Acoustical Treatments Master Thread [Text View] - Page 10

wgilpin

05-02-07, 02:22 PM

I want to cover some wood frames with GOM cloth. Is it hard, or easy to do?

Does the fabric stretch? What about wrinkles? Should I do a small roundover on the edges with a router? Other suggestions?

It can be easy, or it can be hard. It's pretty easy if you're OK with covering the frame, like Pepar's site shows. If you want the wood of the frame to be exposed, it's a little more involved. (See pics here (http://homepage.mac.com/wgilpin/PhotoAlbum12.html))

In either case, if you begin stapling at the center of each side, then gradually work your way out to the corners you'll have a nice flat wrinkle-free surface. It's not the fastest method, since you switch sides 10 or 20 times, but it'll generate the best results. A pneumatic stapler is your friend.

GoM is some pretty tough stuff. There's no real need for rounding the edges over unless it gives you a look that you're after.

The fabric does not stretch much at all. If you pull really hard you can stretch it a bit, but the moderate amount of tugging you'll use to get a flat wrinkle-free surface will not stretch the fabric.

Cheers,

pepar

05-02-07, 03:13 PM

It can be easy, or it can be hard. It's pretty easy if you're OK with covering the frame, like Pepar's site shows. If you want the wood of the frame to be exposed, it's a little more involved. (See pics here (http://homepage.mac.com/wgilpin/PhotoAlbum12.html))

In either case, if you begin stapling at the center of each side, then gradually work your way out to the corners you'll have a nice flat wrinkle-free surface. It's not the fastest method, since you switch sides 10 or 20 times, but it'll generate the best results. A pneumatic stapler is your friend.

GoM is some pretty tough stuff. There's no real need for rounding the edges over unless it gives you a look that you're after.

The fabric does not stretch much at all. If you pull really hard you can stretch it a bit, but the moderate amount of tugging you'll use to get a flat wrinkle-free surface will not stretch the fabric.
Something to keep in mind is that when you are done, you want the material slightly stretched in all directions. To do this w/o creases/wrinkles, the GOM should be stretched outward from the first staple as additional staples are made. Go to the opposite side, stretch it away from the just-stapled side AND stretch it also from the first middle staple as more staples are placed. That way when you start stapling the opposite sides, it will be "pre-stretched" and all you need to do is tighten it up a bit.

Hope this makes sense. I know how to do it and what I was trying to say and it still is confusing to see it in words.

bommai

05-03-07, 11:42 AM

What kind of room treatments do I need? Here are some pictures from my home theater setup. I have never done room treatments before. There is a wall next to might right speaker. But there is plenty of space (18 feet) to the left of the left speaker. This is an L-shaped room in the basement. My rear speakers are mounted on the beam and there is plenty of space behind the rear speakers (18-20 ft). I have a 5.1 setup. Thanks.

http://gallery.avsforum.com/data/503/IMG_8599.jpg
http://gallery.avsforum.com/data/503/IMG_8596.jpg
http://gallery.avsforum.com/data/503/IMG_8598.jpg
http://gallery.avsforum.com/data/503/IMG_8594_2.jpg
http://gallery.avsforum.com/data/503/IMG_8592_2.jpg
http://gallery.avsforum.com/data/503/IMG_8587_2.jpg

eugovector

05-03-07, 12:02 PM

What kind of room treatments do I need? Here are some pictures from my home theater setup. I have never done room treatments before.

Pictures aren't anywhere near as valuable as an overhead sketch w/ room demensions. If you provide those, yo'll get lots of help.l

Terry Montlick

05-05-07, 10:47 AM

Bommai:

Based on your plan view over on "Are Linacoustic and Duct Liner the same?" I would revisit the layout of your room. The "missing" wall directly to the left of your front speakers is a significant issue because it makes the left/right sound field highly asymmetrical. Is there any way you could use the room at the upper right end of the "L" instead, placing the screen at the far end of the L? How about building a wall to create a symmetrical room? These sorts of measures depend on your level of commitment to the acoustic quality of the space, of course.

Oh, and I would definitely get that ugly lady off the TV screen! :D

Regards,
Terry

padd54

05-05-07, 11:21 AM

OK, here a prop[osed layout of my currently under construction.

http://i161.photobucket.com/albums/t212/padd54/05-04-2007043338PM.jpg

I am soliciting any and all comments/suggestions for treatments, speaker placement, etc...

BT = 4" rockwool bass traps. I have lots of 2" rockwool for treatment of room.
Thanks.

BasementBob

05-05-07, 02:51 PM

padd54:

By the dots between the couch and the TV, I'm assuming you drew the room to scale at one square = 6".

Nevertheless, what's the room HEIGHT/width/length.

padd54

05-05-07, 02:56 PM

Sorry, 8.3hX12.5wX17.2l. The dots were me counting, like I do on my fingers.
Thanks,

BasementBob

05-05-07, 08:12 PM

padd54:

from: http://www.rpginc.com/products/roomoptimizer/index.htm
http://www.bobgolds.com/padd54/RoomOptimizer.GIF

from: http://bobgolds.com/Mode/RoomModes.htm
Computed Information:
Room Dimensions: Length=17.2 ft, Width=12.5 ft, Height=8.3 ft
Room Ratio: 1 : 1.5 : 2.07
R. Walker BBC 1996:
- 1.1w / h < l / h < ((4.5w / h) - 4): Pass
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Fail (ratio3 = ratio1 * 2)
Nearest Known Ratio:
- "7) M. M. Louden: 1971: 3rd best ratio" 1 : 1.5 : 2.1
RT60 (IEC/AEC N 12-A standard): 242 ms
- ±50ms from 200Hz to 3.5kHz = 192 to 292ms
- ±100ms above 3.5kHz = 142 to 342ms
- <+300ms at 63hz = 542ms
- 300<RT60<600ms
RT60 (ITU/EBU Control Room Recommended): 199 ms
- ±50ms from 200Hz to 4kHz = 149 to 249ms
- <+300ms at 63hz = 499ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 439 sabins
Volume: 1784 ft^3
Surface Area Total: 920 ft^2
Surface Area Floor: 215 ft^2
Surface Area Ceiling+Floor: 430 ft^2
Surface Area Front Wall: 103 ft^2
Surface Area Front and Rear Wall: 206 ft^2
Surface Area Left Wall: 142 ft^2
Surface Area Left and Right Wall: 284 ft^2
Surface Area 4 Walls: 490 ft^2
Surface Area 4 Walls + floor: 705 ft^2
(sabins - front wall - carpet) / Left+Right+Rear wall: 31 %
(sabins - front wall) / Left+Right+Rear wall: 86 %
Schroeder Fc: 118hz
Frequency Regions:
- No modal boost: 1hz to 32hz
- Room Modes dominate: 32hz to 118hz
- Diffraction and Diffusion dominate: 118hz to 472hz
- Specular reflections and ray accoustics prevail: 472hz to 20000hz
Count (32.8-211hz) : Axials=13, Tangentials=54, Obliques=72
Count (32.8-100hz) : Axials=6, Tangentials=6, Obliques=1
Critical Distance (direct = reverberant field): 13.40ft

Frequency hz Spacing % Wavelength 1/2 Wavelength 1/4 Wavelength p q r Mode
32.8 34'5" 17'3" 8'7" 1 0 0 Axial
45.2 27.4 25'0" 12'6" 6'3" 0 1 0 Axial
55.9 19.1 20'3" 10'1" 5'1" 1 1 0 Tangential
65.7 14.9 17'2" 8'7" 4'4" 2 0 0 Axial
68.1 3.5 16'7" 8'4" 4'2" 0 0 1 Axial
75.6 9.9 14'11" 7'6" 3'9" 1 0 1 Tangential
79.7 5.1 14'2" 7'1" 3'7" 2 1 0 Tangential
81.7 2.4 13'10" 6'11" 3'5" 0 1 1 Tangential
88.1 7.2 12'10" 6'5" 3'2" 1 1 1 Oblique
90.4 2.5 12'6" 6'3" 3'2" 0 2 0 Axial
94.6 4.4 11'11" 5'12" 2'12" 2 0 1 Tangential
96.2 1.6 11'9" 5'10" 2'11" 1 2 0 Tangential
98.5 2.3 11'6" 5'9" 2'10" 3 0 0 Axial
104.8 6 10'9" 5'5" 2'8" 2 1 1 Oblique
108.4 3.3 10'5" 5'3" 2'7" 3 1 0 Tangential
111.8 3 10'1" 5'1" 2'6" 2 2 0 Tangential
113.2 1.2 9'12" 4'12" 2'6" 0 2 1 Tangential
117.8 3.9 9'7" 4'10" 2'5" 1 2 1 Oblique
119.8 1.6 9'5" 4'9" 2'4" 3 0 1 Tangential

padd54

05-05-07, 08:14 PM

Could you please translate this for me??

BasementBob

05-05-07, 08:28 PM

padd54:

There's lots of debate as to wether either of the two algorithms I've choosen are suitable to any purpose. i.e. computer simulation is a waste of time without a lot more thought, and RT60 as a basis ( http://bobgolds.com/Mode/RoomModes.htm ), and simple frequency response modeling http://www.rpginc.com/products/roomoptimizer/index.htm ) is a waste of time.

That said
a) RoomOptimizer. Have a look at the .GIF link I provided. It shows a 'best' (yellow) location for 3-front-speakers/2-dipole-speakers/listener. It puts your speakers in places less likely to energize modes, and your head in a spot least likely to be met by trouble some modes, and reasonable angles for imaging and so on. Basically a possibly good frequency response spot.
b) A sabin is a unit of absorption per square foot. If you've got 1.0 absorption coefficients for some frequency band on the materials on your front walls and floor
http://www.bobgolds.com/AbsorptionCoefficients.htm
http://www.bobgolds.com/Sabin%20Data_sorted.htm
Then the ( RoomModes.htm ) line
(sabins - front wall - carpet) / Left+Right+Rear wall: 31 %
means that you may treat up to 31% of the surface area of your left/right/rear wall with absorption and still be ok. Start with the first reflection point locations shown in the GIF.

For a room of your volume, the ITU formula suggested an RT60 of 199 ms.
That means you can have up to 439 sabins of absorption in your room.
So if you're using things with 1.0 absorption coefficients, that means you can't exceed 439 square feet of absorptive materials (linacoustic, carpet, curtains, fuzzy couches, etc). [gross simplification] That's part of where that 31% comes from -- handilly calculated for you.

The key phrase there is "up to". Build a couple, put them in, if it sounds better, that's good.

If your speakers have bad off-axis response, then toe your speakers in a bit. Try to ensure that all reflections are reduced by 10dB by whatever means possible, relative to the direct sound.

The next thing you do is follow the 10 steps shown here, as far as you can. Ignore the equipment they use, and use whatever you have that does the same job.
http://www.sencore.com/newsletter/Nov03/AudioCalpart2.htm

Position your subwoofers so that they minimally energize modes, and then using the "p q r mode frequency" chart above to decide where to place bass traps and what kind of bass traps for those modes that will still be energized due to the subwoofer placement.

BasementBob

05-05-07, 08:39 PM

padd54:

There are three traditional techniques for room treatment, that seem to be popular at AVS, that each take advantage of different things.

a) dedicated home theater room with leather seating for 5 and 7.1 sound
b) reasonably soundproofed (walls/ceiling/floor, doors, HVAC)
c) front wall covered with 1" linacoustic, including behind the screen
d) side and rear walls covered from floor to half way up with 1" linacoustic. This 'half way point' must be at least 6" higher than the reflection point from the front speakers tweaters to the listener's ears
e) side and rear walls covered from ceiling to half way down with 1" Polybatting 16oz
f) bottom of soffets covered with 1" 703
g) really thick carpet on the floor
h) columns, except where the speakers were, filled with fluffy pink insulation with GoM sides
i) some sort of bass trap system (6" 703 with 4" air gap, membrane absorbers, helmholtz riser, etc)
j) 2 or more subwoofers, placed optimally

1)keep all absorption broad band to the very end - treat specific frequencies only if you can find no way around it;
2) start in the corners (superchunks), floor to ceiling. Panels as wide and as deep as you dare - catch em all big and small;
3) treat the front of the room for early reflections with absorption / front wall-ceiling shaping / adjusting mix-speaker position / voodoo dolls;
4) defeat flutter [either absorbers, or diffusion] keeping in mind that if you have a flat ceiling, the floor to ceiling flutter is by far the largest area of parallel flat surfaces and therefore probably needs the most attention;
5) Add broadband absorption to hit your desired RT60 [wall panels / clouds /
ceiling grid].

Start with the corners and remember that ceiling grid is a cheap and effective tool in trying to piece a solution together for your room - keep in mind that if polys are used for wall
flutter [vs. wall mounted absorption panels] then treating whole ceiling is a great way to go - it just about takes that giant floor to ceiling thingy out of the equation entirely - you can almost forget 3d and start thinking in 2d [plan view].

Jeff adds
"At least 20% to 35% coverage of walls and ceiling with good acoustical treatment fairly evenly distributed will go a long way in a small room. For mixing areas, treating the early reflection points first is key. After that, so on and so forth into bass and diffusion and the rest as appropriate."

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

And there are other styles.

Then there's HAA, and designers (DesignCinema, Alpha Cert, etc).

padd54

05-05-07, 09:43 PM

BasementBob, thanks so much for taking the time to do this. Your input has been the most eyeopening of any that I have been given. I am much more prepared to tackle my room acoustics now. Still very intimidated, but better prepared. This should be fun.
Thanks again, you have been a tremendous help.

S2G-Unit

05-09-07, 02:10 PM

Some help needed here guys.

I drew in some places were I'm guessing the panels should go. Will there be too many in my small 11x20 room?
1st reflections points are all done.

I want to get rid of the little bit of echo above the seat near the side speakers.
So 1 panel above the 1st row? and then panels beside the side speakers?

What do you guys think?http://www.imagestation.com/picture/sraid225/p6b1eb6ed5379adebec92a06aa232e933/e99552ac.jpg

What do you guys think of the huge bass trap I made where the was space for a bookcase before?
http://www.imagestation.com/picture/sraid225/p9c44cfde0f52a06392478d58ae0a955d/e99552a8.jpg
http://www.imagestation.com/picture/sraid225/p0b6d9598ccb74b1e3e957def9f0a74ee/e99552a6.jpg

Ethan Winer

05-10-07, 02:50 PM

So 1 panel above the 1st row? and then panels beside the side speakers?

Absorbers on the sides walls (and ceiling) should go at the first reflection points. These are specific locations and you need to measure to find them, or use a mirror. These two articles explain the basics:

http://www.realtraps.com/art_room-setup.htm
http://www.realtraps.com/rfz.htm

Then feel free to follow up here with any questions. Or better, start a new thread since this one is long past being manageable. :D

--Ethan

S2G-Unit

05-15-07, 09:58 AM

Absorbers on the sides walls (and ceiling) should go at the first reflection points. These are specific locations and you need to measure to find them, or use a mirror. These two articles explain the basics:

http://www.realtraps.com/art_room-setup.htm
http://www.realtraps.com/rfz.htm

Then feel free to follow up here with any questions. Or better, start a new thread since this one is long past being manageable. :D

--Ethan

Sorry, forgot to show in the pictures. My 1st reflection points are already done with the mirror, for the ceiling and side walls.

Any other info would be great

pepar

05-15-07, 10:13 AM

Sorry, forgot to show in the pictures. My 1st reflection points are already done with the mirror, for the ceiling and side walls.

Any other info would be great
Well, how does it sound?

S2G-Unit

05-16-07, 01:44 AM

Well, how does it sound?

Obviously amazing. I was just wondering at what point will I have too much absoprtion?

I don't really plan to use RTA or any fancy gadgets to test and make sure.

myfipie

05-16-07, 07:44 AM

Obviously amazing. I was just wondering at what point will I have too much absoprtion?

I don't really plan to use RTA or any fancy gadgets to test and make sure.

As far as bass trapping you will never have enough, but for the high end you really want to focus on those early reflections and see how it sounds. If all is good then stop! If you feel as you want to tame a little more but not wanting the room to be to dead you can cover the bass traps with FRK which will reflect some of the high end but absorb lows.

Glenn

drin

05-16-07, 08:28 AM

S2G-Unit

05-16-07, 04:07 PM

If all is good then stop! Glenn

thanks

rutlian

05-18-07, 03:06 PM

newbie question here....

Anybody familiar with insulfoam that you can find with lowes hardware store?
can this be use as sound absorber by just covering them with a fabric?
they have a size of 2x4x8 that can be cut into diff sizes. And have anybody use
Owens corning 700 series If I use this 700 series can I just covered it with fabric?

I would like to improve the sounds quality of my hometheater
it is 14x20 room. Any suggestions is very much appreciated.

I have polk audio speakers
Onkyo reciever 6.1

Thanks

eugovector

05-18-07, 03:13 PM

newbie question here....

Anybody familiar with insulfoam that you can find with lowes hardware store?
can this be use as sound absorber by just covering them with a fabric?
they have a size of 2x4x8 that can be cut into diff sizes.

I would like to improve the sounds quality of my hometheater
it is 14x20 room. Any suggestions is very much appreciated.

I have polk audio speakers
Onkyo reciever 6.1

Thanks

Not familiar with the product, but generally speaker:

It it is a glass or mineral based board or sheet that is comprised of woven fibers, it will probably absorb pretty well.

If it is what I think it is, and it's a hard, rigid foam like the kind a beer cooler would be made out of, it will reflect sound, and won't help you a bit unless you're planning on building a diffuser out of it.

If you have a product link, post it.

Thanks,

Marshall

ChrisWiggles

05-18-07, 04:08 PM

If it's the solid foam insulation that I'm thinking about, not that would be a horrible absorber and would not at all be effective whatsoever.

rutlian

05-18-07, 04:33 PM

Marshall and Chriswiggles,

I think both of you are right about this insulation, it is just a solid foam insulation. This are
very visible in lowe's store and I always wonder if they are ok to use as sound absorber.
any other option that you guys might suggest. or a link that I can check out. I am looking for atleast 4 piece of 2x4x8 thank you guys .

Peter

ChrisWiggles

05-19-07, 01:14 PM

You should get fiberglass board as is suggested regularly. EJ Bartells has JM product right there in Renton, I drive out there to get what I need. They usually have everything in stock too.

rutlian

05-20-07, 02:13 AM

rutlian

05-20-07, 02:28 AM

You should get fiberglass board as is suggested regularly. EJ Bartells has JM product right there in Renton, I drive out there to get what I need. They usually have everything in stock too.

Hi there first thanks for giving me this information about ej bartells it is a big help
specially that they are located locally. I checked their product lines and I noticed
they have rigid and semi rigid insulation section under that section they have fiberglass board can you just cover this with tick frabic that you can get at jo-anns?

Thanks

eugovector

05-20-07, 09:12 AM

Hi there first thanks for giving me this information about ej bartells it is a big help
specially that they are located locally. I checked their product lines and I noticed
they have rigid and semi rigid insulation section under that section they have fiberglass board can you just cover this with tick frabic that you can get at jo-anns?

Thanks

Tere are a number of different approaches. Some people, like me, build wooden frames, then cover the fiberglass with thin quilt stuffing to keep the fibers from getting out, and cover the frames with a thin, cotton fabric. Some people forego the frames and just use 3m spray adhesive to glue the fabric to the fiberglass. Once again, stick w/ natural fiber fabric.

Here's a thread with my construction pics:

Pics of Acoustic Frame Construction (http://www.avsforum.com/avs-vb/showthread.php?t=734181)

rutlian

05-20-07, 11:45 AM

Tere are a number of different approaches. Some people, like me, build wooden frames, then cover the fiberglass with thin quilt stuffing to keep the fibers from getting out, and cover the frames with a thin, cotton fabric. Some people forego the frames and just use 3m spray adhesive to glue the fabric to the fiberglass. Once again, stick w/ natural fiber fabric.

Here's a thread with my construction pics:

Pics of Acoustic Frame Construction (http://www.avsforum.com/avs-vb/showthread.php?t=734181)

Thank you very much for the info. I am writing all of this info so this will be a
great help for building the panels again thanks for all the reply.

Peter

BasementBob

05-20-07, 12:43 PM

rutlian:
Consider fire treated fabric (either bought fire treated, or post-purchase treated)

Terry Montlick

05-20-07, 12:55 PM

rutlian:
Consider fire treated fabric (either bought fire treated, or post-purchase treated)
Absolutely! And 100% polyester, though not a natural fabric, is naturally flame retardent. You can often get certified Class A fire rating documentation if it is wall panel fabric produced by a major manufacturer.

- Terry

ChrisWiggles

05-20-07, 11:56 PM

jchretien4

05-21-07, 10:40 AM

Small home theater is halfway there; got 2" x 4" studs up, with insulation between studs (3 - 4" of fiberglass, 16 inches o.c.); wiring and everything else done. To drywall or not to drywall, that is the question. After reading so many discussions re: the need for absorption, I wonder if I should leave off the drywall -- at least in some areas -- and cover the insulation with something acoustically transparent. In other words, I can drywall the whole room and then install absorbent panels at the early reflective points, and basstraps in the corners. But as an alternative, what about leaving sections without drywall where I would otherwise put absorbent panels or basstraps, and instead cover the studs (and the insulation) with something acoustically transparent, maybe covering it with fabric, so that the installed insulation serves as the absorbing panel (and the studs may serve as diffusers, I imagine)? In the corners I could add add to the insulation, building it out so that the corner is no longer 90 degrees, but two 45-degree angles, with about a 12-inch depth to the corner. Then cover the bass trap with transparent fabric. Maybe put something different in the corner to better trap bass frequencies, but you get the idea. Maybe use something with some rigidity for strength to cover the insulation, but not drywall.

This approach saves me the time to drywall those areas/corners and also might increase useable volume, since the walls won't be built out so much.

Am I crazy, or just lazy?

jchretien4

Terry Montlick

05-21-07, 11:00 AM

Dennis Erskine

05-21-07, 01:45 PM

Not to take anything away from Terry's comment, you also run the risk of over absorption in the room.

Sands_at_Pier147

05-21-07, 08:26 PM

Not to take anything away from Terry's comment, you also run the risk of over absorption in the room.

Which brings up a point that has been nagging me for a while. It seems the conventional wisdom is 1" linacoustic on the entire front wall, something diffusive on the real wall, nothing on the ceiling, 1" linacoustic on the lower portion of the side walls, and 1" poly batting on the upper portion of the side walls. I have always just assumed that for the side wall that meant the entire wall. The engineer in me, however, needed to calculate something, and I decided that that much absorption was waaayyyy too much. Multiple methodologies confirmed that for me.

If one were to follow the conventional wisdom, is it true that one would over absorb their room? Or am I wrong in thinking I need to treat the entire side wall on both sides? Does the conventional wisdom need to be applied with the knowledge that treating the entire room is too much, and only a portion of the side walls should be treated?

Terry Montlick

05-22-07, 08:36 AM

Which brings up a point that has been nagging me for a while. It seems the conventional wisdom is 1" linacoustic on the entire front wall, something diffusive on the real wall, nothing on the ceiling, 1" linacoustic on the lower portion of the side walls, and 1" poly batting on the upper portion of the side walls.
The "conventional wisdom" is one particular design strategy. In the rooms that I design, I use many different approaches. It depends on the specific goals of the theater owner, room configuration, constraints, etc. When acoustic measurement and modeling tools are used, the range of possibilities become greater than a one-size-fits-all approach.

Regards,
Terry

Sands_at_Pier147

05-22-07, 09:10 AM

That's what I thought. Thanks for clarifying that for me. I guess I can proceed with my revised plan (less absorption) and still expect satisfactory results.

myfipie

05-22-07, 09:23 AM

The "conventional wisdom" is one particular design strategy. In the rooms that I design, I use many different approaches. It depends on the specific goals of the theater owner, room configuration, constraints, etc. When acoustic measurement and modeling tools are used, the range of possibilities become greater than a one-size-fits-all approach.

Regards,
Terry

There are general things in a room you can do which will yield some pretty nice results,(Bass Trapping and RFZ) but I could not agree more with you, that is why we have guys like you, Dennis and Bryan (bpape) in the world. :)

Glenn

Ethan Winer

05-22-07, 09:58 AM

It seems the conventional wisdom is 1" linacoustic on the entire front wall, something diffusive on the real wall, nothing on the ceiling, 1" linacoustic on the lower portion of the side walls, and 1" poly batting on the upper portion of the side walls ... The engineer in me ... decided that that much absorption was waaayyyy too much.
Yes, that's not only way too much, but also the wrong type of absorption. The problem with using only "thin" absorption is it leads to an imbalanced decay time versus frequency. The room becomes too dead at mid and high frequencies, while the bass still bounces around the room yielding a muddy boomy sound.

Does the conventional wisdom need to be applied with the knowledge that treating the entire room is too much, and only a portion of the side walls should be treated?
In this case the conventional wisdom is wrong. A better approach is as much bass trapping as possible, plus broadband absorption at all first reflection points including the ceiling, and more broadband absorption as needed elsewhere such as on opposing parallel surfaces. By "broadband" I mean effective down to 250 Hz or even lower, which requires using materials at least two inches thick.

--Ethan

daxhughes

05-22-07, 07:51 PM

Ok, I have completed my theater room and I am stupified by the thought that I cannot even tell if my room sounds acoustically good or not.

I have the following equipment:

B&W 804s
B&W HTM3s center
B&W DS8's in the back
Sub is a SVS PB12-Ultra

My receiver is a Denon 4806Ci.

I know I have decent equipment and to be honest, it sounds good to me. This is frustrating to admit but I do not know how to tell if it would sound better with acoustic treatment or not.

I am considering gettign an acoustic package from Ethan whose opinion I trust but I hate to spend the money if my ears are nto goign to eb able to tell the difference.

So why not leave it alone and enjoy? Because I cannot stand the idea that I might be able to hear a difference!

I have this eery feeling that some could come and begin pointing out to me acoustical issues that I would then see but now I am pretty clueless.

Is it a 100 percent fact that if I pur Acoustic shields at first reflective points and bass traps in the corners, that my room will sound better when it sounds pretty good already.

I attached a picture under the attach files. hopefully you see it.

DKaps

05-22-07, 09:03 PM

Dax,

That's a valid question. Keep in mind that we only "know" what we've been exposed to. What sounds great to you now, may not after some 1st hand education of what's possible. That said, there's no question that your equipment is capable of greatness.

You could post your general location and chances are, someone on this forum will have a suggestion for a treated room that you could demo nearby. On the other hand, the trouble with that is, you may not know if that room is actually "good" either. Hopefully, there will be one that you can visit where the design and treatment was done by a known respected designer.

Dan

pepar

05-22-07, 10:33 PM

pepar

05-22-07, 10:38 PM

Ok, I have completed my theater room and I am stupified by the thought that I cannot even tell if my room sounds acoustically good or not.
Is all of the dialog intelligible/easy to understand? Do whispers sound like whispers and explosions like explosions?

brianunknown

05-23-07, 03:47 PM

Just beginning to build my theatre. Some of the answers I am looking for are probably in here but at 77 pages long it would take forever to read.

My room is approx 19' long by 11' wide at the front and 12' wide at the back. Ceiling height is 7' 10". Two walls are exterior walls and I have done nothing except 1/2" drywall. The other two walls have double 5/8" with GG and the ceiling is the same except it is on hat channel. All wiring and lighting will be in the soffit around the room which I will install after I complete the screen wall.

I plan to use screen paint directly on the drywall and then frame around the whole thing to mount the speakers and equipment. This means the framing will come out approx 22" and then be covered with fabric.

Now my questions:
Because I am trying to have the biggest screen possible I will only have approx 16" on either side of the screen. I also have an electric panel to deal with. As a result I can not build triangle style corner bass traps. I will only be able to fit in ones that would be rectangular (approx 15" x 12" and running floor to ceiling) I was thinking of using Roxul Safe n Sound. Will these work? Is it worth it?

If I do the traps described above they will cover both sides of my screen which leaves the only other area left on the front wall what's above and below the screen. Should this area be treated with duct liner? Will it make any difference.

Due to my limited space I may have a similar challenge on the back wall should I put small rectangular bass traps in the corner or is it a waist of time?

I am hoping to put some wall treatments up to at least deal with first reflections. I have seen some threads where people have used there soffits to deal with sound management issues as well but I would prefer the simpler approach of closing them in. How much extra sound quality can be gained by using the soffits in some way?

jv225

05-24-07, 05:46 AM

padd54

05-24-07, 09:14 AM

I would say save your ceiling for last, you may not need to treat it at all :).

Terry Montlick

05-24-07, 09:19 AM

Hi guys. I'm starting to treat my room and had a couple questions. I just picked up some 2" rigid fiberglass and plan to double it up in the corners for bass traps and use a single layer for first reflections.
I have a drop ceiling with 2' x 2' acoustic tiles now. I was planning on cutting some of this rigid fiberglass to drop in the grids and cover them in fabric. But then I got thinking is it really necessary on the ceiling with these tiles? If so could I put a few panels on top of the tiles and get the same effect?
Thanks in advance
Jim
If the room has a high level of wall diffusion, such ceiling-mounted fiberglass with an airspace or light fiberglass batts above can be effective in lowering overall reverberation and improving bass performance. It's hard to say for sure without doing the necessary acoustical measurements and modeling. I have observed this in rooms which had a ton of nooks and crannies, uneven shelves, cabinets, etc.

Regards,
Terry

jv225

05-24-07, 03:42 PM

Ok thanks a lot guys. I think I'll hold off on the ceiling for now and see how it goes after I build the bass traps and panels for the side wall. If I still need more I'll try insulating the whole ceiling with 12" batts since I was thinking of doing that anyway for sound isolation.

surfshoptom

05-30-07, 06:21 PM

There's a source in town for Linacoustic. A 100' roll is $202. Should I shop around or that a decent price?

I plan to attach 2 layers of the 1" Linacoustic to the screen wall and build covered 1" panels for the side walls.

Does Linacoustic have a backing? If so, does the backing go against the wall or on the outside? When I double it up, how do I place the backing?

Thanks.

antropos

06-01-07, 06:23 PM

hi

after thousand search I buy the Daad.
this one is italian product so expensive but really good acoustic tractament for room.this really good beetween tub trubs.
actualli have almost end my room dedicated a home theatre.

:)

Fatawan

06-02-07, 09:48 PM

Terry Montlick

06-02-07, 11:33 PM

Can fabrics other than the GOM types be used to cover the acoustical treatments? I want it to look nice as well, and am looking at a fabric that is 63% polyester/37% cotton with an acrylic latex backing. It's 13 oz. per linear yard.
Two problems come to mind immediately:

Polyester/cotton blends can be highly flamable, and not meet the NFPA 701 flame propagation standard required for safety by most building codes.

The acylic latex backing will likely render the fabric acoustically reflective, at least for medium and high frequencies. This will prevent sound from getting absorbed by porous acoustic treatment materials.

Regards,
Terry

Fatawan

06-03-07, 08:50 AM

Two problems come to mind immediately:

Polyester/cotton blends can be highly flamable, and not meet the NFPA 701 flame propagation standard required for safety by most building codes.

The acylic latex backing will likely render the fabric acoustically reflective, at least for medium and high frequencies. This will prevent sound from getting absorbed by porous acoustic treatment materials.

Regards,
Terry

Thanks Terry--that makes perfect sense. How about something like 100% cotton that I could fire-treat myself?

drin

06-03-07, 09:37 AM

Thanks Terry--that makes perfect sense. How about something like 100% cotton that I could fire-treat myself?

My understanding is that self-treated fabric doesn't conform to building code. I know for sure that if a fire occurs in your home and the insurance company determines you have self-treated fabrics they won't pay out.

I'd be happier personally just spending the money to get pretreated, code-compliant, insurance company happy-fiying :) fabrics.

-drin

BasementBob

06-03-07, 01:32 PM

drin:

I'd be happier personally just spending the money to get pretreated, code-compliant, insurance company happy-fiying fabrics.I thought for it to be code-compliant it was the assembly that had to be code compliant, not just the fabric.
(Although it's likely that if the fabric if flamable, so will be the assembly.)

ddingle

06-03-07, 11:11 PM

Terry Montlick

06-04-07, 09:09 AM

drin:

I thought for it to be code-compliant it was the assembly that had to be code compliant, not just the fabric.
(Although it's likely that if the fabric if flamable, so will be the assembly.)
If the fabric is mounted as a wall or ceiling covering, as specified in International Building Code 2003, section 803.4, then the fabric only is required to have been tested and given a Class A rating according to ASTM E 84. This will be true for typical permanently-installed fabric -- stapled over furring strings, or attached via a track fabric system.

If the fabric is mounted otherwise, as covering an acoustical panel, then NFPA 701 testing applies instead the the ASTM testing. That's where the "701" comes from in "Guilford FR701®," which is used a great deal for commercial acoustical panels. The entire assembly must be tested under NFPA 701, unless it covers less than 10% of the room wall and ceiling area (which would qualify it as a "decorative finish"). Technically, acoustical panel manufacturers must provide proof of this testing.

Regards,
Terry

Fatawan

06-04-07, 10:05 AM

Terry Montlick

06-04-07, 10:17 AM

Terry:

Interesting--that original fabric I was looking at says "Passes California Bulletin #117; ASTM E-84 adhered method Class I; NFPA 260, UFAC Class I. "

How does "Class A" compare to "Class I"?

Different beasts entirely. One cannot substitute one for the other. ASTM E-84 is for building material flame spread and smoke development. NFPA 260 is for upholstered furniture fabric ignition from cigarettes.

Regards,
Terry

Fatawan

06-06-07, 12:05 AM

I asked this question in another thread, but I will repeat it here, where the acoustic folks hang! MY HT is a basement build, with 2 of 4 walls being concrete outside walls. In the rest of my basement that is finished, walls are first covered with a permeable foam board, which is sealed to the concrete, then a 1" air gap, then the 2x4 wall with R-13 fiberglass. I plan the same technique here. Since these walls are against concrete, do they need the whole DD+GG treatment? Any sound that "gets through" will then have to go up and through the floor upstairs to be heard. The joist will be filled with fiberglass insulation 1' thick, plus another 2" below that(ceiling will be suspended with the 2" RSIC clips). Just curious what the latest is on these basement walls.

Lindahl

06-06-07, 01:57 PM

Terry Montlick

06-06-07, 02:14 PM

I can get this locally:

http://www.jm.com/insulation/performance_materials/products/ahs334_matfaced_microaire.pdf

How good would this material be compared to the popular OC703 for both treating first reflection points and making bass traps? It's type 475 and comes in 4x10x1" sheets with FSK. The absorption coefficients look close, but I couldn't find the density spec.

Type 475 = 4.75 pcf. This is about midway between OC703 and OC705, and should work fine for both functions. For early reflection and wideband absorption, you definitely want to have the FSK side so that it is not facing the room.

Regards,
Terry

ddingle

06-09-07, 09:16 AM

I am looking for a quick and cheap upgrade for bass response in a custom built theater. The budget ran out of gas and we compromised(did not use any) on bass traps. Now that we have things fired up somewhat,it seems even more important. I am going to use the Lexicon Equalizer built into their MC12,but I know some bass absorbtion would be valuable. I have a space behind the screen and front speakers that would allow me to stack a few big bags of fiberglass insulation or the like. It is going to be a GOM cover over the whole thing so aesthetics is not important. Am I going to buy anything?? Thanks for any input or suggestions.
We added several bags of insulation behind the scrim wall. Used the auto equalization feature of the Lexicon. Ouila! Great bass! It is better near the microphone location,but functional in most seating locations.
I really like the Lexicon Eq feature. It makes us look good.

drunkpenguin

06-09-07, 09:29 AM

Hey guys, I just bought some owens corning ductliner, type 150 for use in my HT. I hope this stuff will work ok, I live in a small town and it is the only thing I could find. So from my reading I've concluded that I should cover the entire front wall with this stuff. Now the sidewalls I've read 42" and down. Would this be true for a 10' ceiling also? What about the back wall and the ceiling. Should anything be done there?

I also want to look into bass traps, is this something I need in each corner of the room? I generally see them placed up high in the corners, is there a method to determining where the traps would go?

Ethan Winer

06-09-07, 11:20 AM

I also want to look into bass traps, is this something I need in each corner of the room? I generally see them placed up high in the corners, is there a method to determining where the traps would go?

All corners are viable - where two walls meet, where a wall and ceiling meet, and even on the floor at the bottom of a wall. Three-way corners are especially prized. I have many traps in wall-floor corners.

--Ethan

Terry Montlick

06-09-07, 11:35 AM

Hey guys, I just bought some owens corning ductliner, type 150 for use in my HT. I hope this stuff will work ok, I live in a small town and it is the only thing I could find.
This is somewhat on the low density side. I wouldn't use less than a 2" thickness.

So from my reading I've concluded that I should cover the entire front wall with this stuff. Now the sidewalls I've read 42" and down. Would this be true for a 10' ceiling also?
Yes, 42 is the answer. Don't forget to bring a towel! :)

Seriously, different rooms need different treatments. I routinely use side wall absorption right up to the ceiling. And of course the standard poly batting "diffusion" for the upper wall is really absorption anyway.

Regards,
Terry

drunkpenguin

06-09-07, 11:45 AM

Well, its what I've got to work with at this point. I am not going for a THX theater here I just want it to sound alot better than it does with 4 bare walls like I currently have. Plus I think the look of it really adds to a dedicated room. I guess I'll staple it up and do some sound testing.

Couple more questions..

I plan to have 2 rows of seating, the back seats on a riser (which I have not built yet), so should the side walls be treated higher near the back to compensate or will 42" accrost the board be good enough?

Next question, should any of this stuff go on the back wall at all or do I want to leave it untreated?

Terry Montlick

06-09-07, 11:58 AM

If you have depth on the front wall, a few inches of fiberglass thickness will do double-duty for reflections and bass absorption. I have also used the rear wall for bass absorption, but not without verifying that the back of the room will still be sufficiently "live" for the surround channels.

The thing about bass absorption, be it in the corners or on the walls, is that you need to cover a substantial area with the absorber. Little tri-corner absorbers won't make much difference.

Regards,
Terry

drunkpenguin

06-09-07, 12:01 PM

Terry, what do you mean if I have depth on the front wall? My room is 22x17x10.

If I use the stuff I bought, owens corning 150, and build 4 traps like the ones on this web page, will that help?

http://www.runet.edu/~shelm/acoustics/bass-traps.html#BassTraps

Terry Montlick

06-09-07, 12:23 PM

Terry, what do you mean if I have depth on the front wall? My room is 22x17x10.
Only that you will need 4" or more of depth from the surface of the absorber to the wall for significant bass absorption. With screen and seating requirements, this is sometimes too much to ask for.

If I use the stuff I bought, owens corning 150, and build 4 traps like the ones on this web page, will that help?

http://www.runet.edu/~shelm/acoustics/bass-traps.html#BassTraps
Yes, it should make a significant difference! Floor to ceiling corner bass absorbers give you lots of depth in otherwise unused spaces. The WAF can be rather low, though. :(

Regards,
Terry

drunkpenguin

06-09-07, 12:33 PM

I don't have to deal with WAF, I have the luxury of having the GFDWIW (girlfriend does what i want) factor. :D

I am the king of my castle! But my castle lacks sound treatment and a moat! Sound treatment first, the moat is still being dug out, 1 shovel full at a time. Anyways, thanks for the help, Im going to get started today. Wish me luck!

Terry Montlick

06-09-07, 12:34 PM

Luck!

- Terry

drunkpenguin

06-09-07, 12:59 PM

Well I did a quick calculation and the amount of material I have would only only me to do the front wall, side walls, and 2 traps if I built them like the above link. I'd have to buy another 400 sq/ft roll just for 2 more traps. So, would 2 traps be ok or pointless?

What If I framed up the corners for a triangle and just shoved in whatever leftovers I have left, would that work or no? And lastly, I have a huge amount of pink wall insulation left over from building my house, could I utilize it in the traps or is it not dense enough?

Terry Montlick

06-09-07, 01:08 PM

One thing you can do is use (unfaced) fiberglass batting to fill space behind your more dense fiberglass. This often gives very good results. It alleviates the frequency "ripple" that you can get if you have just an airspace behind a layer of fiberglass absorption.

- Terry

drunkpenguin

06-09-07, 06:45 PM

I've started putting the stuff on the front wall. Wow what a difference already in echo reduction! How do you guys fasten this stuff to the wall and keep it smooth and flat without any dents? I've tried screws but they either create a dent or the head sticks out to far.

I also have a question about treating the side walls. I've been planning on ear level down but then I read about batting above that. What is that for? I would like to leave the top portion of the wall untreated for asthetic reasons. Will this still work ok?

Lindahl

06-10-07, 12:20 AM

Kal Rubinson

06-10-07, 12:14 PM

Look at impaling cleats for hanging the fiberglass on the walls. They're flats of metal with screw holes and spikes on them. You screw the metal flats onto the wall, and impale the fiberglass on the spikes.I've had mixed success with those, especially with thicker panels. My preference is to use these: http://www.rotofast.com/

drunkpenguin

06-10-07, 02:16 PM

Screws seem to be working ok if I drive them half way into the duct liner. If I get enough screws I don't think it will go anywhere. Plus the fabric will hold it on once up anyways i think.

New question, It looks like I'm going to have enough left over to cover the back wall from ear level down also. Asthetically this would look nice I think. Any positives or negatives to doing this vs leaving the wall drywall?

hardax

06-12-07, 04:19 PM

New question if I may (just posted this in the main forum but realize it is better suited here).

During really low bass moments I always hear rattling coming from my basement windows. Upon further investigation I see that it is the slats in between the panes of glass that are causing the rattle.

Since I can't really fix that short of getting new windows does anyone have any suggestions on how to dampen the bass hitting the windows?

I have heavy theater curtains covering the windows and bass traps in the corners with GIK panels on the walls already.

I was thinking of buying some OC703 insulation (4 inches thick?) and covering that with fabric - sort of like a big pillow and stuffing that into the window opening. Would that be effective in dampening the bass from reaching the window?

Any other suggestions would be much appreciated.

drunkpenguin

06-12-07, 09:00 PM

I am in no way an expert on sound but I do know somethings about construction and I'm guessing its the base on the walls that are vibrating the walls and causing your windows to shake. Kinda like when you slam the door and the window behind you rattles. I would think filling in the window with sound obsorbing material might stop the rattle sound from reaching your ears, even tho its still rattling. Maybe some ductliner or a whole bunch of wall insulation compressed together and fastened into the window frame?

Just a thought, maybe one of the pros can recomend a doodaddogimmic that will work better.

myfipie

06-13-07, 07:42 AM

Hardax,
Think of your window like a drum set. If the tones hits it then it will vibrate (raddle). If you put 703 on it then the raddling should stop.

Glenn

hardax

06-13-07, 10:31 AM

Thanks drunkpenguin and Glenn. Looks like we are all thinking on the same level.

One other question Glenn (or if Bryan is reading). Do I really have to worry about the material I use to cover the 703 in this application? I have some basic black fabric (old curtains) that I could use but wonder if I would be messing anyhing up acoustically?

Also, I am sure it has been covered here before but can anyone tell me where to get OC703? Searches seem to be coming up short.

pepar

06-13-07, 10:40 AM

Also, I am sure it has been covered here before but can anyone tell me where to get OC703? Searches seem to be coming up short.
Many sharp shoppers buy their acoustical insulation from this company (http://www.spi-co.com/). These materials are generally made for insulating/quieting HVAC ducts and the best prices can always be had when one buys close to the source. All of the commercially available acoustical absorption products for home theater start with these materials.

Terry Montlick

06-13-07, 10:44 AM

tonybradley

06-13-07, 02:05 PM

The fabric can make a difference acoustically. Tight-weave fabrics can reflect high frequencies, making them less able to pass sound through to be absorbed. You are then reducing the absorber's efficiency.

On the other hand, some highs will get through virtually any fabric, so it is a matter of degree. If you don't know what fabric you have, you are taking pot luck.

Regards,
Terry

I'm using Felt over my 2" rigid fiberplass panels. Do you find that acceptable? I originally used Muslin, but felt (pun) it was ugly, so I changed it to felt. It could be me, but it appears that I don't have as much absorption now as when the Muslin was over the panels. I'm wondering if Felt is acceptable, or if I should re-wrap my panels (located at the 1st reflection points) with GOM?

pepar

06-13-07, 02:35 PM

I'm using Felt over my 2" rigid fiberplass panels. Do you find that acceptable? I originally used Muslin, but felt (pun) it was ugly, so I changed it to felt. It could be me, but it appears that I don't have as much absorption now as when the Muslin was over the panels. I'm wondering if Felt is acceptable, or if I should re-wrap my panels (located at the 1st reflection points) with GOM?
You might have increased absorption at some lower frequencies by adding a "diaphram", but felt is NOT acoustically transparent, so you've decreased the overall effectiveness of your absorbers. Why not just bite the bullet and buy the RIGHT product for the job - Guilford of Maine FR701???

myfipie

06-13-07, 03:38 PM

[QUOTE=hardax]Thanks drunkpenguin and Glenn. Looks like we are all thinking on the same level.

One other question Glenn (or if Bryan is reading). Do I really have to worry about the material I use to cover the 703 in this application? I have some basic black fabric (old curtains) that I could use but wonder if I would be messing anyhing up acoustically?

QUOTE]

The thing to do is to use open celled fabric. So if you can blow through it you should be fine. If you are only trying to focus on the low end that it really is not going to matter to much. Bass will go right through it.

Glenn

Fatawan

06-14-07, 01:01 AM

BasementBob

06-14-07, 02:10 AM

Fatawan

re Utratouch cotton:

R-13 3.5" (mm) A 0.95 1.30 1.19 1.08 1.02 1.00 1.15

It's often mentioned when people start talking about avoiding man-made fibers.

But I was watching Holmes On Homes Pasadena part 2 and heard a couple of things:

1) They used to dilute boric acid in water, and use it to wash newborn babies eyes out in hospitals with it
2) The boric acid is added to make it a class A fire retardant material
3) As a side benefit it repells all the insects you might encounter. Termites will not live in it. Repells mice and roof rats.
4) The boric acid, because of the acidic environment mold will not grow in it. If you get this wet and dry and wet and dry 50 times, it'll dry out because cotton breaths and gives off the water, but you'll never have mold or mildew.
5) environmentally friendly (recycling blue jeans)

tonybradley

06-14-07, 07:35 AM

You might have increased absorption at some lower frequencies by adding a "diaphram", but felt is NOT acoustically transparent, so you've decreased the overall effectiveness of your absorbers. Why not just bite the bullet and buy the RIGHT product for the job - Guilford of Maine FR701???

Because I was told by folks on this forum that for absorption (such as panels at the first reflection points), your fabric didn't need to be "acoustically transparent" and that was more for covering your speakers, etc. However, once I changed to felt, it appears I lost some absorption I had when I used Muslin. I wanted to check in again to see if Felt was 'OK' to use to cover Rigid Fiberglass at the First Reflection points. GOM is expensive for me, and when I found out Felt would be ok, that was good for me as it was less expensive. I wanted to find out if someone can tell me "Technical Reasons" why felt would be good or bad to cover broadband absorption panels.

Terry Montlick

06-14-07, 09:36 AM

Question:

http://www.bobgolds.com/AbsorptionCoefficients.htm From Bob's site, it would appear that UltraTouch Cotton batts(Bonded Logic, near the end) would make a great insulation to fill theater walls vs. fluffy pink fiberglass. It is a great absorber, all the way down to 125Hz. I wonder how well it does even lower? Is it worth using? All opinions welcome. An R-13 batt is not as expensive as I thought.
It won't help or hurt as wall cavity insulation. Any low-density porous absorber will work as well. There really isn't any way to get improved performance for this function.

Regards,
Terry

Fatawan

06-14-07, 09:40 AM

It won't help or hurt as wall cavity insulation. Any low-density porous absorber will work as well. There really isn't any way to get improved performance for this function.

Regards,
Terry

Ok--thanks Terry---fluffy pink fiberglass it is then! I am saving money left and right!

John Ballentine

06-14-07, 09:55 AM

What's the best way to attach 4'X8' fabric wrapped panels to the ceiling? Can't screw or nail them as this will ruin the fabric I have chosen (which is black speaker grill cloth).
The panels are only 1/2" thick - so Rotofast Snap-on anchors won't work. Glue? Liquid nails?
And what spray on adhesive works best to ensure the fabric doesn't come loose?
Thanks for your help.

pepar

06-14-07, 10:42 AM

Because I was told by folks on this forum that for absorption (such as panels at the first reflection points), your fabric didn't need to be "acoustically transparent" and that was more for covering your speakers, etc. However, once I changed to felt, it appears I lost some absorption I had when I used Muslin. I wanted to check in again to see if Felt was 'OK' to use to cover Rigid Fiberglass at the First Reflection points. GOM is expensive for me, and when I found out Felt would be ok, that was good for me as it was less expensive. I wanted to find out if someone can tell me "Technical Reasons" why felt would be good or bad to cover broadband absorption panels.
I'd be interested in being pointed to a post where someone said broadband absorbers didn't need to be covered with acoustically transparent material. As your ears have told you, you've lost absorption because the felt is reflecting some frequencies instead of allowing them to pass and be absorbed. GOM certainly is expensive and I understand your desire to find a lower cost alternative that meets your aesthetic sensibilities. As for technical reasons that give the thumbs up or down on felt, see Glenn's post above (http://www.avsforum.com/avs-vb/showthread.php?p=10780435&&#post10780435).

McCall

06-14-07, 10:44 AM

As to fabric adheavsive Super 77. As to nails or screws, You certanly CAN screw through it. you simply punch a hole first. there are various caps you can put on screws as well.

pmeyer

06-14-07, 11:27 AM

Because I was told by folks on this forum that for absorption (such as panels at the first reflection points), your fabric didn't need to be "acoustically transparent"I have seen similar things posted, but you have to be careful. I can see three categories of cloth:

1) Acoustically Transparent:
All (most) sound gets through, any slight absorption is even across frequencies so it won't color your sound.

Uses: covering speakers, covering broadband or mid-high frequency absorbing wall treatments.

Examples: speaker cloth, good AT screen material, some types of GOM.

2) Acoustically non-reflective:
Very little sound is reflected from the cloth. However, some sound may be absorbed by the cloth and not make it out the other side. This would color your sound if put in front of speakers.

Uses: fine for covering treatments.

3) Acoustically reflective:
Reflects significant sound energy back into the room at some frequencies (typically mid to high frequencies are reflected, bass gets through). Sometimes this is what you want (to cover a bass trap if you have enough high frequency absorption.)

So, while it may be true that speaker-cloth quality acoustically transparent cloth isn't needed on your first reflection points, anything that reflects mid-high frequencies defeats the purpose of the panels. Your ears are telling you that the felt is doing that. Trust your ears and switch to GOM or some less expensive non-reflective fabric (muslin, etc.)

Fatawan

06-14-07, 11:36 AM

Where do you think 100% cotton would fall in this list of cloth categories?

tonybradley

06-14-07, 11:55 AM

I'd be interested in being pointed to a post where someone said broadband absorbers didn't need to be covered with acoustically transparent material. As your ears have told you, you've lost absorption because the felt is reflecting some frequencies instead of allowing them to pass and be absorbed. GOM certainly is expensive and I understand your desire to find a lower cost alternative that meets your aesthetic sensibilities. As for technical reasons that give the thumbs up or down on felt, see Glenn's post above (http://www.avsforum.com/avs-vb/showthread.php?p=10780435&&#post10780435).

I'll do some searches and post the links. I was told by a few of the "Acoustic Gurus" on the forum that Felt would be perfectly acceptable for broadband absorption. But, as you pointed out, it does sound different to me in comparison to the ugly muslin I was using. For the price I spent for the Muslin, the dye, and now the felt, I could have purchased the GOM. Price lesson learned I guess.

tonybradley

06-14-07, 12:01 PM

As requested, here is the thread regarding the use of Felt:

http://www.avsforum.com/avs-vb/showthread.php?t=708931&highlight=felt

pepar

06-14-07, 12:18 PM

As requested, here is the thread regarding the use of Felt:

http://www.avsforum.com/avs-vb/showthread.php?t=708931&highlight=felt
There is conflicting information there and, IMO, Bryan's post is at conflict internally. For an absorber to be broadband, it must receive the broadest band of frequencies. Cloth that is not acoustically transparent, and does not outright absorb what it does not pass, will reflect. Therefore, the underlying absorptive material will not do it's thing on those frequencies. Perhaps the different posters in that thread are not on the same page. Anyway, if felt is not appropriate to use in front of speakers, it is not appropriate to use to cover broadband absorbers.

pmeyer

06-14-07, 01:31 PM

Anyway, if felt is not appropriate to use in front of speakers, it is not appropriate to use to cover broadband absorbers.

I will agree that if felt reflects some sound energy back into the room, it is not appropriate for first reflection point treatment coverage.

I disagree that the material used on broadband absorbers must be appropriate for use in front of speakers. In speaker covering cloth there should be very little absorption. In broadband absorber covering cloth, absorption is just fine, as long as there is no reflection/diffusion of sound energy back into the room.

That said, it's definitely safer to go with AT material. You can get data on acoustic transparency. I haven't seen a lot of data on acoustic reflectivity across frequencies.

pepar

06-14-07, 01:38 PM

I will agree that if felt reflects some sound energy back into the room, it is not appropriate for first reflection point treatment coverage.

I disagree that the material used on broadband absorbers must be appropriate for use in front of speakers. In speaker covering cloth there should be very little absorption. In broadband absorber covering cloth, absorption is just fine, as long as there is no reflection/diffusion of sound energy back into the room.

That said, it's definitely safer to go with AT material. You can get data on acoustic transparency. I haven't seen a lot of data on acoustic reflectivity across frequencies.
Ahh yes, I see the distinction now. Transmission good. Absorption good. Reflection bad.

Couldn't one derive reflectivity by frequency by looking at NRC and STC? If it's not absorbed and not transmitted, it is reflected?

pmeyer

06-14-07, 01:48 PM

Ahh yes, I see the distinction now. Transmission good. Absorption good. Reflection bad.

Couldn't one derive reflectivity by frequency by looking at NRC and STC? If it's not absorbed and not transmitted, it is reflected?To add to the complexity: if it reflects the energy back, but in a diffuse way (diffuse reflection as opposed to specular reflection), it might still be ok for first reflection points. The mid-high energy will still be in the room, but will not arrive at the listener's ears as a short-delay echo that would affect localization.

I'd stick with GOM, or go with the 'if you can breathe through it relatively easily it's ok' test.

pepar

06-14-07, 01:55 PM

I'd stick with GOM, or go with the 'if you can breathe through it relatively easily it's ok' test.
I like that; everyone has the necessary gear to do that test. :)

Ethan Winer

06-15-07, 02:06 PM

Paul,

if it reflects the energy back, but in a diffuse way (diffuse reflection as opposed to specular reflection), it might still be ok for first reflection points.

Just to be clear, nothing as thin as cloth can offer a useful amount of diffusion.

--Ethan

tonybradley

06-15-07, 02:36 PM

So,

Should I rip my felt off my first reflection absorption panels and use something else? I'm receiving conflicting information. I was told a while back that Felt would be fine, but am now reading that it probably isn't for the use of covering absorption panels at the first reflection. Does Felt reflect too much sound back into the room, making my panels ineffective at high frequencies? I respect everyone's replies and suggestions, but please note that I was told by two well respected folks in this thread that Felt was fine, so I ask that you aren't harsh to me. I just DON'T KNOW the answers and am willing to follow the suggestions of those that do.

pmeyer

06-15-07, 03:01 PM

Just to be clear, nothing as thin as cloth can offer a useful amount of diffusion.
--EthanThanks. When I think about the depth requirements for the quadratic residue diffusors to get any useful frequency range, that makes sense.

pmeyer

06-15-07, 03:15 PM

Tony,

A few things are clear:

1) first reflection point treatment should not reflect mid-high sound.

2) When you switched from muslin to felt on your first reflection points you did not like the change in the sound.

Assuming nothing else changed, that could indicate that the felt was reflecting more high frequency sound than the muslin was. As muslin is a very open weave and felt is denser, this is plausible.

I don't think you are getting any conflicting advice at this point: if the felt sounds worse than the muslin, switch to a more open fabric. What sounds good to you in your room always trumps any theoretical advice you get.

The fact that previous advice indicated felt would be ok is irrelevant. Perhaps there are different thicknesses/densities/types of felts. Maybe some pass sound better than others. Maybe felt doesn't pass high freq sound and the advice was bad. It doesn't much matter. I'm sure the advice was given in good faith.

Bite the bullet and try again. Let us know what you end up with and whether it works better.

Terry Montlick

06-15-07, 05:36 PM

Ethan Winer

06-16-07, 02:01 PM

Yes, I'm afraid you need to remove the felt and replace it with a much more acoustically transparent fabric.

I wouldn't be so quick to have Tony go to all that trouble. Maybe some felt reflects, but the stuff I've seen does not.

Tony, try this simple test: Stand in front of one of your panels and "talk into" it. Does it sound like you're talking into a total void? If so, then the felt is probably fine. If you still have some raw fiberglass, use that as a comparison. If they both sound the same, then the felt is fine. If you hear more of your voice coming back on the panel with felt, then you must have bought some of that "reflective felt" Terry is referring to.

--Ethan

Ethan Winer

06-16-07, 02:02 PM

Thanks. When I think about the depth requirements for the quadratic residue diffusors to get any useful frequency range, that makes sense.

Exactly.

BasementBob

06-16-07, 03:58 PM

Felt, contact with wall, absorption coefficients
125hz 0.13
250hz 0.41
500hz 0.56
1000hz 0.69
2000hz 0.65
4000hz 0.49

At low frequencies, low absorption coefficients might mean that the sound is going right through it.
At high frequencies, low absorption coefficients mean that the sound is reflecting off it. In this case, at 4000hz, according to that test, more than half the sound energy is reflecting off the felt.

Early reflections are defined as reflections from boundary surfaces or other surfaces in the room which reach the listening area within the first 15 ms after the arrival of the direct sound. The levels of these reflections should be at least 10 dB below the level of the direct sound for all frequencies in the range 1 kHz to 8 kHz.

from: EBU Tech. 3276

50% of the energy is 3dB
90% of the energy is 10dB

tonybradley

06-17-07, 10:36 AM

I wouldn't be so quick to have Tony go to all that trouble. Maybe some felt reflects, but the stuff I've seen does not.

Tony, try this simple test: Stand in front of one of your panels and "talk into" it. Does it sound like you're talking into a total void? If so, then the felt is probably fine. If you still have some raw fiberglass, use that as a comparison. If they both sound the same, then the felt is fine. If you hear more of your voice coming back on the panel with felt, then you must have bought some of that "reflective felt" Terry is referring to.

--Ethan

Thanks Ethan. I can definitely tell a difference when talking into my felt covered fiberglass than say, the wall. However, I haven't tried to test between the felt covered fiberglass and fiberglass in general. Not sure why I didn't think of it. I do have a few pieces of rigid boards left. I'll do this simple test today and see how it fairs. Thanks!!!

Ethan Winer

06-17-07, 11:11 AM

Bob,

> At high frequencies, low absorption coefficients mean that the sound is reflecting off it. In this case, at 4000hz, according to that test, more than half the sound energy is reflecting off the felt. <

Not at all - it depends entirely on how thick the felt is! Most felt is 1/16th inch, so I can see some amount of high frequencies passing through and reflecting back off the wall behind. Now, if you test felt that's half an inch thick and it absorbs only 0.65 at 2 KHz, then I might agree that the rest is being reflected. I also agree that the lower absorption at 4 KHz than 2 KHz in your data implies some reflection. But without testing thicker material we're only guessing.

I imagine that all felt is not the same either. The 1/16th inch felt I've used is mostly acoustically transparent. I once held a large piece in front of my face to hear how it affected the sound from a speaker in front of me, and it made little if any change.

--Ethan

pepar

06-17-07, 12:31 PM

Thanks Ethan. I can definitely tell a difference when talking into my felt covered fiberglass than say, the wall. However, I haven't tried to test between the felt covered fiberglass and fiberglass in general. Not sure why I didn't think of it. I do have a few pieces of rigid boards left. I'll do this simple test today and see how it fairs. Thanks!!!
Get someone to snap your picture when you're talking to your acoustical treatments. This could really be helpful to others. ;) :D

Parkytivo

06-17-07, 12:51 PM

pepar

06-17-07, 01:17 PM

I have 2 windows on each side of my 118" Carada theater screen. What would be the easiest way or cost effective way to treat/cover this area. I know the search function is my friend but my father in-law just passed away unexpectantly and we have family coming in. I want to get it up and running as this is a new build and I don't have a lot of time. I am having a hard time thinking straight. I would like to be able to take their minds off of the situation. Thanks for any suggestions.
Depends on how permanent you want the coverings to be. In a similar situation, I installed strips inside the window "well" leaving 3/4" space between them and the wall surface. I then screwed particle board to the strips for a flush covering and went on about my business of adding acoustical treatments.

eugovector

06-17-07, 01:31 PM

Light blocking drapes from Bed, Bath, Beyond, target, walmart or the like. Unless you're going to make fiberglass plugs/panels for the windows, which will render them usless as windows until you remove the panel plug.

You can still treat below the screen, and @ first reflection points, but it sounds like you have a lot on you plate. Go with the curtains, and worry about the rest later.

I have 2 windows on each side of my 118" Carada theater screen. What would be the easiest way or cost effective way to treat/cover this area. I know the search function is my friend but my father in-law just passed away unexpectantly and we have family coming in. I want to get it up and running as this is a new build and I don't have a lot of time. I am having a hard time thinking straight. I would like to be able to take their minds off of the situation. Thanks for any suggestions.

tonybradley

06-18-07, 07:35 AM

Get someone to snap your picture when you're talking to your acoustical treatments. This could really be helpful to others. ;) :D

LOL!! I made sure I did this test with the door to the HT closed :D It was too dark in the room to take a good pic anyway..heheheh.

Seriously though, I did try testing between the Fiberglass wrapped with Felt and a piece of plain rigid fiberglass (both 2", 3pcf). When talking into them, I heard no discernable difference to my ear in regards to any sound bouncing back to me. I used standard Felt from Joanne Fabrics, so I'm not sure the thickness of it.

pepar

06-18-07, 09:09 AM

LOL!! I made sure I did this test with the door to the HT closed :D It was too dark in the room to take a good pic anyway..heheheh.

Seriously though, I did try testing between the Fiberglass wrapped with Felt and a piece of plain rigid fiberglass (both 2", 3pcf). When talking into them, I heard no discernable difference to my ear in regards to any sound bouncing back to me. I used standard Felt from Joanne Fabrics, so I'm not sure the thickness of it.
I'm a believer in using one's ears to detect gross problems and differences in sound, but maybe the speaking into the absorber wasn't valid test in this situation. More likely in my mind, based on what Terry posted re felt reflecting above 2k, your voice doesn't produce the frequency range where the felt falls down as an absorber covering.

Terry Montlick

06-18-07, 09:10 AM

Talking is not a good test for fabric transparency. Reflection from fabric typically occurs at high frequencies (2-3 kHz and above). However most speech sounds -- the voiced ones (i.e. vowels) -- are below this. The unvoiced sounds, like the fricative [s] and the plosive [t], extend to this higher frequency range. But their timbre qualities may not be easily discerned from talking to a wall.

If you want to do a real test, use a program like ETF or REW (free!). Put your mic at the listening position (though remove any seating right there). Directing the test signal to a single main speaker, take one wideband measurement with the felt absorber covering, and one without, and don't change anything else. Set a time slice (windowed frequency response) after the initial impulse, but including this first reflection off the fiberglass or fiberglass-felt combination. Overlaying these graphs should show pretty clearly the reflection effects of your felt.

Regards,
Terry

Ethan Winer

06-18-07, 12:14 PM

Talking is not a good test for fabric transparency. Reflection from fabric typically occurs at high frequencies (2-3 kHz and above). However most speech sounds -- the voiced ones (i.e. vowels) -- are below this.
Terry, I suggest you record yourself speaking normally, then use an EQ to boost frequencies above 3 KHz and report back what you hear. If you hear no change (implying no content above 3 KHz) I'll be astonished.

If you want to do a real test, use a program like ETF or REW (free!).

Agreed. I already did that. Below is a pair of graphs showing the response with and without one inch thick 705 rigid fiberglass covered with 1/16th inch felt at nearby side-wall reflection points.

--Ethan

http://www.realtraps.com/rfz-response.gif

Terry Montlick

06-18-07, 12:24 PM

Agreed. I already did that. Below is a pair of graphs showing the response with and without one inch thick 705 rigid fiberglass covered with 1/16th inch felt at nearby side-wall reflection points.

No. That is the wrong experiment! In order to see the effect of felt, you need to change just this variable, leaving the fiberglass in place. You also need to set the analysis window so that it only sound during the reflection delay is used.

- Terry

Terry Montlick

06-18-07, 12:27 PM

pepar

06-18-07, 12:27 PM

Terry, I suggest you record yourself speaking normally, then use an EQ to boost frequencies above 3 KHz and report back what you hear. If you hear no change (implying no content above 3 KHz) I'll be astonished.
Perhaps that's why Terry said "However most speech sounds -- the voiced ones (i.e. vowels) -- are below this. The unvoiced sounds, like the fricative [s] and the plosive [t], extend to this higher frequency range. But their timbre qualities may not be easily discerned from talking to a wall." Besides, just how one would boost their 3k and up vocal content while speaking into their absorbers escapes me. Sheesh. :rolleyes:

pepar

06-18-07, 12:28 PM

I did NOT say there was no content above 3 kHz. Please read what I posted again. And again, if necessary.

- Terry
I know you can defend yourself, but I couldn't resist. :D

tonybradley

06-18-07, 02:56 PM

What if I have my 2 year old scream really loud into the treatments? I have a feeling some of those squeels are over 4KHz. LOL!!!! Kidding.

I guess for me, what I can do (I know this isn't very technical) is to listen to a few movie soundtracks I'm familiar with, with the felt on. Take the felt off all the panels and do another listen. It may be a conincidence, but I do hear a difference in my treatments after I placed felt on them from the Muslin I had prior, but no real tests were peformed. If it sounds much better to me with the felt off the treatments, I'll know the felt is not for me and replace them with GOM. If I'm unable to determine a difference in the sound, then I'll put the felt back over my treatments and save my cash.

krasmuzik

06-18-07, 03:10 PM

Crying babies are at 4kHz. This is why many speakers are not accurate and reduce that range - they know the men buying them don't want to really hear crying babies accurately.

tonybradley

06-18-07, 03:19 PM

Crying babies are at 4kHz. This is why many speakers are not accurate and reduce that range - they know the men buying them don't want to really hear crying babies accurately.

Maybe that's why my wife wondered why I occasionally yelled for her to get up when I was listening to a sountrack.

Ethan Winer

06-18-07, 04:42 PM

No. That is the wrong experiment! In order to see the effect of felt, you need to change just this variable, leaving the fiberglass in place. You also need to set the analysis window so that it only sound during the reflection delay is used.

Of course, but my graph shows that normal felt is fine. Which is the real issue. BTW, one of your pals is arguing on another forum that silk and other tight weave fabrics are fine for first reflection treatment. I can't agree with that, but felt is fine. You don't like felt? No problem. Don't use it! :D

--Ethan

BasementBob

06-18-07, 04:52 PM

krasmuzik:

Crying babies are at 4kHz.

I believe babies are loudest between 2khz and 4khz -- and have a scream/cry frequency/volume distribution roughly the equivilent of an inverted Fletcher–Munson curve ( or your pick of any equal-loudness contour: Robinson-Dadson, ISO 226:2003 ). Evolution has made the loudest thing we can hear, a baby's cry.

Stew4msu

06-18-07, 11:55 PM

OK, several of what might be more questions for some kind soul:

1. I want to add some treatments to my front wall. However, my front wall is a bit unusual (see picture). I plan on treating the exposed front wall (around the screen), but should I also treat the angled ceiling/wall where the speakers are? In case it's hard to tell in the photo, the front wall is 8' high and then the wall slopes up to the 10' ceiling. I put my speakers on that slope and they're naturally angled right at the seating area. If I should treat that angled wall/ceiling, how do I do that with the speakers there? If it matters, the rear speakers are at about 7' high.

2. Using the reflection point calculator, my reflection points are quite high (due to the speaker placement), so is there any need to treat the walls below 44" (ear height), or should I just put some panels along the wall where the actual reflection points are (and I'll probably remove the posters that are visible in the third picture)?

3. The wall in the rear of the room is the same as what you see in the front (wall slopes up to meet the ceiling). How do I do a floor to ceiling bass trap in that case (was thinking about the stacked triangle thingamagigs)? Or should I just put an 8' tall bass trap?

4. Due to the equipment/DVD storage shown in the pic, I can't but a bass trap there. I was going to do both back corners, should I do the other front as well? There's open space behind the equipment/DVD storage (about 1.5' deep - see second pic). Should I put bass traps in those corners (there's 2 of them)?

5. I currently have a chair rail around the room (see third pic) with fabric underneath. I have no idea if the fabric is accoustically transparent, reflective or what. When I built the room, I didn't want the fabric right against the wall, so I put extra carpet padding behind it (the 1/2" thick blue stuff - see fourth pic and pardon the quality of the pic). Is that good, bad or indifferent?

I should add that to my ears the room sounds good right now. With no treatments at all, it's very pleasant and everyone raves about it. However, sometimes it seems that dialogue is a bit hard to hear (reflections?) and the bass seems a bit "rattley" from time to time, so I'm looking to make some improvements.

http://www.kellystewart.net/albums/album63/screen_wall.jpg

http://www.kellystewart.net/albums/album63/dvd_storage_rack.jpg

http://www.kellystewart.net/albums/albun05/right_front.sized.jpg

http://www.kellystewart.net/albums/album63/lower_walls_carpet_pad_furring_strips_II.jpg

Thanks

Ethan Winer

06-19-07, 11:51 AM

Stew,

I want to add some treatments to my front wall.

Looking at your setup I'd say you need corner bass traps and side wall first reflection treatment much more than absorption on the front wall.

I put my speakers on that slope and they're naturally angled right at the seating area.

Any chance to change that? All speakers should be at ear level for best results.

or should I just put some panels along the wall where the actual reflection points are

Yes.

Due to the equipment/DVD storage shown in the pic, I can't but a bass trap there.

Then put a trap flat on the front wall, as near to the corner as you can.

I should add that to my ears the room sounds good right now. With no treatments at all, it's very pleasant and everyone raves about it. However, sometimes it seems that dialogue is a bit hard to hear (reflections?) and the bass seems a bit "rattley" from time to time, so I'm looking to make some improvements.

Imagine how great it will sound once it's treated properly! :D

--Ethan

Mr.Tim

06-19-07, 02:12 PM

If the fabric is mounted as a wall or ceiling covering, as specified in International Building Code 2003, section 803.4, then the fabric only is required to have been tested and given a Class A rating according to ASTM E 84. This will be true for typical permanently-installed fabric -- stapled over furring strings, or attached via a track fabric system.
<snip>

True, but where the International Residential Code has been adopted, and the home theater is in a 1 or 2 family or townhome, a Class C rating (200 flame spread) is required. R315. However, as you stated, the testing is required.

You cannot treat with a home-grown solution (eg boric acid) for a compliant installation. You could ask the building official about a product listed for the use (eg fabric shield). Probably not worth the effort.

The fabric is an interior finish, not part of an assembly. The listing of a the fabric alone should be sufficient.

(not all of this pertains to you, Terry-- just answering a few of the questions that came up)

Regards,
Tim

McCall

06-19-07, 02:33 PM

I have a question for you AT experts here, I mean the ones making a living at it, I have two panels in my theater that I covered with felt early on. my others are covered with Stetch velvet that You can easily blow through, yeah I know not a perfect test but has worked great for me, but that is not the issue I am asking about.
the other day I walked very close to each panel the velvet and the felt. Nothing going on in theater at the time, meaning no sound on. when I was close to the velvet covered the everything sounded exactly the same as if I were feet away in the room, but when I walked near the felt covering there was a very perceptible deadening sound change, I mean just the ambient sound of the room itself, nothing on whatever, no fans no AC etc. just different degrees of silence.
What would that indicate with regard to the felt in this case over the velvet?
I found it so strange that I just wondered if you guys could tell me.

Ethan Winer

06-20-07, 12:08 PM

What would that indicate with regard to the felt in this case over the velvet?

If you hear more of a drop in ambient sound level as you approach a panel, that implies more absorption. A better test is to "talk into" each panel and see how dead your voice sounds coming back. If you do that with a bare wall first you'll have something to compare to. After a while you can tell easily which materials absorb (voice frequencies) better than others. :D

--Ethan

tonybradley

06-20-07, 02:56 PM

If you hear more of a drop in ambient sound level as you approach a panel, that implies more absorption. A better test is to "talk into" each panel and see how dead your voice sounds coming back. If you do that with a bare wall first you'll have something to compare to. After a while you can tell easily which materials absorb (voice frequencies) better than others. :D

--Ethan

This is basically what you told me, and others discarded it. Now that you were more detailed in saying it's easy to determine which materials absorb "Voice Frequencies", can we get a little more detailed on which is better for an HT environment, since most of us aren't building one for poetry readings? No disrespect, it's just tough to swallow so many different views. Is there a chart that shows reflective coefficients of various materials (felt, Muslin, Cotton, Velvet, different types of GOM, etc.) when covering absorption material? Otherwise, unless a person spends a great deal of money and time experimenting, we will go into this blindly. I Understand people such as myself could have went with GOM in the first place, and in hind sight, I should have from the time and money I've spent changing out my muslin for felt. But, with all the knowledge around this forum, and true tests that have been done, I'd like to know more about the Plus and Minus of felt outside the voice range. Again, this is of no disrespect to you as I have read many of your posts and I thank you for the wealth of knowledge. Nobody really discards GOM, but some are discarding Felt, and would be good to know how it will really affect my room. In movie soundtracks, is there a lot of information over the 4khz frequencies that felt supposedly reflects, etc.

Terry Montlick

06-20-07, 05:01 PM

Tony,

Here's an ancient graph for felt absorption/reflection/transmission, which I found in my files:

http://www.tmlaboratories.com/hair_felt.jpg

Sorry that I don't have time right now to do some modern tests for you. This is from a 1916 paper by F.R. Watson, "An Investigation of the Transmission Reflection and Absorption of Sound by Different Materials." It may in fact be the oldest journal paper I have!

The felt was hair felt, which would probably be hard to find an exact match for today. Heck, the anechoic wedge tables that Leo Beranek published in the 1940's became obsolete soon after, when the flow resistivity for 3 pcf fiberglass completely changed. The felt thickness layer units are 1/2".

There are a couple of things to notice:
The reflection component is significant.
It does not change nice and linearly with thickness.

Different felt materials will no doubt behave differently. This is the main reason for going with a known material like GOM fabric.

Regards,
Terry

Stew4msu

06-20-07, 05:19 PM

Thanks Ethan for your response.

Looking at your setup I'd say you need corner bass traps and side wall first reflection treatment much more than absorption on the front wall.

I plan on doing that too, should I not do the front wall as well? If I do, should I treat the angled wall too?

Any chance to change that? All speakers should be at ear level for best results.

Probably not, it's a sacrifice I had to make.

Then put a trap flat on the front wall, as near to the corner as you can.

I might not have the room for his either, due to the amount of space between the screen and the equipment rack. Would it not be beneficial to put some type of bass trap behind the DVD/equipment storage. It's just a cavity back there and the built in DVD storage is just made out of 2X6's with plywood backing.

What about where the wall corners hit the angled ceiling/wall in the front and back? I can't really to floor to ceiling, because of the angle. Just make the bass traps 8' high?

Thanks,

Stew

uxbridge

06-20-07, 06:53 PM

Phil Olson

06-21-07, 03:06 AM

The problem is that you have to account for all the 'natural' treatments like couches, rugs, shelving, windows, even people, in addition to the room size.

If you want to do better than just ballpark standard treatments like front wall/lower half of side walls, etc., pick up a copy of ETFA and measure where you are. You can then ask what treatments to add for any deficiencies you may find.

pepar

06-21-07, 09:48 AM

Does anyone know of a calculator/spreadsheet that you can input your room size and your acoustical treatments specs. to determine how much you will need to reach the RT60 you desire? Thanks in advance.
Be prepared to be daunted; the more accurate detail you feed it, the more accurate will be the results. Phil's right about simply getting some free software, a mic and a laptop and actually measuring, but here ya go (http://www.peparsplace.com/Control Room Calculator V2.61 XL2002.zip). Prepare to be daunted! :)

Ethan Winer

06-21-07, 03:31 PM

Tony,

can we get a little more detailed on which is better for an HT environment, since most of us aren't building one for poetry readings?

For panels at reflection points you want the absorption to be as high as possible at all frequencies. It's that simple.

No disrespect, it's just tough to swallow so many different views.

I agree fully, and that's the main problem with this thread. It's too long, it's full of conflicting opinions expressed by experts and newbies alike, yet it's stuck at the top so people feel they need to read and understand it all. Nobody can understand it all because much of it is not understandable. And much of it is wrong.

Is there a chart that shows reflective coefficients of various materials (felt, Muslin, Cotton, Velvet, different types of GOM, etc.) when covering absorption material?

Not that I know of. Even if there were such a thing, its value would be limited. For example, Terry's graph is really neat from a historical perspective, but nobody makes felt from horse hair today, and nobody uses 1/2 inch thick felt over rigid fiberglass. Likewise for cotton. There's a lot of ways to make cotton fabric, and they're not all equivalent acoustically.

All that said, in my experience typical 1/16th inch felt is fine. :D

--Ethan

Ethan Winer

06-21-07, 03:35 PM

Here's an ancient graph for felt absorption/reflection/transmission, which I found in my files
Very cool! Thanks for posting that.

The reflection component is significant.
It sure is. Now, if only there were an axis showing frequency this would actually be useful information. :eek:

Useful for half inch thick horse felt, that is! :D

--Ethan

Ethan Winer

06-21-07, 03:39 PM

I plan on doing that too, should I not do the front wall as well? If I do, should I treat the angled wall too?

I won't say don't treat the front wall, but it's less important than other places in the room. Also, treating a room is often an ongoing process, especially for DIY'ers. You start with a few panels, and see what that does, then you're in a better position to know what else is needed.

What about where the wall corners hit the angled ceiling/wall in the front and back? I can't really to floor to ceiling, because of the angle. Just make the bass traps 8' high?

The more bass trapping the better. Always.

--Ethan

pepar

06-21-07, 03:39 PM

Other than Linus Van Pelt, I've never seen anyone hang onto a piece of cloth so tightly. ;)

Terry Montlick

06-23-07, 08:46 AM

Now, if only there were an axis showing frequency this would actually be useful information. :eek:

Useful for half inch thick horse felt, that is! :D

--Ethan
Would pass your criticisms on to the paper's author, Floyd R. Watson (first editor of JASA), but he died in 1974. :eek:

- Terry

Ethan Winer

06-23-07, 03:07 PM

Would pass your criticisms on to the paper's author, Floyd R. Watson (first editor of JASA), but he died in 1974. :eek:

I'm not criticizing at all! I think it's really cool. Just irrelevant today. :D

--Ethan

Stew4msu

06-25-07, 01:21 AM

I won't say don't treat the front wall, but it's less important than other places in the room. Also, treating a room is often an ongoing process, especially for DIY'ers. You start with a few panels, and see what that does, then you're in a better position to know what else is needed.

--Ethan

Will do, but I have no idea whether it will matter or not to treat the angled ceiling/wall where the speakers are (not the front wall). Would that have any benefit if I treated it like the front wall, if I deem it necessary.

Here's the pic again as a reminder:

http://www.kellystewart.net/albums/album63/screen_wall.jpg

Ethan Winer

06-25-07, 01:22 PM

I have no idea whether it will matter or not to treat the angled ceiling/wall where the speakers are (not the front wall).

Yes, all junctions are a great place for bass traps, even if the angle is not 90 degrees. Do it. :D

--Ethan

Stew4msu

06-27-07, 12:33 AM

Thanks Ethan, but I actually meant the entire angled wall (behind the speakers), as if it were an extension of the front wall.

I was already planning bass traps at the junctions.

Ethan Winer

06-27-07, 11:24 AM

I actually meant the entire angled wall (behind the speakers), as if it were an extension of the front wall.

I don't see the value unless your speakers happen to send sound that way making the angled part a reflection point.

--Ethan

pepar

06-27-07, 01:08 PM

Thanks Ethan, but I actually meant the entire angled wall (behind the speakers), as if it were an extension of the front wall.

I was already planning bass traps at the junctions.
Well, I would treat it the area *just* behind the speakers. As the distance between them and the wall is essentially nil, an area perhaps only 3" beyond the footprint of the mounted speaker would do it. Sound does emanate from the rear of the speaker cabinet and this treatment will address that particular first reflection.

Just my $.02.

rutlian

06-27-07, 05:14 PM

Anybody ever use ATS ACCOUSTICS? service wise and feedback of their wall panels
seems that they have a good price.

bpape

06-28-07, 07:24 AM

If the speakers are relatively close to the wall, treating it is a good idea to minimize the impact of SBIR.

Bryan

dae3dae3

06-28-07, 01:27 PM

I was pricing materials to build my acoustic panels and found that the cotton batting that I was planning to put over the rock wool to prevent it from sending insulation dust into the room when the panels are handled is about four times the cost of the polyester batting. Is there any reason the polyester would not be suitable? It seems just as light and airy as the cotton.

dae3dae3

07-02-07, 01:14 PM

Geez, I've always suspected that I had the skills to kill a thread. I've never done it to a 2400+ post thread before though.

I don't know if I should be proud of myself or not. :)

eugovector

07-02-07, 01:27 PM

Poly batting should be fine. Go to Joann's, and buy some quilt padding. Thinner is better unless you're really going to be roughing up your panels.

BasementBob

07-02-07, 01:29 PM

dae3dae3:

I haven't subjected this to any ASTM C423 testing nor fire testing, but I can tell you it absorbs pretty good:
http://www.bobgolds.com/Absorber/home.htm

The white stuff in the pictures is polyester batting I bought from wall-mart. I used it as a wrap.

dae3dae3

07-02-07, 02:51 PM

Thanks for the replies. :)

drunkpenguin

07-04-07, 01:58 PM

whats wrong with skipping the batting part? Is the fiberglass really going to float around the room if nobody is touching it?

eugovector

07-04-07, 03:38 PM

whats wrong with skipping the batting part? Is the fiberglass really going to float around the room if nobody is touching it?

Probably not, but for most people, it's a better safe than sorry approach. For me, I didn't have to worry about breathing the stuff, irritating my hands while cramming it into my frames if I wrapped it in poly first.

RobertR

07-07-07, 09:37 PM

I don't know if this question has been answered in this thread. The first post says use Linacoustic up to ear height (about 44 inches) for side walls. But what about risers? Is the same height maintained all the way to the back of the room? If so, "ear height" is no longer maintained for rows further back. For a 12 inch riser, there's only 32 inches of Linacoustic for the back row.

eugovector

07-07-07, 09:49 PM

Yep, if you have a riser, it would be a good idea to treat that area up to ear height.

BasementBob

07-07-07, 11:08 PM

RobertR:

The rough idea is to do the walls up to the point that the mirror reflection point is six inches lower than the top of the linacoustic. (The assumption is that imaging, over many seats, is more important than room reverb and spaciousness. You can go higher if you need to reduce room reverb further)

You can use that rough idea to determine how high to put the linacoustic on the walls, combined with knowing how high your mains tweaters are, and where your front row ears are, and where your riser row ears are.

If your mains tweaters are higher than your ears, then having the linacoustic just up to your ears is too short.

If your mains tweaters are the same height as your ears, then having the linacoustic up to your ears is too short, but six more inches would be fine.

If your mains tweaters are under your screen, then having the linacoustic up to your ears is just fine (unless your screen is really way up there).

RobertR

07-08-07, 01:18 PM

Thanks for the detailed response, Bob!

wgilpin

07-10-07, 02:34 AM

Here's a site detailing how I built my DIY absorbers. (http://thegilpins.org/Projects)

Cheers,

BasementBob

07-10-07, 06:38 AM

wgilpin
Good jointery you have there (http://thegilpins.org/Projects/Site/Projects/5A5066F2-EBDE-4AE2-B1AC-E1A700A8F17F.html).

pepar

07-10-07, 08:47 AM

Here's a site detailing how I built my DIY absorbers. (http://thegilpins.org/Projects)
Very nice, and nice website, too. Your mounting method spaces them away from the wall; was this intentional to get some beneficial acoustical effect, or just a by-product of the mounting method?

wgilpin

07-10-07, 02:13 PM

Very nice, and nice website, too. Your mounting method spaces them away from the wall; was this intentional to get some beneficial acoustical effect, or just a by-product of the mounting method?
Thanks!

Spacing them away from the wall was intentional. I wanted to use both sides of the insulation to maximize their effectiveness. Plus, it looks kinda cool. :D

bpape

07-13-07, 07:07 AM

Nice looking wes. The Cherry and black is a nice combination.

Bryan

Fatawan

07-13-07, 05:02 PM

If one was to do a star ceiling using black velvet as the covering material on the ceiling, what would the acoustics effects be?

Thanks

McCall

07-13-07, 06:16 PM

It really depends on what velvet you are using here. I use stretch velvet in my theater it is over my speakers and does not affect them any more than speaker cloth did. I also have it over my acoustic all treatments.
A solid velvet, non stretch, may absorb more but the stretch one, WHEN STRETCHED if pretty transparent.

Stereodude

07-22-07, 03:02 PM

I read through the entire thread and have a question that wasn't exactly answered. I understand a bass trap can be nearly any size shape, but both obviously of those dictate effectiveness... Most bass traps get placed into a corner at a 45 degree angle. What is the impact if the bass trap isn't at a 45 degree angle?

For example, how would these (see attachment) bass traps work? They are in the corners of the walls and ceiling. Would they be only marginally effective? What could be done to improve them without having them extend down more than 1 foot from the ceiling?

bpape

07-23-07, 07:09 AM

They'll still work - they just won't have the hump in absorbtion nor extend as deep (depending on thickness) as the same thing stradding the corner. The difference is the distance from the leading edge of the absorbtion to the boundary behind.

Bryan

Stereodude

07-23-07, 11:54 AM

They'll still work - they just won't have the hump in absorption nor extend as deep (depending on thickness) as the same thing straddling the corner. The difference is the distance from the leading edge of the absorption to the boundary behind.

BryanSo, does 4" of 705 8" from the wall have nearly the same effect as 8" of 705" 4" from the wall? Also, at what point does the thickness of the material hit the point of diminishing returns, or is that material dependent? Is there a rule of thumb for surface area on bass traps? Like less than 4 square ft of surface don't bother?

bpape

07-24-07, 07:44 AM

Generally, the max 'extra benefit' IMO is an airspace equal to the thickness of the absorbtion. So, 4" gap behind 4" of material. More than that, and it can actually begin to be more like a filter and introduce a different peak in absorbtion.

Also, once you start getting thicker, you can save some money and use 703 instead of 705. How thick you go depends on how deep you need to go. More is better to a point. As far as surface area, it's really more a function of what else is going on in the room and how large the room is (proportion of control to room volume). 4 sq ft in a 3x3x8 closet is absolutely worth doing. In a 15x20x8 room, it certainly won't hurt but don't expect miracles.

Bryan

Deathwish238

07-27-07, 08:39 PM

Moved...

techshare31

07-28-07, 05:44 PM

techshare31

07-29-07, 02:57 PM

Hopefully, the pictures say it all. I'm just looking for some ideas on how I can make this kind of undefined room sound better. You'll notice on the rear of the room I've got three windows. I'm planning on addding some heavy curtains to those windows anyway ... however I'm not sure how much benefit that will give me in the way of acoustics as it's only the rear wall.

The room has no right wall with just a half "bar" type wall which joins into the kitches as you can see. On the left there is a wall which opens on the front left corner to a rather large opening to the next room and hallway. I believe the room is roughly 15X18ft with "vaulted" ceilings that go from 8-10ft. Thanks for any ideas and as always I'm looking for the most bang for the buck. I'm not opposed to the pre-fab acoustic stuff, but I think I'll need to try something I can experiment with do to the odd shape and setup of this room.

Well! No replies yet but as an update I went out and got some fairly heave suede type drapes. They aren't even pressed yet but I got 'em up there and played some movie sound. I am now a believer in room treatment. Just those drapes on the rear window seemed to improve the sound. I was able to hear more surround and the clarity at higher volume was better. For lack of a better word, there seems to be less "racket" between the sound I want to hear.

Now what to do next ....

jeppe

07-30-07, 10:34 AM

hi,whats up with them stacked triangle corner traps floor to ceeling in each corner of the room? sounds like a great idea
whats the imortant notes on the size, density&windfloow of the mineralwool ?
im from europe and sorry too say it seems that i cant find any Owens corning over here...
just isover,paroc and knauf insulations.

Jason Jones

07-31-07, 10:30 AM

BasementBob

07-31-07, 02:22 PM

jeppe:

What you're talking about is called a Studiotips SuperChunk (http://forum.studiotips.com/viewtopic.php?t=535).

http://www.bobgolds.com/TrapHarder/home.htm

The largest that I know of anyone making diagonal corner Studiotips SuperChunks is this
http://www.bobgolds.com/CornerTrapCut.GIF

You can use anything on this page: http://www.bobgolds.com/AbsorptionCoefficients.htm
In your case perhaps RW3 or RWA45 is what you want. I think there's a store called "Travis Perkins" that sells the stuff.
http://www.bobgolds.com/InsulationContractors.htm might have an address near the bottom.

Generally speaking, the bigger you make them, the less dense you want to fill it with, but not so loose that it falls over.

jeppe

08-03-07, 04:11 PM

hi thanks for them very nice links man ;)
so more absorption volyme on the tringle superchunks than a simple 4"board against the corner right...does it have any negative effects when the triangle are right against the wall whith no air behind?

BasementBob

08-03-07, 08:03 PM

jeppe

so more absorption volume on the tringle superchunks than a simple 4"board against the corner rightYes, a Studiotips SuperChunk uses a lot more material to get a slighly more even broadband absorber than just a simple 4" board placed diagonally across the corner.

does it have any negative effects when the triangle are right against the wall whith no air behind? No. For any single diagonal size, filling the space right to the wall is believed to be optimum. For any single triangle cut size, it's possible to pull them out from the wall and that might or might not be better acoustically/absoratively, but I'd think it would fall over to make a in-the-room-pillar like that without wall support.

jeppe

08-04-07, 12:23 AM

:) man thats great too hear,so now i try too find me some nice 4" rockwool or something like that and start cutting hallelulia, i must match my room acoustics with my 15" sub... some modal ringing there...

bpape

08-05-07, 10:36 AM

Just for completeness, if you're going to do the chunks (which work very well), the amount of material is exactly the same as straddling the corner with 6" of thickess (assuming a 2' face) and will use less space in the room.

Each 2'x4' piece will cut into 8 pcs that are 17x17x24". So, a 2" thick 2'x4' piece will give you a solid triangular chunk that is 17x17x24 and 16" tall. For an 8' ceiling, you'll need 6 pcs - same as 2'x4'x6" straddling the corner on top of each other.

Bryan

QueueCumber

08-05-07, 04:42 PM

I'm constructing some panels and was curious about using 3M 77 Spray adhesive to attach the GoM fabric. What is the best way to do this so that it won't affect the acoustic properties of the 2" OC 703? Can I spray it on the front face of the OC703 and the fabric that will be on the front of the OC703 to bond them together, or will this seal them and make the OC703 useless underneath? What do people recommend?

Also, if anyone has worked with Rotofast Snap-ins before and had to remove treatments from them, does anyone have a method that will work without destroying the absorption panel?

Thanks.

BasementBob

08-05-07, 05:06 PM

QueueCumber:

The usual recommendation is to wrap the 703 like a christmas present, spraying the 3M 77 only on the back.

If you use 3M 77, do it outside -- when it sprays it puts glue on everything in the room.

jeppe

08-05-07, 06:04 PM

:) hello again thanks for that idea...
but maybe a little bit to small for me?
my rectangular room is; 1579^3
16.1'
12,0'
8,2'

first length specific roomresonance is @35hz.rigth?

i think i would need some bigger triangels than that no?
i was aiming to cut 3 pieces of one 2'wide 4'long piece
each triangle to measure= 33*33*47"
now thats something for my ugly standing wawe @70hz on my wall behind my chair where i am seated right?
now thats pretty big too have 4 of them the same size in my thiny little living room (i would like to have a place where i can have my sofa!) so i was thinking what about only putting one 12 feet tall @ the ceiling/wall corner angle horizontally....
now seriosly what do you think about it? is this a good idea or is there something better that comes too your mind? it is doable...

(sorry i am not so good on english)
/cheers jeppe

Petrucci

08-06-07, 01:12 PM

I am about to treat the front wall of my theater with linacoustic duct liner. I am only gong to need about 90sq foot of duct liner to do the front wall so I will have alot of linacoustic left over. I was considering using the leftover linacoustic to build corner traps. Do you folks think it would be effective to cut the duct liner to about an 8ft length and then just roll it up like a poster to stand 8ft vertically and then fasten it to the corners with some kind of adhesive??

eugovector

08-06-07, 01:15 PM

How thick/Wide is the linacoustic?

Petrucci

08-06-07, 01:25 PM

How thick/Wide is the linacoustic?

I havnt purchased the roll yet but the local HVAC supplier in my area sells rolls that are 1" thick and 48" wide. I think the smallest roll would be 200 linear feet.

Eric

eugovector

08-06-07, 01:28 PM

I think you'd be better off building a panel to straddle the corner, 6" thick or so. Or cut it up super chunk style. I just don't think that rolling 48" is going to give you enough mass, but someone here may correct me.

It's more work, but I think it will be more effective and look better when it's done.

nathan_h

08-06-07, 05:12 PM

I'm building a dedicated room inside my detached garage.

Main thread: http://www.avsforum.com/avs-vb/showthread.php?t=782601

Without filling this thread with posts copied from my main thread and the specific topic on what size to build the room-within-the-garage -- or whether to just Green Glue more drywall to the existing drywall -- I'll reference the thread and just include some of the details, here.

Here are the details of what I'm struggling with now: http://www.avsforum.com/avs-vb/showthread.php?p=11233278#post11233278

-----

Now it's time to make some dimension and construction decisions. From what I can estimate, the cost different between putting a second layer of drywall over the existing drywall (using the case of Green Glue a gracious fellow AVS-er set me up with) is less expensive than building four new interior walls... though I will have to build one new interior wall, anyway, to break up the room.

But I'm thinking it may be worth it to essentially build a room within the garage, that is almost as wide, and similarly as tall, as the current space -- because it lets me choose a more optimum size for acoustics, and the air gap between the false room on the slab, the walls of the actual garage, perhaps 6 to 12 inches, will help contain sound within the space AND prevent sound from leaking in.

And building a 2x4 frame for four walls to enclose a space of approx 13' x 16' is not astronomically more than doing a single wall....

But it raises the question of the RIGHT dimensions.

I've re-oriented the room to have the screen on the long wall -- so the room is wider than deep. I've got it figured out to have the seating at 2/3 of the way back from the screen. And, of course, the sweet spot seat will be centered on the screen and equidistant from each side wall.

Plugging all this into the calculators tells me:

13 x 17 x 7 room (17 is the max width, and 7 is the max ceiling with out having some cross beams visible): I've got single peaks at 66,161, and 199 hz. Double peaks at 132 and 256 hz. And single nulls at 33, 80,100, 166, and 299 hz. And a double null at 242 hz. AND 5 problem frequencies: 132, 166, 173, 241, 256.

NOT SO GOOD!

But, if I do 12.5 x 16 x 7.33, I get no peaks and no nulls! Of course, there are still 4 problematic frequencies, according to the calculator: 141, 180, 230, and 282 hz.

Other options can reduce the "problem frequencies" to just two, BUT then introduces two peaks. 13 x 16 x 7.33 is an example.

Calculators are attached:

http://www.avsforum.com/avs-vb/attachment.php?attachmentid=86462

The best bet according to the experts appears to be to remove the drywall on the existing wall and increase the cavity between that and a new wall I build.

BUT: The existing walls are insulated, which is nice. That's one reason I hesitate to pull the drywall off and create a VERY WIDE cavity between the garage exterior and the new "wall" inside the garage: I'll lose that insulation. I also REALLY like the idea that this theater could be an isolated room within the garage -- only really touching the garage in that it sits on the same concrete slab.

Plus, one day if we reconstruct the theater, we'll be left with a garage without drywall and insulation (which I realize is not that unusual but still).

Budget is always of concern BUT I already have a case of Green Glue. And if doing it "right" (or better) costs a bit more, and that becomes a budget issue, I'll just push out my timeline a bit. Luckily, I can watch movies in the living room for now. It's far from ideal, but it works.

What I don't want to do is save $1k in materials and end up with something far less workable (sound bad inside and sound leaks more outside) because I was cheap/impatient.

And the layout:

http://www.avsforum.com/avs-vb/attachment.php?attachmentid=86552

Note that the entrance to the garage is at the bottom of the picture and is cut off. Right now, the garage is empty, so I have a blank slate.

Another idea is to use non-parallel walls -- which is intriguing to me. I guess that would be good -- but it's not clear to me whether that helps only with problem frequencies related to combing, modes/peaks/nulls, and/or? And then, would I want to maximize my square footage and stop trying to build to "ideal dimensions"?

Deathwish238

08-06-07, 11:05 PM

What's the best acoustical material to buy on a budget? I assume there'ld be a best for bass traps and another for normal panels

jeppe

08-06-07, 11:51 PM

well arent you a lucky guy to live in US i have a hell of a problem finding me some decent wool over here in europe check out this man it seems pretty nice to me!

RHT 40 Industrial Board

some really nice absorptioncoefficents numbers in the pdf-file on the roxull homepage...

nathan_h

08-07-07, 02:36 AM

What's the best acoustical material to buy on a budget? I assume there'ld be a best for bass traps and another for normal panels

For bass traps, try doubling or tripling up 2" thick boards of Owens Corning 703 brand 3 lbs. per cubic foot density semi-rigid fiberglass board -- 48"x24"x2" Panels at about $15 each. Of course, you'll want to cover them up, which adds to the cost, and you'll need to pay for shipping, since it's only sold to contractors and not directly to consumers.

pepar

08-07-07, 10:17 AM

For bass traps, try doubling or tripling up 2" thick boards of Owens Corning 703 brand 3 lbs. per cubic foot density semi-rigid fiberglass board -- 48"x24"x2" Panels at about $15 each. Of course, you'll want to cover them up, which adds to the cost, and you'll need to pay for shipping, since it's only sold to contractors and not directly to consumers.
Not completely true. Specialty Products & Insulation Co. (SPI) (http://www.spi-co.com/) sells to end-users and at very favorable prices - IMO - as well. They have branches all over the U.S. Of course, they will not sell individual sheets, but most home theater projects (can) use bulk.

jeppe

08-07-07, 11:10 AM

speciality products&insulation co.
is a buisness partner with Roxul, maybe they have the rth-40 industrialboard

the absorption numbers for 4" are; 1.07 1.01 1.07 1.06 1.07 1.06 1.05
isnt that better values than owens corning 703?

wonder how many dollars they would quote me for one pallete to europe hmm... probably over 1000$

nathan_h

08-07-07, 11:21 AM

Not completely true. Specialty Products & Insulation Co. (SPI) (http://www.spi-co.com/) sells to end-users and at very favorable prices - IMO - as well. They have branches all over the U.S. Of course, they will not sell individual sheets, but most home theater projects (can) use bulk.

Thanks for the tip about other suppliers. Very good to know.

jeppe

08-07-07, 11:30 AM

if you like to go with thicker like 6"
here another tipp for you..

owens corning 1240

absorption numbers; 1.32 1.14 1.11 1.09 1.06 1.07 1.10 thats some nice numbers allright...

lavarenne

08-08-07, 01:37 PM

This approach has worked for me on the basis of having the wall behind the front speakers needing replastering - therefore the acoustic high density foam approach with overlaying quilt wadding and a final layer of suede efffect material seemed much cheaper and more appealing (I am no plasterer). Furthermore the rear wall is divided by a large double french door with a thick velvet curtain across, so there didn't seem much point in any further treatements. There is also a small diagonal wall (where the chinmey was once in the corner next to the front wall) which has the same treatment as the rest of the front wall. Overall the room is adequately assymetrical and sounds dead without deadening the AV sound. Thick curtains, a sofa complete the sound absorbtions as well as the door having the same treatment as the front wall. Bass has not been a problem as the sub is kept under check and the main fronts with their transmission line construction handle bass in the lower ocatves quite well. It was not scientific in its approach but more driven by decorative requirements and circumstance. However, the soft wall behind the screen also does a good job of mopping up stray light reflection as well.

nathan_h

08-08-07, 01:51 PM

haslip

08-10-07, 01:32 PM

I am looking for outside the box acoustic treatment looks, and thus have a question.

I can put two pieces of Owens Corning 703 behind this 53" x 53" tapestry. I have black walls, and I was just going to put black around the edges of the 703 and put this over top? Could it work?

http://imagecache2.allposters.com/images/pic/PUR/2888WH-IronWork~Iron-Work-Posters.jpg

This finely crafted wall tapestry is made in the USA by skilled artisans, using Jacquard looms and pure cotton yarn. An iron rod and finial are included, in addition to brackets and hardware for easy hanging.

Ethan Winer

08-10-07, 02:49 PM

Yes, that'll be great, as long as the tapestry is reasonably "soft" and absorbent.

--Ethan

GB_KSU

08-10-07, 03:25 PM

I have a couple of questions for the experts:

First off, this past winter I did some DIY treatment to my room, consisting of front corner treatment and an angled soffit using 703 in a super wedge fashion. (I believe that is what it is called). The only difference is that I used 1' wedges vs. 2'. I also hung some 2x4 panels for first reflection points on the side walls. To my ear the room improved a good deal. However I am looking to rework the room as I am unhappy with how the fabric coverings turned out. When I do this I will essentially be removing all of the treatment. I only took simple measurements of the room with an spl meter before adding the treatments. With that said I would really like to take some good base measurements of the room minus treatment before I finalize another plan. I have been looking at the software and equipment on the Rives site and was curious as to what the opinions are regarding these programs. Is it worthwhile to invest in one of the test kits? I will say that I am young, and this is my first home so it certainly won't be the last room I ever work in.

I also noticed a room on the Audiogon forums that I found very attractive. The owner had some very unique absorption panels installed. Here is a link to a site documenting the build:
http://www.zerogain.com/forum/showthread.php?t=15669
I love the look of these panels, but I don't quite understand how they "work". I am assuming that the size and spacing of the openings in both the "top" panel and mdf panel would make them more efficient at certain frequencies? I would think that they would be highly reflective for the most part? Please enlighten me!

Mike N Ike

08-10-07, 11:45 PM

I have a less than ideal room, 19' x 16', carpeted , drapes, sofa, loveseat and one wall of bookcases. I think my biggest issue is the cathedral ceiling. Starts at about 10' and is 18' high. At at the high point it opens into a loft area. Lots of cubic ft.! Room seems to have a certain amount of echo/reverb. I was considering absorption panels at the side 1st reflection points and the back wall. Possibly in the front below the screen also. If it matters, the screen is along the 19' wall and the ceiling rises frm left to right when facing the screen.

Will acoustic treatments be a bit of wasted effort given the ceiling? Anyone have any suggestions?

Thanks,
Mike

BasementBob

08-11-07, 12:08 AM

nathan_h

08-11-07, 01:06 AM

nathan_h

08-11-07, 01:10 AM

GB_KSU

08-11-07, 11:18 AM

GB_KSU:

What you're looking at is a slot absorber, a variation of the Helmholtz resonator.

It tends to resonate at a single frequency (sort of a bell curve with a single peak), depending on the ratio of slot width to surface area, depth of the cavity, and amount of absorption within the cavity.

This page will give you some of the ideas, but unfortunately some of the formulas are wrong
http://www.mhsoft.nl/helmholtzabsorber.asp

The correct formula can be found here
http://forum.studiotips.com/viewtopic.php?t=94

In practice, getting these things to resonate/absorb at the desired frequency is hard, as is keeping them from ringing (also bad). Ringing is when the panel continues to vibrate at that frequency, emitting sound, after the speaker has stopped producing it.

Thanks for the links Bob I appreciate it. I was considering making just the faces of the corner treatments and soffits similar to this but it sounds like it would be a bad idea. Am I correct to assume that any sort of wood panel, slotted or not will resonate at a given frequency?

Any input at all on the software? I don't own a PARC, so the BARE software seems unnecessary? Would ETF with a quality mic setup give me enough information to make good choices for treatment options?

Ethan Winer

08-11-07, 12:32 PM

Would ETF with a quality mic setup give me enough information to make good choices for treatment options?

Yes, and you don't even need a "quality mic" since even the cheap ones are fine at bass frequencies - below 300 Hz is where all the action is.

--Ethan

GB_KSU

08-11-07, 01:18 PM

Yes, and you don't even need a "quality mic" since even the cheap ones are fine at bass frequencies - below 300 Hz is where all the action is.

--Ethan

Thanks for the advice Ethan. I know that a Radio Shack spl meter can be used with the ETF software, would I gain anything by using a mic? I assume that using a mic would allow for the data to be automatically inputted? If so do you have suggestions for something that would be adequate?

monkeychucker

08-13-07, 12:54 AM

I have a question about bass trap construction. I am using 1" linacoustic to treat first reflections and the front of the theater. I will likely have a fair amount left over and am wondering if I can some how use the remainder to build some base traps? Also, for decorative purposes we are creating faux columns using 10" cardboard tubes used for concrete. If I packed some sort of material inside such as compressed regular fibreglass insulation or even paper would this create an effective trap?

Thanks,
Dwayne

pepar

08-13-07, 11:11 AM

. . . for decorative purposes we are creating faux columns using 10" cardboard tubes used for concrete. If I packed some sort of material inside such as compressed regular fibreglass insulation or even paper would this create an effective trap?

Thanks,
Dwayne
Only if the sonotubes are acoustically transparent at bass frequencies. (I'm sure that they are not.) :)

Ethan Winer

08-13-07, 01:45 PM

Thanks for the advice Ethan. I know that a Radio Shack spl meter can be used with the ETF software, would I gain anything by using a mic?

A Radio Shack SPL meter is a microphone, and it also has a preamp which makes it easier to connect to consumer-grade sound cards through their line input. The next step up in microphones probably costs more than you want to spend, and won't be appreciably better for "home" use anyway.

--Ethan

Ethan Winer

08-13-07, 01:47 PM

wondering if I can some how use the remainder to build some base traps?

If you stack four pieces adjacent to be four inches thick you can use them as corner traps as explained in my Acoustics FAQ:

http://www.ethanwiner.com/acoustics.html

--Ethan

jeppe

08-13-07, 05:32 PM

;)
Todays scope;

Here are the Most important site for you northern americanos...
that are on the hunting for some nice insulation products check it out
it list EVERY insulation plant in north amerika from mexico up to canada...

also links to every insulation manufactor.and much more...

www.naima.org

http://www.naima.org/pages/about/members/map.html

-------------------------------------------------------------------------------------------------------
AND for mechanical&special insulation products only...

http://www.insulation.org/about/

nathan_h

08-13-07, 05:53 PM

jeppe

08-13-07, 05:58 PM

:)
Todays scope number 2;

Here are the Most important site for us european folks thats on the hunt for some nice insulation...
the European eqivalent from spain to russia...even turkey

www.eima.org

http://www.eurima.org/our_members.cfm

--------------------------------------------------------------------------------------------------------

AND for mechanical&special insulation products only...

http://www.insulation.org/links/fesi.cfm

whith memberlinks for many countries all over europe...
now aint that something!!!

jeppe

08-13-07, 06:51 PM

:)
i dont know if there are any japaneese folks reading this forum but anyway...

http://www.glass-fiber.net/

australian folks...look at; www.farima.net

Fibreglass and Rockwool Insulation Manufacturers Association of Australia (FARIMA)
under construction for now...

jeppe

08-13-07, 08:49 PM

That's funny! Actually, I can see an Owens Corning facility when driving to and from work, but trying to find a place that will sell their quietzone products or the rigid insulation that is ideal for bass traps, locally in person, is almost impossible.
have you tried to e-mail them
or; rbergman@wica1.com (Western Insulation Contractors Association) ?

http://www.insulation.org/links/regional.cfm#8

seems vierd if they dont have some information...

naima.org for regular home insulation products
insulation.org for special insulation (like industrial ventilations etc.. i think...)

nathan_h

08-13-07, 09:07 PM

I'm sure I'll be able to find a place to sell me what I want, but Owens Corning's customer support said, essentially, that they are not consumer products so I won't be able to buy them.

jeppe

08-13-07, 09:43 PM

man that sucks!

i talk to owens corning here in europe and they said something similar to me too
one container or more! , they dont distubute smaller to europe...
any nice ideas on Certain tead wool?
i read its a part of the giant
Saint gobain/Isover.
europes biggest manufactor of rigid fiberglass...

haslip

08-14-07, 12:03 PM

I am framing 2inch Owens Corning in 1x3s and placing them on my walls with a little spacing.

I wrapped them first in batting material which is very porous, but I wonder if I choose wisely for the black fabric covering and need help.

For some reason, I thought that a natural material, like wool or cotton was superior to a man-made like polyester, but now I see a major manufacturer of wraps uses man-made, so I don't know if that is correct.

I choose 100% cotton, and my question is, is the weave to tight. If I put it up to light, i can see some filter through, but the blow through test is where it may fail.

I can blow through it, and breath in through it, but it takes effort. Do I need to rethink my material choice??

Scott

nathan_h

08-14-07, 08:59 PM

While I haven't resolved my room dimensions issue noted above, yet -- it's nice to be able to create a room of "any" size, but it's tough deciding what size is best because though the calculators are awesome it's hard to decide which peaks and which nulls and which problem frequencies matter most -- I'm working on other angles as well.

Today's question:

I've got REAL bass traps (thanks, Ethan), auralex foam, and a desire to add diffusion to the mix. Remember, this is a dedicated, custom built room and I won't have anything like shelving in there.

I've seen lots of info about building one's own bass traps, and one's own absorption panels. But I've not seen any DIY info about building diffusion panels. Can anyone point me in that direction?

Scott R. Foster

08-14-07, 09:16 PM

DIY diffusers... scroll down

http://forum.studiotips.com/viewtopic.php?t=48

For ratio exploration err to the side of larger room volume.

A comprehensive tool for looking at the modal structure of a proposed room

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

Some very neat charts that map the phase space of "good" ratios

http://forum.studiotips.com/viewtopic.php?t=685postorder=asc&start=40

Good Luck!

PS: try these guys for mineral fiber

http://www.spi-co.com/servicecenterdirectory.html

nathan_h

08-14-07, 10:04 PM

Thanks. That's a great calculator. It doesn't take into account seating position, and speaker position, which some do -- but it's a really quick easy way to see what dimensions are doing -- and then once I find a good dimension, I can go to the more complicated calculator and worry about speaker and seating location.

The thread about homemade diffusers was interesting. Not sure how ambitious I am yet but the idea of using curved surfaces is very interesting. I was wandering around Lowes looking for stuff that I could adapt into one of a panel of many different height surfaces and didn't find anything. The idea of using curved items is appealing.

(I was going to buy a bunch of 2 inch PVC pipe, and cut pieces of random lengths between one inch and three inches, and then clue them perpendicular onto a board.... When on the wall, it would look like you're flying above a city full of round buildings with not roofs. But now I'll keep thinking about ideas.)

Ethan Winer

08-15-07, 03:47 PM

I've not seen any DIY info about building diffusion panels. Can anyone point me in that direction?

See this:

http://www.mhsoft.nl/user/acoustic%20calculator.asp

--Ethan

nathan_h

08-15-07, 04:28 PM

That looks very promising. I submitted me email address and will hopefully get the download link, soon. Thanks.

drunkpenguin

08-15-07, 07:45 PM

(I was going to buy a bunch of 2 inch PVC pipe, and cut pieces of random lengths between one inch and three inches, and then clue them perpendicular onto a board.... When on the wall, it would look like you're flying above a city full of round buildings with not roofs. But now I'll keep thinking about ideas.)

depending on how you do it, it could look like the death star in star wars! that would be neato.

Jason Jones

08-16-07, 09:21 AM

(I was going to buy a bunch of 2 inch PVC pipe, and cut pieces of random lengths between one inch and three inches, and then clue them perpendicular onto a board.... When on the wall, it would look like you're flying above a city full of round buildings with not roofs. But now I'll keep thinking about ideas.)

For the diffuser design to work as intended, your buildings will need roofs. :)

Jason

nathan_h

08-16-07, 11:57 AM

! That's funny, but after looking around a bit more, I see what you mean.

I'm actually thinking that buying a batch of 2x2 boards, and cutting them into pieces of predetermined lengths, might be easier and look better.

But I think that once I get access to the software on the mentioned site:

http://www.mhsoft.nl/user/acoustic%20calculator.asp

I'll have more detailed understanding. Trouble is, one has to wait for that site owner to send one the link, and that person hasn't responded to my emails, yet :(

Jason Jones

08-16-07, 02:11 PM

nathan_h

08-16-07, 02:52 PM

eugovector

08-16-07, 04:01 PM

I'm actually thinking that buying a batch of 2x2 boards, and cutting them into pieces of predetermined lengths, might be easier and look better.
(

I think the problem with this approach when building a skyline style is that it will weigh a ton.

Jason Jones

08-16-07, 05:43 PM

I'm thinking the skyline type is easier to create (with my limited skills). If there's a handy way to figure for a given number of "buildings" what the relative heights should be, etc., I would love to be pointed to that information. Thanks!

Use this map: http://www.mhsoft.nl/DiffusorCalculator.html

You then need to pick a depth for your longest "building" :) . Six or seven inches is about ideal for this plan. Now convert your map into inches. So, where you have a 1 on the map your "building" will be 1/4*6", where you have a 2 it will be 2/4*6", etc.

After the heights are figured then you need to decide the size of board (or whatever) to use. Here 2" by 2" is a good size. This will give you a 24" x 24" panel.

Yes, it will be really, really heavy. Good luck!

Jason

nathan_h

08-16-07, 10:11 PM

Very cool. Now I gotta figure out the weight thing.... I wonder if Home Depot carries balsa wood?

tonybradley

08-23-07, 08:00 PM

I wouldn't be so quick to have Tony go to all that trouble. Maybe some felt reflects, but the stuff I've seen does not.

Tony, try this simple test: Stand in front of one of your panels and "talk into" it. Does it sound like you're talking into a total void? If so, then the felt is probably fine. If you still have some raw fiberglass, use that as a comparison. If they both sound the same, then the felt is fine. If you hear more of your voice coming back on the panel with felt, then you must have bought some of that "reflective felt" Terry is referring to.

--Ethan

Sorry to bring this up again, but I need some more answers. I was surfing the web trying to find some Acoustically Transparent Fabric that was not $15-$20 a yard like GOM. I then remembered I had some left over MUSLIN and FELT.

I did the 'blow' test and blew through both fabrics. I felt much more air when blowing through the FELT than I did when I blew through the MUSLIN. Some said Felt would reflect at frequencies higher than 4khz. My question is this: Since I've determined that I can blow more air through my Felt than my Muslin, and Muslin is acceptable to cover Fiberglass at the 1st reflection points, can one assume the Felt I have (based on the air test) will work as well as the Muslin?