Effectiveness of pink fiberglass for corner bass traps

Post and discuss acoustic topics, Studio design, construction, and soundproofing here

Effectiveness of pink fiberglass for corner bass traps

Postby DelPhi » Sat Jan 24, 2009 11:41 pm

Hi,
I'd like to tighten up the low-end in a boomy room that is generally hard-surfaced, approx 22'x24' with 14' ceiling. The room seems particularly resonant at about 60 Hz (b-flat). There's currently a patchwork of Sonex in some places on the walls but of course this does nothing for the lows. And there is not a lot of budget to work with.
We were thinking of using some corner bass traps and maybe also some hanging plywood sheets ("resonance panels"?).
For the corner bass traps, I read all about the "Studiotips SuperChunk." I believe that the SuperChunk discussion states that densities lower than that of rigid fiberglass (703) may actually perform even better. So I wondered about using standard "pink" insulation, such as unfaced r-30, which is 9.5-inch thick and substantially less expensive than rigid fiberglass. Standard width is 15 inches, yielding triangles 15x15x21.2 (the side facing into the room).
I have searched the forum for a definitive statement regarding the effectiveness of this material for corner traps, particularly at lower frequencies (40-100). So forgive me if this was already covered somewhere, but there were so many mentions of "fiberglass" that it was hard to hone in on these specific issues:
- How well will unfaced "pink" insulation work in place of 703 or equivalent for a Studiotips SuperChunk installation that is intended to reduce low-bass boom?
- If it will work, to a degree, then what are the "buts" about using it?
- What role might hanging plywood sheets ("resonance panels") play in soaking up excess bass energy and thus tightening up the low end sound?
Thanks very much for any help you can give on this.
DelPhi
 
Posts: 1
Joined: Fri Jan 23, 2009 9:15 pm

Re: Effectiveness of pink fiberglass for corner bass traps

Postby Rod Gervais » Sun Jan 25, 2009 6:02 pm

DelPhi wrote: For the corner bass traps, I read all about the "Studiotips SuperChunk." I believe that the SuperChunk discussion states that densities lower than that of rigid fiberglass (703) may actually perform even better. So I wondered about using standard "pink" insulation, such as unfaced r-30, which is 9.5-inch thick and substantially less expensive than rigid fiberglass. Standard width is 15 inches, yielding triangles 15x15x21.2 (the side facing into the room).
I have searched the forum for a definitive statement regarding the effectiveness of this material for corner traps, particularly at lower frequencies (40-100).


From what I see in the discussions with Suntower - that is not the concensus.

- How well will unfaced "pink" insulation work in place of 703 or equivalent for a Studiotips SuperChunk installation that is intended to reduce low-bass boom?


It won't - i seem to remember Jeff (Savant) saying that if you had room for about 4' thick of the material it would probably work fairly well - but most people can't afford to give up that much real estate.

- If it will work, to a degree, then what are the "buts" about using it?


The only but I can think of would be the real estate but........

One of the problems here is (of course) that this has never really been tested to prove out one way or the other just how effective it is for these purposes...... and I am a strong believer in sticking with tried - true and tested - at least in that manner you know what you're getting for your investment.

- What role might hanging plywood sheets ("resonance panels") play in soaking up excess bass energy and thus tightening up the low end sound?


I would have to say little to none at all.

Panel traps work with the principal of a spring behind the face of the trap....... and a panel hanging free doesn't provide that.

I (BTW) do not tend to favor panel traps........ Too much space for too little return.

Sincerely,

Rod
Rod

If you view life with the knowledge that there are no problems, only opportunities, you will find the load to be a lot lighter then it might be otherwise......... this is my personal philosophy
Rod Gervais
 
Posts: 1035
Joined: Sun Feb 22, 2004 2:34 am
Location: Central Village CT USA

Re: Effectiveness of pink fiberglass for corner bass traps

Postby PsychicDriver » Fri Feb 13, 2009 7:28 pm

I would really like to see some tests done on R-30, etc.

Doing the calculations myself based on the formulas, running Chris Whealy's Porous Absorber Calculator, using Winflag or Zorba, assuming a flow resistivity (based on density and fiber diameter measurements and calculations) of 5,400-8,000 for 701, 5,000-10,000 for pink fiberglass, 14,000-16,000 for 703 and 31,000 rayls/m for 705 as likely values, fluffy fiberglass appears to be profoundly superior to 703 and 705 at frequencies below 100Hz, for pretty much all thicknesses above 4" and distances from the wall above a few inches. Not only that, thin sheets of 703 or 705 perform extremely unevenly if placed away from a wall. They also perform little-to-no better than common thicknesses of fluffy pink when placed against a wall. All materials perform better when spaced from the wall, and the evenness of absorption is much greater as soon as the thickness of the material is greater than a few inches for all materials.

I am genuinely curious as to how these denser materials can perform better than less-dense material when the basic physics seems to clearly dictate against it. I worry that the trend of using 700-series is based more on fashion/sales techniques and the fact that it is more expensive and seems more "custom-purpose" than fluffy pink than on actual performance.
PsychicDriver
 
Posts: 2
Joined: Mon Jan 05, 2009 2:04 pm

Re: Effectiveness of pink fiberglass for corner bass traps

Postby bert stoltenborg » Fri Feb 13, 2009 7:37 pm

What happens when you measure 'm?
If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy
bert stoltenborg
 
Posts: 4570
Joined: Sun Apr 18, 2004 11:03 am
Location: Achterhood, Netherlands

Re: Effectiveness of pink fiberglass for corner bass traps

Postby Paul Woodlock » Tue Feb 17, 2009 7:32 am

DelPhi wrote:
I have searched the forum for a definitive statement regarding the effectiveness of this material for corner traps, particularly at lower frequencies (40-100). .


If you want any noticeable damping between 40 and 100Hz then you need a 703 type glasswool or equivalent rockwool at least a couple of feet thick and around 10 to 25% of your room volume as absorption. and strategically placed

I know this from actually doing it and measuring. See my studio build diary for test results and much anecdotes :D

Even 25% of room volume as quality absorption is going to do little at 40Hz
Last edited by Paul Woodlock on Tue Feb 17, 2009 7:33 am, edited 1 time in total.
Paul Woodlock
Strange Being
 
Posts: 2808
Joined: Mon Feb 02, 2004 1:32 am
Location: Peterborough UK

Re: Effectiveness of pink fiberglass for corner bass traps

Postby Paul Woodlock » Tue Feb 17, 2009 7:32 am

,,,,,
Paul Woodlock
Strange Being
 
Posts: 2808
Joined: Mon Feb 02, 2004 1:32 am
Location: Peterborough UK

Re: Effectiveness of pink fiberglass for corner bass traps

Postby PsychicDriver » Wed Feb 18, 2009 5:00 pm

That's a long thread! I couldn't find the tests you did with pink fiberglass.
PsychicDriver
 
Posts: 2
Joined: Mon Jan 05, 2009 2:04 pm

Re: Effectiveness of pink fiberglass for corner bass traps

Postby Paul Woodlock » Thu Feb 19, 2009 2:20 am

PsychicDriver wrote:That's a long thread! I couldn't find the tests you did with pink fiberglass.


Yeah fair comment. :) When I get around to publishing the diary in a non censored and better format it'll have a proper index and contents


Anyway I found roughly the page ....


viewtopic.php?f=1&t=107&start=1500


Here's one of the graphs I made comparing an empty corner with 50mm, 100mm and 150mm thick corner traps using mineral wool slabs and also compared to a huge absorber ( Portatraps™ - read dairy from that page )

As you can see the normal corner traps did nothing under around 100Hz. but the huge volume of absorption ( purple line ) actually did something worth bothering about.

IIRC the mineral wool slabs I used performs better than R30

Image

There's a whole wealth of real world testing and commentary in the diary around that point. hope it helps :)
Paul Woodlock
Strange Being
 
Posts: 2808
Joined: Mon Feb 02, 2004 1:32 am
Location: Peterborough UK

Re: Effectiveness of pink fiberglass for corner bass traps

Postby Scott R. Foster » Thu Feb 19, 2009 6:06 pm

I would not deny the veracity of Paul's anecdote but it is well established that one need not use "massive" absorbers [on the order of 24" thickness] to effect reduced room resonance well below 100 Hz. With proper mounting techniques one can have significant impact below 100 Hz with panels as thin as 4".

Below is an animation of a series of 13 measurements made by David French in a small listening suite. The series starts off with a bare room and proceeds with the addition of twelve, 4" thick, medium density mineral fiber panels [703 core]. A successive measurement is made and added to the animation as the panels were added to the room one at a time. Note the significant cumulative change below 100 Hz of both the +/- 75 Hz and +/- 85 Hz resonances.

CaseStudyFinal.gif
CaseStudyFinal.gif (431.88 KiB) Viewed 8085 times


You can review reverb chamber test data for the same Ready Acoustics panels David used in his case study here:

http://www.readyacoustics.com/documents/137_EwApp.pdf

These results are representative of this class of device whether made using Ready Acoustics parts or building your own panels from scratch. The bottom line is that 4" panels work quite well above 60 Hz.

While 4" thick panels do have effectiveness below 100 Hz, if frequency ranges below 100 Hz be the area of primary concern, a better choice would be to follow the spirit of Paul's suggestion and use a thicker 6" panel, or better yet a nested dual panel array [a 6" panel backed by a 4' panel], especially if you have concerns in the 60 Hz area. Below is a comparison of of these three units in corner mountings. Note the results below 100 Hz are markedly improved for the thicker devices. See the StudioTips "Treatment" FAQ for more details.

NEST-v-RT426-v-RT424-800.jpg
NEST-v-RT426-v-RT424-800.jpg (133.37 KiB) Viewed 8084 times


Using a lower density material will work as well or better as any of the three medium density units graphed above, but device thickness will need to increase to match performance - and I must mention that devices of this size can become inconvenient or even impractical in typical circumstances. But if you have the room and inclination to mount very thick devices you can use Chris's porous absorber calculator [see the FAQ] to make estimates on thicknesses needed to achieve performance with varying densities of material. As a rule of thumb I suggest you try to maintain, in the least case, an approximate linear relationship in making the trade off between density and thickness [if you reduce density from 3 lbs. to 1 lbs. then triple the thickness]. Following that rule of thumb you will probably be able to achieve a device which more or less matches normal incidence performance of the abovelisted devices and has improved off-axis performance.

Far be it from me to dissuade thoughtful experimentation but Rod's admonition about sticking to the tried and true has much merit - if there is a "known good" solution available, why re-invent the wheel?

My $0.02
SRF
Scott R. Foster
 
Posts: 3854
Joined: Mon Feb 02, 2004 12:41 pm
Location: Jacksonville, FL USA


Return to Discussion

Who is online

Users browsing this forum: No registered users and 3 guests

cron