
Tumara Baap

In order to effectively use soffit mounting, one must use a speaker that is designed for that. It's not simply edge diffraction but also how the crossover is designed in terms of baffle step compensation - which will be totally messed up if soffit mounted and no way to compensate.

Also, simply crossing a speaker over at 80Hz doesn't do anything to eliminate SBIR - it simply removes the lower few octaves to a speaker better designed and more flexible in placement for smoothest response. SBIR will have an effect well up into the hundreds of Hz.

Bryan

I am severely limited in my options for room treatments(WAF). I got the big TV an speakers and she gets the majority of the aesthetics. I was hoping someone could give me a "real world" thought on use plants as a supplement to soft furniture area rugs and a few bass traps in the corner. My room is about about 15x19 and has an angled ceiling. The right side is 9 feet and slants up to about 13-14 feet. I use it 70/30 HT/2channel. The linked website shows the absorbant coefficients of certain plants. Could I put the ficus at the first reflection point of my mains and expect any improvemnets?Any thoughts? Am I hoping for too much??

P.S I am a newbie

http://www.ri-research.com/tropplan/envben/acoustic/acoustic.htm

Hang treatments in a complementary color and put a plant in front of it. I really like the way mine turned out and think they add to the aesthetics, not detract from it. Let you wife go to the fabric store and pick out the fabric, any loosely woven, natural fiber fabric will work.

I am severely limited in my options for room treatments(WAF). I got the big TV an speakers and she gets the majority of the aesthetics. I was hoping someone could give me a "real world" thought on use plants as a supplement to soft furniture area rugs and a few bass traps in the corner. My room is about about 15x19 and has an angled ceiling. The right side is 9 feet and slants up to about 13-14 feet. I use it 70/30 HT/2channel. The linked website shows the absorbant coefficients of certain plants. Could I put the ficus at the first reflection point of my mains and expect any improvemnets?Any thoughts? Am I hoping for too much??

P.S I am a newbie

http://www.ri-research.com/tropplan/envben/acoustic/acoustic.htm

I was hoping someone could give me a "real world" thought on use plants as a supplement to soft furniture area rugs and a few bass traps in the corner.

Don't expect much from plants. Maybe really big plants can help reduce the worst of the echoes a tiny amount. But all rooms need absorption well down into the bass range, and no plants will help there.

--Ethan

Simply plopping a monitor into a wall not specifically designed for soffit mounting will invariably color the sound. But those with the money and intention to undertake such projects usually know better. Even Mackie HR824's have been successfully soffit mounted with provision for redirection of rear passive radiator output and the requisite outboard equalization.

The topic of soffit mounting was brought up to shed light on a few acoustic principles. I doubt anyone here will actually commit to something so unwieldy ... who knows, this is the dedicated theater forum and WAF is as good as it gets...

When optimizing loudspeaker placement in conjunction with subwoofer crossover for its effect on SBIR, the operative word is amelioration, not elimination. What matters is that having a loudspeaker 4 feet away from the wall behind, instead of say 2 feet away, will yield advantages. Whereas a frequency is almost obliterated at where distance from transducer to wall is 1/4 wavelenth, there are further tooth-like distortion dips across the bass spectrum. Judicious loudspeaker placement/ crossover selection will ameliorate (not eliminate) that distortion profile.

Tumara Baap

In order to effectively use soffit mounting, one must use a speaker that is designed for that. It's not simply edge diffraction but also how the crossover is designed in terms of baffle step compensation - which will be totally messed up if soffit mounted and no way to compensate.

Also, simply crossing a speaker over at 80Hz doesn't do anything to eliminate SBIR - it simply removes the lower few octaves to a speaker better designed and more flexible in placement for smoothest response. SBIR will have an effect well up into the hundreds of Hz.

Bryan

Agreed. Your previous post(s) seemed to color you a proponent for just the opposite - as in getting everything close to a boundary to 'engage the acoustic space'.

... and you'd be amazed how many people try to build subs into cubicles in walls, put speakers inside shelving units (just as bad if not worse than in-wall mounting), etc.

Bryan

Don't expect much from plants. Maybe really big plants can help reduce the worst of the echoes a tiny amount. But all rooms need absorption well down into the bass range, and no plants will help there.
A VERY large Venus Flytrap next to his wife's seat may help. :)

I posted this in a new thread but no one responded so I'll ask in here.

I have extra Acoustik mat. When building my front stage would it help to put Acoustik mat between the plywood layers instead of 30# roofing felt?

If not then I will sell the extra Acoustik mat. If it helps, fine! I'll still have extra Acoustik mat just not as much. :D

I already have a layer of Acoustik mat between my concrete slab and my 2 x10 framing (that is filled with sand).

Stack up is as follows

3/4" plywood
roofing felt or Acoustik mat?
1/2" plywood
roofing felt or Acoustik mat?
3/4" plywood
2x10 framing, 1' on center, filled with sand
3/4" plywood
Acoustik mat
concrete slab

Thanks!

edit to add 3/4" plywood between framing and Acoustik mat

If you want to use 1 layer of the mat, that'd be fine. I think 2 is a bit of overkill. If you can get some money back out of it, go for it. Heaven knows you'll go over budget elsewhere! If not, then it certainly won't hurt to use it.

Bryan

Thanks Bryan! Hope you get caught up soon. I'm waiting to hear from you! ;)

When you are looking at RT60 values. What is it that you want to have as an optimum RT60 value after treatments.

Also, is there a starting point or a calculator that shows "approximate" square footage of treatment based on room size, speaker location...etc.

for example my room is 17 x 12 x 8 - carpet on a pad and false ceiling tiles at this time.

thanks

When you are looking at RT60 values. What is it that you want to have as an optimum RT60 value after treatments.

Also, is there a starting point or a calculator that shows "approximate" square footage of treatment based on room size, speaker location...etc.

for example my room is 17 x 12 x 8 - carpet on a pad and false ceiling tiles at this time.

thanks
There are a few Excel spreadsheets available for download that will do this. Some are very detailed with hundreds of materials with acoustical properties integrated into the sheet. Selecting a material and inputting the surface area that it covers results in its properties being incorporated into the overall room equation.

Kermie:

is there a starting point or a calculator that shows "approximate" square footage of treatment based on room size

http://www.bobgolds.com/Mode/RoomModes.htm

Computed Information:
Room Dimensions: Length=17 ft, Width=12 ft, Height=8 ft
Room Ratio: 1 : 1.5 : 2.12
R. Walker BBC 1996:
- 1.1w / h < l / h < ((4.5w / h) - 4): Pass
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Pass
Nearest Known Ratio:
- "7) M. M. Louden: 1971: 3rd best ratio" 1 : 1.5 : 2.1
RT60 (IEC/AEC N 12-A standard): 238 ms
- ±50ms from 200Hz to 3.5kHz = 188 to 288ms
- ±100ms above 3.5kHz = 138 to 338ms
- <+300ms at 63hz = 538ms
- 300<RT60<600ms
RT60 (ITU/EBU Control Room Recommended): 193 ms
- ±50ms from 200Hz to 4kHz = 143 to 243ms
- <+300ms at 63hz = 493ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 413 sabins
Volume: 1632 ft^3
Surface Area Total: 872 ft^2
Surface Area Floor: 204 ft^2
Surface Area Ceiling+Floor: 408 ft^2
Surface Area Front Wall: 96 ft^2
Surface Area Front and Rear Wall: 192 ft^2
Surface Area Left Wall: 136 ft^2
Surface Area Left and Right Wall: 272 ft^2
Surface Area 4 Walls: 464 ft^2
Surface Area 4 Walls + floor: 668 ft^2
(sabins - front wall - carpet) / Left+Right+Rear wall: 30 %
(sabins - front wall) / Left+Right+Rear wall: 86 %
Schroeder Fc: 122hz
Frequency Regions:
- No modal boost: 1hz to 33hz
- Room Modes dominate: 33hz to 122hz
- Diffraction and Diffusion dominate: 122hz to 488hz
- Specular reflections and ray accoustics prevail: 488hz to 20000hz
Count (33.2-217hz) : Axials=13, Tangentials=54, Obliques=72
Count (33.2-100hz) : Axials=6, Tangentials=6, Obliques=1
Critical Distance (direct = reverberant field): 12.90ft


A sabin can be defined loosly as "an open window one square foot in size".
So, if you have a material that absorbs 100% of the sound at all frequencies, and you need 413 sabins, then you'd need 413 square feet of that material.

For HF absorption, the above line
(sabins - front wall - carpet) / Left+Right+Rear wall: 30 %
means assuming you have the front wall and floor completely covered, then you should cover about 30% of the left/right/rear walls with HF absorption, assuming there's nothing else in the room.

In practice, different materials absorb different amounts per frequency band (as well as placement, diminishing returns, etc)
For example carpet tends to absorb lots of HF, and less LF.
Leather couches tend to reflect HF, and absorb more around 200hz.
Your walls tend to reflect HF, and absorb low frequency.
What you want to do is add up the sabins for each frequency band, and add (or possibly remove) material until you hit around 413 sabins.
I say 'around' because who can really tell the difference between RT60=.20 and RT60=.30.
Once you have the right amount of material in the room, then it's a question of placing it to deal with other things. You don't want to put it all on one wall for example. Imaging might be improved if you put it on the front wall and first reflection points (particularly the absorber on the right wall at the left front speaker reflection point).

http://www.bobgolds.com/AbsorptionCoefficients.htm
http://www.bobgolds.com/Sabin.htm

Thanks BasementBob - I will have to study some of that info to understand what half of that means. I will surf arounc bobgold.com to help understand.

thanks

KERMIE:
The best book I've ever read on RT60 calcs for studio design is How to Build A Small Budget Recording Studio From Scratch : With 12 Tested Designs by Michael Shea (http://www.amazon.com/dp/0071387005)

I wasn't sure where I should post this question, but is seems mainly an acoustical question. I've done searches throughout the forums and can't seems to find anything on this specific topic. Most sound isolation searches come back with green glue and drywall techniques.

I am interesting in sound isolation pads to place underneath my speakers (honestly only my sub really needs a pad). They currently sit on/in a cabinet and transfer some of their vibrations to the cabinet. DIY methods or cost effective bought pads are what I am looking for.

In my search I did see one picture of a person who put their sub on a scap piece of carpet padding, but the thread made no mention if it helped or not. Anyone have any ideas that would help?

I wasn't sure where I should post this question, but is seems mainly an acoustical question. I've done searches throughout the forums and can't seems to find anything on this specific topic. Most sound isolation searches come back with green glue and drywall techniques.

I am interesting in sound isolation pads to place underneath my speakers (honestly only my sub really needs a pad). They currently sit on/in a cabinet and transfer some of their vibrations to the cabinet. DIY methods or cost effective bought pads are what I am looking for.

In my search I did see one picture of a person who put their sub on a scap piece of carpet padding, but the thread made no mention if it helped or not. Anyone have any ideas that would help?Do a search for the Auralex SubDude or Gramma.
http://www.stereophile.com/musicintheround/1204mitr/index.html

I wasn't sure where I should post this question, but is seems mainly an acoustical question. I've done searches throughout the forums and can't seems to find anything on this specific topic. Most sound isolation searches come back with green glue and drywall techniques.

I am interesting in sound isolation pads to place underneath my speakers (honestly only my sub really needs a pad). They currently sit on/in a cabinet and transfer some of their vibrations to the cabinet. DIY methods or cost effective bought pads are what I am looking for.

In my search I did see one picture of a person who put their sub on a scap piece of carpet padding, but the thread made no mention if it helped or not. Anyone have any ideas that would help?
Suspend it?

Do a search for the Auralex SubDude or Gramma.
http://www.stereophile.com/musicintheround/1204mitr/index.html

"Auralex Subdude a MUST HAVE!!" (http://www.avsforum.com/avs-vb/showthread.php?t=644330&highlight=Subdude)

Thanks! After reading about the subdude I ordered one.

Acoustical Masters---I have a question. My HT is finally to the point where I can ask this question...Can I create my fabric panels with OC Pink Foamboard 3/4? ( I got a great deal on 4 pieces).
My HT room is in my basement. The left side wall is all concrete, the front wall is 1/2 concrete, and the right wall has a window and is 1/3 concrete. I have insulated the walls which are studded 16oc with rock wool and I've blown insulation into the ceiling. There are 2 layers of 1/2 drywall with gg and the whole font wall, back wall and the top side walls are covered in 3/4 Oak HardwoodPlywood which is gg'ed and nailed into studs.The floor will have carpet and I have installed an 3/4 OSB subfloor. I am only putting the gom fabric on the bottom half ( at about 49"). My LCR speakers are inside a column built ofthe 3/4 Oak and my sub is in a hidden window seat which is located at about the first 1/3 of the room (about 8 feet in the room).

Acoustical Masters---I have a question. My HT is finally to the point where I can ask this question...Can I create my fabric panels with OC Pink Foamboard 3/4? ( I got a great deal on 4 pieces).
My HT room is in my basement. The left side wall is all concrete, the front wall is 1/2 concrete, and the right wall has a window and is 1/3 concrete. I have insulated the walls which are studded 16oc with rock wool and I've blown insulation into the ceiling. There are 2 layers of 1/2 drywall with gg and the whole font wall, back wall and the top side walls are covered in 3/4 Oak HardwoodPlywood which is gg'ed and nailed into studs.The floor will have carpet and I have installed an 3/4 OSB subfloor. I am only putting the gom fabric on the bottom half ( at about 49"). My LCR speakers are inside a column built ofthe 3/4 Oak and my sub is in a hidden window seat which is located at about the first 1/3 of the room (about 8 feet in the room).
You could create panels with that stuff, but it would not do much more than keep your room warmer. It is an insulation, not an acoustical absorber.

Thanks pepar! Having said that then I guess you would reccomend that I get some linacoustic or something to put behind the fabric. Do you think that would add anything to the sound quality? Just trying to see if the extra money for the linacoutic is justifiable.

Thanks pepar! Having said that then I guess you would reccomend that I get some linacoustic or something to put behind the fabric. Do you think that would add anything to the sound quality? Just trying to see if the extra money for the linacoutic is justifiable.
I'm not an expert, but I can say that from my experience most rooms benefit from absorbers at the first reflection points. I've got 2" OC SelectSound Black, but some recommend 4". For me that would have have negative aesthetics.

Here (http://www.bobgolds.com/AbsorptionCoefficients.htm) is a helpful chart listing absorption coefficients of "Fiberglass, Rockwool, Polyester, Cotton, and Sheep." (I think they mean "wool" for the last one, at least I hope they do.) :)

I'm not an expert, but I can say that from my experience most rooms benefit from absorbers at the first reflection points. I've got 2" OC SelectSound Black, but some recommend 4". For me that would have have negative aesthetics.
Yup. Absorbers at first reflection points kill two birds with one stone: They reduce said reflections to prevent poor accuracy in localizing the front sound stage, and they add general wide-band absorption which lowers reverberation time to reduce the intrusion of the room's own acoustical signature on that of the recorded sound.

1" of rigid or semi-rigid fiberglass is all you need for first reflections, but 2" or more extends the absorption to lower frequencies. It's generally a practical and space issue. High performance rooms are professionally designed to yield an optimal sound treatment for room geometric, aesthetics, and the specific listening needs/preferences of the owner.

Regards,
Terry

I have a 'music' room with grand piano, drums, and guitars. The room has 2 windows and is hardwood floor, so it is VERY loud and sound is reflecting off the walls and floor. The piano's upper keys are especially harsh.

I am looking into buying an 8'x10' wool rug for the floor.

Any low-cost suggestions for the walls?

Any low-cost suggestions for the walls?

Rigid fiberglass wrapped in soft open weave fabric is the standard material for DIY acoustic treatment.

--Ethan

Yup. Absorbers at first reflection points kill two birds with one stone: They reduce said reflections to prevent poor accuracy in localizing the front sound stage, and they add general wide-band absorption which lowers reverberation time to reduce the intrusion of the room's own acoustical signature on that of the recorded sound.

1" of rigid or semi-rigid fiberglass is all you need for first reflections, but 2" or more extends the absorption to lower frequencies. It's generally a practical and space issue. High performance rooms are professionally designed to yield an optimal sound treatment for room geometric, aesthetics, and the specific listening needs/preferences of the owner.
If I were to build another home theater, I'd build the room and then build a room inside of that so that absorption/diffusion/whatever would present smooth walls, as opposed to the "wall hangings" I have now protruding into my room. I guess this would be like the panelized systems commercially available.

Picking up a set of two tri-traps to see if they make a big difference in my basement home theater.

Just wondering if anyone has an opinion if these should go in the back corners of my room or the front corners?

I do have my sub in the front left corner of the room so it kind of seems silly to have a bass trap directly behind that?

Thanks all.

hardax:

If it's a very powerful sub, the sub probably shouldn't be in the corner anyway.
If it's a weak sub (i.e. underpowered for the room) then put your absorption as far away from it as possible (the back), and leave your sub in the front corner.
Putting broadband absorbers/traps on the front corners may help imaging/speach, at the cost of reducing envelopment/spacousness a bit.
I've seen people put deep absorbers on top of their front corner subs, and at least one manufacturer sells absorbers to go under front corner subs.

Thanks for the reply BasementBob.

My sub is pretty powerful. It is a HSU STF-3 in a room aproximately 19x24x7.

doing the crawl test I did determine that the front left corner was the best place for it.

Based on the above do you still think they should go in the front or the back?

Thanks

Someone found sheets of fiberglass backed ceiling panels (2' x 4')(1" thick), $4.74 each at Menards. Is this similar to OC 703? If so, sounds like a great low cost solution!

Unfortunately, there is no Menards near me. Any other ideas of where I can find this?

Someone found sheets of fiberglass backed ceiling panels (2' x 4')(1" thick), $4.74 each at Menards. Is this similar to OC 703? If so, sounds like a great low cost solution!

Unfortunately, there is no Menards near me. Any other ideas of where I can find this?
Without knowing anything about the stuff at Menard's, it's impossible to say. There are a number of different types/densities with different properties.

Where is the best place to purchase Mass loaded Vinyl?
Thanks
Chris

In the near future I will building some bass traps. I have some questions though. Each trap will be 2'x4' My traps will consist of 2" thick mineral wood and 2 pieces of OC 705 2" thick apiece all covered with GOM fabric. My question is what should I use to bond the mineral wood with the 2 pieces of fiberglass. Should I use chalk or glue or some spray on adhesive glue or maybe even green glue. Input on this subject would be much appreciated.

longfellowfan:

Why not just make the GoM into a bag. Then you won't have to bond them together with anything. Or wrap the mineral/705 up in GoM like a christmas present, and glue the GoM to at the back, using 3M 77 spray adhesive.

Chalk wouldn't hold.
Certainly don't use green glue in a porous absorber.

I don't know what mineral wood is. I thought it might have been a typo, but you did it twice. Mineral wool is anything that's made out of rocks (mineral) that have been made into fibers (wool). So mineral wool includes rockwool and fiberglass. 705 is made of fiberglass.

With your corner absorbers now being 6" thick, you might want to use 703 instead of 705. It's probably cheaper too, unless you already have 705 lying around.

Mineral wood showing here (http://www.atsacoustics.com/item--SAFB-Mineral-Wool-2-inch-Case-of-6--1006.html)

Anyone try fiberglass ceiling panels from Lowes or Home Depot? It's called "Strata", yellow on one side and white on the other. (2'x4') one inch thick.

EDIT: Apparently, the person got it from Menards. Has anyone checked Lowes or Home Depot for fiberglass panels? I'll check this weekend.

Mineral wood showing here (http://www.atsacoustics.com/item--SAFB-Mineral-Wool-2-inch-Case-of-6--1006.html)

What would work better for room panels, mineral wool or 703?

Your floor should be carpeted but do not use a foam or rubber pad. Horse hair jute is the best but is generally no longer available because of youths smoking it for the hemp. 1/2 inch felt padding to me is the next best thing BUT put the bonding surface side down (normal carpet insulation is to put it up so that the tape the installers use to hold pad sections together will not tear the pad).

I may have missed this but, why would you not want to use a foam or rubber pad under the carpet?

703 is more user friendly for panel construction but mineral wool will work and is cheaper - as long as you don't jostle it too much - crumbles easily.

On the floor pad, the foam or rubber will do nothing to assist with absorbtion. The felt or jute will effectively thicken the absorbtive layer ande broaden the frequency range over which it is effective.

Bryan

703 is more user friendly for panel construction but mineral wool will work and is cheaper - as long as you don't jostle it too much - crumbles easily.


Bryan
Could I then use one layer of mineral wood as the back with 2 layers of 703 2" thick apiece in front with a frame and wrap it in GOM fabric.

It's not actually wood. It's mineral wool.

So I am a skim reader and it looked like wood my bad.

Thank goodness! I was thinking I had to pressure treat all my trim. :D

So here is what the wife and I want to do. My room is 16x11x8. The room is a living room and wear we watch all of our movies.( I may post pics later some older pic are in my signature. I wanted to by two panel bass traps for the back two conners being 2'x4' and 4 to 6" thick. We also want 4 absorption panel 2'x2' 2 to 4" thick for the first reflection point and 2 for the back wall of the room. I wanted to simply buy them but my wife want to go the diy method so she can pick out the fabric from GOM and it is a little cheaper for diy. I was going to use a pine frame to around the absorption material and wrap it in GOM Fabric. My question is what to use as the absorption material. 4 to 6" of 703 for bass traps and 2 to 4" of 703 for the absorption panels. I am open to suggestions I am not going to built them for a few month after my wife goes over the fabric color samples and a income tax refund comes. Thanks in advance.

Can someone give me some ideas about my basement theater area. The room is 30'x12' with a strange layout. The large window opening on the left side is open to a playroom and the large doorway behind the theater is open to a small kitchenette.

http://i18.photobucket.com/albums/b118/causeofhim/basementtheater.jpg

I plan on acoustical treatment surrounding the projection screen. I'm not sure if I should do the whole wall or just a few feet aroundthe screen, behind the speakers. I really dont have any side walls. Should I place acoustical treatment behind the seating on the back wall? What about bass traps?

Thanks

Could someone give me some suggestions on what I should or might be able to do with reguards to accoustic treatment, and toning down the Bright/reflective nature of this room..


http://i34.photobucket.com/albums/d109/Warpdrv/home%20theater/IMG_1643.jpg
http://i34.photobucket.com/albums/d109/Warpdrv/home%20theater/IMG_1642.jpg
http://i34.photobucket.com/albums/d109/Warpdrv/home%20theater/IMG_1641.jpg
http://i34.photobucket.com/albums/d109/Warpdrv/home%20theater/AVsetup003.jpg
http://i34.photobucket.com/albums/d109/Warpdrv/home%20theater/SVS-PB12Plus2006.jpg

Im not sure what company's are out there, asthetically pleasing.. form and function..

thanks

Warp

Can someone give me some ideas about my basement theater area.

My first suggestion is to rearrange things so you're not right in front of a wall. That's where the inevitable peaks and nulls are worst.

> Should I place acoustical treatment behind the seating on the back wall? <

Yes!

> What about bass traps? <

Yes!

See this for much more information and advice:

www.ethanwiner.com/acoustics.html

--Ethan

Warps,

Nice clock!

> Could someone give me some suggestions on what I should or might be able to do with reguards to accoustic treatment, and toning down the Bright/reflective nature of this room. <

This is a deep subject, and a complete answer requires far more than will fit into a single reply here. So here's the short version. All rooms need:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption and/or diffusion on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective.

For the complete story see my Acoustics FAQ. (www.ethanwiner.com/acoustics.html)

--Ethan

There's no picture of what it looks like directly behind the couches.

That would be a challenging room, especially without moving anything around. It's in a corner itself, facing out, without many real "corners" to put bass traps in. Plus the walls and ceilings are extremely high.

You can't put a 1st ref absorber in front of the fireplace (well, you could...) or a big bay window (I actually have a panel in front of a window - and a very understanding wife - see this picture (http://gallery.avsforum.com/data/503/rightcornerfar.jpg)). The left side, where the window is, probably isn't too bad for direct reflections, because it's so open.

A panel behind the TV might help, as would some bass traps in corners, if you have any regular corners that could hold bass traps. Triangular columns, like GIK Acoustic's Tri-Traps (http://www.gikacoustics.com/product_info.html), allow you to add bass traps that don't stand out like big acoustic panels.


The rest depends on how many panels you are willing to put on the walls. I suggest getting fabric to match the color of your walls so they don't stand out like sore thumbs - unless you're divorced and don't have a wife to worry about. ;)


But for starters, covering more of your hardwood floor with a bigger rug, especially directly in front of the speakers, is something that is relatively painless.

Can someone give me some ideas about my basement theater area. The room is 30'x12' with a strange layout. The large window opening on the left side is open to a playroom and the large doorway behind the theater is open to a small kitchenette.

http://i18.photobucket.com/albums/b118/causeofhim/basementtheater.jpg

I plan on acoustical treatment surrounding the projection screen. I'm not sure if I should do the whole wall or just a few feet aroundthe screen, behind the speakers. I really dont have any side walls. Should I place acoustical treatment behind the seating on the back wall? What about bass traps?

Thanks


Project onto the left wall, not the top wall. Rerrange everything around that.

Just a quick question about placing panels on the front wall behind the center speaker.

I have a left-over 2" thick panel (4" w/ frame) that I currently have stacked between two bass trap panels in the front right corner. It would take some effort to put it on the front wall behind the TV/center speaker, but if it would be worth it for sound quality, I'll do it.

What benefits could I expect by putting the 2'x4' panel on the wall behind the center speaker here?

(Note - image was taken before panels purchased)
http://gallery.avsforum.com/data/503/DSC06624.JPG


This is one side my room w/ the panels (center channel seen on left edge of picture) and very close to what it looks like now:

http://gallery.avsforum.com/data/503/rightcornerfar.jpg

Project onto the left wall, not the top wall. Rerrange everything around that.

I cannot. There is not enough room on that wall to project a picture. That would be much nicer if it was possible.

A wall 12' wide isn't big enough to project a picture?

A wall 12' wide isn't big enough to project a picture?
The wall is not 12' wide. There are two doors and an opening in that 12' space.

A wall 12' wide isn't big enough to project a picture?
The diagram is a little confusing, but I think he has a doorway and window on that wall.

Maybe a pull down screen?

It really can only work with the rest of the basement if it is configured the way that it is. I just have to design my theater to work with what I have.

Back to my question - what benefit would there be to putting an absorber panel behind the center channel on the front wall?

Back to my question - what benefit would there be to putting an absorber panel behind the center channel on the front wall?

Sound radiates in all direction from a speaker (stick your head back there, it's alittle muffled, but it's there). By putting some absorption at the first reflectionpoint behind thespeaker, you'll improve clarity. Not as beneficial as hitting the first reflection points on your sidewalls (and back wall in my opinion), but if you've already done those, it definately can't hurt.

P.S. Unlike many in this forum, I'm no professional when it comes to this stuff. I just know from personal experience.

Sound radiates in all direction from a speaker (stick your head back there, it's alittle muffled, but it's there). By putting some absorption at the first reflectionpoint behind thespeaker, you'll improve clarity. Not as beneficial as hitting the first reflection points on your sidewalls (and back wall in my opinion), but if you've already done those, it definately can't hurt.

P.S. Unlike many in this forum, I'm no professional when it comes to this stuff. I just know from personal experience.


Thanks. The sides are covered (no pun intended). I just had the third extra panel left over and it's just between two thicker bass trap panels in the front right corner. If I can get around to it, I'll try to put it up on the front wall.

Hello everyone, I'm still in the planning stages of my theater as my basement remodeling project gets underway. I'm currently working on the adjacent bathroom and will move to the theater next. (hopefully I can get some pictures up). I've been trying to educate myself as much as I can by reading from this forum. I've got to get my theater moving quickly as we are having a baby in July. :D Consequently I have to scale things back - including the theater budget. :eek:

Anyway - my question is will plain old pink fluffy fiberglass insulation work for treating the screen wall? My thought is I would attach 2x3 furring strips to the poured concrete wall, two layers of rigid foam insulation between strips, then attach two layers of drywall (with GG depending on budget). From there I thought I could build a false wall/proscenium a few inches back and staple in some R-13. I would then cover the wall in fabric and a nice velvet curtain. The wall is only 10' 6" wide and will have columns built into the sides (~ 10" wide) to cover some piping. Will this effective treat the screen wall? I'm planning on a 100" screen. Thank you all for the help.

David

Hello everyone, I'm still in the planning stages of my theater as my basement remodeling project gets underway. I'm currently working on the adjacent bathroom and will move to the theater next. (hopefully I can get some pictures up). I've been trying to educate myself as much as I can by reading from this forum. I've got to get my theater moving quickly as we are having a baby in July. :D Consequently I have to scale things back - including the theater budget. :eek:

Anyway - my question is will plain old pink fluffy fiberglass insulation work for treating the screen wall? My thought is I would attach 2x3 furring strips to the poured concrete wall, two layers of rigid foam insulation between strips, then attach two layers of drywall (with GG depending on budget). From there I thought I could build a false wall/proscenium a few inches back and staple in some R-13. I would then cover the wall in fabric and a nice velvet curtain. The wall is only 10' 6" wide and will have columns built into the sides (~ 10" wide) to cover some piping. Will this effective treat the screen wall? I'm planning on a 100" screen. Thank you all for the help.

David

I think it's been noted several times in this thread that the pink stff will do nothing more than keep your room warm.

I'd just look to do it right the first time. I got 12 sheets of 2inch 703 for $120 shipped from ejdavis. Assumming your wall is 10'x6', this will be more than enough to do your whole wall. Even if you have to pay $200 to do it, it will be worth it to do it right.

In case you need anecdotal evidence to convince you, I've hung 8 pieces of 2 inch 703, framed and covered in my 13x14 livingroom/theater. My girlfriend, who loathes my constant tweaking, and wierd stuff hanging on the wall, has begrudgingly admitted, unsolicited, that dialogue is much clearer now and that she can tell the difference, especially when she watches movies at a friends house.

12 sheets of 703 - $120
Fabric, PolyBatting, and Frames - $80
Vindication from the girlfriend/wife - Priceless

In short, it's the best $200 I've put in my audio this year.

Thanks Eugovector, I've been trying to get through this whole thread but it's a daunting task (63 pages).

I'll pass on the pink insulation then. Is the 703 typically installed right onto the drywall or should it be moved back a few inches? Another question I have is fabric - I see a lot of folks using fabric from GOM or Dazian - is there an accoustical consideration here or is it because of design? I guess what I'm asking is can I use any old fabric on this wall as I'm most likely putting a curtain in front of it? Thanks again!

Thanks Eugovector, I've been trying to get through this whole thread but it's a daunting task (63 pages).

I'll pass on the pink insulation then. Is the 703 typically installed right onto the drywall or should it be moved back a few inches? Another question I have is fabric - I see a lot of folks using fabric from GOM or Dazian - is there an accoustical consideration here or is it because of design? I guess what I'm asking is can I use any old fabric on this wall as I'm most likely putting a curtain in front of it? Thanks again!

Anyone else, feel free to chime in...pretty much everything I know, I learned in forums like these (and this one specifically), so you are technically my source.

Tiga,

I think there is a question here of what you are trying to achieve. Most of the time, by treating a front wall, you are creating a "dead end", a wall that will not create unwanted reflections that mask/muddy the sound created by the main speakers. You'll want to treat all frequencies equally (not just high or mid).

To this end, you will want 2" of 703 outside the drywall. If you space it out 2 inches, all the better (you'll extend slightly the lower frequency absorption). This won't absorb a lot of low, low bass frequencies, but if you're going to put 4" of 703 anywhere, the tri-corners are a more effective spot.

To cover, I used thin cotton fabric from the $1 bin at walmart (and I think it looks great). Natural fibers is the key. Hell of alot cheaper than GOM, easier to find, just as effective, and not bad looking (though not as duriable).

Some curtains are designed to absorb sound. If you are going to put a sound absorbing curtain up, you can probably save putting insulation on the front wall. These curtains can be very expensive though, and hard to find. You can also stick with the 703, not even cover it all all (though I would put a layer of polybatting over the top to keep the fibers in) and get an acoustcally transparent curtain. This may not be the velvety look that you are going for.

The trouble with shiny, velvety curtains made from synthetic fibers is that some are actually very reflective. Put these in front of your 703, and it's like the 703 isn't even there. If this is what you have your eyes on, ust make sure that you get a very large curtain that, when hung, will have lots of folds in it. This will act to difuse the sound, i.e., send it out in all directions instead of straight at your ears. Make sure that you have plenty of absorbtion on your side walls, and this would still help to make you sound more defined.

12 sheets of 703 - $120
Fabric, PolyBatting, and Frames - $80
Vindication from the girlfriend/wife - Priceless

In short, it's the best $200 I've put in my audio this year.

What size sheets are those? How long did it take to arrive after ordering them? Did you use a piece of plywood on the backs of those panels or just frames around them? Your pictures were not detailed in the making of them.

Thanks

You just need some thin polyfill and loose cotton fabric. See the pictures and walkthrough in my thread: http://www.avsforum.com/avs-vb/showthread.php?t=734181

Post 18 in this thread. Stadard 2x4x2", no plywood.

OK, this seems straightforward from searching AVS and studying theater wall treatment...

FRONT WALL: Acoustical treatment (1" Insul-Shield) floor-to-ceiling.
CEILING: No acoustical treatment - none, nada.
FLOOR: Thick, plush carpet is fine.

But here's where it gets confusing, and I need help...

SIDEWALLS
A) Acoustical treatment (1" Insul-Shield) from floor to ear-height (44"), with 16oz polyester batting above.
--or--
B) Acoustical treatment (1" Insul-Shield) from floor-to-ceiling on all 1st reflective surfaces.

These 2 theories seem to contradict each other. So which is it?


BTW, for those searching for Insul-Shield type product, here are the substitutes which seem to have identical acoustical absorption ratings:

Owens Corning Select Sound Black Acoustic Board
Owens Corning Fiberglas 703 Series duct insulation.
Johns Manville Insul-Shield
Johns Manville Linacoustic Permacoate rolls.
Certainteed Certpro Acoustaboard Black
Knauf Duct board EI-475
Knauf Duct liner EM

...personally, I found the Knauf EI-475 easiest to find (4' x 10' sheets @ $40) from a general heating and air conditioning company.


Just wanted to find out out whether the insul-shield product (like Linacoustic) goes on top of drywall? or do you attach it directly to the studs?

eugovector

I think it's been noted several times in this thread that the pink stff will do nothing more than keep your room warm.
From a practical point of view, that's sort of true.

But actually, as it gets thicker, the adding denser stuff does nothing, because the lower frequency sound doesn't go through it, it just sort of bounces off.
If you're building an absorber that's more than 12" deep, fluffy fiberglass pink is the stuff to use. Not rigid fiberglass.
But for 2 inches, or 2 inches with a 2 inch air gap, rigid is the way to go.

http://www.bobgolds.com/Suntower/AbsorptionCoefficients_8inch_to_24inch_rockwool_fluffy_fiber glass.gif

Tiga

GoM is acoustically transparent (more or less), and fire resistant. Fire resistant is a big plus when you start doing entire walls with it.


If you're curious, you may as well read this if you haven't already.
http://www.infinitysystems.com/homeaudio/technology/whitepapers/inf-rooms_3.pdf


I'm not saying that I'm recommending this, or that it's a good idea, but I covered a significant amount of my front wall in absorption.
http://www.bobgolds.com/LivingRoomPlasma/Construction/home.htm

Thanks Bob - so it sounds like if I can find a fabric that is acoustically transparent I'm ok. I'm thinking about going with a medium grey fabric around the screen wall with a dark blue curtain going across the front. However I'm considering building out the columns around the corner piping out to the screen and placing the speakers inside of these and covering them with an acoustically transperent fabric and skipping the curtain.

Just curious if others regret using a curtain? Any issues with it. cleaning nightmare? Thanks.

My first suggestion is to rearrange things so you're not right in front of a wall. That's where the inevitable peaks and nulls are worst.

--Ethan

I will not be able to move the seating off the wall. What can I do to keep the peaks and nulls to a minimum?

Bass traps, lots. But still, room boundaries (right next to walls) are the worst spots in the room for bass.

I will not be able to move the seating off the wall. What can I do to keep the peaks and nulls to a minimum?

Use RoomEQ wizard and a BFD to EQ your sub. You'll be able to kill your peaks, and boost your nulls slightly, but don't get carried away.

[QUOTE=eugovector]Use RoomEQ wizard and a BFD to EQ your sub. QUOTE]

I'm sorry but you may as well be speaking Dutch. I dont know what any of those letters stand for. But, thanks for trying. :p

Use RoomEQ wizard and a BFD to EQ your sub.

I'm sorry but you may as well be speaking Dutch. I dont know what any of those letters stand for. But, thanks for trying. :p


Room EQ Wizard is a freeware program for taking instant measurements of frequency response (need: computer, SPL meter, tripod, cables)

BFD = Behringer Feedback Destroyer, $100 piece of pro audio equipment people use as a customizable "parametric eq" to equalize subwoofer output to attain flatter frequency response

eugovector:

Once upon a time, Room EQ Wizard (http://www.hometheatershack.com/roomeq/) was written to make setting the Behringer Feedback Destroyer DSP1124P (http://www.behringer.com/DSP1124P/index.cfm?lang=ENG) and FBQ2496 (http://www.behringer.com/FBQ2496/index.cfm?lang=eng) easy. Last I heard, they were no longer for sale. This is the list of currently available equalizers (http://www.behringer.com/02_products/group_index.cfm?mid=2&ID=100&lang=ENG#EQUALIZERS%20&%20ACCESSORIES)

Room EQ Wizard should be good for doing room measurements though. Instead of an SPL, I'd use a pre-amp (http://www.behringer.com/MX602A/index.cfm?lang=ENG) and a microphone such as the ECM8000 (http://www.behringer.com/ECM8000/index.cfm?lang=ENG).


causeofhim:
EQ is Equalization. In this case it's multiple parametric equalization filters. Each of these has a center frequency and bandwidth (bell curve center and width), and an amplitude -- basically a boost percentage or cut percentage. It gives you the ability to make some frequencies louder or quieter. If you have a modal peak(s), that's too low to absorb, PEQ (parametric equalization) can be used to tame it/them a bit.

eugovector:

Once upon a time, Room EQ Wizard (http://www.hometheatershack.com/roomeq/) was written to make setting the Behringer Feedback Destroyer DSP1124P (http://www.behringer.com/DSP1124P/index.cfm?lang=ENG) and FBQ2496 (http://www.behringer.com/FBQ2496/index.cfm?lang=eng) easy. Last I heard, they were no longer for sale. This is the list of currently available equalizers (http://www.behringer.com/02_products/group_index.cfm?mid=2&ID=100&lang=ENG#EQUALIZERS%20&%20ACCESSORIES)



Behringer-Feedback-Destroyer-Pro-DSP-1124P (http://www.musiciansfriend.com/product/Behringer-Feedback-Destroyer-Pro-DSP-1124P?sku=182467)

You can also find them all day long on ebay. Look into the BFD 1100 also, it's what I use, is identical except for a lower sampling rate, works perfectly with REQW, and can be found on the cheap.

This system costs hundreds less then systems from sub companies such as velodyne, offers much more customizability, and improves your low end significantly. For a $150 investment, everyone with a decent sub should invest in this solution.

The hometheater shack has a great forum post about a wish list for a product that Behringer could make specifically for hometheater subs. Everytime behringer make a product announcement, I hold my breath hopeing that they will, officialy, enter the Home Theater market.

I will not be able to move the seating off the wall. What can I do to keep the peaks and nulls to a minimum?

The best (only, really) solution is a broadband absorber that's as thick as possible so it works well to low frequencies.

--Ethan

eugovector:

The hometheater shack has a great forum post about a wish list for a product that Behringer could make I'd read it. I concur that it's a great post. :)
The day I read it I was looking for something in that forum that said what Behringer products Room EQ Wizard currently suported. I haven't played with Room EQ Wizard myself. I've used RplusD (http://www.etfacoustic.com/) which lists the parameters (frequency, bandwidth, boost) for as many filters as you'd care to try.
Nice to hear that it works with something else.
I was looking at Behringer FBQ2496 (http://www.behringer.com/FBQ2496/index.cfm?lang=ENG) the other day on their website -- it comes with a Panic button. :)

Going far far the other way in terms of money is this gaget http://www.audyssey.com/faq.html

Do you think that 2" 703 would be enough or should I try to make it 4"?

Do you think that 2" 703 would be enough or should I try to make it 4"?

I'm not even sure where are you putting the abosrbers yet. Behind you?

I hate to say it, but you've got a little bit of a mess here. Maybe you could post some pics or a different sketch? I'm just not seeing a lot of options.

How tall is your ceiling? Where are your speakers?

Going from the info that you've given, I'd put 2" panels on the wall behind you and at the 1st reflection points behind the front/center speakers. Put 2" on the ceiling and a thick rug/carpet on the floor if it isn't already carpeted. Put 4" at the corners where 2 walls and the ceiling meets as much as possible, and use the Room EQ/BFD solution described to try to tame other peaks.

Ethan will tell you that te BFD solution will do nothing to tame how long the waves bounce around the room, only how loud they are when they do (you can take out boominess, but not droning/smearing). He'll also tell you that you should cover every wall intersection in your entire room in 4" fiberglass (and, other than being overzealous, he's probably right). But, for a cheap, unobtrusive bandaid, the $100 BFD does wonders.

I'm not even sure where are you putting the abosrbers yet. Behind you?

I hate to say it, but you've got a little bit of a mess here. Maybe you could post some pics or a different sketch? I'm just not seeing a lot of options.

How tall is your ceiling? Where are your speakers?

Going from the info that you've given, I'd put 2" panels on the wall behind you and at the 1st reflection points behind the front/center speakers. Put 2" on the ceiling and a thick rug/carpet on the floor if it isn't already carpeted. Put 4" at the corners where 2 walls and the ceiling meets as much as possible, and use the Room EQ/BFD solution described to try to tame other peaks.

Ethan will tell you that te BFD solution will do nothing to tame how long the waves bounce around the room, only how loud they are when they do (you can take out boominess, but not droning/smearing). He'll also tell you that you should cover every wall intersection in your entire room in 4" fiberglass (and, other than being overzealous, he's probably right). But, for a cheap, unobtrusive bandaid, the $100 BFD does wonders.

I'll post a different pic when I get home later tonight. My ceiling is 7'6" and I will have a 5.1 set-up. The two fronts will be on each side of the screen with the center directly below. The rears will be on each side of the seating, facing the seating. The sub will be on the front wall, with the screen, I'm not sure where yet.

I was planning on placing 1" on the screen wall and ceiling reflection points and then placing 2"-4" on the back wall (behind our heads). Do you think I should go 2" everywhere? The floor had thick pad and carpet now.

I hope that helps.

I was planning on placing 1" on the screen wall and ceiling reflection points and then placing 2"-4" on the back wall (behind our heads). Do you think I should go 2" everywhere? The floor had thick pad and carpet now.


2" is significantly more effective, just ask Bob:

Bob Gold's Extensive Measurements (http://www.bobgolds.com/AbsorptionCoefficients.htm)

2" is kind of the sweetspot for sound-suck. 4" minimum is the rule for bass absorption.

I would not use the 2" material...it will very likely be too absorptive.



I was using info from this thread. It seems that the consensus on here that 1" is the "sweet spot".
If people think that 2" would be better in my situation, I will use it.
:confused:

I was using info from this thread. It seems that the consensus on here that 1" is the "sweet spot".
If people think that 2" would be better in my situation, I will use it.
:confused:

I'm not sure where the 1" comes from. The idea behind broadband absorption is that you want to absorb all frequencies equally, so you're not changing the tonal response of your room.

Now some rooms need a little tuning. If you have lots of hard reflective surfaces, you may want to focus on the high frequencies with 1". If you have a smaller room that has bass problems, but you don't want to make it too dead (can sound like listening to your room with a headcold, just very unnatural), you can used faced (FRK) fiberglass (better low end absorption, much less high end absorption).

But, a safe starter solution is almost always attacking 1st reflection points with broadband. This will help with dialogue clarity in movies and definition in music. In my experience, probably the biggest improvement you can make in a system for $150.

Then, look at low end control. This will balance your sound so it doesn't seem boomy or too thin. Try the BFD for an inexpensive half-solution, and add some corner traps as time, money, space, and significant others will allow.

From there, you can hit up the rest of the room with more absorption if it's too live, or diffusion if it's starting to sound dead (diffusion should also help to expand the listening sweetspot).

To others out there: Am I off on any of this?

My situation is a little tricker I would guess. I am moving into a house with an attached garage. The original owner closed off the garage and made it into a room with a dropped ceiling. I have been in this has before as I know the current owner and I would imagine that the garage has no real insulation as its hot in the summer and cold inthe winter.

I am not planning on doing any real construction to this room. Both the front wall where the screen would be and the right wall have long built in closets that go from one end of the wall to the other. They have metal folding doors.

I am going to replace the dropped ceiling tiles with black accoustic tiles.

I guess my question is, what should I do about the screen wall and the right wall. As my wife wont let me close off the closets space, at the very least I will need to change out the metal doors to wood.

Is there anything I can do to treat these wood closet doors which basically will wind up being the side and screen wall and secondly, as the rear and left walls are completely walls and cannot be touched, is there anything I can do for them

Although its not part of the topic, but woild placing insulation of over the top of the dropped ceiling and possibly in the closets help with the heat and cold.

Have read most of this thread. Lots of opinions! Am ready to apply some treatments using panels of 1" Knauf duct board, which I was able to find locally without trouble as opposed to 703, which has eluded me. Acoustic properties are close.

My question has to do with how to treat rear wall ompared to the front wall. My screen is painted directly to the drywall, so getting an absorbing material behind it is not going to be possible, unless you count the R11 behind the drywall already. I will make panels to surround the screen as best I can. The images below are what the room looks like, although there have been some minor changes.

The general consensus I have been able to glean is that the panels for first refelction points along the side walls need to extend from floor to ear height, more or less.

What about the rear wall? Should these extend from floor to ceiling, or continue with the ear height concept? Should I make the panels on the rear wall thicker than the front wall?

I am sure that if I build a dozen or do panels for the room, I will improve the sound quality over that of my drywall box regardless, but it would be nice to have made the most out of my effort.

I am planning using the mirror method to help me locate the panels for the side walls and maybe for the ceiling as well, although I will have to see how this all looks. The dimensions of the room are approx. 23' front to back 12' wide along the screen wall, and 15' wide at the seating area. Preliminarily, my plans are as follows. I hope that someone will leap in and either applaud me, rescue me from ruin, or offer a couple of tweaks:

http://www.chriswhitworth.com/finished1.jpg

I will flank the screen with panels along the left and beneath. I have a new PJ, and have grown the screen size to the right almost to the wall to the right and up, almost to the ceiling, so ther is no option to the right or above.

Along the left wall where the left channel and sub sit there will be a panel coming out of corner about 3' towards the sconce shining down as well as a matching one in the opposite corner. The speakers have been change to Klipsch Heresys for the front line, sitting on the floor. I will have panels behind these. Going down the right wall will be floor to ear height panels at probably two reflection points.

http://www.chriswhitworth.com/finished2.jpg http://www.chriswhitworth.com/rearcorner.jpg http://www.chriswhitworth.com/finished4.jpg

Looking back to the rear, you can't see because I compressed the images too much, but there are two rear surround in-walls that will impact how I treat this surface. A bass trap straddling the corner from floor to ceiling is planned but may be no more than a double layer of the 1" board (foil backing removed). It is the rest of the rear wall that I am unsure of. How tall should they be? Ceiling height at the rear of the room is barely 7'. I am thinking about a panel on the door. What about the rest of that wall? With the equipment rack where it is, trapping across the rear corner is not going to work. All the cabling emerges from a good sized opening behind the equipment. What would anyone suggest for this corner? Coming down the wall from the equipment rack corner I will place probably two panels at the reflection points. This has been complicated by the addition of a relatively large free-standing open shelf which replaces the black shelf shown in the pictures. I will have to pull it out from the wall to determine the locations for these panels. If you want to see all the pictures of my completed room, take a look here:http://www.chriswhitworth.com/complete.htm

I am looking forward to this project to tighten up my sound. I can tell it just isn't what it should be. Will be very grateful to anyone offering some advice.

Christer Whitworth

That is a nice little theater! Those seats look pretty comfy for having a slim profile.

Very nice room.

A few questions...

So the screen isn't centered on the wall, but up against the right wall (you say the screen has grown to the right wall)? Meaning the right speaker is basically up against the right wall? That's how it looks in the pictures, anyway. And now the speaker is in front of the screen?

Ideally the screen would be centered and the speakers would be much further away from the side walls, symmetrically spaced from the front and side walls. That would be ideal, even if it meant reducing the size of the screen slightly.

Can you center the seating and screen in the room? That would be the absolute best for the sound, and allow you to properly place 1st ref point absorbers on the sides.

But the speakers should also be moved forward more, away from the front wall. You can place bass panels in the front corners, either straddling the corner, or cut into triangles and turned into wedges. Do the rear right corner, but don't worry too much about the corner behind the equipment rack. If you treat the other three corners, you're already doing much better than most people, even here on AVS.

What are the areas that you feel your sound is lacking? Is dialogue unintelligible? Boomy or flabby bass? Instrument imaging lacking?

My opinion, if this were my room:

Front wall: the off center screen is throwing me. You're going to wind up w/ asymetrical sound regardless w/ center channel off center, more so if you treat one side of the wall. With no room for a bass trap in the right corner, I'd leave the front as is, with the possible exception of treating the 1st reflection points behind the speakers themselves. If you can bring the fronts forward a bit, and have enough room, then try a bass trap in the right corner (superchunk style)

Side Wall: 1st reflection points for sure (all the speakers, don't miss center, side, or back), sandwich 2 layers to give you 2". Focus on ear level, don't need to go to the floor or the ceiling.

Rear wall: Put 2 inch on as much as possible, focusing on the first reflection points. Bass trap in corner? Why not. Once again, Superchunk seems to be the easiest and most effective (fiber cut into triangles and stacked in corner to make a solid fiberglass tri-post)

Ceiling: 1st reflection point between your center channel and your seating positions.

Speaking of bass traps, if your material is anything like 703, you'll want 4 inches (had this pointed out to me when I asked a similar question). 2 inches won't do much of anything (trust me, I've tried and had Room EQ wizard confim that I was wasting my fibergass)

That is a nice little theater! Those seats look pretty comfy for having a slim profile.


If those are the poyang (sp?) chair, they are amazing comfy (and should be for over $100 for wood and a pad). They have a new chair that looks like the poyang, only cheaper, stay away!

That was my first reaction too, but he says the screen is painted on. Re paint, I guess, is an option.

Very nice room.

A few questions...

So the screen isn't centered on the wall, but up against the right wall (you say the screen has grown to the right wall)? Meaning the right speaker is basically up against the right wall? That's how it looks in the pictures, anyway. And now the speaker is in front of the screen?

Ideally the screen would be centered and the speakers would be much further away from the side walls, symmetrically spaced from the front and side walls. That would be ideal, even if it meant reducing the size of the screen slightly.

Can you center the seating and screen in the room? That would be the absolute best for the sound, and allow you to properly place 1st ref point absorbers on the sides.

But the speakers should also be moved forward more, away from the front wall. You can place bass panels in the front corners, either straddling the corner, or cut into triangles and turned into wedges. Do the rear right corner, but don't worry too much about the corner behind the equipment rack. If you treat the other three corners, you're already doing much better than most people, even here on AVS.

Chris,
Other than the tweaks you know you need, you might want to move the left speaker the same distance from the center of the screen as the right speaker. An SPL monitor wouldn't hurt.

Winkelmann

Talk about speedy replies! Don't you guys work? :D

In looking at my photos again, I can see your confusion. What you don't see is that I have a length of soffit running the full length of the left wall which houses HVAC vent and gas line. It starts out about 30" wide at the screen wall and grows to nearly 6' by the time it reaches the rear of the room as you can see here. You can also see how the riser has nowhere to go as far as re-positioning:

http://www.chriswhitworth.com/soffit.jpg

This gives you a better idea of the design issues I faced. In my previous shots, you can't see the entrance to the room. The white door in the shot above is to access HVAC and water heaters, not the entrance to the room. The shot below shows how the soffit and entrance (door with poster on it) affected the look of the room.

http://www.chriswhitworth.com/drywallup2.jpg

The screen is centered on the section of wall which has full ceiling height (8'). You can see a vertical seam that drops straight down from the soffit just to the right of the two electrical boxes in the corner in the picutre above. This section to the right is what the screen is centered on. The seating is centered in front of the screen. The speakers are in the corners. When you are in the room, if you really pay attention, you can tell the screen if offset to the right relative to the speakers , but not to the wall/ceiling interface. If I had centered the screen on the wall, not the ceiling, the left section of the screen would be under the soffit. If I did that, apart from making the room look out of balance, it would also have meant having to extend the riser to the left (looking forward) to center the seating, blocking access to my furnaces and water heaters. I really did give this a lot of thought. Regarding the perceived problem of the speakers being offset to the screen, I think the visual imbalance of having one speaker in the corner and the other two feet in from the corner is too high a price to pay for the very nominal improvement in imaging I would experience, but I will give it a try! The center channel is centered under the screen which is centered relative to the seating. Since in a movie, all/most dialog comes out of the center, I think my problems in this area are not as great as you may think. The only thing off center is the left speaker.

Funny, when I got my Heresys back in the 70's Klipsch themselves counciled putting all their speakers in corners. You may have heard of Klipschorns? I have always had them in the corner of every room they have ever been in. Nothing else ever ocurred to me. I suppose I could move them forward and inward, slightly. With grandkids LEAPING on to the Lovesac (basically a giant beanbag you can see in the earlier post), the idea of having the speakers out in the room is not one that thrills me. As you get older, the idea of life being a series of compromises comes home, over and over! :o

The screen itself is a product of Mississippi Man's Mudd formula that was popular when I built this three years ago. A combination of silver metallic udercoat and top coats consisting of a mix of clear base, ultra pure white and pearl opalesence. At Home Depot, they thought I was crazy when I had them mix it up for me. I have since re-painted it so that it is still in the same space, but slightly wider, and slightly taller. It was 106", now up to 118" diagonal. The black frame is now butting up against the right wall, and the top molding is pretty close to the ceiling, so there isn't any way to get anything meaningful on either side. Bottom and left are what's available.

The chairs are indeed from IKEA. I paid 69.00 for the Poang chairs and 40.00 for the ottomans. You could spend far more for something far less comfortable, so I consider them a good buy. Also, their trim lines keeps the room 'spare' if you will. They are very comfy. I went to a friend's house who had his HT done professionally and watched a movie sitting in his Berklines. I didn't find them any more comfortable, and they had no head rest support.

Eugovector,

I really appreciate your input on the treatments. I doubt that I would have doubled up all the panels. Maybe I can get a discount now that I will have to buy twice as much or perhaps I will get the 2" stuff to start with.

I see. Didn't realize the room was wider in the back, or that there was a riser. But you said the screen now goes to the edge of the wall on the right.

No matter what, the screen and speakers should still ideally be symmetrical on the wall they reside, even with the soffit in the upper left corner. The screen area needs to be moved to the left, in the center of the wall (regardless of the soffit - move the screen down if needed).

Try putting on some 2-channel music, and play around with the location of the speakers. Even if they are close to the front wall, changing their proximity to the side walls will drastically change their sound. The point of side-wall absorption is to absorb the sound at the first reflection point. But with the speakers right next to the side walls, you are making that much worse than it should be. And you don't want to put a panel to the side of a speaker inches away from it.

cyberbri,

Your suggestion means my seating will not be centered, or best case, the floor seats are centered, but the riser seats are off-set to the right.

In your gallery you have a picture of your daughter(?) kneeling on a bench/shelf. Next to her is an absorber shown wrapped in lilac. Is that mounted there full time? If so, I think we are coming from very different spaces in regards to how the balance of aesthetics vs sound performance needs to be addressed.

Don't get me wrong, and I am not criticizing, but I cannot imagine moving my screen down and to the left. The sight lines for the rear viewers, offest to the right in this new scenario would be like being in an old theater; they would have to look around the heads of the people in front of them to see the bottom of the screen. With my Heresys in place before I moved the screen up, the center was just flush with the bottom of frame. Moving it down at all would require either laying them on their sides, or making the screen narrow enough that the L&R would fit on either side and perhaps a different center channel. Neither of those sound good to me, no pun intended. :D

I just said "ideally." In the end, you have to do what works for you. Having speakers right next to the wall, and/or place asymmetrically, is very bad for the sound. If you only watch movies and don't listen to music in the room, that's probably not much of a concern for you. If you can find a way to treat the side walls and maybe the ceiling, that should help a lot, especially with the speakers so close to the side walls.

And no, the panels are not mounted or permanent. But they are there full-time. There's a window there, which is presumably even worse for reflections than a regular wall. We need the bench/shelf there, so putting the panel sideways on top of it worked the best. On the other side, the matching panel is sitting on the floor, propped against the wall.

So the balance of aesthetics vs sound for my living room is 45-55. If it was a dedicated room not used for anything but TV/movies/music/games, it would be 10-90 or 20-80, aesthetics vs sound. I would make sure everything (screen, speakers, seating) was centered and symmetrical and set everything up for the best sound and picture. Plus a lot more room treatments. I have done that as much as I can in my living room, to the extent that we have to have other furniture in the room because it functions as a living room as well, with a fireplace on the left and a large bay window on the right (and a desk w/computer in rear of room under R surround speaker). But I have kids (8yo and 2yo) and I still have my speakers out and not against the walls. They know not to touch or play around with them, and this is in our living room.

When I get everything put together, I will post new shots and PM you and eugovector.

Thanks again for your input.

[QUOTE=christer W.]Talk about speedy replies! Don't you guys work? :D /QUOTE]

Nope, I retired in 96'. Piddling around with construction projects, art and the like keeps me busy. :cool:

Christer,

I think you've been given some very good advice and I agree with it for the most part. Normally with 3 seats in the front you want to keep the main center position just a bit (6-12") off dead-center but with only 2 in the front it'd be perfect to center the seats exactly. IMO the solution for you is to make the screen smaller. A large screen is not necessarily better. What's needed (IMO) is a screen that's large enough to see all of the detail presented in the image. Too close and/or large and you see imperfections that you're better off never seeing, and too small will have you missing details. I suspect even an 70-90" screen would be plenty but you could test this yourself by just projecting a smaller image for a bit and seeing how the PQ looks. Some of the benefits of a smaller screen is that it'll be brighter and will also look like a more clear, detailed image from any given distance compared to a larger screen.

What I'd like to stress is for you to try things out for yourself. For Sound Quality, get some good music that you know inside and out, and then listen to it with your speakers where they are, vs pulling them 2 feet out from the rear and 2 feet in from the side walls. Then you can hear the difference that pulling them off the side walls makes, and judge the tradeoff for yourself. The consensus is that even toed in towards the listenner, speakers should be at least 18" away from the sides and from the rear also. Being too close to the sides will affect the voices and highs, while being to close to the rear will affect bass and lower frequencies.

Felgar,

Thanks for your reasoned response. I have been grateful of the advice given and will use it to the best advantage for my room.

Regarding the screen, what you may have missed is that I have made by screen BIGGER after having lived with the one you see in the pictures for near on 3 years, so this is not an impulsive newbie move. My earlier PJ was the Panasonic L200u that had/has 1/4 HD panels. On my 106" diagonal screen at 12", if I really looked hard, I could see a little SDE. So what? Still looked great. Still would have looked great if I had sprung for a new bulb. But, for only a little more, a 720p seemed like the way to go.

I went over to a fellow AVS'er who has a Panasonic L500 with 720p panels and the difference was very noticeable, this in spite of his projecting onto a 122" diagonal screenl. I was amazed at how those extra inches seemed to make such an impact. Had to go home and plan it all out. While I was at it, the idea of doing some sound treatments came to mind, which is how we all got here.

I am looking forward to making the panels. I am figuring about a dozen in various shapes, thicknesses,, and types. It should be fun and for not very much money.

I'm with you on some level, as viewing distance is, IMO, the most overlooked aspect in our bigger is better world. However, Christer is right on THX spec w/ his screen/seating distance. As long as he's watching high-res material on good equipment, it'll look fine. In the end though, unless you have a acoustically transparent screen and have positioned speakers behind it, you'll likely be sacrificing acoustics for image size in THX spec.

The rule of thumb that I use is seating distance should equal 2 times the 16:9 screen diagonal. Now, THX specs will tell you that this is way to small. Check out this calculator here:

THX Seating Distance Calculator (http://www.myhometheater.homestead.com/viewingdistancecalculator.html#anchor_13194)

I currently sit 7.5 feet away from my 51" screen, a little closer than 2x the diagonal. THX tells me that I should either be sitting less than 6 feet away, or that I should have a 67" screen. But I won't bemoving closer, or buying a bigger TV, and this is why.

Let me start by saying that I'm throwing out approximate numbers here, just working off the back of a piece of scrap paper. I'm sure my math is a little off with rounding and what not, but close enough for our purposes.

Speaker placement: Dolby recommends front speaker placement 22-30 degrees off center. THX suggests similar placement. Many opinions that I've read say that for movies, you should shoot for the 22 degrees, for stereo music, the 30. Break out our 11th grade trig books and we see that the distance between speakers should be between 0.8 (for movies) and 1.15 (for music) of the seating distance.

My screen is about 45 inches wide, with the bezel my TV is 48. On my fronts (JBL S38II), the tweeters are atleast 14 inches from the side of the speaker. That means that if I butt the speakers right against the edge of my screen, the tweeters are 73" apart. Realistically, leaving an inch or two in between, we're at 75-77". At my THX recommended seating distance of 5.7 feet (68.4 inches), the tweeters of the speakers should be between 55 (movies) and 79 inches (music) apart. That doesn't leave a lot of wiggle room, and I found that in my room, the 79" was even too wide for music. I also needed a wider sweetspot, as I'd be watching most movies as at a pair, not a single.

So what did I do? Buy smaller speakers? Nah, I compromised. Good sound was more important to me than the biggest picture image (especially considering that I won't be watching HD exclusively, but also a lot of upscaled and processed 480P). I spent a lot of time listening, and moving, and listening, and measuring, and listening, and moving, and listening some more.

So, long story short, I postioned my speakers correctly and use a rule of thumb that you should sit slightly less than 2x the screen diagonal away from your display. No complaints yet.

Christer, with your current screen size, you'll probably be sacrificing acoustics for screen size. If that works for you, don't worry about it. Do what you can with your current setup, and sit back, and enjoy. However, if you want to improve your sound, positioning everything correctly is the start.


IMO the solution for you is to make the screen smaller. A large screen is not necessarily better.

I plan on moving things around a little to see what sounds best. It should be interesting. Documenting all the changes will be the hardest part :D

Getting ready to enlist some help from a family member to sit in the chairs while I wander around the room with a mirror to figure out where to place my yet-to-be-built panels/traps. Was thinking about the idea of putting an incandescent light where the speakers are to help you get your reflection points, as suggested elsewhere on this thread.

What exactly do you get out of seeing the bulb that you don't get out of seeing the speakers themselves in the mirror? I am guessing you are trying to make it easier to see??? Why not just have your assistant aim a flashlight at the speaker itself, if necessary? Place the center of the speaker in the middle of the mirror, attach piece of tape/Postit note on wall behind mirror to mark center of panel....

Is there something I am missing?

Getting ready to enlist some help from a family member to sit in the chairs while I wander around the room with a mirror to figure out where to place my yet-to-be-built panels/traps. Was thinking about the idea of putting an incandescent light where the speakers are to help you get your reflection points, as suggested elsewhere on this thread.

What exactly do you get out of seeing the bulb that you don't get out of seeing the speakers themselves in the mirror? I am guessing you are trying to make it easier to see??? Why not just have your assistant aim a flashlight at the speaker itself, if necessary? Place the center of the speaker in the middle of the mirror, attach piece of tape/Postit note on wall behind mirror to mark center of panel....

Is there something I am missing?

Hi Chris - The main thing is to see the speaker in the mirror at your seated position. Whether the speaker is lit up, there's a light bulb in place of it, or there's a small statue of Elvis where the speaker will be, should pose no difference in the outcome. There could be some unexpected trauma for the seated person suddenly seeing Elvis when he really should be working at the 7-11 across town, but that's not an acoustic issue and outside the scope of this discussion.....

Going solo? Use a laser with the mirror method to find first reflection point.

Ahh,

The laser. Hmm....something to use my pointer for other driving my cat crazy making her chase the red dot on the floor.

Not sure how the laser helps with going solo. Can you elaborate on this technique? Doesn't the mirror have to move back and forth until the person in the chair sees the speaker? I suppose if you had a large enough mirror, you eye-ball where you think it should appear, place the mirror there (hoping you have the correct vertical angle so your beam doesn't go right over or under the target) and then use the laser to pinpoint the location of the center of the panel....

christer W.

I'd use the laser for direct pointing your speakers, and not for the mirror trick.

The problem with the light bulb, is that you have to move your speaker to put it there. And it would only work if you walls were painted gloss so the light would reflect. Or for example if you have a plant in the way, it's not going to work.

You can calculate mathematically where the wall reflection point is (if your walls aren't square mathematically is a little trickier, and if they're curved use a mirror), or if you have a 3"x3" mirror and some post it notes, then you can sit and someone else can move the mirror along the wall until you can see the speaker in the mirror and then they can put a post it note there labeling the name of the speaker you can see. So each left/right wall should have three post it notes (left speaker, right speaker, center speaker) for each seating position. Then where you want first reflection point absorbers is a minimum 1' outside of all the post it notes.

The phrase you may recall from grade school is "angle of reflection equals angle of incidence". Sound is bouncing off that wall.

Later, if you do measurements with RTA software, the difference in time/distance (because sound travels at 1130ft/s, 1 foot is approximately 1ms) between the direct sound path length (e.g. 3'), and one of The Mirror Trick reflection sound path lengths (e.g. 13'), is the corresponding spike that appears in your impulse graph (e.g. 13' - 3' = 10', aka a spike that appears 10ms after the direct sound).
In this graph (http://forum.studiotips.com/download.php?id=3669) there's a spike at 29.9ms (direct sound), and another one at 31.1ms (reflection) and another one at 39.5ms (reflection).
31.1 - 29.9 = 1.2 feet. (approximately)
39.5 - 29.9 = 9.6 feet.
On a frequency response graph it appears as comb filter dips.

See the Direct vs Reflected macromedia flash at
http://www.acoustics.salford.ac.uk/acoustics_world/duck/duck.htm

http://www.audioholics.com/news/uploads/slide02.gif
http://www.audioholics.com/techtips/roomacoustics/roomacoustictreatments3.php

http://www.msr-inc.com/sp_installation.php

http://www.etfacoustic.com/mirrortrick.html

http://www.bryston.ca/newsletters/43_files/vol4is3.html

http://www.asc-hifi.com/acoustic_basics.htm

http://www.auralex.com/auralex_acoustics_faqs/mirrortest.asp

http://www.stjohngroup.com/downloads/CINEPANEL/040712_CINEPANEL_install.pdf (see page 2)

http://forum.studiotips.com/viewtopic.php?p=14288#14288
look at "1st Ceiling Reflections.pdf", "1st Side Reflections.pdf"

http://www.audioholics.com/techtips/roomacoustics/Acoustics101THX2.php

http://psbg.emusician.com/ar/emusic_welltempered_studio_2/

http://www.realtraps.com/art_room-setup1.gif

http://www.realtraps.com/art_room-setup3.gif

BasementBob,

Thanks for the links. Most interesting. I have now come upon something that has me even more slightly confused than before. The MSR site you suppled to a link to has a very complete installation guide to their products. What has me confused is this image and subsequent text:

http://www.msr-inc.com/pics/installation_vbar.gif

My confusion stems from the advice given throughout this thread that the treatment of side walls should extend up to ear level, or a figure of 44"- 48" is seen often. The diagram is hard to make out, but their instructions are not:

"Fasten a V-Bar so the bottom of this bar is 64 inches from the floor onto the wall using either drywall screws into studs, using wallboard inserts and screws, or other appropriate fasteners."

You then hang the panel with its already attached V bar mate. In the diagram, you can see that their panels extend a couple of inches higher than the V bar, and they are off the floor about 18-24" - hard to tell exactly.

So which is it? Obviously, I can experiment, but am loath to put holes in my walls that may later need to be patched and painted

christer W:

Both are valid.

There are a bunch of different styles of applying acoustical treatment.

One is Dennis Erskine Style (i.e. copying the romours, not an actual DE designed theater which is almost certainly better).
Another is putting a bunch of 2'x4' panels, roughtly evenly spaced throughout the room.
There are others.

The only example of a bunch of 2'x4' panels, in a home theatre, that I have handy are these:
http://www.realtraps.com/cust_ht1.jpg
http://www.realtraps.com/cust_ht2.jpg
http://www.realtraps.com/cust_ht3.jpg
http://www.realtraps.com/cust_ht4.jpg
http://www.realtraps.com/cust_ht5.jpg
http://www.realtraps.com/cust_ht6.jpg

In a DE Style theatre, the rule is
a) front wall, floor to ceiling, wall to wall, 1" of linacoustic
b) side and rear walls, floor to half way up the wall, 1" of linacoustic. Assumption that the mirror point of all speaker drivers to all listener's ears is lower than the half way up the wall point.
c) side and rear walls, half way up the wall to ceiling, polyester batting
d) lots of leather covered couches (bass absorption)
e) rear riser and columns with bass traps (helmholtz, membrane)
f) deeper absorption (e.g. 6" 703 with 4" air gap behind) on some side/rear wall surfaces
g) carpet with thick underlay
h) soundproof rigid walls, preferably decoupled with something such as RSIC, and green glue to damp the wall resonance.

So, the absorption is used to do two things:
1) change the RT60 of the room so it's a little on the dead side
2) handle first reflections and SBIR issues.

Where the absorption is not, the idea is to let the sound reverb (bounce) around the room to increase ambiance and spaceousness, and reduce knowledge of directivity. Notice how the front 3 speakers have absorption on all sides, but the left/right/rear surround speakers have reflective surfaces near them (walls without absorption). Imagine the sound bouncing around above your head for many reflections.

What it sounds like where your ears are not, who cares.

An obvious side effect of treating the entire room's bottom half, is that it doesn't matter where the seats are placed, or where the listener sits, it's guranteed that first reflections are handled. No mirror trick is required.

If you're putting 2'x4' panels up, the mirror trick is required. If it's possible to spread them out with space between each, that's better (a diffusive and a LF absorptive effect) -- but for the main left/right reflection point in a home theatre with 3 or 4 front seats, and a second row, this is usually impossible.

So, in summary, you want to absorb the actual reflection. But you also want to have sound bounce around the room a bit. Both the designs/recommendations you spotted do that in different ways.

BasmentBob,

Thanks very much for your concise distillation of the entire 64 page thread. Had I known to ask, I could have saved myself hours of reading.

I look forward to the the mirror exercise.

Chris,

> I look forward to the the mirror exercise <

I don't understand why Bob linked only to the pictures on the RealTraps site but not the accompanying articles, because that would have been much more useful to you. While you're at our site, click Acoustics Info at the top of any page, then Acoustics Articles. There also are videos that show how to set up a room properly for speaker and bass trap placements etc.

--Ethan

christer W:

Another is putting a bunch of 2'x4' panels, roughtly evenly spaced throughout the room.
There are others.

The only example of a bunch of 2'x4' panels, in a home theatre, that I have handy are these:
http://www.realtraps.com/cust_ht1.jpg
http://www.realtraps.com/cust_ht2.jpg
http://www.realtraps.com/cust_ht3.jpg
http://www.realtraps.com/cust_ht4.jpg
http://www.realtraps.com/cust_ht5.jpg
http://www.realtraps.com/cust_ht6.jpg




If I'm not mistaken, that's Ethan's house. May not be your cup of tea, but probably sounds great.

I have started a new thread on needing help with Acoustical Treatment with room dimentions and graphs. I did not where would be the best place to put it so Here (http://www.avsforum.com/avs-vb/showthread.php?t=796208) is the link over to my thread in the audio theory section.

Great reading. Thank you one and all for the primer. Now, lets talk specifics about ME! I am building a new room. I don't need to worry about sound bleed to other parts of the house. The room is approx.. 17' long and 15.5 wide. I treated under the drywall with a sound barrier material (about 5/8" thick soft fiber material recommended by the builder). At one end is screen. Screen is surrounded by a full wall cabinet. Two ends of cabinet are tall storage to ceiling. Screen is centered on room between two tall end cabinets (106" horiz.). Under screen across bottom is OPEN area of cabinet (fabric covered) where I plan to include center speaker and a sub (hidden away). Two front speakers sit 5' from front wall on carpet. Room has two levels, with first row of seats back about 11/12' and second row against back wall (17'). I will have a second, smaller sub in back of room to supplement bass. Here's my plan--
NO treatment for front wall (behind screen and cabinets). Use pre-made 1" thick fabric covered panels all around room, starting at chair-rail height and going up to ceiling. I want to find the best of both worlds for listening to 2-channel (hence no treatment on bottom 24" of all walls) and heavy treatment above 24". 2 side and 2 rear speakers are NOT dipole -- placed just above ear level. Ceiling has a 1' soffit all around (except front) but I was thinking about NOT treating that. I want to keep some liveliness to room because I am, at heart, a 2-channel guy struggling to get great sound from both HT and stereo. Am I completely off base???

Interesting article, rather technical, but good reading:
http://support.siasoft.com/Downloads/binary/TechNotes/CaseStudy2/case2.pdf

cyberbri, good info. Did you ever actually address these issues with specific tools/solutions? What was the outcome after solutions?

No, someone just posted it on a thread at hometheatershack.com. I'm on those forums mainly for REW/BFD stuff. I'm learning as well.

But I do have some room treatments (@ side wall 1st ref points, 1 behind center channel, and panels in front corners for bass traps), plus a BFD for my sub.

Treatments made a dramatic difference. I could elaborate...



Here's a few more good reads, although it's more fundamental stuff:
http://www.soundandvisionmag.com/idealbb/view.asp?topicID=28194
http://www.soundandvisionmag.com/idealbb/view.asp?topicID=38945


And another article:
http://www.prosoundweb.com/install/sac/v28/2/interact.php

Thanks. I will review this.

Be carefule putting your center channel in a bookshelf or other "box", it can dramatically affect the Sound Quality, and not in a good way.

I found wall treatment beneficial, even in 2 channel listening. With out reflections smearing and masking the sound, I started hearing instruments and background noises that I never heard before. If you want to keep the room live, treat the first reflection points only and keep the rest of the walls bare, but treat on as many of the 6 surfaces as you can.

Great reading. Thank you one and all for the primer. Now, lets talk specifics about ME! I am building a new room. I don't need to worry about sound bleed to other parts of the house. The room is approx.. 17' long and 15.5 wide. I treated under the drywall with a sound barrier material (about 5/8" thick soft fiber material recommended by the builder). At one end is screen. Screen is surrounded by a full wall cabinet. Two ends of cabinet are tall storage to ceiling. Screen is centered on room between two tall end cabinets (106" horiz.). Under screen across bottom is OPEN area of cabinet (fabric covered) where I plan to include center speaker and a sub (hidden away). Two front speakers sit 5' from front wall on carpet. Room has two levels, with first row of seats back about 11/12' and second row against back wall (17'). I will have a second, smaller sub in back of room to supplement bass. Here's my plan--
NO treatment for front wall (behind screen and cabinets). Use pre-made 1" thick fabric covered panels all around room, starting at chair-rail height and going up to ceiling. I want to find the best of both worlds for listening to 2-channel (hence no treatment on bottom 24" of all walls) and heavy treatment above 24". 2 side and 2 rear speakers are NOT dipole -- placed just above ear level. Ceiling has a 1' soffit all around (except front) but I was thinking about NOT treating that. I want to keep some liveliness to room because I am, at heart, a 2-channel guy struggling to get great sound from both HT and stereo. Am I completely off base???

Be carefule putting your center channel in a bookshelf or other "box", it can dramatically affect the Sound Quality, and not in a good way.

I found wall treatment beneficial, even in 2 channel listening. With out reflections smearing and masking the sound, I started hearing instruments and background noises that I never heard before. If you want to keep the room live, treat the first reflection points only and keep the rest of the walls bare, but treat on as many of the 6 surfaces as you can.
I agree completely. We strive for timbre match of all speakers in a surround system, especially the LCRs. Placing one closer to a boundary - or in a "box" - will change it's sound.

My experience with adding absorbers at the first reflection points is that it made a dramatic difference in the clarity of everything, especially speech, and greatly improved mains/surround integration. The space behind my false wall is lined with 2" J-M Linacoustic, the front floor has a thick rug with the heaviest rubber pad I could find and the ceiling, front left & right walls and the back wall have 2" OC SelectSound Black. So that I wouldn't use more absorption than I needed, I was very careful to cover only the area needed to do the job. BTW, the absorber that made the BIGGEST difference? Rear wall.

If I'm not mistaken, that's Ethan's house. May not be your cup of tea, but probably sounds great.

Yes, it's my home and it sounds excellent. Hey, what's wrong with acoustic panels hanging all over the place?! :eek:

If audiophiles will accept huge tower speakers with a pile of gear in the middle of the floor, all on pedestals and with cable elevators holding up speaker wire as thick as garden hose, then why not 40 bass traps? :D

--Ethan

I put a bunch of new pictures of my home theater and treatments (GIK Acoustics) in a new gallery (see signature). I don't have a ton, but I do have enough to make a big, noticeable difference. I have bass traps in the front corners and absorber panels on the left/right sides at the first reflection points, with a panel behind the center speaker.

cyberbri, have you considered a helmholtz resonator at 95 Hz to try to do something about that null? Or is that not a concern for you?

Yes, it's my home and it sounds excellent. Hey, what's wrong with acoustic panels hanging all over the place?! :eek:

If audiophiles will accept huge tower speakers with a pile of gear in the middle of the floor, all on pedestals and with cable elevators holding up speaker wire as thick as garden hose, then why not 40 bass traps? :D
Ummm . . . our wives? ;)

cyberbri, have you considered a helmholtz resonator at 95 Hz to try to do something about that null? Or is that not a concern for you?


I haven't thought about it much. That dip/null appeared when I recently moved my speakers to their new location - it wasn't there with the speakers at their previous location. I'd have to run some 0/180 degree phase sweeps again, but assuming it's due to interaction between sub and speakers, I plan on adding some more bass traps in the future anyway. I am hoping to build some wedges to go behind the current corner panels. Hopefully that will fix or at least alleviate that drop.

I haven't thought about it much. That dip/null appeared when I recently moved my speakers to their new location - it wasn't there with the speakers at their previous location. I'd have to run some 0/180 degree phase sweeps again, but assuming it's due to interaction between sub and speakers, I plan on adding some more bass traps in the future anyway. I am hoping to build some wedges to go behind the current corner panels. Hopefully that will fix or at least alleviate that drop.
If you're crossed at 80Hz, then the subs are probably not involved in producing such a steep/deep null.

I'll have to run some 0/180 phase sweeps again. But I think, at least in my situation, changing the phase had a large effect on the 80~160Hz range.

That's cool cyberbri. I'm no expert but I interpretted those results as possibly needing a resonator, and was wondering if you'd tried it and what success you'd had. I'll be interested to see what your further efforts yield...

I'll have to run some 0/180 phase sweeps again. But I think, at least in my situation, changing the phase had a large effect on the 80~160Hz range.

I think moving the speakers might be a much more effective and less costly solution than more bass traps.

I think moving the speakers might be a much more effective and less costly solution than more bass traps.


Before I had them in an equilateral triangle, spread pretty far apart. Then I used the formula provided by Ascend to reposition them (340SEs), which tightened up the already tight center stage - and the sweet spot on the couch is wider now too. I can experiment a little more with placement, but imaging and soundstage are more important overall to me than a narrow null there.


Actually, I went back and looked at my old graphs. I had them up on the HSU Research forum. These show the response of the sub in its current location, combined with the left/right mains in the previous location (equilateral triangle):
http://forum.hsuresearch.com/showpost.php?p=21739&postcount=10

You can see the dip/null in the "crossover disengaged" graphs. The 0/180 degree phase interaction at 60-80Hz and 100-200Hz is interesting to watch.


Phase = 0, Sub Crossover Engaged (max 80 or 90Hz):
http://forum.hsuresearch.com/attachment.php?attachmentid=609&stc=1&d=1168319600


Phase = 180, Sub Crossover Engaged (max 80 or 90Hz):
http://forum.hsuresearch.com/attachment.php?attachmentid=610&stc=1&d=1168319600



Phase = 0, Sub Crossover disabled (playing full signal):
http://forum.hsuresearch.com/attachment.php?attachmentid=611&stc=1&d=1168319600


Phase = 180, Sub Crossover disabled (playing full signal):
http://forum.hsuresearch.com/attachment.php?attachmentid=612&stc=1&d=1168319600

Howdy Y'all,

I wasn't satisfied with anything I saw commercially available, so a few months ago I bought a bunch of 8lb rock wool insulation to treat my room. Until now, it's just been leaning up against the walls in the theater, doing a fine job making the room sound good, and look awful.

I finally got going on doing something about it, and today I finished building my first panel absorber. I'll make 4 more to hang between each of my poster frames, then tackle the problem of dressing up the 4" thick corner pieces.

Eventually the wall and ceiling will be painted more appropriate colors, but that'll be no problem since the panel is hung on cleats. Easy on, easy off!

The vitals:

84" x 25.5" x 2.25" hardwood frame (stained & oil-rubbed)
Open back, spaced 1.75" from the wall
GoM Black fabric on the front
8lb 2" thick rock wool insulation

More pics here. (http://homepage.mac.com/wgilpin/PhotoAlbum12.html)

Thoughts?

Thanks to everyone who posted information about room treatment, sound absorbent materials and GoM fabric! This forum is an inspiring place.

Cheers,

They look great!

Wes those are sweet. I am going to make some panels in a few months and I never thought of staining the frames that was brilliant. And my wife saw it and fell in love with the idea.

Nicely done. I like that color combo of the cloth and stain.

Bryan

The vitals:

84" x 25.5" x 2.25" hardwood frame (stained & oil-rubbed)
Open back, spaced 1.75" from the wall
GoM Black fabric on the front
8lb 2" thick rock wool insulation



Looks great. Where did you get the rockwool? How much was it? I'm assuming it's stiff like 703, or atleast stiff enough to stay in the frame with only your two braces?

I asked a similar question about rockwool vs. 703 in this thread:
http://www.avsforum.com/avs-vb/showthread.php?t=794904

Thanks for all the compliments y'all!

Looks great. Where did you get the rockwool? How much was it? I'm assuming it's stiff like 703, or atleast stiff enough to stay in the frame with only your two braces?
I bought the rock wool from SPI (Specialty Products & Insulation) here in Austin. They had the 4" thickness in stock, but I had to order the 2". Still, it was MUCH less expensive than similar OC products. I got 8 4" batts and 12 2" batts for approx. $150.

8lb rock wool is denser than OC703 or OC705. That's part of the reason I chose it. It's relatively stiff, and will stand up on its own. In fact, the 4" pieces will stack vertically without the bottom one collapsing. You can see a couple of the remaining 2" pieces leaning up against the wall in one of my pictures.

The two braces you're seeing don't actually touch the insulation. They're the cleats that the frame hangs on, and are attached at the ends of the spacers.

The frame is 1/4" deeper than the insulation, so there's room for me to staple in some retainers behind the batt if I need to. However, the pieces that are in this first panel are just friction-fit. The frame ended up a little bit tighter than I wanted it to be, so the insulation is in there quite snugly and won't be going anywhere. I'll build the rest of them 1/8" wider so the fit is looser.

Cheers,

Wow, that sounds like an amazing price. I bought 12 4'x2' of OC 703 for $120 and thought I was getting a deal. I take it these pieces were 4'x2'?

Any concerns about the fibers getting into the air from the back?

Thanks for all the compliments y'all!


I bought the rock wool from SPI (Specialty Products & Insulation) here in Austin. They had the 4" thickness in stock, but I had to order the 2". Still, it was MUCH less expensive than similar OC products. I got 8 4" batts and 12 2" batts for approx. $150.

8lb rock wool is denser than OC703 or OC705. That's part of the reason I chose it. It's relatively stiff, and will stand up on its own. In fact, the 4" pieces will stack vertically without the bottom one collapsing. You can see a couple of the remaining 2" pieces leaning up against the wall in one of my pictures.

The two braces you're seeing don't actually touch the insulation. They're the cleats that the frame hangs on, and are attached at the ends of the spacers.

The frame is 1/4" deeper than the insulation, so there's room for me to staple in some retainers behind the batt if I need to. However, the pieces that are in this first panel are just friction-fit. The frame ended up a little bit tighter than I wanted it to be, so the insulation is in there quite snugly and won't be going anywhere. I'll build the rest of them 1/8" wider so the fit is looser.

Cheers,

Wow, that sounds like an amazing price. I bought 12 4'x2' of OC 703 for $120 and thought I was getting a deal. I take it these pieces were 4'x2'?

Any concerns about the fibers getting into the air from the back?

Yes, they're 24" x 48" batts. The rockwool I have is not Owens Corning brand. I think it's Roxul brand. SPIs price on OC was much higher than what I got, but after checking the acoustic performance numbers for the rockwool, I decided that it would do just fine for me.

I'm not too terribly concerned about the fibers from the back. Unless someone reaches back there and pokes at the insulation, it should be stable and not just spontaneously throw off fibers at random. If I'm ever convinced that it's an issue, I can just staple some of my left-over GoM scraps in the back, since the frame is deeper than the insulation.

Cheers,

I have heavy velvet curtains on both sides of my screen. Is there a reason to put Insul-Shield on the front wall behind the curtains?

I have heavy velvet curtains on both sides of my screen. Is there a reason to put Insul-Shield on the front wall behind the curtains?

If the curtains are acoustically transparent, yes. Odds are they're not, so no, not really. In theory, you could put ~4" panels behind to absorb bass, but you'd probably be better going with corner placeet on those anyway.

I finally got going on doing something about it, and today I finished building my first panel absorber. I'll make 4 more to hang between each of my poster frames, then tackle the problem of dressing up the 4" thick corner pieces.
They look great. One thing I couldn't tell from the pics is how you fastenned the GOM to the frame. It looks like it's attached to the inner side wall but I couldn't see how you did that while making the GOM flush with the front and pulled nice and smooth. It surely isn't just stapled, right?

They look great. One thing I couldn't tell from the pics is how you fastenned the GOM to the frame. It looks like it's attached to the inner side wall but I couldn't see how you did that while making the GOM flush with the front and pulled nice and smooth. It surely isn't just stapled, right?
Good catch! No, it's not just stapled.

I wanted to avoid the pillow-like look that would result from just stapling the fabric to the inside of the frame. I needed a sharp, crisp corner, but it was also important to me that the nice wood frame remain a visible part of the design.

I figured that the best way to do this would be to sandwich the fabric between the frame and a thin strip of wood around the inside perimeter of the frame. However, I didn't want the strip to leave a "step" on the the inside of the frame. Such a step would get in the way of installing the insulation. So, I made a rabbet in the inside-front edge of the frame to allow the fabric and the retaining strip to be stapled flush with the inside of the frame.

I've attached an image that shows the inside of the frame after the upholstery is stapled and trimmed. You can see the strip stapled into the rabbet, with the fabric sandwiched in between.

Maybe a little bit of overkill, but the results are worth it, IMO.

Cheers,

I've attached an image that shows the inside of the frame after the upholstery is stapled and trimmed. You can see the strip stapled into the rabbet, with the fabric sandwiched in between.

Maybe a little bit of overkill, but the results are worth it, IMO.
Thanks for the extra description. Going back I can see the rabbet is just barely visible in some of the pictures of the frame also. Excellent work, and I agree that the results are most certainly worth it.

Wgilpin,
What did you use to fasten your panels to your wall. I am going to make some diy panels this weekend or next.

Wgilpin,
What did you use to fasten your panels to your wall. I am going to make some diy panels this weekend or next.
I used french cleats. They're easy to make and even easier to use. Just rip a board with the saw blade set at 45 degrees. Trim one piece about an inch shorter. Attach the longer part to the frame with the cut pointing down, and the shorter part to the wall with the cut pointing up.

In my case, I used the cleat as a horizontal support as well, spanning the width of the frame between the spacers. Since I didn't want any visible fasteners, I used dowels to attach the cleats to the spacer blocks.

If you look at the attached picture you can see the cleat in action. The top part that's attached to the frame is stained, and the part screwed to the wall is not, so the parts and how they mate is easy to see.

Cheers,

Hi All:

Please for give me if these questions have already been asked and answered. There is tons of info in this thread. I intend on fabricating some acoustic panels for the first reflection points for my 12'x16'x10 listening/theater room.

From what I’ve been seeing on the board many of the DIY’ers use Owens Corning 703 semi ridged fiberglass insulation in the construction of their panels. Where have you been able to buy this stuff? I’ve tried Lows, Home Depot, & Menards no joy. It looks like the OC 703 and 705 are readily available from on line retailers but I’d like to avoid the shipping cost. Plus I enjoy making that extra trip back to the store after realizing that I forgot to buy something for a project. :D

Also, while doing some research on the Owens Corning website I found a product called SelectSound Black Acoustic Fiber glass. From the spec sheet it comes in one or two inch thick, 4’x8’ sheets. Is anyone familiar with this product? Would this be better for making bass traps?

If you call Owens Corning's 1-800 # they will tell you places that locally carry a particular product.
I called them and they directed me to a place locally (in St. Louis) that carry it and it was 703 2" thick 2'x'4' for 10.75 a sheet no min. order.

Where have you been able to buy this stuff?

I see you're in Milwaukee. You may want to try SPI...
http://www.spi-co.com/servicecenterdirectory.cfm

The location in Lake Bluff, IL is probably ~an hour from you. I got very good prices from them, and they were able to get the material I needed within about a week.

I've seen it on eBay in cases, and here in cases:
http://sensiblesoundsolutions.com/product_info.php?cPath=21&products_id=29

I'm planning on trying some Superchunk style corner bass traps. It seems the Roxul RHT 40 semi-rigid boards at 3.5 pcf are close to OC 703 at 3 pcf.

Any recommendations regarding this particular density vs. more or less dense mineral wool for a corner bass trap in the Superchunk style?

I'm planning on trying some Superchunk style corner bass traps. It seems the Roxul RHT 40 semi-rigid boards at 3.5 pcf are close to OC 703 at 3 pcf.

Any recommendations regarding this particular density vs. more or less dense mineral wool for a corner bass trap in the Superchunk style?
http://www.hometheatershack.com/forums/home-audio-acoustics/3028-bass-traps-eq.html

http://www.hometheatershack.com/forums/home-audio-acoustics/3309-living-ht-layout.html

Here are a couple of informative threads regarding corner traps that may help. :) .

http://www.hometheatershack.com/forums/home-audio-acoustics/3028-bass-traps-eq.html

http://www.hometheatershack.com/forums/home-audio-acoustics/3309-living-ht-layout.html

Here are a couple of informative threads regarding corner traps that may help. :) .

Thanks!!! Those are excellent threads. They lead me to this thread which also helped.

http://www.hometheatershack.com/forums/home-audio-acoustics/2259-bass-traps.html

Looks like my answer is to stay with the lower density 3.5 pcf mineral wool!

First thanks for all of you responses to my inquiry.

The fine peeps at SPI (Lake Bluff Ill) were able to point me in the direction of a retailer in the MKE area. If you need to contact them there info is as follows.

Lake Bluff, IL
1301 Laura Lane
Lake Bluff, Illinois 60044
847-362-0925
847-362-7889 FAX
http://www.spi-co.com/servicecenterdirectory.cfm

For anyone looking in Milwaukee or Madison check out.

Acoustech Supply Inc
1710 South 106th Street
Milwaukee, WI 53214
http://www.acoustechsupply.com/

Both of these vendors are very helpful and do have OC703 & 705 available at very reasonable prices. You must purchase a full carton of either though.

703 2” comes 12ea 2’x 4’ sheets to a carton. $1.30 sq/ft
705 1” comes 10ea 2’ x4’ sheets to a carton. .60 sq/ft

Dom

I was at a local JoAnn's Fabrics store today and came across some nice synthetic suede material. I'm considering it to cover the 1" thick Linacoustic panels I'll be putting up on my side and rear walls. Trouble is, it didn't pass the "blow through" test.

I noticed SoundSuede at AcousticalSolutions.com and SonoSuede at Auralex.

I'm guessing they are similar to what I saw at JoAnn's, but perhaps they are more "acoustically transparent."

Anybody having experience using this type of fabric to cover panels for first reflections care to comment on how well it works and whether SoundSuede or SonoSuede passes the "blow through" test?

I was having a hard time finding OC703 here in Salt Lake, but did find a source for both Knauf and Johns-Manville who make similar products with similar acoustic properties. the J-M was slightly less money for 2" - 1.40/ft compared to 1.75 for the Knauf, so I was all set to go. When I got there, a very helpful guy asked me what I was doing with this stuff, so I told him and he suggested Rockwool. Said a local HT installer bought tons of it all the time. Same size panels - 2X4', 6 pcf, slightly better performance on paper, and barely half the cost.

I bought black burlap at JoaAnn's for 2.99/yd. They thought I was nuts when I told them I wanted 15 yards! The burlap was a bit of a mess to work with (leaves a lot of broken fibers on the table you are working with, but it does look good. No sheen to it, and it has a nice texture.

I faced the panels with 1/2" poly batting to give the panel surface some 'spring'. Spray adhesive to attach the batting to the panels. Hot glue to fasten the fabric over the batting onto the back of the Rockwool. It would be a stretch to say they have a lot of structural strength, but all they have to do is look good. Doing it again, I would frame the Rockwool to give me something solid to work with for mounting. If you go here (http://frenchcanvas.com), you can find pre-cut artist frames for making canvases for painting. The come in all sizes, require no tools other than a mallet to pound the corners together, and are pretty cheap when you consider you can put together a rock-solid frame in a matter of a couple of minutes without creating a ton of sawdust. A 2X4' panel frame would run you less than $10. Interesting, anyway.

I tried using Velcro to attach them to the walls, but the Rockwool panels (and OC too, I suspect) just don't have enough density for the Velcro adhesive to grip onto. Probably wind up using hot glue to fasten a couple of relatively large (6"x6") piece of thin board to the panel that I can then either screw eye hooks into, use Velcro though kind of pricey, or the 45 degree miter cut board trick.

Pretty happy with the results. Dialog is more distinct, sound overall is more precise. Subtle, though. Perhaps more panels?

Pretty happy with the results. Dialog is more distinct, sound overall is more precise. Subtle, though. Perhaps more panels?
If I've missed it, I apologize - did you "do" the ceiling and back wall?

Hi all.

Got a question about treating my first reflection point.

Quick diagram attached to show you what I mean below.

I purchased some acoustical panels from GIK (fantastic company to deal with BTW).

I have a panel at my first reflection point (Red).

I have an extra panel and am wondering if I need to put it in the green area?

Since that far wall is over 18' away and partially blocked by the stairwell walls I am not sure if it would do any good there? My screen and speakers are blocked by the right hand side (stairwell walls) so wouldn't all the reflections just happen there?

Bryan? (sorry I lost your e-mail address) any comments?

Thanks for any suggestions

Edit: fixed the link. Sorry about that. Any ideas all?

Pepar,

I did three panels under the screen measuring 17" high by 36" long, covering most of the lower portion of the screenwall. I may place a couple of smaller panels to the left of the screen above the lower panel in some sort of decorative pattern. Need to resolve the mounting solution first.

I also placed two 24"x48" panels on their sides along the back wall just above the riser. This spans most of the width of the riser Ear height for the two front seats is about 36", so this puts the rear panels at that height. There are seldom viewers in the rear row, so it is not of consequence. I have considered using the remaining three 7"x48" strips as some sort of corner trap where the rear wall meets the ceiling at the rear of the riser.

I put panels coming out of each corner flanking the screen, as well as another at the first refelction point, all 36" high. The left panel could be moved and replaced with corner trap. No such option on the right side. So, a total of 8, all 2" thick. I did not put a panel on the ceiling.

My overall sense is that it is a good start, but for not a lot more dough, I could add another half dozen panels here and there. One of the problems I ran into when I did the mirror trick was that there always seemed to be something in the way where I wanted to place a marker for a panel. Like a door, or electrical outlets, or speaker hookups. Thought I had planned it all out. :D

Given the relative incremental improvement in sound, not sure how far I want to go with this experiment. I like my rooms to have clean lines with spare furnishings, so am not too gung-ho about filling this room with panels on every surface. May need to find a different color to provide some contrast to the heaviness of the black.

I will get some shots taken this week.

I'd say that you should be getting very significant changes, unless things are positioned wrong.

What do I mean by significant?
1) My Girlfriend noticed the dialogue being easier to understand.
2) Her friend who still watches his 37" LCD with a composite cable connecting the DVD player, and listens through the built in speakers, made an unsolicited comment about how the room didn't sound "like a small livingroom. It's creepy actually"

I have 9 2'x4' panels up in a 14x15 room, so t be 10 if I get around to covering the final one this weekend.

Pepar,

I did three panels under the screen measuring 17" high by 36" long, covering most of the lower portion of the screenwall. I may place a couple of smaller panels to the left of the screen above the lower panel in some sort of decorative pattern. Need to resolve the mounting solution first.

I also placed two 24"x48" panels on their sides along the back wall just above the riser. This spans most of the width of the riser Ear height for the two front seats is about 36", so this puts the rear panels at that height. There are seldom viewers in the rear row, so it is not of consequence. I have considered using the remaining three 7"x48" strips as some sort of corner trap where the rear wall meets the ceiling at the rear of the riser.

I put panels coming out of each corner flanking the screen, as well as another at the first refelction point, all 36" high. The left panel could be moved and replaced with corner trap. No such option on the right side. So, a total of 8, all 2" thick. I did not put a panel on the ceiling.

My overall sense is that it is a good start, but for not a lot more dough, I could add another half dozen panels here and there. One of the problems I ran into when I did the mirror trick was that there always seemed to be something in the way where I wanted to place a marker for a panel. Like a door, or electrical outlets, or speaker hookups. Thought I had planned it all out. :D

Given the relative incremental improvement in sound, not sure how far I want to go with this experiment. I like my rooms to have clean lines with spare furnishings, so am not too gung-ho about filling this room with panels on every surface. May need to find a different color to provide some contrast to the heaviness of the black.

I will get some shots taken this week.

I didn't say it wasn't significant, only that from this point forward, the improvement would be incremental. I would say the room is still 'lively', but 'better' than it was. Not my goal. Dialog is more distinct, staging is more precise. Clearly, if I put enough Rockwool in there, I could smother all the highs and create a 'dead' room. As I did not take any measurements (not that I know how to do that anyway), it is all gut feel.

Still, for only $125, it has been a fun experiment. Just have to figure out a good way to fasten them to the walls and move on to the next project - bigger screeen, and then on to the next: rope light in a crown molding trough up near the ceiling. Good excuse to buy a compressor/nailer.

I didn't say it wasn't significant, only that from this point forward, the improvement would be incremental. I would say the room is still 'lively', but 'better' than it was. Not my goal. Dialog is more distinct, staging is more precise. Clearly, if I put enough Rockwool in there, I could smother all the highs and create a 'dead' room. As I did not take any measurements (not that I know how to do that anyway), it is all gut feel.

Still, for only $125, it has been a fun experiment. Just have to figure out a good way to fasten them to the walls and move on to the next project - bigger screeen, and then on to the next: rope light in a crown molding trough up near the ceiling. Good excuse to buy a compressor/nailer.
The biggest improvements in my room were made by placing absorbers at the first reflection points that produce delayed sound at 0° and 180°, i.e. the front wall (behind the LCR spkrs), the ceiling and the rear wall. I "think" the left and right front wall panels made a difference as well, but no where near as much as the ones I just mentioned. Beyond the FRP panels, I would only use additional absorption if the acoustics of the room needed it.

I realize in my previous post that there is a line out of place. My phrase "Not my goal" was meant to go AFTER my assertion that I could load the room up with Rockwool and make the room dead.

I think the rear wall will get more attention next. The front wall just doesn't have the real estate to work with.

Without frames, these panels that are 2'x4' weigh about 8-9 lbs. I wonder if I couldn't do a picture hanger method. IOW's secure two anchors to the back of the panel with a wire across and a nail-syle hanger in the wall. Don't like punching holes in the wall unless I have to.

Pepar,

Where did you put your panels in the ceiling relative to your speaker placement and seating position? I am sitting about 12' from the back. Ceilings are 8'. speakers are flanking the screen with the center in the center.

pepar, where did you put your panels in the ceiling relative to your speaker placement and seating position? I am sitting about 12' from the back. Ceilings are 8'. speakers are flanking the screen with the center in the center.
Tip: Forget about the mirror trick. Think pool and bank shots. Angle of incidence = angle of reflection. Stand to the side and look at a front speaker and the seating positions. Visualize a line from the speaker to a seat bouncing off the ceiling in between "leaving" at the same angle that it "arrived." Repeat for all front speakers and all seating positions and cover the "bounce points."

I was able to cover three speakers to six seating positions with a panelized 4x8 sheet of OC SelectSound Black. You can click on the link in my sig and see the whole process documented.

First(or early reflection) points question. Do Dipole front speakers have a first reflection point like a typical box-type speaker? Specifically a Magenpan panel type speaker. Do they need to be treated differently?

First(or early reflection) points question. Do Dipole front speakers have a first reflection point like a typical box-type speaker? Specifically a Magenpan panel type speaker. Do they need to be treated differently?
Oh man, dipole fronts certainly complicate things, but yes. Obviously, you wouldn't be treating the first reflection point behind the speaker, but all of the others, especially floor, ceiling and rear wall would benefit from proper treatment.

For more (much more) on dipole's and dipole placement see the Linkwitz Lab.
http://www.linkwitzlab.com/

For more (much more) on dipole's and dipole placement see the Linkwitz Lab.
http://www.linkwitzlab.com/
And probably MUCH more than he needs - or has time - to read. If he's going to get anything usable at all from that site, he should probably start with the room acoustics (http://www.linkwitzlab.com/rooms.htm) section.

Oh man, dipole fronts certainly complicate things, but yes. Obviously, you wouldn't be treating the first reflection point behind the speaker, but all of the others, especially floor, ceiling and rear wall would benefit from proper treatment.


Technically, I would be treating that point with bass traps in the corner, would that have a detrimental effect on the dipoles?

Technically, I would be treating that point with bass traps in the corner, would that have a detrimental effect on the dipoles?
The point behind the dipoles would get traps? Wouldn't that suck out the highs along with the lows?

The point behind the dipoles would get traps? Wouldn't that suck out the highs along with the lows?


How would you deal with bass traps in the corners then? I'm all ears.

How would you deal with bass traps in the corners then? I'm all ears.
Well, there are more "corners" in a room than the vertical ones at front left and front right where the L&R mains are located.

How would you deal with bass traps in the corners then? I'm all ears.

And you can always go with FRK 703 foil side out. Highs will reflect off, and it's actually better at absorbing low Freqs according to Bob Gold.

And you can always go with FRK 703 foil side out. Highs will reflect off, and it's actually better at absorbing low Freqs according to Bob Gold.
Wouldn't it just be better to avoid any treatments around the dipoles?

Wouldn't it just be better to avoid any treatments around the dipoles?

No, I agree. I'm just offering options. His room setup and sense of asthetics may not allow him to adequately treat the room otherwise, and if he doesn't like the sound of FRK, simply peal the foil off, and you've got the makings of a broadband panel that can go elsewhere in the room. It can't hurt to try.

Wouldn't it just be better to avoid any treatments around the dipoles?

Maybe I can clarify something. :D

The fact that dipole speakers radiate equally front and rear is a byproduct of their design, not necessarily a design goal. Sort of like a figure 8 microphone. It is what it is. This does not mean the rear radiation is a good thing. IMO it is not because it guarantees you'll have SBIR peaks and nulls up into the higher frequencies, not just at bass frequencies as with typical box loudspeakers.

If it were me I'd put a fair amount of absorption on the front wall behind the speakers. In fact, this is one of the few cases where I think front wall absorption is really necessary.

--Ethan

So then you disagree with many of the conclusions of that Linkwitz lab Room Accoustic site posted a few days back Ethan? Some of the arguments showing the level of ambient noise vs. sound directly from the speaker I felt were very convicing. Since I've spent 20K+ on monopoles I'm not about to switch, but if you shared your thoughts about that topic it might make me feel a bit better. :)

The fact that dipole speakers radiate equally front and rear is a byproduct of their design, not necessarily a design goal. Sort of like a figure 8 microphone. It is what it is. This does not mean the rear radiation is a good thing. IMO it is not because it guarantees you'll have SBIR peaks and nulls up into the higher frequencies, not just at bass frequencies as with typical box loudspeakers.
I'm not so sure it's a byproduct. I'm more sure that it's the way the designer wants them. Which is why I haven't liked anything other than front radiators including Amar Bose's claim to fame. Sorry, not looking to flame or get flamed; it's just my personal taste. :)

Maybe I can clarify something. :D

The fact that dipole speakers radiate equally front and rear is a byproduct of their design, not necessarily a design goal. Sort of like a figure 8 microphone. It is what it is. This does not mean the rear radiation is a good thing. IMO it is not because it guarantees you'll have SBIR peaks and nulls up into the higher frequencies, not just at bass frequencies as with typical box loudspeakers.

If it were me I'd put a fair amount of absorption on the front wall behind the speakers. In fact, this is one of the few cases where I think front wall absorption is really necessary.

--EthanI am not so sure that's the case. The rear radiation does contribute considerably to the overall sound field resulting in a difference in how the sound pressure falls off with distance. In my experience with Apogee full range dipoles, putting absorbtion across the front wall (behind the speakers) made them sound closed in and undynamic. Diffusion worked well.

If two speaker systems sound different, at least one of them is wrong. If that isn't controversial, the rest of it might be: And probably both are wrong.

If we are to be transported to the "environment" created by the artist/producer/enginer, the room needs to be REMOVED from the equation. Dipoles depend mightily on the room.

Dipoles are intended to create non-localizable sound. They do this two ways, firstly they are out of phase so the direct sound from the speaker is not localizable, and secondly they bounce the sound off multiple walls enhancing the effect. This is optimal for movie background sounds such as music, raindrops, crouds, and traffic noise -- which are often delivered through the side and rear surround speakers, taking advantage of this intended and expected effect.

Personally I watch a lot of action movies, so I prefer monopoles for my side surrounds, giving me more directionality than is recommended by THX. This is optimal for sounds like bullets and jets flying overhead from front to back. I bought surrounds with a monopole/dipole switch in them, and I've tried both settings.

IMO, buying dipole surround speakers, and then absorbing the front and rear walls (or side walls for rear dipoles in a 7.1 system), is probably silly. Diffusion on the other hand is probably a good idea. You may have noticed that in DE Style theatres, the side and rear walls do not have absorption above the ear level, and that's where the dipole speakers go -- far away from absorption at their level, to maximize bouncing of that sound around the room, increasing ambience.

Dipole front speakers would be odd. I can't see a point in those. Since localization is required for imaging, and there's lots of intended and required L/R imaging in the front speakers in movies.

Dipole front speakers would be odd. I can't see a point in those. Since localization is required for imaging, and there's lots of intended and required L/R imaging in the front speakers in movies.
BINGO!

Dipole front speakers would be odd. I can't see a point in those. Since localization is required for imaging, and there's lots of intended and required L/R imaging in the front speakers in movies.Good point. They rely more on room acoustics for their soundstage presentation than do monopoles. Of course, such soundstaging is artificial and particular to each room. I used to have dipole and bipole front speakers when I was a 2 channel guy but I realized how incompatible they would be in multichannel. By extension, I also realised the same about their stereo performance, as well.

Kal Rubinson:

I was just about to post something very similar. Heck, I'll post anyway :)

For stereo music, thin dipoles placed close to the front wall, or omnipole speakers also close to the wall, sound great. I've heard them. It's not so much that it's relying on the room (well, speakers always do that) but rather that they give the room another opporutunity to create spaciousness by bouncing off the unabsorbed front wall. And the delay is pretty short, so you probably won't notice any degridation if you get the distance from the wall right.

But I once did a test with an omnipole, and the results kinda scared me for home theatre -- even though off axis response with omnipole is pretty even (i.e. almost exactly the same awful curve as the straight out axis).
http://www.bobgolds.com/SpeakerTests/20060810/home.htm
A monopole speaker response (http://www.bobgolds.com/SpeakerTests/20060810/PsychoAcoustic01.GIF)
An omnipole speaker response (http://www.bobgolds.com/SpeakerTests/20060810/PsychoAcoustic09.GIF)

On the one hand, one can criticise your tests because all these speakers require different boundary relationships to sound right and you tested them even-handedly.

On the other hand, the more they depend on those relations, the more sensitive they are to particular rooms and placement and the more the overall sound is that of the room, rather than the speaker.

Hmmm, now I am even more confused. I know that I was warned before I purchased my Maggies for Home Theatre use, but the love of thier sound was too good to ignore. When I called Magnepan, they told me that I could reduce the reflective sound(from the rear) using extra acoustic fabric attached to (or under the existing fabric), they told me that using wall treatments behind them is not necessary.

My main problem in my room is a spike @ 500hz and I need to tame that (in addition to some minor bass trapping ) and I have modal ringing that needs to be addressed. My ceiling is acoustic-type ceiling tiles(NRC rating of .75) and carpeted floor (on Drycore) with a 1/2" solid rubber padding(commercial quality). The room is a small room, approx size of 10x15 with 7' ceiling height.

Jim

Felgar:

> So then you disagree with many of the conclusions of that Linkwitz lab Room Accoustic site posted a few days back Ethan? <

I didn't see that article, but if it says that the sound of your room being imparted onto everything you hear is a good thing, then I guess I disagree. :D

Kal:

> The rear radiation does contribute considerably to the overall sound field <

Sure, just as Bose did many years ago with their 901s. :D

Again, this comes down to whether someone prefers the sound of their room being added to everything they hear, or prefers to hear what the mix engineers intended. This is also the point pepar made. I would never tell someone what they should prefer. All I can do is publish response graphs showing the options and let them decide.

BTW, not all dipole manufacturers recommend leaving the front wall bare.

> Diffusion worked well. <

Yes, and at least then the diffusion will break up the reflections to minimize the SBIR at mid and high frequencies.

--Ethan

Perhaps a "preference" is, as with an opinion, to be more respected (and valid) when it is an educated one. Are dipoles the Pepsi Challenge of speakers? Is the rear radiation - in the right room - the sugar that causes people to prefer dipoles even though they are probably not hearing a faithful reproduction of what the engineer/producer heard? When I was young, I preferred a goosed bass. Not until I became more experienced and educated in sound reproduction did I learn what "flat" was. Until I was enlightened, flat bass sounded anemic. When I finally heard flat bass down to 20Hz, I realized that that was correct. Almost immediately, goosed bass sounded artificial. I overcame my preference for the sugar of a fat bass with education.

I've heard Magnepans a few times and they sounded incredible, but I couldn't say that what I heard was accurate.

Felgar:

> So then you disagree with many of the conclusions of that Linkwitz lab Room Accoustic site posted a few days back Ethan? <

I didn't see that article, but if it says that the sound of your room being imparted onto everything you hear is a good thing, then I guess I disagree. :D
This is the link. http://www.linkwitzlab.com/rooms.htm

The article is agreeing with you that less ambient sound and more sound directly from the speaker is desirable. However the article asserts that the dipole actually has more directly radiated SPL at the listenning position than a monopole in a given room. From section C3 in the link:
A typical reverberation distance is actually quite small, 0.72 m (2.4 ft) for the monopole and 1.24 m (4.1 ft) for the dipole in the example room. Never-the-less, the ratio of direct sound Ld to reverberant sound pressure level Lr is 4.8 dB greater for the dipole than for a monopole with the same direct sound output. Thus, at 3 m distance from the source, the direct sound would be 20*log(3/0.72) = 12.4 dB below the reverberant sound field for the monopole and only 20*log(3/1.24) = 7.7 dB below it for the dipole.

The 4.8 dB lower level of the reverberant field in the case of the dipole significantly reduces the masking influence of the room upon sonic detail.
Would love to hear your thoughts on it, because from my limited understanding the facts presented seem to make sense.

the article asserts that the dipole actually has more directly radiated SPL at the listenning position than a monopole in a given room.

It's not clear if those numbers were predicted or actually measured. Small rooms don't really have true reverb, so I'm not sure the same metrics can be applied.

I don't have a lot of personal experience with dipoles, though of course I've heard them. When people used to ask me if they should put absorption on the front wall, I'd always tell them to ask their speaker maker and report back. Finally someone did, and the speaker maker told them that absorption there is good. I don't recall which brand of speaker it was though. Then a few months later I visited a customer with a pair of dipoles, and the speaker maker's rep was there. The rep told me he always recommends front-wall absorption.

If anyone reading this who has dipoles, and is local to me (near Danbury CT), and wants to experiment and run a few tests, send me an email from my company's web site:

www.realtraps.com/contact.htm

Then we can report the results here.

--Ethan

However the article asserts that the dipole actually has more directly radiated SPL
You sure it says SPL not energy? There would be more energy but less audible sound due to phase cancellation...at least in the case of surrounds.

You sure it says SPL not energy? There would be more energy but less audible sound due to phase cancellation...at least in the case of surrounds.
I haven't gone through the calculation myself, but I believe that the on-axis gain property of a dipole is being used here. A doublet sound source will produce more concentrated on-axis sound pressure at low frequencies*. Same as a dipole surround which is aimed front-rear will produce more pressure along the front-rear axis, rather than the sides. No energy gets lost, of course -- only redirected by a change in directively pattern.

- Terry

* with respect to the source spacing distance

You sure it says SPL not energy? There would be more energy but less audible sound due to phase cancellation...at least in the case of surrounds.
Well, I interpret "Thus, at 3 m distance from the source, the direct sound would be 20*log(3/0.72) = 12.4 dB below the reverberant sound field for the monopole and only 20*log(3/1.24) = 7.7 dB below it for the dipole." as being SPL, but admittedly it's a little over my head which is the reason I'm asking for more input from the experts here. I believe in this context the speakers in question are the LR mains in a stereo configuration.