Stupid? Cornertrap Construction Question

Posted: Sun Aug 06, 2006 5:07 pm

The issue or corner traps keeps coming up over and over and over...

I have to ask for the sake of the bulk of the community that has no direct access to OC703, or the cost of 703 is more than the average person is wanting to spend.**

Will standard unfaced fiberglass insulation work in a corner trap?

This is such a blatantly obvious question. I can't help but think this has been asked before, but upon searching, I haven't been able to find the question posed before now.

The idea is to place layers of insulation flat and stack them, superchunk style.

HOWEVER, since the density of standard insulation is less than that of 703, the resulting effectiveness of using a typical "Homecenter"/homeowner insulation will be one of two results;

1) If using the dimensions of a "Superchunk" or 703 corner trap, the effectiveness will be reduced by the difference in lower mass of the standard insulation. (Typical 48" diagonally across corner)

2) The physical dimensions of a standard insulation corner trap will be significantly larger to compensate for the lower density.

So, the question then becomes; What is the density difference between 703 and redily available homeowner fiberglass insulation?

AND

Is there enough consistancy between all of the different manufacturer's to make a formula that will work for most instances where a corner trap installation makes good acoustical treatment sense.

Assuming that the densities among mfr's is consistant (R-Value consistancy) then;

What would be the equivalent size of a "Superchunk" style corner trap if made from regular fiberglass insulation?

Please discuss.

Thanx,

Max

**As of 8/1/2006, approximate internet based price for OC703 is $175 for 6 sheets - 4'x8'x2" plus shipping.

Posted: Sun Aug 06, 2006 9:32 pm

You're pretty much buying fiberglass insulation by WEIGHT; if you figure that typical "fluffy stuff" runs around 0.8 PCF and 703 is 3 PCF, then it would take about 8" thick "fluffy stuff" to weigh the same as 2" 703 per square foot. If you were to price 8" thick "fluffy stuff" per square foot, the price would be comparable to 2" 703; only you'd need to compress the fluffy stuff 4X in order to see similar absorption qualities, and then you'd need to find a way to KEEP it compressed.

Then there's shape - no way will fluffy stuff maintain its shape without external help; either some sort of wire "cage", tightly stretched (strong) cloth, etc -

I 'spose you could cut the fluffy stuff into triangles (ala "superchunks") and put it in a corner, weighting the pile with a 1" steel plate or something - but steel ain't cheep either - a triangular 1" plate 30" on the square sides would have 450 cubic inches - mild steel weighs about 480 lbs/cubic foot, so this plate would weigh about 120 pounds at approx. $1 per pound, plus it would fall off the stack and break yer foot at just the wrong moment Confused

If your corner treatments will be covered, you might look at mineral wool instead; it's a bit less durable in some ways than 703, but usually about half to 2/3 the cost... Steve

Posted: Mon Aug 07, 2006 2:19 pm

MadMax wrote:

**As of 8/1/2006, approximate internet based price for OC703 is $175 for 6 sheets - 4'x8'x2" plus shipping.

WOW!!!

Someone is screwing you!!! I just picked up 3 packs of 705 for less than that price (total including 3M Super 77 was $156)

The only problem that I had was - they only want to sell by the truckload. Their OC distributor said that they have to special order it and won't do it for less than a truck. Fortunately, he just happened to have 3 packs laying in his warehouse.

I have also gotten both Roxul and 705S (the "fire safing" version of 705 - not as rigid but very dense nonetheless) from the same distributor.

If you have problems getting any, let me know. I can get you in touch the with folks here that I deal with. They are literally less than a 1/2 mile from my house - works out great!! I'm not too far from NC, you could swing up and pick some up.

J.

Posted: Mon Aug 07, 2006 8:04 pm

Cucco wrote:

MadMax wrote:

**As of 8/1/2006, approximate internet based price for OC703 is $175 for 6 sheets - 4'x8'x2" plus shipping.

WOW!!!

Someone is screwing you!!! I just picked up 3 packs of 705 for less than that price (total including 3M Super 77 was $156)
J.

J,

Ain't nobdy screwing ME... they're screwing a LOT of other people!

That's partly why I posed the question. After seeing these kinds of prices, I thought about the other guys/gals out there that are "forced" to buy at these over inflated prices just because 703 isn't readily available at most US home centers.

I know Steve's answered my question, but being rather stupid, I wanna' run a proof here.

The ratio is .80::3.0 - "fluffy"::703

At a ratio of 3.75::1, a corner trap of "fluffy" insulation would need to be 3.75 times the volume of a standard "Superchunk" corner trap. (uncompressed fluffy stuff)

That would mean that a 48" corner of 703 would need to be something like a 15 foot diagonal of "fluffy stuff"? Jebus!?!? Is that right?

WOW... that's... uhhhhh..... big

Posted: Tue Aug 08, 2006 5:59 am

Not quite that simple, Max - in addition to the size having to be that large for LF absorption to be close to the denser stuff, the highs would get MORE absorption than with a denser, smaller trap because of greater surface area; in most rooms (meaning relatively small ones), this is NOT a good thing, since we typically ALREADY have too much HF absorption relative to the lows.
Not to mention the actual SPACE such a trap would need...

As to higher than 3 PCF density (705 isn't 5 PCF, but really 6) I'd be really careful; unless you (for some reason) WANT more directionally oriented absorption (IOW, more absorption at 90 degree incidence than at grazing incidence) the higher density stuff can throw you a curve ball with early reflections at higher frequencies... Steve

Posted: Tue Aug 08, 2006 11:08 am

Max,

> approximate internet based price for OC703 is $175 for 6 sheets - 4'x8'x2" plus shipping. <

4 by 8 feet or 2 by 4 feet?

--Ethan

Posted: Tue Aug 08, 2006 11:30 am

knightfly wrote:

As to higher than 3 PCF density (705 isn't 5 PCF, but really 6) I'd be really careful; unless you (for some reason) WANT more directionally oriented absorption (IOW, more absorption at 90 degree incidence than at grazing incidence) the higher density stuff can throw you a curve ball with early reflections at higher frequencies... Steve

In that vain, is it wise to face the 703/705 with 2" Aurelex Pyramid foam?? Or will this just make things worse?

J.

Posted: Fri Aug 11, 2006 5:19 am

Ethan Winer wrote:

Max,

> approximate internet based price for OC703 is $175 for 6 sheets - 4'x8'x2" plus shipping. <

4 by 8 feet or 2 by 4 feet?

--Ethan

Six sheets of 4 feet x 8 feet x 2 Inch thick.

Posted: Fri Aug 11, 2006 5:32 am

knightfly wrote:

Not quite that simple, Max - in addition to the size having to be that large for LF absorption to be close to the denser stuff, the highs would get MORE absorption than with a denser, smaller trap because of greater surface area; in most rooms (meaning relatively small ones), this is NOT a good thing, since we typically ALREADY have too much HF absorption relative to the lows.
Not to mention the actual SPACE such a trap would need...

As to higher than 3 PCF density (705 isn't 5 PCF, but really 6) I'd be really careful; unless you (for some reason) WANT more directionally oriented absorption (IOW, more absorption at 90 degree incidence than at grazing incidence) the higher density stuff can throw you a curve ball with early reflections at higher frequencies... Steve

Yup... it's always a bit more complicated that one would expect.

So the bottom line is what I suspected...

It is counter productive to use standard home center type wall insulation as the absorbtion material in a corner trap. The density is in excess of 3x less than that of OC703 and as such, will not absorb enough low frequency energy to produce an effective bass trap.

Thanx!
Max

Jeremy, I may take you up on that offer... but it's gonna be at least a coupla' months before I'm ready for it. (Still waiting on the appraisal!)

Posted: Fri Aug 11, 2006 9:01 am

"In that vain, is it wise to face the 703/705 with 2" Aurelex Pyramid foam?? Or will this just make things worse?"

I wouldn't be likely to do that with 703, but would with 705; either a face layer of foam or of softer fiberglass... Steve

Posted: Fri Aug 11, 2006 9:41 am

Glad to hear you say that Rod.

I have made several 705 (2") panels which I have faced with various acoustic foam. Simply upon listening, I find it to be quite effective.

J.

Posted: Fri Aug 11, 2006 12:37 pm

Max,

This has nothing to do with the current thread. I got an "email refused" type error yesterday indicating an email I'd sent you bounced. I didn't see any emails to you in my Sent folder though. So if you tried to email me, this is to let you know it didn't get through. Smile

--Ethan

Posted: Fri Aug 11, 2006 5:06 pm

Ethan,

Sent you an email from the day gig. That addy should work.

Don't know what's going on with my domain... Spam doesn't seem to have a bit of trouble making it through... go figure, huh?

X

Posted: Tue Aug 15, 2006 9:43 am

MadMax wrote:

Ethan Winer wrote:

Max,

> approximate internet based price for OC703 is $175 for 6 sheets - 4'x8'x2" plus shipping. <

4 by 8 feet or 2 by 4 feet?

--Ethan

Six sheets of 4 feet x 8 feet x 2 Inch thick.

Hmmm. I would think that would be a very decent price then....
Do you have a link to where this is available? I can't imagine the rediculous box this would have to be shipped in.

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