Acoustical Treatments Master Thread - Page 16

I have some nasty echos in my family room which houses my home theater system. Hardwood floors, lots of glass (30%) and relatively bare walls. My wife has agreed to covering some of the bare walls with sound absorbing materials if that in turn can be covered with wallpaper. GOM or fabric may not be acceptable.

The room is 18x30 with 14ft angled ceiling. The rear of the room is open to the kitchen (18x15) and a hallway to the rest of the house.

The wallpaper is not extremely hard, but definitely stiff (but thin). I am considering covering areas with a .25" to .5" materials, some of which are recommended in this thread. My questions are as follows:

1) Will the wallpaper surface defeat the purpose here and be reflective?
2) Must I use instead a more absorbant fabric (GOM?) over the panels?
3) Is .25" or .5" enough to kill the echo and give a relatively damp room? I could do about 35% of the wall area with it if needed.
4) Should I just cover the maximum amount of wall area I can with .5", wallpaper it and hope for the best?

Thanks very much.

The paper isn't the issue as much as the adhesive that soaks into it and dries stiff which makes that paper so crispy. If you havce ever removed old paper without a steamer or the release agent, you understand the term.

I have seen some wonderful papers based on softer materials that look tremendous. It's just that they get stiff as a board when the adhesive soaks into the back layer of paper.

Some of the finest homes I have ever been in had expensive fine fabric with a wallpaper style pattern strecthed over the walls and suspended just off the wall surface. I don't know what this method is called, but then again I don't subscribe to Architectural Digest...
There was a little bit of deflection to another wall substrate if you pressed your finger against it. Something like this would allow you to use a thin duct liner of fiber panel material in the trouble spots determined by the mirror method or a ray trace.

This may be a better solution if you can give up a little more space and fit it into your budget.


.5" is better than .25", and .25" is better than nothing...
I am still not sure that fiber panels are the best solution for your application.
Even if the stiff paper didn't reflect, I doubt it would bond well to fiber panels.

If you research the stretched fabric method and it is not your wife's cup of tea, or it is a budget breaker, another option to look into is a skimcoat of acoustical plastering.

Nearly any plaster contractor in the phone book has availiability to acoustical plaster and understands it's application.

The absorption characteristics, and therefore the results, are based on variables like how thicky it is applied, etc. and an acoustician would generally specify these variables for it's use.

To read more for yourself, go here:
http://www.usg.com/navigate.do?resou...ter_Finish.htm

Another choice is a new system from Switzerland called BASWAphon that RPG offers in the US.

Famous acoustical guru John Storyk used this system on a This Old House project, and you can read about that here.
http://www.thisoldhouse.com/toh/know...216779,00.html

Read the section of the article called "Mid- to High-Frequency Reflection Control" where he descibes a new product he used in that room.

As I said, RPG distributes this material, and you can read more info here:
http://www.rpginc.com/products/baswaphon/

I am not positive if you can paper over this.
I'm thinking you cannot, because you actually don't even paint it.

You tint the plaster material before it is troweled and skimmed.

I would send out a letter to RPG to confirm.

Either this new material, or the skimcoat method with traditional acoustical plaster to a lesser extent, can help make a room less "live" yet still retain the traditional aesthetic apperance.

Either method should allow your wife to paper the space, but as I said, double check with the manufacturer of the panels before you order them.

If you want the best results (and some quality entertainment) call in a acoustician and an interior designer and let them battle it out.
Right now you and your wife are having that debate on a smaller scale, when it's two pros that are each dead set against each other's plans and both very good at what they do, it's not pretty...

Any words of wisdom for non-standard rooms?

All the advice in this thread seems to assume a basic rectangle / shoebox / golden ratio room. What about sloping ceilings/walls on both sides? Basically a barn like room that many people get when they finish off attic space. Also, how about half walls that form ear level and below U shaped squares in the back of the room. Or hallways / stairwells leading into the room?

Such rooms can make excellent theaters. Acoustical modeling and prediction isn't straightforward, however. Ray-tracing will model a room well at most frequencies. But it doesn't perform well at the lowest frequencies, so it won't tell you much about room modes. The Finite Element Method (FEM) is the technique of choice for analyzing modes in odd-shaped rooms. We do pre-construction HT analysis at reasonable prices, and have capabilities to do both professional ray-tracing and FEM. If interested, PM me.

Regards,
Terry

Every room is different. We'd need more information and specifics like sizes, seating locations, speaker locations, how many people, usage, etc. before being able to give even a basic recommendation.

That said, the basics are pretty much the same. Kill the front wall, kill the reflection points, address the reverb time in the room appropriately throughout the spectrum, etc. How much, what kind, and where will depend on the answers to the specifics.

I want to treat my dedicated theater for absorbtion at first reflection points. My first question is: (1) What are the pros / cons of attaching OC 703 / 705 / or equivalent (covered in acoustically transparent fabric) directly to the drywall rather than in wood framed panels? If attached directly to the drywall, am I really helping any or just spending money?

My second question pertains to sound insulation (i.e., keeping outside of the theater sounds out, and inside the theater sounds in). My construction is double 2x4 walls with a 1/4 inch air gap between the 2 walls. The outer wall will be filled with 3 1/2 inches of expanding polyicynene foam (the spray in stuff that expands 120x). The inner wall I intend to fill with fiberglass batts.

(2) For the fiberglass batts, does it matter if they are faced or unfaced, and if faced, whether the face "faces" in or out? And does the foam or fiberglass in the wall provide any acoustic benefit?

Thanks

First for the isolation... IMO the expanding foam does little or nothing to assist in isolation as I believe most of them are closed cell foams. You'd be better off with standard fiberglass and a barrier on the outside of the outer wall.

For the absorbtion inside the room... You can certainly be effective mounting 703 directly on the wall - provided it is thick enough to do what you need done. 2" of 703 framed 2" out from the wall will reach deeper than 2" directly on the wall but not as deep or as tight as 4" directly on the wall. Also, the 4" and the 2" spaced off the wall will do no more from say 1kHz up than the 2" mounted to the wall. What changes is how far down they're effective and at what level of effectiveness.

As for facing, again it depends on what you need. Usually one uses unfaced. However, if you only want bass/low mids absorbtion, you can certainly use FRK with the facing out into the room.

The insulation inside the wall keeps it from ringing and assists the drywall over stud construction to act like a broadband resonant panel trap that is pretty effective from say 100Hz through around 250Hz+.

Bpape - Thanks for the info.

Next: Is there a material that can be used in place of gypsum drywall (i.e., paintable, firm, etc.) but has the characteristics of rigid fiberglass with respect to absorbtion? If so, wouldn't that be a good solution for walls and ceiling? That way, all surfaces are built in bass traps, then, to prevent room from being too dead, reflectors / diffusors could be added as needed. Benefit would be that a diffuser / reflector doesn't need to be inches deep.

Most expanding foam insulation in the wall is worse than having nothing in the wall. It's rigid and closed cell and conducts sound. It's a good thermal insulator, but worse than useless for acoustics and sound proofing.
'Expanding polyicynene' you mention may be Icynene, which is an open cell foam with absorbtion, in which case it's fine. Less absorbtion than some other products, but probably better air tight seal. Search for Icynene at AVS and you'll find someone who's had it installed.

If you can avoid faced fiberglass, it's probably better. But if you must use faced, I believe the recommendation is to put the facing against the drywall rather than into the gap, both because that has acoustic benefits, as well as it's the way it's designed to be installed. There may be vapor barior issues. Lightly filling the entire cavity (no airgap) with insulation may have firestopping benefits.

Attaching the absorber directly to the wall is fine. Impailing clips may be what you want to attach it with. Spacing it out from the wall gives you more absorbtion at lower frequencies for free, which may be a good or bad thing depending on what other absorbtion you have in your room (e.g. 20 leather seats).

The job of gypsum/drywall is to be cheap and reflective and firesafe, i.e to use it's mass and reflectivity to keep the sound energy in the room, rather than letting it out of the room. Similarly to keep the sound energy outside of the room out, to lower the noise floor and thus increase the dynamic range of the HT. If you're into soundproofing, don't think of it as an absorber, and don't try to make it into an absorber.

Thanks. It is icynene foam. I'll do the search for icynene & see what the avs experience / expertise is.

Greg

There are two types of polyicynene spray in foams, high density and low density.

The high density variety is the closed cell product that the fellows are warning you to avoid. It makes a very rigid wall system that will transfer noise through with little loss.

This type of foam is generally used below grade where moisture is a concern.
Remodelers love to use it against stacked stone and block foundations because it expands into every crack and crevice and has enough structural holding power to bond the wall together and help keep the foundation from future disentegration.
In addition, it is an absolute moisture barrier for these notoriously leaky foundations.

Low density, or open cell polyicynene foam insulation is a great product to use in your application, but in the outer most portion of the double wall. It has similar vapor barrier characteristics of the closed cell products, but it will not trap moisture. (no mold)
It is generally specified for use above grade.
http://www.icynene.com is the major player in open cell.

Faces in or out on batts has to do with vapor barrier, and this varies by your location.
Gulf coast areas need the barrier out, or more likely they will use an external barrier and unfaced batts. The rest of the country requires it to be on the inner most section of the cavity.

If none of these walls is an exterior wall, use unfaced batts. If one or more walls are exterior, use the open cell spray, or consult the insulation contractor or building inspector to make sure your walls will meet any code requirements.

Nothing will slow down a project faster than having to re-do an expensive part of the project that you have done incorrectly. It's worth getting right the first time, air quality concerns are high on everyone's list when selling/buying a home, and mold remediation is EXPENSIVE.

In the wall closest to the room, I would recommend acoustic fiberglass batts. I like the Johns Manville batts because they perform well and are also formaldehyde-free.

It sounds like you have a nice project going, you should create a thread and post photos and updates as to the progress.

Best of luck.
--Rick

Rick - thanks for the help. I agree that getting it right the first time costs a lot less than changes later. I'm trying to do everything possible to get it right! In fact, I made the a/c people come out today and replace the existing "boots" on the end of the ducts with oversized boots, so that the conditioned air as it enters the room will be slowed down somewhat.

Is creating a thread for one's own room pictures ok? Not sure of the protocal and whether that is something ya'll do and is in good "form" or whether that is "bad form," etc. If it's "proper", I'd be pleased to share my labor of love (or maybe lust is a better word when talking about a home theater!) with all of you!


Greg

I personally did use closed-cell foam in my basement HT, and I'll tell you why.

I'm firmly convinced that the BSC method of insulating basement walls is the correct way to go. This method employs no vapor barrier but instead a vapor retarder, to allow moisture to dry to the interior at a slow, controlled rate (since it cannot dry to the exterior below-grade).

Closed cell foam of approx. 1" is a vapor retarder (perm ~1.4). Open cell foam is not (perm ~15). I've also heard a lot of bad things about open cell foam - the expansion rate is so great that there are often huge (ie. inches wide) air bubbles in the foam that severely compromise the R-rating.

Yes, this may mean I have compromised sound attenuation. IMO the fact that they are foundation walls (ie. only consideration is flanking noise) and the fact that double-drywall w/ damping is going to do 100X more than 3.5" of fiberglass ever would just isnt worth the tradeoff of possible mold issues. Yes lots of homes dont face mold but lots do. If you consider all those older homes that have a 'musty basement', thats a mold issue.

Just my 2 cents.

Andy K.

I have a friend with a set-up that is on the bright side. (Klipsch 7.1 with a Yamaha 2500 receiver)
Originally, his room was horrible. His system was in an 18X23 drywalled room with 9 foot ceilings and a ceramic tiled floor. It was an echo chamber.
He has since put in two large, thick rugs and hung some dense curtains all the way across the front of the room. (Helped a ton) Now that he has seen these improvements, he wants more.
He now wants to tone down the brightness of his set-up.
He really does not want to put up GOM if he does not have to, but would if there are no alternatives.
I told him he should treat the room (Knauf/batting/GOM) and be done with it.
It is probably what he will end up doing anyways.
Is there a way to reduce brightness in a room with out going all out with treatments.
And, if he does treat the room, will his speakers not sound as bright?

Craig

Treating the room will not change the frequency response that the speakers yield. What it can do is to tame the reflections and bring the reverb time more under control.

However, treating only the mid/top of the spectrum is not a good idea. The whole spectrum should be addressed.

As for covering, you can use Muslin dyed to the color of his choice - for treatments this will work just fine. You can get lightweight muslin at JoAnn Fabrics for < $15 for a whole bolt. Use the money saved to purchase the appropriate materials to address the bass in the room.

Thanks bpape,

I will show him this post... except the part I called his room an echo chamber.
I think he is seriously considering using wall treatments.
He is not a real audiophile and at least for now I think he is going to live with what he has.
He wants to see what my theater sounds like when I am finished with mine before he undertakes it though.
Next, I have to get him to paint his white walls and ceiling a dark color.
If anyone has more to add on this please feel free to chime in.

Craig

Hi all, great thread - I finally made it through! I'd like to post some questions and get expert feedback.

Building a dedicated theater room in the basement of my new home. The room will be 16' x 24' with two levels of riser. Top level will have concession stand, equipment rack, maybe a popcorn machine, etc. 2 theater seats centered on it, room permitting. Next level, row of 4 reclining theater seats. Floor level, another row of 4 theater seats. When they frame it I'm going to just have them mud, tape and prime the front wall but not texture it, and that will be my screen, after I've Goo'd it and trimmed it. 7 speakers in the ceiling (I was thinking of the Russound series of ceiling speakers that you can aim so the sound goes in the right direction instead of straight down).

So, for acoustic treatments, I was reading from this article which maintains it's acceptable to keep some of your painted drywall as reflective surface and put up panels in the hot spots. I was thinking of building shaped panels like in their models and putting them in the primary reflective areas as discovered using the mirror test. I would also put bass traps in each corner like the ones described here. There will be thick carpet and I'll also put panels on either side of the screen, and perhaps a bookshelf along the back wall to diffuse some of the sound without deadening.

Do you think this would work well? The room doesn't have to be perfectly tuned but I'd like it to be nicely acoustic with not too much echo.

Also, does the subwoofer have to be in the front? I was going to put it next to my equipment rack in the back.

And how thick do those panels have to be? I think anything more than 4" would stick out like a sore thumb.

Thanks for your advice!

Equus

Yes. That plan will work fine. The trick is getting not only panels in the right places, but getting the right balance of materials so you're dealing with the enitre spectrum equally from a decay time standpoint.

The thickness of the panels will be determined by what the room needs and what the specific application of each panel is.

As for speakers, at a minimum, get speakers that fire toward the audience for the front 3. If you must do in-ceilings for the rest, at least that's not as bad. If you put in-ceilings in the front, you'll have absolutely no shot at locking the sound to the image and you won't get anything in the way of an aural image. Check out some other companies. If you're budget challenged, there are still other companies that make reasonably priced ceiling and/or in-wall speakers that will do a lot better than the Russounds.

Good luck.

Hi bpape:

Thanks for your response. I know in-ceilings are generally not good for imaging, but I was "told" these Russound speakers with their aimability would work well. Do you think that's not the case? If so, do you then have better suggestion in the same price range? I don't think I'm going to have much room over the top of the screen for the center-channel speaker, as I'm going to try to make the screen height almost the entire 10' floor-to-ceiling distance. That's what got me looking at in-ceilings in the first place.

And do you think it's OK to put the subwoofer in the back? Or is that a bad idea? I forgot to mention that each of the seats also has a "buttshaker" sub in them as well.

Equus

First, you need to see what your room, your seating distances, and your PJ will support in terms of picture size. Bigger is not always better. On top of that, if your screen is almost to the ceiling, you're probably going to be pretty uncomfortable watching movies with it up that high. Usually, you want your eye level about 1/3 up on the screen.

If you can't put the center above, then do it below. No. I don't think ANY in ceiling speaker is going to do a good job across the front. You really need to lock the sound to the image. The movable tweeters are OK but the rest is still firing straight down and that extreme off axis response is not going to be even close to flat across multiple seating positions.

You might want to put this in the normal area of home theater construction. It really doesn't belong in the acoustics thread.

Well bpape my main questions were of acoustic panels and bass traps, so I though appropriate to this forum. I'll look into what you said about ceiling speakers and screen size. Thanks for the advice.

Equusz

My room is 22x14x8. I am looking at bass trapping and first reflection sidewall treatments as a staring point. My thought on corner bass traps: floor to ceiling OC 705 two foot hypotenuse with no airspace behind - basically fill the entire corner out to two feet. My grade school math is a little rusty but my calcs make it: 2' hypotenuse = 1.4142 feet out on each side wall = 1 square foot = 1 cubic foot per vertical foot x 8' = 8 cubic feet per corner. I can only do 3 corners because a door is in one corner - I could put 1 cubic foot above the door. That's 25 cubic feet and that's before any first reflection point treatment. My questions: is 25 cubic feet of 705 as a starting point too much? I know that different frequencies are absorbed at different rates, but I have no idea what this will do to the sound of a room that size - any opinions? Also: to FRK or not FRK? My plan was to cut triangles of 705 and stack them - that puts the FRK (if any) as a horizontal sandwich.

usualsuspects :

Studiotips Super Chunk including 24" and 34" cut pattern
Harder's super chunk
48" cut pattern

Studiotips Corner Absorber


Left/Right symmitry is a good thing. Consider 2 corners.

Just say no to FRK.


Yes, but two corner chunks, even floor to ceiling, are not very much surface area. As you'll likely have modes down to 25hz or so, broadband traps effective down to bass are a good thing -- big traps are probably fine. Consider wall/ceiling corners (overhead like soffits).

Hi - If I want to do some sound deadening between rooms (not theater, just other rooms like bedrooms and bathrooms) and plan to use fiberglass battes between the 2x4 wood studs, am I better off with 3 1/2" batts (those that are designed for thermal insulation between 2x4 studs), OR going with a 5 1/2" thick thermal batte, and "squishing it in" between the sheet rock (probably not good for thermal insulation, but possibly better for killing sound transmission)?

I'm not interested in double sheet rock, green glue, quiet rock, RC, staggered stud, etc., etc., etc. Just what is the best thickness of fiberglass batte to use in a 2x4 interior stud cavity for reducing sound transmission.

Any ideas?

Thanks.

Greg

For that application, the more the better.

Westshores,

You may want to check with your friendly HVAC guy before throwing that kind of insulation between interior walls. Unless you have air returns in each room, you may be causing some issues with your air flow and temperature regulation... just a thought.

Hi Guys,

I'm toying around with the idea of using acoustical ceiling tile to cover the walls of my theater (velcroed onto the walls - floor to ceiling - either wrapped in fabric or painted). These acoustic panels have a Noise Reduction Coefficient (NRC) of .55 up to .90. Can some of you sound experts help explain what this would do to the acoustics in the room? Also, are the acoustical properties of these panels affected if you paint them? The panels are 5/8 of an inch wide... which is good, because I don't have any inches to spare in the width of the room. Please help...

I think it was mentioned earlier in this thread that ceiling tiles are too rigid and not as effective at the necessary frequency ranges. The fiberglass materials mentioned in this thread are a better option.

Do you know of any fiberglass panels that are approximately 1/2 inch wide that would help?

Also, I'm not sure I understand what rigidity would have to do with sound absorption...

Hi Todd,

1/2" thickness is usually too thin to extend down enough into the bass frequencies. There is actually an acoustical tile which works very well. This is Armstrong OPTIMA Open Plan, but it is 1" thick and fiberglass.

Rigidity doesn't effect sound absorption, but fiberglass density does. The best fiberglass for HT sound absorption ranges from around 2.5 pcf to 6 pcf.

Regards,
Terry