Axiom Home Page Forums General Discussion Home Theater Simple sound treatment

There are a ton of sources about acoustical treatment around, but all the ones I find are super complex. The fact is that I am not rebuilding my HT room . Not redoing the drywall etc -- it is what it is. What I am doing first (like next week...) is putting up a false wall to put the screen on.

What these complex resources did tell me is that I need to sound treat the front wall ie behind the false wall. I had honestly not thought of this, but it makes perfect sense. I am looking for something realtively affordable and readily available. I can't go with a specialty store that needs 3 weeks to manufacture and ship etc. Can anyone recommend something or a thread that gives you the "must-do" and "how-to" for simple sound treatment stuff.

After that I am looking for material readily available to build sound panels and besides the acoustic fabric in-front of the speakers that is going to be "all" that I do as start-up for the HT.

Am I missing something big that doesn't involve tearing down the walls? Am I missing something big that can't be done after everything else is installed? The panels, diffusers in the corners etc etc can all be installed after the fact so really not as concerned about those right now.

Thanks! And I did try posting this in the appropriate forum which led to a calculator that is really cool BUT way above what I am trying to do. There is something such as not perfect but good enough and I guess that is what I am trying to do

If you are building a false wall anyway, you can just use 3lb (or more dense) fiber or mineral board. These are the standard materials used in all the commercial pannels anyway. Owns corning 703 is one brand, but you might be able to find something less expensive. I used stuff from Ottawa Fibre that I found locally. Call around to building/construction supply places to see what you can find. As long as its 3lb/cu.ft. or more dense you're good.

Also, try posting your questions on this forum or this one
There are a couple of pros that hang out and give advice on both forums. They will help you keep it as simple as you want.

Thanks Fred.
So with the false wall I could simply attach these to the back of the studs ie the part that is towards the wall. That would be smart so the actual wall is undamaged if we ever go to sell.

I did look at Owens corning 703 but can't find it up here in Alaska so the 3.b/cu ft is great advice! Guessing that I either need to specify rigid fiberglass as well / or all rigid is 3lbs / cu ft.

Will check those forums out too - thanks. I did see the links here about corner traps etc and they are very useful. One of the threads had some nice panels on the walls with the Owens corning, but didn't see how the wall panels were built up so need to look at that as well

You can get pannels in Anchorage. I forgot the name of the place where I got mine, but will get that info to you. I build corner base traps with the stuff. It's off International Drive.

Treatments are as follows, either bass traps that go in corners of rooms, which includes floor/wall and ceiling wall, if done correctly. However, most people start with the front and rear corners of a room which make a huge difference to your frequency graphs. Bass collects in corners of rooms, by addressing this you will flatten out the overall frequency to suprising results.

Secondly, you have FRZ's (first reflection zones) which are placed on the side walls and ceilings to tame the first reflection to the listener. Otherwise, the sound that arrives, direct and indirect, is skewed at your ears. To much treating is not good, but the above added to normal room furniture makes a huge difference.

I have never read about treating behind a false wall, at least on the reputable websites that know about this topic. I can't see why it would be worth your time.

Finally, using multiple subs in your room AND treating your room properly will result in a great outcome.

Like Randy I’m wondering why you need to treat behind the false wall.

My screen “wall” only extends about 1/3 way across that end of the room the rest opens up into the dinning area. Rather than build a false wall I’m just making a wooden frame to hang the screen from. I don’t even plan to drywall it.

Now this is based on being able to pull my speakers out 3 1/2 feet or more from screen so even though there will be a wall close behind the right main there won’t be one for more than 10 feet behind the left and center but the soundstage is not effected.

More important in my room as Randy suggests are the corners (bass) and FRZs (front soundstage).

Well my reading told me that putting up fiberboards on the front wall and first reflection zones really made a difference. I looked at sirquacks thread and that looked super simple for something looking very very nice -- thanks for the good write-up

Just to explain. My front wall has a window and then a ledge that is 45 inches high. So i am going to cover the window with plywood for total blackout (no window sill so I can get it in there). Then I was going to do the false wall for two things 1) Hang the screen on and build it out in the corners and put the speakers there and basically frame in the screen if that makes sense.

Now two issues -- 1) if I do the bass traps in the corners then the speakers will be pretty darn close to them. Which is worse no bass traps or no space behind the speakers?

2) What material are you guys using up front around your screen? I guess the black material around the screen doesn't need to pass the "breathing test" -- you agree? If it does then how do you cover up behind so you don't see right through?

Thanks!

Was it Mechanical Insulation Services Inc?

They want $3.25 per sq. ft if I don't find anything else I will get some there and keep looking for more

Or was it Uresco Construction Materials Inc -- just got an email back from an installer that said they carry Owens Corning

So you’re saying you are putting the fiberboard on the outside of the wall behind the speakers? If so that makes sense, sorry if I misunderstood it sounded like you wanted to put it inside the false wall which would help dampen outside sound some but not do much for interior reflections.

I’ve read and found from testing that if I keep the drivers of my M80s at least 3 1/2 feet or more from the wall the reflections don’t have any negative impact on the soundstage. OTHO putting temporary absorptive material at the first reflection points actually shrunk the soundstage making it seem less wide.

However if I put the speakers closer than about 3 1/2 feet from the wall, absorbing the first reflections improves the front soundstage. I’m assuming from your post you won’t be able to pull your speakers that far out.



Well if having bass traps in the corners means no space behind your speakers then it sounds like your speakers will be “corner loaded” which will usually colour certain frequencies and reinforce some of the bass quite likely in ways you don’t want. So I would probably use bass traps up front as long as you can have a few inches between them and the rear ports on the speakers.

Not sure if your room is symetrical but if the front and back corners are similar you could make a pair for the back and also try them up front to see what effect that has on the speakers.

Personally I wouldn’t do everything all at once. I did that in my apartment and found out I did much more work than I needed to because I was going of theory and not listening to what was actually happening to the sound in my room. That’s why this time around I’ve spent 4 months moving speakers, furniture, wall coverings etc… around to see what effects it’s having before committing to anything. I’m very happy I have because I’ve already found I don’t need to absorb first reflections off my walls. I don’t need to build a full wall up front just a wooden frame to hang the screen on so the aluminum frame won’t sag. And that I don’t want thick fluffy furniture because it sucks the life out of the room (just killed the ambience). So before building a bunch of stuff you might want to start listening to your system moving and tweaking it as best you can. Perhaps use some temporary sound treatments (pillows, even mattresses can work) and see what effects you hear before deciding what will work best.



Right now I’m planning to use this for around my screen, it’s probably overkill but I want no reflected light other than my screen in my field of view.

http://www.fpi-protostar.com/flock.htm

If by “pass the breathing test” you mean acoustically transparent (AT) because you are putting your speakers behind the screen then yes you probably want it to also be AT material. However, if your speakers are going in front of the screen I wouldn’t worry about it.

It was AIS off 56th street. The stuff they sell is not Owens Corning, some other brand. I looked up its density and found it comparable to Owen’s panels that you see recommended all over the net. They have both foil faced and un-faced. They are 24” X 48” panels. Not exactly cheap, but nothing is up here right?

I went through the same thing you are now. I asked a few questions, had conversations with the experts and ended up just knocking out corner traps to see if they would make an improvement or not. They did. If I ever get around to it, I plan on making a couple more panels. One will be hung from the ceiling and another will mount on a wall. Furniture and shelving take care of the other wall. My room is pretty small, so my M80 mains are pretty close the corner traps. The rear of the speakers are about 6” away from the traps. This thread has some pictures of how I built mine and what they look like in my room……

http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=248931&fpart=2

I assumed from the above that you would be covering the false wall in fabric, though re-reading it I don't know why I reached that conclusion. Thats why I suggested putting the fibre board behind the false wall.

Putting fiber board behind drywall would still give you absorbtion, but I don't know what the effect would be. That would be a question to post on one of the two forums I linked to.

Hi Mikeak,

With all due deference to SirQuack, the advice on the first reflection zones is wrong, based on bogus information often intended for studio control rooms.

"Secondly, you have FRZ's (first reflection zones) which are placed on the side walls and ceilings to tame the first reflection to the listener. Otherwise, the sound that arrives, direct and indirect, is skewed at your ears."

When you place absorbers to kill the first and secondary lateral reflections from the main left and right front speakers, you greatly lessen the spacious character of the stereo soundstage. MOre than 20 years of research at Canada's National Research Council led by Dr. Floyd Toole established this beyond question. A normal mix of reflective and absorptive surfaces is ideal. Axiom goes to great lengths to design its speakers to have excellent on- and off-axis frequency responses, and when you damp the lateral reflections, you significantly alter the mix of on and off-axis delayed sounds that normally reach your ears and give a speaker a wide and spacious soundstage.

Concert and recital halls never install absorption panels on the side walls because the lateral reflections are key to giving the hall a spacious pleasant sound quality.

You don't want everything reflective, of course, but it's essential to maintain the lateral reflections if you wish to preserve the speaker's essential balance and spatial character.

Regards,
Alan

I have a question for you on that Alan. It is my understanding that reflected sound that arrives at less than 10ms. after the direct sound actually negatively affects the soundstage, collapsing it. This is supposed to be an issue in very small rooms. Do you disagree with this as well?

It seems to me that there is no 'one rule' that applies in all situation and that you need to take a look at the specifics of size construction materials and furniture in each room to decide how to tackle room response issues.

Hi FredK,

I can't comment on the 10-ms statement other than to say that it doesn't make sense, because our ears and brain combine the on-axis sounds arriving directly from the speakers at our ears with the lateral first and secondary reflections, which contribute a great deal to the perceived sound quality of the speakers. I don't see how the 10-ms sounds could "collapse" the soundstage; they'd have the opposite effect, of widening the soundstage, because they're slightly delayed, but our brain integrates them with the direct sounds so the lateral image is widened (the 10-ms reflections are from points beyond the physical boundaries of the speakers, hence we seem to perceive a wider, more expansive soundstage).

The tests at the NRC were all double-blind and the speakers that had smoother and more linear frequency responses off-axis (which were congruent with the on-axis responses) were all judged in the double-blind tests to be more "spacious-sounding".

Regards,
Alan

I spent a lot of time researching this topic, and I highly respect Toole's work, however, he is one human being. There are many other scientists and audio engineering experts that have been around just as long, and provide factual proof that proper acoustics in a home theater environment are every bit as important than in a recording studio.

I can assure you I have lost no lateral reflection issues by placing ONE 2x4 panel at each first reflection location. There is truth about over deadening a room, that is not what I have done.

My sound stage is still VERY wide, and the vocals are dead center and very tight and clear. What your doing is flattening the frequency response in the lower regions, say 60hz to 300hz, high frequencies are not affected.

Since this topic comes up all the time, I ran a little test not long ago. I had 3 friends sitting in the front row. I blind folded them. Over the next hour I played a variety of classical, rock, blues, soft pop, etc. music. I would play the same track twice, randomly removing my side panels which are hung by wire and light weight. The users would raise their hands and either hold up 1 or 2 fingers, telling me which time the song sounded the best.

Out of about 10 songs, there was only 3 occasions where one of the guests picked the wrong song.

In follow up, I've posted my graphs many times and not going to do it again, but it was pretty obvious how the frequency response improved by adding the bass traps in the corners.

Yeah, but your room is haunted. So there's a variable that needs to be factored in.

Since vampires don't have reflections, how big/small is their soundstage?

Just to perhaps clarify or at least expand upon Alan's comments about early side wall reflections and the work of Dr. Toole and his colleagues, some references to his book "Sound Reproduction" might be helpful. There are numerous discussions, including graphs, which cite his research and other scientific investigations in this area over many years. Just a few relevant summaries will be quoted.

At p.161: "In the audio community,it is popular to claim that reflected sounds within small listening rooms contribute to degrade dialog intelligibility. The concept has an instinctive "rightness", and has probably been good for the acoustical materials industry. However, as with several perceptual phenomena, when they are rigorously examined, the results are not quite as expected. This is another such case".

After pointing out that the architectural acoustics field has long recognized that early reflections improve speech intelligibility, there follows at p.162: "For speech, reflections at the same level as the direct sound contribute usefully to the effective sound level, and thereby the intelligibility, up to about a 30 ms delay".

Suggestions about acoustical treatment which is actually beneficial for home listening are given at several points, but as to attempting to eliminate early side wall reflections, this was due to "...alarmist cautions about comb filtering(see Chapter 9)or degraded speech intelligibility(see Chapter 10)or masking of other reflections within recordings(Olive and Toole, 1989). When examined, none of these turned out to be problems"(p.503). Specifically, p.504: "If the loudspeakers have good off-axis performance, and especially if the customer likes to listen to stereo music, my recommendation is to leave some blank wall at the location of the first lateral reflections from the front loudspeakers. An area with a small dimension of at least 4 feet(1.2 m) centered on the reflection path is sufficient".

I guess my experience more or less fits with what you posted John. I haven’t noticed speaker placement near the wall degrading speech intelligibility, I have however, noticed that it effects the discrete placement of sounds tending to smear or spread them out, but keeping the driver portion of the speakers about 3 1/2 or more feet out from the front and side walls eliminates this.

Adding temporary acoustic treatments (pillows/cushions) at the first reflection points narrows the width of the front soundstage and reduces how enveloping it sounds. The only place where I’ve had wall treatments at the first reflection point help was in the apartment where there was a wall 3’ from the right main and out to 8’ from the left main. Here absorbing the first reflection from the right main balanced out the front soundstage, however, adding a reflecting surface 3’ feet from the left main not only balanced the soundstage but widened and made it more enveloping.

Before I ramble on to much Mike, my point is to listen to your system in your room for a while. Move your speakers around play with the toe-in, height use temporary treatments and see what various thing do before starting down a treatment path based on theory. I guaranty your room is too complex for anything but your ears to tell you what does and does not work for you.

I have proven to myself time and again that theory and conventional wisdom seldom stand up to the complexities of real world situations. I wouldn’t buy a speaker based on other peoples opinions or how it should theoretically sound based on it’s design neither would I (this time around) treat my room based solely on theory or other people’s opinions. IMO the best way to tweak your system is to learn what various tweaking sounds like to you in your room and then start adjusting things from there.

First of all thanks for everyone that replied so far. I realize two things 1) there is no "easy setup" and 2) The specs decides the product and I was simply not clear enough in detailing my setup so I am going to try again since some answers are based on the correct setup and some are not.

1) Existing front wall is dry-walled, painted and has a window in the middle. It also has a ledge that sticks out 6 inches and goes from the floor and up for 40 inches.

2) I want the screen to go down to 30 inches over the floor so I have to start in-front of the ledge (or I couldn't go down far enough).

3) So in order to attach the screen I am going to do a "false-wall" from each side of the room all across. Basically a wall with studs 12-16 inches apart.

The speakers will be in FRONT of the false wall so between the couches and the wall. So the fabric covering the false wall will not have to be acoustic in the sense of letting sound through

OK so current thought after the posts

1) Put bass trap in the corners - try to make it so I can access and pull out if I don't like how it sounds

Question -- would it defeat the purpose if I built the bass trap from the ledge and up (subwoofer and speakers will be on the floor)

2) Put a few panels of Owens Corning or similar on the back wall (behind the false wall). One reason is that the window will only be covered by plywood. These panels will be 2 inches thick and with gaps between them in order not to kill the sound

Question: Same as for the bass traps. It is significantly easier to just do over the ledge, but I am guessing that would defeat the purpose so will do between the studs on the area below the ledge - does this sound ok?

3) The False wall will be covered with a thicker black fabric that is not see-through so you can't see the studs.

Question -- this material should not matter correct?

4) I will put the speakers in the right and left corners. I may do some kind of cutout so the speakers get more space to the wall. Then I will frame around the speakers and put up acoustical fabric in front of the speakers so they are not visible (young son that gets into everything).

Question: Should I have some kind of hard material under the speakers or just putting them on the carpet is fine?

5) I was planning on building something to put the Center on in the middle -- any suggestions or is it simply better to just put it on the floor and angle it up? (24 ft long room)

Now the stuff that is up front is obviously of main importance to me right now. This involves construction that is not so easy to change. Panels on the wall etc can be built later and added to or subtracted from as I test out different things

Thanks to everyone - your help is very much appreciated

Michael -- http://www.knaufusa.com/ -- is this the brand?

The only product they had in here in Anchorage was what is called IB-300. I searched the knauf site over and over again for specs (AIS didn't know if they were the 3lbs / cu. ft)

Price for the other stuff I found was 3.25 / sq.ft so yeah - Alaska pricing

Hey did you see that thread about the guy putting M80's in a cabinet? Alan posted a link to 'in-cabinet' M80's. These might work very well with your false wall. Take a look at them and then perhaps email Alan or JC and see what they say. I think they would look fantastic, and your son wouldn't be able to get into them!

It won't defeat the purpose, but the general rule for bass trapping in small rooms is the more, the better. Also, extend the corner bass traps as much into the room as you can. The further out they are the lower they will absorb. Bass traps are most effective at the half wave length away from the wall. So take the distance from the front of the trap to the wall and double it and that is the frequency it will be most efficient at absorbing. Go as thick as you can for the corner traps as well.

Since you are putting in a false wall, you can bass trap the ceiling/wall and floor/wall corners as well.



I have seen everything from 2x4' panels back behind the speakers to the complete wall covered. I'm not sure which is best or if it varies by room.

I would post this description and your questions on one of the two forums I linked to. The guy who answers the bulk of the posts is one of the tech guys from GIK Acoustics and is quite generous with his advice and suggestions.


It does make a difference. As the material starts to get heavier it will reflect more and more of the higher frequencies. How much difference it will make in practice, or in your room, I don't know. The guy from GIK will give you a much better answer.

#4 I like Micah's suggestion. Front porting would work best if you build the speakers into the wall. Play with the placement of the speakers before you build them in to get the best sound-stage.

#5 I would put the center up just under the screen. It probably makes it easier to center the dialog vertically. When I first set up my system, I had both my centers (dual M2s) on the floor under my RP pointing strait out. The whole sound-stage was pulled down. Angling the speakers up would have improved things, but I bet its easier if the center is up off the ground.

You have a very solid plan. Now you just need to tweek the details.

Fred and Micah - thanks for the reply.

I haven't found the thread about the front-ported M80s yet, but will keep looking. I did find the actual speakers on the store though and they look interesting.

I would probably go with the "regular" finish since I want to have the option of pulling them out.

Can someone confirm if there are any audible differences between the rear-ported and front-ported M80? The Center doesn't look like v2 for the front-ported - is that a big trade-off?

Thanks!