Acoustical Treatments Master Thread - Page 4

Dennis,

In the deciding the height for the insulation on side and rear wall where should the refelection point for the front speakers to the listening positions be with respect to the top of the insulation? Above, at, or below? Which elememt of a 3way speaker to use as the reference?

Thanks

Dale

Thought I would give this a bump as a great thread, thanks everyone!

Does this hold true when using Bi-Polar speakers for LR? Would the treatment of the front wall then change?

Regardless of the intended purpose, polyester batting is a very efficient sound absorber. We have certified lab test data, but it is proprietary. Sorry!

Regards,
Terry

Polyester Acoustical Blanket Absorption Coefficients

inches mm 125 250 500 1000 2000 4000 NRC
1/2" 12.7 0.05 0.1 0.18 0.28 0.39 0.48 0.25
1" 25.4 0.08 0.18 0.33 0.49 0.61 0.66 0.40

from: http://www.jm.com/insulation/perform..._insultone.pdf

For more polyester data, please see
http://www.bobgolds.com/AbsorptionCoefficients.htm

patrickwebb,
Thanks for bumping this. Great information!

I have a question though . . . where is everyone buying their insulshield?

This is a great thread...

I have a question.

How much of an acoustical difference will it make if I treat the upper walls and have painted sheet-rock on the lower three feet of the wall?
My thinking is, I have a 5 year old and sooner or later he or one of his toys will make its way through the GOM. Actually it just seems like it would be vulnerable to accidentally being kicked. My ceilings are 9+ feet tall and the room is going to be about 16X23. (Roughly)

Thanks

Craig

Craig,
The typical thinking is (in part) the "lower wall" treatments are to minimize the fronts first reflections (indirects) of the speakers back to your ears muddying up the sound due to timing differences. Where one draws the line how far up to go depends on multiple factors that others are more qualified to answer but one important one is how tall are your seats and the people who sit in them (ie ear level), vs tweeter/speaker level.

Good luck,
Adam

So this is a bad idea then? About 2/3 of the wall would be treated. Roughly three feet from the floor to the crown molding.
Thankns

Craig

Hi Craig,

Use the mirror method. If a mirror placed flat against the wall at your treatment area will reflect the front speakers when viewed from your sitting position(s), you are OK for early reflections from that wall.

- Terry

As Terry said....

One compromise would be to do the drywall as you note but use just a couple treatment panels mounted on the walls (sort of like long pictures) in select areas of the first reflections (ie those you see in the mirror from your prime seat/sweet spot). There are examples of this in several HT mags showing this concept/idea.

Good luck.

Terry, adam... thanks!

Craig

My question was never answered, so I thought I would try again....

How does the acoustical treatment change (if at all) when you are using bi-polar speakers (Def's in my case)?

My guess is that the only change might be the treatment of the front wall. Would I then NOT want to treat the front wall OR would I want to treat the front wall with diffusion?

Also, Dennis or someone more familiar with it.....is the key to treating the side walls really only important for the ear levels of the listerners? Here's where I'm going with this.....can you INSTEAD of treating the ENTIRE bottom portions of the walls (as seen and described in this and many other threads) just treat a PORTION of the side walls (I am thinking of treating my walls similar to a racing strip on a car---i.e. the treatment would not go all the way to the floor. Would this provide the same benefit as treating the entire bottom below ear level?

I think this might be of benefit to others who don't or can't go back and retro-fit adjustable outlet boxes etc (although I installed them--I was merely thinking of others in this case). If this would provide the same results, it might be a way for others to achieve the same benefit without all the hassle of trying to modify or work around things that might not have been planned for.

It's a VERY crude illustration, but see attached for what I am talking about. Thanks for your help.

-Jason

Jason:

There are two matters to consider when looking at placement of the acoustical materials:

1. The total amount of absorption across the frequency spectrum required to meet target reverberation times in the room; and,
2. The placement of those materials to address such considerations as early reflections, speaker boundary interface response, etc.

You can certainly create a "racing stripe" type of layout. On the other hand, if the entire wall is fabric covered (without regard to the colors, placement of colors, etc), there is no reason to restrict the placement of acoustic materials to match the layout of the fabrics.

Bipolar speakers would not be handled significantly different than dipolar other than perhaps placement of the speakers.

Where in the Atlanta area can I purchase the Insul-Shield type insulation?

Dennis:

Way back on 05-04-03 in this thread in this post you wrote when given a choice between 1" and 2"
That has me very confused.

I thought that thicker made it more broadband (more lows), which is usually a good thing.
The only reason not to go with thicker I thought was economics -- it just costs twice as much to double the thickness.

Jeff - The JM Coated Insul-Shield Black (or Theater Shield) is available from Alpha Insulation in Marrietta.

Bob - 2" is not enough for broadband (low frequency) applications when placed on a wall surface. On the other hand, in most of our rooms, using the 2" material provides more absorption than we need (or want). It is a balancing act. Once we determine all the absorptive surfaces we want and model 2" we're too absorptive.

Bob,

> I thought that thicker made it more broadband (more lows), which is usually a good thing. <<br />
That's how I see it too. Aside from the larger edge surface, which is not irrelevant, switching from rigid fiberglass one inch thick to rigid fiberglass four inches thick absorbs exactly the same amount above 1 KHz. All that changes is how low in frequency "complete absorption" extends to.

--Ethan

I agree with you, Ethan.

Furthermore, if you cover a wall with an absorber which abuts other surfaces, there is no extra edge absorption effect like that in a reverberation room measurement. The absorption coefficients cannot go above 1, as when the edges are exposed. So the extra thickness simply extends bass absorption.

Regards,
Terry

When you do the calculations for the other bass absorption in the room which likely cover <250Hz - adding a treble absorber that also goes down to 250Hz would cause excess absorption at 250Hz. An HT has much more potential for bass absorption in architectural features and furnishings that must be accounted for.

Though if edge effects are measured with data above 1 - that means it impacted the data below 1 as well. And you do not know what that edge delta is!

what is the most cost effective way to measure a rooms RT60 Value?

proud: you can do it crudely, but cheaply with an impulse response program (i have a cheesy one if you want it), a cheap mic, and some loud noise like a clap, a wood clap, a starter pistol.

As the fiberglass increases in depth, it's absorption characteristics at lower frequencies improves (the greater improvement occurs from 1" to 2"); however, one is wanting to achieve a reasonably uniform RT60 across the frequency spectrum requiring a balance in the materials utilized in the room. The would include the absorption characteristics of people in upholstered seats, unoccupied leather covered upholstered seats, gypsum board, etc. These are also small rooms where typical RT60 prediction models are less than reliable. In our experience, we find we're over absorbed in the general area of the 250-500Hz range with the 2" product

Maybe it's just me but.........I have always sat in the front middle seats of my theater(see my gallery) and thought that it sounds great. However, we had company over the other night and I sat in the left end seat which is turned slightly sideways to the front wall because of the curvature of the seating arrangement. I swear that I picked up more detail in this seat than ever before. Is this because the angle of seat (and my ears) changed the reflection points? If so, and it's not just in my head, than I definitely need to get some treatments on my walls. I swear I heard things in the movie that I hadn't before!

Dennis, do you know of anyone in St.Louis that can come out and do a reading for me? I have DIYed my entire theater and would like to build my own panels, but need someone to lay it out for me.

Thanks so much for all your help!

Mike

Mike:

Gerry Lemay, founder of the Home Acoustics Alliance (www.homeacoustics.net) is based in the St. Louis area.

Dennis:

I was always curious of your preference for 1" on the side walls. Thanks for the explanation!

Andre

OK,
I had decided to use the OC703 but it is becoming a major pain to find it and once I did find it, the shipping was ridiculous. I assume Insul-Shield and Linacoustic are both similar products used for treating reflections. I'll now check DE's suggestion.

QUOTE]Originally posted by Dennis Erskine
Jeff - The JM Coated Insul-Shield Black (or Theater Shield) is available from Alpha Insulation in Marrietta.

Bob - 2" is not enough for broadband (low frequency) applications when placed on a wall surface. On the other hand, in most of our rooms, using the 2" material provides more absorption than we need (or want). It is a balancing act. Once we determine all the absorptive surfaces we want and model 2" we're too absorptive. [/quote]

Jeff:

You can visit my showroom in Marietta and "hear" for yourself.

Dennis,
I plan to do just that! I can only hope I don't spend too much money while I'm there.

It's been a couple of months and as members near this phase of their project this thread becomes VERY important....so BUMP!