Acoustical Treatments Master Thread - Page 19 - AVS | Home Theater Discussions And Reviews
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Dedicated Theater Design & Construction > Acoustical Treatments Master Thread
piercedb's Avatar piercedb 08:50 AM 08-01-2005
Thanks bpape and Ethan! The density study was quite interesting and helpful. I think its interesting that the panels can be set in the corner and still work without rigid mounting. That is good though, it means less work!

mbegala's Avatar mbegala 03:07 PM 08-15-2005
I am in the process of acoustically treating my dedicated home theater. I'll be installing JM Insul-Shield on the walls and am looking for advice on locations for bass traps.

My room is 23 x 14. The ceiling slopes from the side wall to the ceiling starting at 70" up from the floor (see diagram below). The flat part of the ceiling is approximately 5' wide and 9' tall.

__
/ \\
| |
-------

The "barn" shaped walls are at the two ends (long dimension) of the room, one of which has the screen and front speakers, and the opposite wall contains the entry door as well as equipment and storage cabinets. Links to pictures of each can be found in my signature (sorry no URL's allowed as this is my first post).

On the front (screen) wall, there is 70" of vertical corner available to install a corner base trap. On the back (equipment) wall the vertical corners are occupied by cabinetry. Above the cabinetry there is an open area along the sloped portion of the ceiling.

With this limited space, I was planning on installing base traps in the front vertical corners, as well as above the cabinets on the back wall.

Is there an alternate placement that would work better?

Thanks...

Michael
bellm's Avatar bellm 11:54 AM 08-18-2005
I am in the process of deciding how acoustically treat my dedicated home theater.

My room is 20' 7" x 17' 1" with 9' drywall ceiling. I have Jamo D7 THX Ultra II speakers (7) and a Martin Logan Descent sub. There will be a 7' riser the width of the room along the back wall. front speakers will be mounted at 5' and surrounds and rears will be mounted at 6'. If I will use the room for 80% home theater and 20% music, what acoustic treatments should I install?



Thanks,

Michael Bell
ChrisWiggles's Avatar ChrisWiggles 11:59 AM 08-18-2005
Quote:


what acoustic treatments should I install?

A combination of absorption and some diffusion, basically, like always.

I recommend F Alton Everests master handbook of acoustics.
Ethan Winer's Avatar Ethan Winer 09:11 AM 08-19-2005
Michael,

> what acoustic treatments should I install? <<br />
Bass traps in as many corners as you can manage, and mid/high frequency absorbers at the first reflection points. If you have hardwood floors you'll probably want a little more mid/high absorption on the ceiling. If you have large areas of bare wall, you'll need some absorption there too. That's the short answer. For the complete story see my Acoustics FAQ:

www.ethanwiner.com/acoustics.html

--Ethan
SevenOut's Avatar SevenOut 11:23 PM 08-20-2005
Great info, thanks for the help!
almd's Avatar almd 08:31 AM 09-11-2005
I am building a room 14'x9'x28' with the ceilings sloping to 6'5" because it is a bonus room above the garage. the rest of the house is on the first floor. Screen wall and left wall are to exterior. Right wall is to attic. floor to garage. back wall to pretheater room.
I am concerned about sound in the rest of the house. I do not intend on watching loud movies into the wee hours of the night but I just don't want the attic or garage to act like a speaker box. I used to live in a poorly constructed apt and the guys TV upstairs would just echo in my bedroom so I am fearful of this. my AV guy says I don't need special insulation techniques...just using cocoon blowin insulation around the room and regular drywall with 2x4 framing. Anyone have experience with this. I was thinking about greenglue or quietrock but would love to save the money.
He is also recommending Sonance inwall/inceilings and sunfire sub. Do the Sonance inwalls allow a lot of sound out the back of these and can I still blow insulation over them?
One more random question. The HVAC guy has started to put the 3 vents along the right side of the room at about 5 feet off the ground. I just realized there has to be a grill or something on the wall there which will be ugly. Any ideas on where else to put them?
ARthur

ESGSeattle's Avatar ESGSeattle 10:52 AM 09-18-2005
I was hoping that someone could connect me to a good acoustic guy in Seattle. Any Ideas?

Thanks

Evan
ChrisWiggles's Avatar ChrisWiggles 10:54 AM 09-18-2005
How good is good?

i.e. what are you trying to, and budgetwise?
ESGSeattle's Avatar ESGSeattle 11:07 AM 09-18-2005
My theater is built, at least the room and sound system. I have an inwall Triad system. However, I'm experiencing a lot of reflected sound. The room has just aquired carpet. I have seats on order. But, playing audio sounds like I'm waiting for a concert and the sound is bouncing around the auditorium. Well, I've been reading about others making their own panels. Sounds interesting. But, I want the job done right. I see you're in Seattle, what's your experience? Would you like to see my echo chamber?
ChrisWiggles's Avatar ChrisWiggles 11:10 AM 09-18-2005
I'm just a DIYer, so if you want to go that route...

I've pmed you some other info though.
SuprSonik's Avatar SuprSonik 03:12 PM 09-22-2005
Hi everyone, I am just about finished painting my theatre room and am ready to do some acoustic treatment. I needed a few things cleared up though...

When finding the first reflection points using a mirror, am I supposed to do this for just the Front R/L speakers, or the center/rears as well? I read that only the point up to where your ears are should be covered as well, does this mean I shouldn't put any rigid fiberglass above ear level or on the ceiling?

I'm not totally sure why the entire front wall needs to be covered too. It seems like no sound would be bouncing off that area. But if it's recommended, I'll do it. However, what about the area with the screen? Should I put the fiberglass up all over the wall first, then put the screen up? Or put the fiberglass around the screen (making the screen appear as though it's impressed into the wall?)

I'm planning on using 2" thick stuff, and I want to space it out from the wall a bit. What would be the best material to mount between the fiberglass and drywall? Wood?

Thanks for any help. I'm almost done with the painting, so I hope to get started on this soon.
BasementBob's Avatar BasementBob 04:55 PM 09-22-2005
SuprSonik:
Quote:
I'm not totally sure why the entire front wall needs to be covered too.

'Needs to' depends on how good you want it.
Have a look for SBIR and 'speaker radiation pattern'.
You can still hear music and lyrics if you are beside, or even behind, a speaker. So sound bounces off the front wall, and superimposes with the sound that you hear, perhaps cancelling out some frequencies.

I recently found this good explanation of Speech Intelligibility
http://meyersound.com/support/papers/speech/index.htm
Terry Montlick's Avatar Terry Montlick 08:14 PM 09-22-2005
Quote:
Originally Posted by SuprSonik View Post

Hi everyone, I am just about finished painting my theatre room and am ready to do some acoustic treatment. I needed a few things cleared up though...

When finding the first reflection points using a mirror, am I supposed to do this for just the Front R/L speakers, or the center/rears as well?

No. Only the front speakers need to have their early reflections absorbed. This is to keep the front sound-stage tight and accurate. Reflection is good for the surround speakers.

Quote:


I read that only the point up to where your ears are should be covered as well, does this mean I shouldn't put any rigid fiberglass above ear level or on the ceiling?

Not necessarily. It depends on how much absorption your room needs. As for the ceiling, sometimes there are early reflections which need to be absorbed there. This depends on the directivity pattern of your speakers, as well as how they are place.

Quote:


I'm not totally sure why the entire front wall needs to be covered too. It seems like no sound would be bouncing off that area. But if it's recommended, I'll do it.

It may not be absolutely necessary. If you know beforehand that your front speakers do not significantly radiate at medium to high frequencies toward the screen wall (considering toe-in!), you don't need it. It is always a good safety measure, however. In commercial cinemas, where the speakers are located behind a perforated screen, front wall absorption is used largely to kill reflections from the screen back towards the front wall.

Absorption on the front wall also follows the live-end dead-end model (room is live in back, dead in front), which works well for home theater surround sound. The front wall is also generally a convenient, available area for absorption.

Quote:


However, what about the area with the screen? Should I put the fiberglass up all over the wall first, then put the screen up? Or put the fiberglass around the screen (making the screen appear as though it's impressed into the wall?)

If you are using an ordinary non-perforated screen, you don't need fiberglass behind it.

Quote:


I'm planning on using 2" thick stuff, and I want to space it out from the wall a bit. What would be the best material to mount between the fiberglass and drywall? Wood?

You could space it out with furring strips. Spacing the absorption from the wall enhances low frequency performance.

Regards,
Terry
bpape's Avatar bpape 08:41 PM 09-22-2005
Just for clarity, all 3 front speakers should have reflection points covered - not just L and R.

Also, I've found in some cases that even without a perforated screen, having some 3lb fiberglass behind the screen tends to help focus things from a center image standpoint. I don't worry about this too much unless the person is also going to be doing a lot of music listening - especially 2 channel. However, this is WAY less important than taking care of the reflection points elsewhere IMO.
BasementBob's Avatar BasementBob 10:38 PM 09-22-2005
bpape
Quote:


However, this is WAY less important than taking care of the reflection points elsewhere IMO.

Yep.
It's a time and volume thing.
The volume/loudness/signal (speaker radition pattern) out the front of the speakers is louder out the front than the sides.
Reflections off the side walls (and floor and ceiling) arrive much closer in time to the dirrect sound than any reflection off the front wall.
KWhite's Avatar KWhite 06:23 AM 09-25-2005
"Spacing the absorption from the wall enhances low frequency performance."

Do you have any absorption coefficients for 1" OC 703 mounted with 1" spacing off the wall?
Ethan Winer's Avatar Ethan Winer 09:50 AM 09-25-2005
K,

> Do you have any absorption coefficients for 1" OC 703 mounted with 1" spacing off the wall? <<br />
It will be very similar to 703 2 inches thick.

--Ethan
SuprSonik's Avatar SuprSonik 01:24 AM 09-26-2005
Thanks guys, I think I've got it now. If I have enough spare fiberglass left over, I'll put it behind the screen like bpape suggested. I've always preferred headphones for music, so this is mostly home theatre I'm talking about here.

The only place I've been able to find OC703 is this place, and I'll have to order in bulk of 96ft, and it will have to be shipped to me. I'd prefer to avoid this problem if possible. I know John Manville makes a similar material called Spin-Glas, but I haven't been able to find that locally either. Do you know of any other brands that make rigid fiberglass so I could check on those too?
bpape's Avatar bpape 04:57 AM 09-26-2005
CertainTeed makes a 3lb/cu ft equivalent as does Johns Manville

96sq ft is a pretty standard purchase for 1" - that's half a carton (12 pcs). For 2", it's a whole carton.

You can get less but by the time you pay the shipping, the cost per piece will kill you if you're only buying a couple of pieces. Shipping cost on something that size is purely by size - not weight. IOW, you'll pay the same amount to have 2 pcs of 1" shipped to you as you will 12 pcs.
SuprSonik's Avatar SuprSonik 04:08 PM 09-26-2005
I see...thanks. I have one more question; which is best for this type of use? "Plain", "Foil Scrim Kraft", or "All Service Jacket"? I decided on going with 1" because I don't want it to sound too dead. Here's the specs of Plain vs FSK vs ASJ according to Knauf's site:


---------------125hz 250 500 1000 2000 4000 NRC
Plain 1" (25mm) .08 .23 .62 .88 .96 .99 .65
FSK 1" (25 mm) .21 .63 .84 .93 .51 .22 .75
ASJ 1" (25 mm) .15 .71 .65 .82 .41 .16 .65

(Sorry, it's hard to get the frequencies to line up with the numbers.)

I'm not sure which frequencies I want the most absorption at for the best results?

Wouldn't the foil material reflect sound rather than absorbing it? Or am I confused? I was planning on wrapping it in some cloth material.

FSK and AJS seem to be better at low/mid frequencies, while plain is better at higher frequencies. Should I assume that plain is the best choice then?
stef2's Avatar stef2 07:58 PM 10-03-2005
Hi everyone. I live in Quebec, Canada:


Around here I'm having a hard time finding OC 703 or OC 705 to treat my home theater.


At the local Home Depot, they sell some Roxul Safe and Sound Mineral Wool which is 3 inches thick and 2.5 pcf. The absorption coefficients for this material looks a lot like the ones listed for OC703 (2 inches thick), according to bobgolds.com tables (The only significant difference I see is more absorption at 125Hz).

I've worked with this material in the past for wall insulation. To me it looks more like normal (not rigid) wool than rigid fiberglass.

Does anyone know if I can use those roxul "panels" instead of OC703 for every well described OC 703 usage? From an absorption point of view, they seem to be quite equivalent (am I right?). But if I use the Roxul Mineral Wool, lets say to treat first reflection points ,my whole front wall or to build corner bass traps, is there any special thing I must do (for example, should I compress it? Should I space the panels from the walls or leave them flat on the wall since Roxul seems to absorb more of the low freqs?)

To summarize, how can I get the OC703 effect while using the Roxul Panels?

Your help will be greatly appreciated...I've been reading this whole thread with a lot of interest!


Stephane Olivier
bpape's Avatar bpape 06:11 AM 10-04-2005
Having additional absorbtion at 125Hz is not generally a problem. Also, the difference between the 2 sets of specs is pretty insignificant - even at 125Hz.

I'd plot out what the room needs from a decay time perspective and plug in those values. I doubt you'll have any issues using it.
tonybradley's Avatar tonybradley 12:52 PM 10-04-2005
I'm on vacation this week and have been reading a lot of the acoustic threads. I can't remember where I read this, as it may have been a link from a link from a link. Anyway, for Bass Traps, I read that you could purchase Rolls of Fluffy insulation (didn't matter which type, i.e. R13, R19, R25), stack them three high with the plastic wrapping on, and cover them.

Will this work as an effective bass trap? If so, does it matter which thickness I purchase or if I buy them faced or unfaced?
ChrisWiggles's Avatar ChrisWiggles 01:04 PM 10-04-2005
that would work ok, the reason to leave it in the packaging is because it's compressed down to a lot denser, similar to the density of fiberboard that is often discussed here as the effective and economical route to treatments.

On the other hand, you could just buy batts of fiberboard and leave the batt in the corner if you wanted, too. Don't think the cost would be too different, and then if you did want to make some absorbing panels for reflection points etc to tame the RT60 time of the room, you could use some of those boards for that. Fluffy fiberglass rolls insulation won't be useful for that.
tonybradley's Avatar tonybradley 05:23 AM 10-05-2005
Thanks Chris. I'm definitely going to either use 1" or 2" OC703 Rigid Fiberglass for the First Reflection points. I've read quite a bit on here and it appears the rule of thumb is to use the 1" OC703 panels over the 2"?

I'm trying to decide now whether to use Rigid Fiberglass boards for the Bass Traps, or the rolls of fluffy insulation.
Terry Montlick's Avatar Terry Montlick 05:34 AM 10-05-2005
Quote:
Originally Posted by tonybradley View Post

Thanks Chris. I'm definitely going to either use 1" or 2" OC703 Rigid Fiberglass for the First Reflection points. I've read quite a bit on here and it appears the rule of thumb is to use the 1" OC703 panels over the 2"?

If I might jump in, either 1" or 2" will work for early reflections. 2" gives you some addition absorption toward the bass because of the added depth. However early reflections are strictly higher frequency effects, so bass absorption doesn't matter.

Regards,
Terry
tonybradley's Avatar tonybradley 07:02 AM 10-05-2005
Thanks Terry. So, as long as I use some Bass Traps in my theater for the lows, I should be OK with 1" OC703 panels for my first reflections?
Dennis Erskine's Avatar Dennis Erskine 07:24 AM 10-05-2005
...that's where doing some models is helpful. Early reflections are a higher frequency issue; but, we also find most residential sized rooms will have a bump in decay times in the 250 to 500Hz range. So if that will be an issue, that can be part of an overall strategy to address both issues.
Terry Montlick's Avatar Terry Montlick 08:26 AM 10-05-2005
Quote:
Originally Posted by Dennis Erskine View Post

...that's where doing some models is helpful. Early reflections are a higher frequency issue; but, we also find most residential sized rooms will have a bump in decay times in the 250 to 500Hz range. So if that will be an issue, that can be part of an overall strategy to address both issues.

I agree, Dennis. And measurement can trump models. I recently measured a built but not treated room which had extremely good bass through mid-frequency reverberation times -- not so good high frequency characteristics.

Turns out that the room had an acoustical tile ceiling, which would explain the response I measured in this bare-walled, carpeted room. Now, I didn't have the specifics on the tiles, or how they had been installed. A model would have been a shot in the dark.

But the measurements told me what I need to know for treatment. This room is going to get 1/2" thick fiberglass absorption on the walls. Any thicker, and we run the risk of deadening the mid-range too much.

Regards,
Terry
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