Dear Ethan,

I have built the room described in your article with Wes Lachot. Or, perhaps not quite. I may have errors with the ceiling and insulation. Had questions about mitigating those, and a couple general questions ...

Thing 1:

You recommended 703 (or 705) rigid fiberglass for the nine 2" absorber panels. While looking for info on various absorber panels, I found this info at Auralex:

"SonoFlat Panels: [2"] made of our industry-leading Studiofoam. offers great absorption of mid to high frequencies"

"ELiTE B24 Pro Panels: [1" only] perfect choice for absorbing slap and flutter echo in a wide array of applications"

The B24 panels seem closest to the 703 fiberglass, although the B24 is only 1" thick. The B24 info makes no mention of its absorbtion capability at mid/high frequencies; it mentions absorption characteristics for slap and flutter echo. Your article says that the splayed walls avoid flutter echoes by design. Would the B24 be appropriate for Wes' design, or would it be redundant? I ask because I may have access to a nice deal on nine of those B24 units, but if they're wrong for the job, a bargain is still wasted money.

Thing 2:

Your recommendations are repeatedly for "fluffy fiberglass." My insulation, including in the ceiling, is blown-in cellulose. [Web description: Usually composed of recycled newspaper, this organic, loose-fill insulation is blown into walls. It has been treated with a flame retardant.] Is this similarly effective compared to fluffy fiberglass, or is the density and lack of comparable airspace a problem? If I must/should, I'll pull all the insulation out of the ceiling (what a mess that would be) and redo it fluffy and pink ...

Thing 3:

I have the 14'x8' "cloud" built into the ceiling by having fabric pulled under the joist bottoms. The rigid ceiling was originally at 8'. So, the cloud fabric, and the reflective border from the remaining ceiling around it, are at 8'. Is this a big mistake? ... because NOW the rigid boundary above the cloth and blown-in cellulose and ceiling joists is closer to 9'4".

Thing 3.5:

The thing I most believe is a mistake is my reflective boundary (what's left of the 8' ceiling). It's not a low-pass filter made from 1/8" plywood as you suggested. It's 5/8" drywall on resilient channel on soundboard onto the ceiling joists.

I have eight four-inch-thick 2'x4' bass traps in the corners, as laid out in your top view of the design. Can I compensate for my too-reflective, not-very-low-passable barrier by putting additional bass traps in the corners up by the ceiling? Perhaps one of the common LENRDs in each corner?

Thank you so much for even glancing at this long series of questions. I can promise to pay close attention and put your suggestions into practice as closely as possible from this point.

Best,
Jeff

Hi Jeff,

> The B24 panels seem closest to the 703 fiberglass, although the B24 is only 1" thick. <

I'm sure that will work, and there are other commercial products available in varying thicknesses you could consider. I don't know if Auralex offers those 2 inches thick, but such panels are definitely available.

> Your article says that the splayed walls avoid flutter echoes by design. <

There are two issues. One is avoiding flutter echo, and even a slight angle as in Wes' design will do that. The other issue is avoiding early reflections, and for that a much larger angle is needed. So you still need absorption at the first reflection points.

> My insulation, including in the ceiling, is blown-in cellulose. <

That's probably okay. Without acoustic data I can't say for sure, and maybe someone else here has more to offer. If you stand on a step stool and "talk into" the insulation, does it sound dead? Like you're talking into a void? If so, it's probably okay.

> I have the 14'x8' "cloud" built into the ceiling by having fabric pulled under the joist bottoms. <

With insulation filling all the space between the joists, yes?

> NOW the rigid boundary above the cloth and blown-in cellulose and ceiling joists is closer to 9'4". <

Yes, for modal purposes the room is 9'4' inches high.

> my reflective boundary (what's left of the 8' ceiling). <

Now I'm confused. Is the ceiling reflective, or is it fabric over cellulose?

> Can I compensate for my too-reflective, not-very-low-passable barrier by putting additional bass traps in the corners up by the ceiling? <

The more broadband bass trapping you have, the better. Always.

--Ethan

Thank you for the reply, Ethan.

comparing Auralex B24 to 703 or 705 rigid fiberglass:

>I don't know if Auralex offers those 2 inches thick, but such panels are definitely available.

Auralex does not appear to make their Pro Panels available in 2" width. I'm planning to follow your suggestion of using 2" rigid fiberglass for absorption of early reflections.

re: blown-in cellulose.

> stand on a step stool and "talk into" the insulation, does it sound dead? Like you're
> talking into a void? If so, it's probably okay.

i'd be curious to compare the "deadness" of cellulose to fluffy fiberglass, but yes, when speaking into the blown-in material, it's much dead-er than talking into a reflective wall.

>> 14'x8' "cloud" built into the ceiling by having fabric pulled under the joist bottoms.

> With insulation filling all the space between the joists, yes?

correct. the joists extend 11.5" from the rigid ceiling above. all that space is filled with cellulose.

>> my reflective boundary (what's left of the 8' ceiling).

> Now I'm confused. Is the ceiling reflective, or is it fabric over cellulose?

Originally, there was a reflective ceiling hung at 8'. This ceiling was made of:
1) a layer of 5/8" drywall
2) 1/2" resilient channel
3) 5/8" soundboard

A 14'x8' rectangular hole was cut from that ceiling, exposing the insulation. Fabric now covers the hole, so the insulation doesn't fall down. The perimeter of the ceiling is a reflective barrier, made from the old 8' ceiling.

This barrier is where your article said I should use something like 1/8" plywood, in order to allow low freqs through while mid/high freqs would be reflected.

So, what I think I have is a rigid, dense perimeter at 8' which will bounce back lows instead of allowing them through to the insulation. Then, in the middle of the room, I have an effective ceiling height of about 9'4" as you've said.

So, I've defeated the math and physics which were planned into the room by you and Wes. But I hope to correct what I can and make it a good environment.

Thanks again for the feedback, and this great resource. I intend to learn a lot here, and will happily contribute when I'm able to help others.

Jeff,

> what I think I have is a rigid, dense perimeter at 8' which will bounce back lows instead of allowing them through to the insulation.

Now I get it. If you can, I suggest you cut through the ceiling around the perimeter too. That will expose the insulation in the all-important ceiling corners.

--Ethan

Dear Ethan,

I'll take your advice. One more opinion, if you please:

By "cutting around the perimeter too" I believe you mean removing the entire reflective surface. What would you think of installing something like SoffitTraps in order to retain some reflectivity while still trapping bass around the permiter?

http://www.realtraps.com/products.htm#soffittraps

-thank you-

Jeff,

> By "cutting around the perimeter too" I believe you mean removing the entire reflective surface. <

Right, I mean basically removing the sheet rock for entire ceiling.

> What would you think of installing something like SoffitTraps in order to retain some reflectivity while still trapping bass around the permiter? <

Sure, that would work great. That's the whole point of those traps.

--Ethan

Dear Ethan,

Are SoffitTraps' effectiveness diminished if they're rotated by 90 degrees, such that their 12.5" side is flat to the ceiling, rather than the 16.25" side?

For rooms with splayed walls, may the traps be cut at angles other than 90 degrees for the corner pieces?

Thank you - Jeff

Jeff,

> Are SoffitTraps' effectiveness diminished if they're rotated by 90 degrees <

Not at all. They're described as 12-1/2 inches "high" simply because I assumed most people would rather have them extend downward as little as possible.

> For rooms with splayed walls, may the traps be cut at angles other than 90 degrees for the corner pieces? <

Not easily by end users, but we could certainly do that at the factory.

--Ethan