# Sound Treatment



## ledgerdc (Aug 4, 2011)

I recently designed and created a dedicated home theater, and thought I had done the research necessary to provide good acoustics. What I failed to research, though, was sound treatment thinking that this could easily be added after the fact. Dumb...dumb...dumb:rolleyesno:.

I am now left with trying to design and implement an acoustic treatment that will fit into my existing room. I've been doing the research and trying to piece together a good course of action, and was hoping this group would chime in and make sure I am not heading in the wrong direction.

*The Room:*
The room is 16' long, 13.5' wide, with a 9' foot ceiling. The floor has a step down to create a stadium seating effect and within the step down, the ceiling is 10'. The front side has a screen wall built out of 2x4 that sits about 12" from the exterior wall and has been insulated with R-13 batts. There are two 'columns' on either side of the screen which houses the main fronts and subwoofers.
All walls are drywall with underlying sound proofing materials, except for the exterior wall behind the screen which is comprised of 2" foam insulation and concrete. Floor has a tight weave carpet.

*The Current Problem:*
This room is VERY lively. A clap of the hands will yield audible second and third echos. When watching movies, there is very little distinction in the sound fields so everything is wall of noise and it is almost impossible to discern and spatial location of the side and rear channels. Bass is just terrible, and the dialog is often times hard to hear.

*My Research So Far:*
...is indicating that you cannot have enough bass traps, especially when trying to set up a small room, hence the 127 sq/ft of proposed bass traps (see below). I've also found that the first and second reflection points are critical to create a larger, more distinct sound stage. Through this forum I've found that it is also critical to dampen the wall behind the main speakers.

*The Treatment Plan:*
-Install floor to ceiling 4" mineral wool 6lbs panels behind the front main speakers and subwoofers (within the side columns).
-Install mineral wool 6lbs 'superchunk' style bass absorbers at:
1) floor to ceiling on the back two corners,​2) the length of the back wall/ceiling corner,​3) the length of the two side wall/ceiling corners​-Install 2" 703 absorbers at the first and second side wall reflection points.
-Install 2" 703 absorbers at the first and second ceiling reflection points.
-Install 2" 703 absorbers on the back wall wherever I can get one to fit (back wall currently has a door, equipment cabinet, and projector portal.

I have given very little thought (read this as 'none') to diffusers. These are a mystery to me and didn't think they would be necessary until I started researching on this forum.

Again, any help would be much appreciated. This HT has been a dream of mine for a very, very long time. I would very much like the reality to come closer to my dreams.


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## bpape (Sep 14, 2006)

Is the front screen wall just studs and cloth or is there drywall on it? An easy way to get some hidden bass control in the room is to just use cloth and the 12" of insulation. That will do double duty for bass control and also to stop reflections from the surrounds contaminating the front soundstage.

You said the subs are built into columns. Are they solid? If so, you've changed their response characteristics by building them in. Again, just framing, cloth and maybe some decorative trim would mitigate this problem.

2' 703 on the side walls for reflections will be fine.


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## ledgerdc (Aug 4, 2011)

The front screen is a stud wall with 5/8" drywall. The screen is painted on.

The columns are framed 2x4 with drywall, but not fully enclosed. I'm attaching pictures of the room.


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## ledgerdc (Aug 4, 2011)

Based on your response, I could cut out the middle of the columns and replace it with cloth. If I were to do this, would it be better to install superchunks in the corners or 2" panels to absorb the sound from the surrounds?

I'm thinking I could also put some 2" panels on either side of the center speaker, as well as some curtains on either side of the screen. I'm guessing that I would need some sort of panels behind the curtains for them to really be effective.


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## bpape (Sep 14, 2006)

Sorry - been pretty swamped with work. 

If you cut the sides, that would certainly open things up for bass control. At a minimum if you don't want to cut, basically fill the entire cavities around the speakers with insulation to help mitigate the resonances.

Bryan


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## ledgerdc (Aug 4, 2011)

Cutting out the front of the column won't be an issue. When this is done, should I put in superchunks, 4" flat panels, or just stuff the entire column?

Also, do I need to concern myself with discusses?

Finally, for the ceiling panels, should the be mounted flush or with some sort of air gap?


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## ledgerdc (Aug 4, 2011)

Spell checker woes...

Diffussers, not discusses.


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## bpape (Sep 14, 2006)

Like I said, after looking at it, I would just fill the cavities around the speakers and subs with insulation.

There are other things I'd do before worrying about any diffusion.

Bryan


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## ledgerdc (Aug 4, 2011)

What are the "other things" you would do before diffusion?


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## Owen Bartley (Oct 18, 2006)

ledgerdc, I'm just working on learning about acoustics now myself, but if your room sounds very live, I think you're on the right track by adding panels at the main reflection points. Maybe consider a larger "cloud" on the ceiling since you have the height, and I think you should have room on the back wall for something like this:










That should help to tame all of the reflections, along with Bryan's advice to clean up your bass.


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## bpape (Sep 14, 2006)

Additional broadband bass control where you can fit it to address a proper decay time curve.

Bryan


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## fitzwaddle (Aug 25, 2010)

Wouldn't 3 pcf be preferable to 6 pcf for the super chunks?


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## bpape (Sep 14, 2006)

From the data I've seen on most materials, yes, the lighter density would work as well or better for less money. The higher density really only does a better job when you're doing something like straddling a 4" panel across a corner.

Bryan


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## JCD (Apr 20, 2006)

Owen Bartley said:


> ledgerdc, I'm just working on learning about acoustics now myself, but if your room sounds very live, I think you're on the right track by adding panels at the main reflection points. Maybe consider a larger "cloud" on the ceiling since you have the height, and I think you should have room on the back wall for something like this:
> 
> 
> 
> ...


I have a question about this one -- my very basic understanding is the the current conventional wisdom is that you want a dead-ish front with a live-ish back. With this in mind, would having absorbers in the back be good? Or would diffusers be better? Again, assuming I'm "correct", what about a situation where the back wall is relatively close to the sitting position like the one in this picture?

Sorry if I'm hijacking the thread, but I thought it might help the OP as well.


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## bpape (Sep 14, 2006)

It's kind of a tradeoff. One first has to be far enough away from diffusion for it to be effective. Second, close to the corners like that, 1/2 of the diffusion pattern is going to bounce pretty quickly off the side wall. Lastly, overall decay time curves for multichannel are usually lower than they would be for 2 channel. 

Bryan


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## ledgerdc (Aug 4, 2011)

Wanted to give everyone an update on this project. Based on the feedback I've gotten from this forum, I've changed direction slightly as well as shamelessly stole some really cool ideas that I've seen done by other members of this forum. The work is still on-going, so give me a shout if you see anything that looks wacky.

The first step was to build the super chunks along the side and back wall / ceiling corners.

1. I cut a bunch of short 2x2's at a 45 degree angle.








2. Blocks were attached to the wall 16.5" from the corner.








3. I cut 2" strips from 7/16" OSB and attached these to the blocks.








4. In goes the Roxul AFB








Next up is adding superchunks in the front and back corners, along with building the cover panels for all of them.

After that, I move on to the side wall and ceiling panels.


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## Sirbrine (Sep 27, 2009)

Cool idea. It looks like you are going to lower your rear speakers a bit because of your wall/ceiling treatment? I'm really interested in seeing pictures of the finished product.


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## MikeBiker (Jan 3, 2010)

With the improvements that you have made to the room acoustics, have you noticed the sound being improved yet? I'm curious about how much needs to actually be done to improve the room. I'd hate for you to get all finished and find that the room is now too dead.


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## bpape (Sep 14, 2006)

If you can, try to tack some sort of thin reflective membrane over those wall/ceiling absorbers. That's a LOT of high frequency absorption in the room assuming you're also doing all the rest of the things. Doesn't have to be anything special - just something that will pass below say 1kHz and start to reflect at least somewhat above 1kHz. THink heavy brown shipping paper, relatively 'thick' sheet plastic like heavy mil drop cloths, etc.

Bryan


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## ledgerdc (Aug 4, 2011)

What nil plastic? Would 4 suffice, or should I step up to 6?


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## ledgerdc (Aug 4, 2011)

I have noticed a big improvement in the sound. The reverberations have dropped off greatly. Haven't played any music yet, and probably should try to get some measurements...not sure how to do this though.


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## bpape (Sep 14, 2006)

4 mil will pass more than the 6 mil in the upper mids and highs. Contrary to some other opinions, there is nothing wrong with using a THIN facing like this to minimize over-absorbing the upper registers. All of that said, the 4 mil should be just fine. 

Bryan


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## Owen Bartley (Oct 18, 2006)

You're not messing around, ledger! Great work on the corner traps, and I'm glad to hear they made a difference. How are you planning to finish them after applying the plastic?


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## ledgerdc (Aug 4, 2011)

For the coverings, I've built a series of frames using more of the OSB and corner brackets. I ordered some fabric (thanks BPAPE) which will be used to cover them.

As another update, I put in superchunks within the front two corners in the speaker columns. If I have any Roxul left, I will put some in and around the center channel as well as stuff some more behind the screen wall. Pictures on this to follow shortly.


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## Irishsaab (Jan 26, 2011)

Nice work and some very interesting custom designs. Looking forward to you posting the final product pictures! I probably missed this but where did you buy the material you used for the ceiling angles?


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## ledgerdc (Aug 4, 2011)

Well, the project is moving forward and I have some more pics. I'm not completely done, but I had a very productive weekend and wanted to share the results.









Completed installing the insulation for the superchunks.








Added superchunks behind the front mains.








Used some of the left over Roxul AFB to fill the void around the center channel.








Covered the ceiling / wall areas with 4mil plastic. I didn't do the wall / wall corners as the structure in place didn't really support this (no place to staple the plastic).

More pictures coming...


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## ledgerdc (Aug 4, 2011)

Pictures continued...








Start of the panel covering process.








Covered panels ready for the install.








Panels installed. I used a brad nailer rather than velcro due to concerns of holding strength.

So far, I am really, REALLY happy with the results. Aesthetically speaking it looks better than I anticipated. Sound wise, it is SOOOO much better than it was. I need to perform a sound test to confirm the results (any suggestions here?), but the sound staging difference is night and day compared to what it was.

Next Steps:
1. Build the triangle corner pieces to cover the last remaining exposed insulation.
2. Build the 1st and 2nd wall reflective panels.
3. Build the ceiling cloud.


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## stump (Sep 14, 2011)

Looks sweet.Hope you don't over do it before you test it with music.Im about to do my room and will do in stages till I get the sound right....


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## Kaisergrendel (Jul 19, 2011)

That looks insane! At some point you should start calling these megachunks


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## ghost rider (Dec 29, 2010)

Nice job how much of a difference did it make? I'm guessing if you did any room testing you would have posted the results. I did far less treatment in terms of sq footage but could definitely hear it and the measurements I made with REW confirmed that.


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## ledgerdc (Aug 4, 2011)

The difference in sound staging has been huge. Instead of the wall of noise I was getting, I can actually hear 'fly-bys'. Bass has also been improved in terms of clarity.

I have noticed that the overall volume of the room has decreased greatly, meaning that I have to push my amp a good deal more to achieve the same enveloping sound. That being said, when the sound is at volume, it is more clear and distinct across the channels.

My testing equipment arrives on Friday and I'll be able to post the results, assuming I get it running, next week.


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## ghost rider (Dec 29, 2010)

ledgerdc said:


> The difference in sound staging has been huge. Instead of the wall of noise I was getting, I can actually hear 'fly-bys'. Bass has also been improved in terms of clarity.
> 
> I have noticed that the overall volume of the room has decreased greatly, meaning that I have to push my amp a good deal more to achieve the same enveloping sound. That being said, when the sound is at volume, it is more clear and distinct across the channels.
> 
> My testing equipment arrives on Friday and I'll be able to post the results, assuming I get it running, next week.


That's pretty much what I heard with my treatments. With music I noticed I could crank it like I never could before. I always had that room distortion. I now know it was just all that sound bouncing around.


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## ledgerdc (Aug 4, 2011)

My measuring equipment came today and here is my first 'waterfall'. Really haven't much of a clue as to what it is telling me, other than I have a dead spot at around 55Hz.


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## bpape (Sep 14, 2006)

Using the same measurement file, window the bottom axis to say 20-400 and bring more of the traces up above the floor of the graph so we can get a better feel for what's going on.

Bryan


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## ledgerdc (Aug 4, 2011)

Modified waterfall.


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## ghost rider (Dec 29, 2010)

to bad you didn't have the gear to measure the room prior to all the treatments. Seeing the before and after was very cool. Here's a link to mine

http://www.hometheatershack.com/forums/home-audio-acoustics/38545-got-my-treatments-installed.html


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## Kaisergrendel (Jul 19, 2011)

ledgerdc said:


> Modified waterfall.
> View attachment 32875


The decay times seem to have about doubled?


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## ledgerdc (Aug 4, 2011)

I changed the dB axis per the request from BPAPE. It is the same measurement, just on a different scale.


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## Kaisergrendel (Jul 19, 2011)

ledgerdc said:


> I changed the dB axis per the request from BPAPE. It is the same measurement, just on a different scale.


I see, I probably don't know how to read it properly since it still looks like the decay times have increased.


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## bpape (Sep 14, 2006)

The levels are the same. We're just seeing more range on the left axis telling us a little more about what's happening instead of 1/2 of it being under the floor of the graph and hidden.

Decay times don't look too bad other than below 40hz where it's pretty tough to deal with them via standard broadband treatments. 

The next thing is to identify what response aberrations are coming from where to know how to address them. Taking relative measurements with the mic farther forward and off to one side (2 different tests) will help you see what impact the current seating position in the length and width of the room are having on response. 

The null in the 50Hz area may well be positional.

The longer tails in the 70ish Hz range are typical of 8' tall rooms.

There's a lot more to look at other than just FR and decay times but this gives us a good starting point for improvment.



Bryan


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## ledgerdc (Aug 4, 2011)

Are there resources available that cater to newbie's like me that can provide an education on how to read these graphs and adjust the room to address the issues?

Feels like I'm stumbling around in the dark.


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> The levels are the same. We're just seeing more range on the left axis telling us a little more about what's happening instead of 1/2 of it being under the floor of the graph and hidden.


Ah that's it, I hadn't notice the floor had changed.


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