Acoustic placement and recommendations

[bass addict]

I finished my theater last year and have been putting off treatments for too long. After buying the new Onkyo 905 as well as a BR player to complement my HDDVD player I am a little low on funds. I figure if I don't start now though I will never do it, and I really feel it will make a big difference. My theater dimensions are 10'6"x24x9. I really wish it was wider but that's what I had to work with. Here is a pic before the framing was finished being wrapped. Yes the center speaker has since been raised.

As you can see the mains are within a few inches of the wall. With the width of the room I would really like the front reflection panels to be 1" thick to keep the room from looking more claustrophobic than it is (fortunately the 9' ceilings help). I am looking at the Auralex B24 Pro panels. Now Glen and Brian are done helping me. They are 4x2x1" thick and look really classy with the beveled edges. They also claim a NRC rating of .8. I don't know how accurate this is. I could live with 2" up there if that is really a better way to go. Here is a pic of a program showing predicted room reflections.

If starting with just four 4x2 panels would you recommend mounting two 4x2x1 panels vertical next to each other or just one sideways to cover the first reflections and another one next to the second row of seats? Within the next few months the back wall will get GIK corner traps and probably 3 4" traps to help tame the lower frequencies. Glen and Brian, are you back on board now?
Also the wall behind the screen is getting a layer of 1" linacoustic at the same time as the 1" panels.

Sorry for the long post. Any and all recommendations are appreciated.

Travis

 

[bpape]

Nope - we're still here...

Seriously, you've obviously spent a lot of time and money doing the room right - why stop now. Whether you buy product from us or not - please use something that will do the job you need done. 1" foam is only 1" at it's thickest point - the rest is barely 1/4". Even 2" Auralex (the best of the foam) will not perform as well IMO as 1" fiberglass even.

Remember that NRC doesn't consider anything below 250Hz so in terms of truly dealing with reflections and overall decay time, it's a useless measurement. YOu need to look at the individual absorbtion coefficients. Look at what the 1" and 2" foam are going to do in an A mount (flat on the wall like you will use it) and compare to other options.

If it was me, I'd personally wait until I can put up what the room really needs - even if it needs to be done in stages. No need to do something now just to do it and then replace it later. If you really want to get something going now, what about some 703 on the front wall? That's something that will need to be done eventually anyway. No, it's not something sexy that is visible, but it will make a nice difference and help knock down the decay times in the room.

Bryan

 

[bass addict]

Bryan, thanks for the response. I would love to go with your 242's but as mentioned, I am running on limited space and your panels are 3-1/2" thick which is really pushing it, at least for the first reflection points. At the back of the room the 244's would work out just great. If I plan on treating the front wall, and eventually the back wall with 4" treatments are the first reflection points as critical? I read on one of the forums that in smaller rooms you actually don't want to absorb as much of the first reflections as a wider room as it will kill the "liveness" of the room.

 

[bass addict]

Nope - we're still here...
1" foam is only 1" at it's thickest point - the rest is barely 1/4". Even 2" Auralex (the best of the foam) will not perform as well IMO as 1" fiberglass even.
Bryan

Bryan, I just caught this part. The pro panels are not foam, they are fiberglass.

If you still feel 2" would be better served I can probably get away with that instead of the 1". Looking at the chart the 2" definitely have better absorption below 1000 hz. I just don't want to deaden the room too much (if that's possible). I have also decided on starting with 6 total panels. Seeing as I have rear seating as well I am thinking about placing 3 panels on each wall, to kill the 1st reflection points for the front and rear row of seating.

 

[bpape]

2" isn't going to deaden it any more. It's just going to reach down farther into the midrange. Trust me, reflection panels with a coefficient of MAYBE .3 at 125Hz isn't going to hurt you. People don't realize that male vocals can easily go into the low 200's.

My pad on the pro panels. If they're 2" fiberglass, they'll work just great.

Even though you're going to do the front and back eventually (and should), the reflection points on the side wall are still just as important.

Bryan

 

[bass addict]

I thought I'd give an update to my progress and decision. I ordered 6 1" finished panels for the first reflection points and some OC 703 1 and 2" panels. I just finished lining the front wall with 1" 703 and added some 2" to the front corners. I am extremely pleased with initial listening tests. While I never felt I had a real bass problem (felt real even and smooth after eq'ing with the 1124), it is noticably improved now. I lost some of the fill but it has really been cleaned up. Music sounds much tighter, decay times have dropped quite a bit, and more pronounced. It should sound 100% better after re eq'ing the sub. I am in the process of wrapping the left over 2" (combined for 4" total) to put in the back corners of the room.

I really have to thank BPape for his patience and time dealing with a lot of questions I threw at him. He is a stand up guy.

 

[Johnd]

Even though you're going to do the front and back eventually (and should), the reflection points on the side wall are still just as important.

Bryan

Why do you write that Bryan? I've always thought the first reflections are most egregious, and are therefore most important.

 

[bpape]

I guess I don't understand the question. I'm agreeing that the first reflections on the side wall are important. But, in a multi-channel environment, the front wall IS the reflection point for the surround speakers coming off the front wall and messing up your front imaging.

The rear wall is generally at the end of the longest dimension and a good place to deal with those modes and the nulls that can occur based on distance from seating to rear wall. Also, one can generally go thicker back there as it doesn't interfere with walkways. Lastly, in many rooms, the rear seats are placed too close to the rear wall resulting in boomy bass that isn't dealt with simply by absorbtion in the front corners. Thicker treatment back there helps to minimize this.

Bryan

 

[Johnd]

I guess I don't understand the question.

You wrote:

"the reflection points on the side wall are still just as important"

Even in multi channel mode, most of the sound still emanates from the front. How then, could the sidewalls be "just as important"?

 

[bpape]

OK. In one question you ask why front and back are just as important as sides. Now you want to know why sides are just as important. Are we playing word games? I would disagree that most sound comes from the front. Regardless, ANY sound coming from the surrounds that come off the front wall have it acting the same as the side walls - as a first reflection point.

The answer is that they're both equally important - but for different reasons. Side wall reflections must be dealt with for 2 reasons:

- The waves off the side walls from the front 3 are going to arrive out of time from the direct sound.
- The response off axis from the tweeter in almost all speakers is significantly different than the direct sound frequency response.

So, now we have sound coming off the walls that are out of time and of a significantly different frequency response. They need to be killed.

Front wall is as I previously explained and additionally to deal with SBIR issues.

Rear wall is as I explained - to assist in dealing with the lower length modes of the room and providing distributed absorbtion throughout the space.

All of those things by themselves will help but non by themselves are a complete solution. All together are a complete solution which addresses all of the issues in the room:

- SBIR (a first reflection in it's own right - just of bass frequencies rather than what we normally think of)
- Front soundstage contamination
- Side wall reflection timing and response abberations
- Additional low frequency control in the longest room dimensions
- Balanced decay time control throughout the frequency spectrum and throughout the space for more efficient usage of absorbtion.

Bryan

 

[Johnd]

OK. In one question you ask why front and back are just as important as sides. Now you want to know why sides are just as important. Are we playing word games?

No. Not a word game. That is the same question. I think it is written rather plainly. Why do you write that the sides are just as important (as the backwall since this is the area of first reflection for most of the sound)? I disagree with you that most of the sound does not emanate from the front. This has invariably been my experience in both movies (including -es and -ex) and sacd. The overwhelminging majority (I don't know, if I were to guess, 60% - 80% if we dismiss the sub for the purpose of this discussion) of the sound emanates from the front. Given that fact, (it is a truth in my experience), why would you write that "wall treatment is just as important on the sidewalls?"

I have read your entire thread, and while I believe I understand it, I cannot get past the fact that most sound emanates from the front, and therefore the first reflection area will be the backwall, and consequently the most important to treat. This is not as academic as you seem to make it. Many of us have budgets, and with that limited funding where would we first begin treating? If funding and inclination and need so availed additional treatments beyond the backwall, that is another matter.

 

[bpape]

Even though you're going to do the front and back eventually (and should), the reflection points on the side wall are still just as important.

Doesn't what I said above agree with that? Didn't I say you SHOULD treat the back wall?

Even if we agree that most of the sound is coming from the front, there is just as much coming off the side walls from the fronts as there is off the back wall from the front. At least the sound coming off the rear is somewhat the same in terms of frequency response. So, it is NOT as large an issue nor IMO up on the priority list as those off the side wall.

Front wall is once again also a first reflection point - not only for surround information messing up imaging and screen lock - but also in terms of SBIR (bass anomolies caused by the spherical nature of low end sound radiation patterns which are unlike the more ray-like dispersion as you get higher and higher in frequency). Failing to deal with SBIR causes boomy bass, dialog intelligibility issues, etc.

Now, if money is tight and it is many times.... Would you rather deal with dialog, bass response, imaging, screen lock, and time/frequency abberations by doing the front and side walls - or - deal with only reflections off the sides and rear and leave the bass, imaging, dialog clarity, and screen lock as a mess by only treating sides and rear?

If one can only do 2 out of the 3, I'll take front and sides any day. But, I'll repeat once again, the rear should also be done - it's just IMO not AS critical INITIALLY as the others in terms of overall benefit for the money spent.

If you want to do the sides and back instead, go for it. That's your choice. I've been doing this a lot of years and would never recommend that as the initial steps over front and sides.

Bryan

 

[Johnd]

Doesn't what I said above agree with that? Didn't I say you SHOULD treat the back wall?

Even if we agree that most of the sound is coming from the front, there is just as much coming off the side walls from the fronts as there is off the back wall from the front. At least the sound coming off the rear is somewhat the same in terms of frequency response. So, it is NOT as large an issue nor IMO up on the priority list as those off the side wall.

Front wall is once again also a first reflection point - not only for surround information messing up imaging and screen lock - but also in terms of SBIR (bass anomolies caused by the spherical nature of low end sound radiation patterns which are unlike the more ray-like dispersion as you get higher and higher in frequency). Failing to deal with SBIR causes boomy bass, dialog intelligibility issues, etc.

Now, if money is tight and it is many times.... Would you rather deal with dialog, bass response, imaging, screen lock, and time/frequency abberations by doing the front and side walls - or - deal with only reflections off the sides and rear and leave the bass, imaging, dialog clarity, and screen lock as a mess by only treating sides and rear?

If one can only do 2 out of the 3, I'll take front and sides any day. But, I'll repeat once again, the rear should also be done - it's just IMO not AS critical INITIALLY as the others in terms of overall benefit for the money spent.

If you want to do the sides and back instead, go for it. That's your choice. I've been doing this a lot of years and would never recommend that as the initial steps over front and sides.

Bryan

Thank you Bryan, but no. My question (point) was if one had to choose only one wall to treat (for financial and aesthetic reasons), would it not be the most offensive one (usually the back, but not necessarily)? Maybe it's just me, but I understand your posts to mean that treatment of all 4 walls is equally important...albeit for different reasons. Whilst that may be true, most of us will never treat all four walls. Thus the conundrum...a choice of something less than all four walls.

Many of us have neither the funding nor desire the aesthetics of treatments on all four walls. So I guess my point (question) was if one were to do only one wall, would it not be the rear (usually, but not necessarily always, depending on the acoustics of that particular room)? I understand that this vastly oversimplifies treatments...bass treatment is of the first order in some situations. However, I think you understand that most of us do not have 2k for treatments, nor do they want their living room looking like an anechoic chamber. In an ideal situation, aesthetics and funding would never be an issue, and the necessity of treatments would be minimized through properly designed and built theaters/rooms. Cheers.

 

[bpape]

Agreed. Nobody ever said anything about treating the WHOLE wall. Also, my original recommendation was to treat 3 - not 4. Many people have excellent results with front and sides. Most people leave the rear until last if at all.

Let's set a reasonable budget - say $500? For that, I can treat behind each speaker and beneath the screen on the front wall for SBIR, reflections, etc. I can also do a couple reflection points on the side walls for the reasons I outlined above. I can do that WELL within the $500 budget with money left over. This will hardly sound like an anechoic chamber. As for aesthetics, that's a completely different story. I was coming at it purely from a performance for the money standpoint which is what I thought the OP had been discussing.

If I personally had to pick one wall to do, I'd do the front (I'm assuming the sides are out too since that would be 2 walls ). Just doing the back leaves so many things unaddressed. Doing just the front may leave some reflections from the rear but overall addresses many more general room problems.

Bryan

 

[bass addict]

I was coming at it purely from a performance for the money standpoint which is what I thought the OP had been discussing.
Bryan

I agree that people budget less for room treatments than they probably should. Do I have more money to spend, sure. Is it tougher to justify the extra money for treatments as opposed to a shiny new amp, of course. I think that's just inherent to human nature.

Based on not only Bryan's recommendations but a combination of others (slodging through pages and pages of HT builds on the different forums) I came to the following conclusion. In an order of importance, generally speaking, the front wall plays a huge role in the overall sound characteristic of the movie/music. While the back wall is important, it has less effect on the overall dynamic (not only bass but dialog, soundstage, etc.), than the front wall. Or in otherwards, for the money spent, the front will do more to benefit the overall soundstage than the back. The front for most dedicated theaters also does not have to be as expensive as you are not paying for aesthetics. I tacked up a wall of 1" OC 703 and draped grille cloth over it to keep the yellow from being seen through the screen wall. The front wall is accounting for about a 1/4 of the overall cost of the room treatments, while I feel contributing to close to 2/3 the overall sound.