Acoustical Treatments Master Thread - Page 40

I think I am embarrassed by what I paid for OC 703!! That sounds pretty good to me.

I just ordered 2" Owens Corning 703 plain (unfaced) 24" x 48" for $.65/SF. That's $5.20 per panel with 12 per pack being $62.40. If all things are equal, the price you paid seems pretty good.

Agreed. Knauff makes several 2" products - just verify what you're getting. If it is the equivalent product, it's a very good price.

I paid $.91 \\sq ft. 1 1/2 years ago. I'd say it was a very good price.

Thank you everyone, I just wanted to make sure that it is a good price before I purchase

Really guys if you plan to build them then I would go with Sensible Sound Solutions.. Yes you may pay a little more but you can rob Bryan of free advise..

Glenn

I recently purchased DIY material from Bryan, so I hope I have a few credits for a bit of free advice that might help some others at the same time.

My room is about 16.25 x 22.75 and has a ceiling that starts at 8' along the long walls rising to 10' in the center of the room. Facing material came this week and we are ready to make the frames for the 703 material and acoustical cotton corner traps, but I'd like to take into consideration anything that you smart guys deem important due to the ceiling. We are going to do some corner traps for the bass and some panels to tame slap echo on the walls and ceiling.

I'm curious if there are any "general rules" that apply to non parallel ceilings when it comes to additional treatments, especially as it pertains to the lower registers. I have some problems with a couple of nulls in the bottom end (mid-30's and early 60's) and and mid-bass (don't recall the frequencies offhand). Any general hints that apply when we are dealing with something other than a traditional 6 surface cubical room (ceiling soffit at the peak, higher likelihood of needing soffit treatments at the wall/ceiling vertex).

Thanks guys.

Hey John.

There are a couple of things with a ceiling like that.

- There is no real corner so you can't run bass absorbtion there (unless you want to square it off and make it look like a rectangular soffit - done that before - works well)

- Angles surfaces like that can reflect things back at the seating position at odd angles. Just like the others though, you can plot the points with a buddy and a mirror and address them. Also potentially right beside each row of seating on the angle.

If you did the fake soffit thing, it will deal with both issues if you fill it with absorbtion - you get some bass control, good speading of absorbtion throughout the space, and killing any direct reflections off that angle.

Bryan

What's the best way to cut a rigid fiberglass panel if you need to contour it?

What kind of contour? If you're just wanting to cut a bevel, you can use a table saw with a very fine blade. If you want a radius, you'll almost have to resin harden the edges and use a router on it though that's pretty tough.

I've done contouring with a cheap electric razor. I emphasize "cheap" because you will not want to shave with it after cutting 'glass. Cutting it in a straight line, as Brian said, can be done with a fine blade on a table saw. If precisenss is not an issue, a very sharp - razor-sharp six-inch knife works.

The method I used was a cheap electric knife I bought
at the grocery store (Procter Silex Easy Slice 9.99.) It will cut any contour you
throw at it. Best 10 bucks I ever spent. No mess to boot.
Matt

Cool, that sounds even better. I've got a bass trap project coming up soon and will give it a shot. Thanks!

I want to make absorbtion panels to tone down the mid to low high (basically foot traffic and speech and radio) frequencys in a bonus room which is being turned into an art studio for teaching. I'm not concerned about low / subwoofer type frequencies.

The room is about 900 feet, with wood (laminate) floors, windows, and sheet rock walls. There will not be carpets, rugs, etc. The room is very, very, very live. I have a few questions:

1. Is there a formula / rule of thumb for determining how many square feet of absorbtion panels I need to tame this room?

2. I plan to buy OC 703 (3 pound density rigid fiberglass) and wrap those panels in fabric (adhere fabric to fiberglass with spray adhesive), then velcro the panels to the walls and/or ceiling. For simplicity, I don't really want to build frames around the fiberglass.

Is this a recommended way to do this? Or do I need the frames for structural integrity? If the frames are needed, I can do that, but from a time and money standpoint, if they aren't necessary, I'd rather not.

(The panels need to look good, but not as good as GPowers theater! )

Thanks for you help.

I finally found a good search that answered some of my questions. I still need help with:

1. Is there a formula / rule of thumb for determining how many square feet of absorbtion panels I need to tame this room?


Thanks

Hi-

I found a great deal on Speaker Cloth to use for acoustic panels that you might like. I posted it here.

Hope this helps,

I've been auditioning speakers ($2,000 to $2,500 for full 7.1) and thought I had made up my mind using Def Tech BP7006 Fronts. However, these are Bipolar speakers and I have read some earlier comments in this thread that even with Bipolar speakers the screen wall should still be treated with 1" of acoustic material.

This obviously is going to wipe out majority of that rear propagated sound.

I just can't get my head around why a reputable company like Def Tech (and others) design Bipolar front speakers if these rear reflections are so bad.

I'm no audiophile and room will be 99% movies.

I'm really not sure what to do.

My options seem to be:
1) Stick with the Bipolars and not treat screen wall (just 1st reflections that impact listening position and bass traps) and hope I still like the sound (and make sure good return policy).
2) Keep looking for Mono pole speakers (going to try to adition 3x CLR2003 to see if they sound similar)

Are there are others out there that have used Bipolar speakers in a HT proscenium build? (especially if your in the NoVA area).

[EDIT] I did ask some Q's in Speaker Forum but thought some advice from the acoustic folks would be useful [/EDIT]

I'm not the expert here, nor did I stay at a Holiday Inn Express last night , but I *think* the front wall should be covered regardless of the speakers used. I happen to have a false wall to hide such things, but my front is completely lined with 2" J-M Linacoustic.

The issue with a bipole in a multi-channel environment is that you're between a rock and a hard place. The speaker is voiced and balanced to have that back information as part of the balance. But if you leave the wall live, then you're messing up your front soundstage with information from the surrounds coming back at you. In a 2 channel environment, this is not as much of an issue as the front wall can be left a bit less dead.

I think you have 3 options.

1. Use diffusion behind the speaker. This will at least still scatter the sound from the rear wave and from any reflections to minimize the effects. Downside is that effective diffusion is relatively 'thick' for front wall usage unless you have a false wall.

2. Do nothing behind the speaker. ONLY do this behind the rear driver(s) over maybe a 30 degree cone. This will still keep most of the wall relatively dead but allow the speaker to retain it's voicing and balance with a minimal compromise to reflection control.

3. Don't use a speaker with this type of design so it's a non-issue.

To me, in your situation where you don't yet have speakers and HT is 99% of the usage, #3 seems like a no-brainer. If not, then #2.

bpape - for now I'm going with #3 and will revert to #2 should I not find anything else to my liking (and in my budget).

Thanks,
Mark

Don't get me wrong - #2 will work if you have the room and money for the diffusion.

By diffusion you mean using Linacoustic or similar accross screen wall and 2ft up side? If yes this is my plan.

I'm going to continue to demo speakers ----- got at least a month before I need to start making final decision ---- so plenty of time.

I was really trying to home in on speaker choice so I can build for my in-ceiling rear surrounds. From those I've looked into so far (DefT, Polk, Sonance) providing I box and leave 0.75 to 1 cu ft of volume I should be OK.

Linacoustic, as far as I know, is only a fiberglass product. I've never heard of it as being anything else.

But this is what many have been using on their screen walls and along side walls up to 44" (or so).......are you saying this is wrong?

No, I have it there too, but it's fiberglass for absorption. Diffusion is always hard - reflective. Go here and click on the two styles of diffusion they sell.

OK - Thanks - Think I get it now

Diffusion is not in my current plan - just absorption on Screen wall and on panels along the side walls. Not decided yet about bass traps (still need to do some research)

Skip the research, unless you have a HUGE room, you will benefit from bass traps. Notice I did not say you NEED them, only that you'll benefit. Of course, once you have them, you will NOT want to be wthout them. And then you'll think that you needed them.

Gentlemen,

I don't understand which type of acoustical backing I should use on my back and side walls. What is the rule of thumb? Over 40 pages of posts, and I still don't understand what you all are talking about.



I was thinking of using homosote? Would that do the trick?

Danny

Panels can be done several ways. Some people use Linacoustic up to ear level then batting above. Others use hard or empty panels in some places and 703/cotton panels in others depending on reflections and general distribution of absorbtion througout the room.

Whether or not you want diffusion or absorption in the areas indicated will depend on several factors:
1. Are these panels in mirror points for the seating positions? If so, if your speakers have excellent off axis response, you want diffusion. With poor off axis response you'll want absorption.
2. Based upon the total of all materials in the room, what is the predicted decay time and, based on that, is more, or less, absorption needed (at what frequency ranges)
3. And, be real careful about bass traps. Most of them do nothing in the 80Hz and below range ... the first three or four (and most audible) axial modes in the typical room are below 80Hz. Most bass traps are also serious absorbers at all frequencies above 120Hz and can result in over absorption, reduction of room reverberation way below what you'd want, and you can find yourself needing to get more powerful amps and then speakers that can handle the addition power.