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Could someone help out interpreting material's gas flow properties Bass Traps
Old 8th March 2011
  #91
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Confusion

Jeez, we are both editing simultaneously....
Must cause confusion.....heh

Firstly, I spoke wrongly, the Nasa test does indicate to the point of them acting on it, that a less dense material, absorbed more LF.
That was a great find by Andre and I would feel confident of applying that wisdom to flat boundaries at least.

However in terms of corners, I am not aware of any test of say a SuperChunk, or 4, first with light fluffy, then with say 50KG. Or for that matter any test which indicates that a membrane on the front of SSC's does anything other than a HF decay increase. There are many untested scenarios not covered by extrapolation from Lab results.

There are some tests of SuperChunks and Studiotips Corner Absorbers, both using 703 I think, in a Lab under supervision by a probably trusted acoustician. In corners as they would be applied.
I believe the information there is interesting and close to applied reality.

e.g. The Corner Absorber, much smaller than the fully filled SuperChunk and Lenrd, performs remarkably well. Much better than it's size and depth would suggest. The Drum head effect of a partly rigid panel in a corner is not in the algorithms of Whealy etc. Sometimes denser may be a better choice, or not, who knows?
Another aspect of corners, they look like bass horns to me. The 'impedance' even of air must be altered by this IMHO.

I am good with Ethan's real room density and depth tests. As best I can remember he concluded that 705FRK was a better choice than 703 or 701 at six inches thick. This doesn't seem to correlate with Bob Golds data.

Andre has been quoting 703 as 16000 for yonks. I am sure he trusted his source and it would be a very big typo to change that to 27000.

Given the above facts and contradictions I think confusion is inevitable.
Personally, I am very dubious of certainty. At least I was up to now.....heh

DD

Last edited by DanDan; 8th March 2011 at 11:57 PM.. Reason: Ribbing Hannes
Old 9th March 2011
  #92
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DanDan,

let us leave out FRK for a moment since membranes are a different topic (very interesting but different).

If you look at the 6" results that Ethan got for OC 703 and OC 705 (see attachment), what do you see?

Firstly, I think you have seen so many measurements in your life that you will agree with me that the differences are marginal. Certainly not significant to disprove any theory.

Then, if you look very sharply, I think that you will agree with me that the 35 Hz mode is probably a bit better with the OC 705, but the 65 Hz mode is quite better with the OC 703. Just as it should be according to the theory.

(That being said the overall bracket is 20 dB), so the whole method as applied here is not very effective but that is a different topic).
Attached Thumbnails
Could someone help out interpreting material's gas flow properties-ethan_01.jpg  
Old 9th March 2011
  #93
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Quote:
Originally Posted by DanDan View Post
e.g. The Corner Absorber, much smaller than the fully filled SuperChunk and Lenrd, performs remarkably well. Much better than it's size and depth would suggest. The Drum head effect of a partly rigid panel in a corner is not in the algorithms of Whealy etc. Sometimes denser may be a better choice, or not, who knows?
DanDan, this is a different case. If we deal with multiple layers of different impedance we have resonance effects and that can be used very nicely. Even extremely nicely if I may say so. This is all covered mathematically and in experiment in a paper that I can PM to you (but again in german, sorry). There is also a new software coming out soon that allows the calculation of this (sugar, really).

But membranes etc. are not the content of this thread, at least as I understood it.
Old 9th March 2011
  #94
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Intriguing

I would love to see that paper Hannes, my brother has pretty good German and a Scientific understanding.
I find it interesting that you refer to a semi-rigid panel straddling a corner, as a 'membrane'. It partly is.
That Corner Absorber seems to punch way above it's weight in that studiotips test. Makes me wonder are SuperChunks really better?
I agree that the signals in Ethan's test are subtle. Even the FRK conclusion is not that convincing IMHO.
However, just to continue stirring the confusion. Here's a comparison between the light 701 and the dense 705.

Could someone help out interpreting material's gas flow properties-6_pcs_701_6-inch.gif
Could someone help out interpreting material's gas flow properties-6_pcs_705_6-inch.gif

Clearly the denser 705 has better absorption at LF.
DD
Old 9th March 2011
  #95
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Interesting discussion. To put a damper on some of it, instead of comparing different densities of materials with the same gap, as Ethan's very good tests did, compare the same overall depth keeping the surface impedance the same. Then it is acoustic apples to apples.

With an apple,
Andre
Old 10th March 2011
  #96
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Apples are healthy

Quote:
Originally Posted by avare View Post
Interesting discussion. To put a damper on some of it, instead of comparing different densities of materials with the same gap, as Ethan's very good tests did, compare the same overall depth keeping the surface impedance the same. Then it is acoustic apples to apples.

With an apple,
Andre
Andre, you mean something like a layer of higher gas flow resistivity behind a front layer of lower resistivity?

Actually this has been patented a while ago.

However I am not sure how well it works. See here
500 mm TP1 (5 krayls/m)
500 mm Thermarock 50 (16 krayls/m)
100 mm TP1 in front of 400 mm Thermarock 50

Calculated for diffuse incident with Miki model, AFMG SoundFlow beta.
Again, the TP1 material absorbs best for this width down to 40 Hz but if your focus is on 30 Hz then you need something else.
Attached Thumbnails
Could someone help out interpreting material's gas flow properties-tp1_100mm_tr50_400mm.jpg   Could someone help out interpreting material's gas flow properties-tp1_500mm.jpg   Could someone help out interpreting material's gas flow properties-tr50_500mm.jpg  
Old 10th March 2011
  #97
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Excuse me for going totally off topic for a moment, but I had to tell Andre that I love his "sign offs"

Signing off
Max
Old 10th March 2011
  #98
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Quote:
Originally Posted by Hannes_F View Post
Andre, you mean something like a layer of higher gas flow resistivity behind a front layer of lower resistivity?
Close. 100 mm of Thermarock 50 with 200 mm gap compared to 300 mm of TP1. Same depth and just about the same surface impedance. Thanks for the more appropriate comparison.

Andre
Old 10th March 2011
  #99
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Quote:
Originally Posted by Max Dread View Post
Excuse me for going totally off topic for a moment, but I had to tell Andre that I love his "sign offs"
Thanks Max. I was starting to think they were not noticed since Frank left. He got a good chuckle out them.

Thankfully closing,
Andre
Old 10th March 2011
  #100
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Quote:
Originally Posted by avare View Post
Thanks Max. I was starting to think they were not noticed since Frank left. He got a good chuckle out them.

Thankfully closing,
Andre
Andre, some of us appreciate some things more than we admit.

Appreciatingly admitting,
Hannes
Old 10th March 2011
  #101
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yeah! What happened to Frank?!?
Old 10th March 2011
  #102
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Quote:
Originally Posted by avare View Post
Close. 100 mm of Thermarock 50 with 200 mm gap compared to 300 mm of TP1. Same depth and just about the same surface impedance.
Ah, now I understand. The idea is to have basically the same amount of fibres, but in one case more or less evenly distributed over the depth, in the other case concentrated at the front of the absorber. Results attached (Miki model).
Attached Thumbnails
Could someone help out interpreting material's gas flow properties-tp1_300mm_rc.jpg   Could someone help out interpreting material's gas flow properties-tr50_100mm_air_200mm_rc.jpg  
Old 10th March 2011
  #103
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BTW the surface impedance does not seem to be equal. The idea of this comparision is really good but imo the higher compression causes a higher real part of the input impedance in the range of 40 - 400 Hz and this is then the reason for the higher reflectivity.

Actually we are still comparing apples and oranges here because one material is glass fibre and the other is rockwool. I need to repeat that with glass fibre only later.

Curiously interested
Hannes
Attached Thumbnails
Could someone help out interpreting material's gas flow properties-tp1_300mm_impre.jpg   Could someone help out interpreting material's gas flow properties-tr50_100mm_air_200mm_impreal.jpg   Could someone help out interpreting material's gas flow properties-tp1_300mm_impimag.jpg   Could someone help out interpreting material's gas flow properties-tr50_100mm_air_200mm_impimag.jpg  
Old 10th March 2011
  #104
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I love andre's sign offs.
Old 10th March 2011
  #105
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Quote:
Originally Posted by Hannes_F View Post
BTW the surface impedance does not seem to be equal. The idea of this comparision is really good but imo the higher compression causes a higher real part of the input impedance in the range of 40 - 400 Hz and this is then the reason for the higher reflectivity.

Actually we are still comparing apples and oranges here because one material is glass fibre and the other is rockwool. I need to repeat that with glass fibre only later.
You have it! That is what I was meaning about equivalent absorbers. Your research has shown new, at least to me, effects of different absorber materials.

Thank you Hannes! thumbsup

Learning from the best,
Andre
Old 10th March 2011
  #106
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Quote:
Originally Posted by johndykstra View Post
yeah! What happened to Frank?!?
Frank has left GIK Acoustics, on good terms. He still lurks here every once in a while. Yes, he is missed.

Andre
Old 15th March 2011
  #107
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Quote:
Originally Posted by avare View Post
You have it! That is what I was meaning about equivalent absorbers. Your research has shown new, at least to me, effects of different absorber materials.

Thank you Hannes! thumbsup

Learning from the best,
Andre
Hi Andre,

I am the one that is learning here ...
Old 21st March 2011
  #108
What a thread!

So to be at peace with god and the devil, we shall choose denser FG for corners and lighter and thicker for plain walls (like RFZ)

In this way I'm not going against Ethan test and bob golds test, we may assume that corners have a differet behavior. Am I wrong?


Edit:
To go on, someone did measurements of fluffy pink vs 705 or denser stuff for corners?

Edit 2:
Same thickness
Old 21st March 2011
  #109
SAC
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Quote:
Originally Posted by Sebastian Vera View Post

So to be at peace with god and the devil, we shall choose denser FG for corners and lighter and thicker for plain walls (like RFZ)
You have this reversed.

Low density Pink fluffy stuff for corner LF absorbers.

~3#/ft^3 for gapped broadband panels (4" or greater thickness and 4" gap)
Old 22nd March 2011
  #110
I know, but then how can you explain Ethan density test, the test done with denser fiber (705) proved to be more effective than less dense fiber (701) both 6" thick.?

There is lack of test, but this only suggest that denser is better for corners

Edit: and, porous absorber calculator gives data for direct incidence, or am I wrong? Corners are not that case so this reinforce my idea.

I must be wrong some how, because everybody would make it that way if that is so!
Old 22nd March 2011
  #111
SAC
Registered User
 

First, if you feel the results of the tests you cite are adequate, well, you are certainly not difficult to please...heh

Please go back, review statement #25, and review this and the Q4Avare thread regarding gas flow resistance.

And I would SERIOUSLY suggest that if you are considering using porous material for LF bass traps, that you consider at least doubling and preferably using triple the 6" or more depth for your absorptive material.
Old 22nd March 2011
  #112
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Quote:
Originally Posted by Sebastian Vera View Post
explain Ethan density test (results added by AAV), the test done with denser fiber (705) proved to be more effective than less dense fiber (701) both 6" thick.?
The test was with an air gap. The 705 was exhibiting absorption at low frequencies from diaphram action. The same as the FRK covered material.

If you have read Ethan's report, which you obviously have, it behooves you include a link so that people who are not familiar with it can read it and learn from it.

Rigid Fiber Density Tests

Andre
Old 22nd March 2011
  #113
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DanDan's Avatar
Cornering

Quote:
porous absorber calculator gives data for direct incidence, or am I wrong? Corners are not that case so this reinforce my idea.
Nobody is ever wrong, or right, but the information can be....

Whealy defaults to 0 degrees, direct /normal incidence.
You can input 0-90 in there, but not Random unfortunately.
AMG Soundflow does it all I believe. In fact I got the impression it can also take into account that diaphragm effect Andre refers to? Maybe Jens would confirm that or no.

Using Whealy,( which, deep joy, now works fine on my new Macs btw), I have recently shown a predicted performance for the large SSC using light fibre.
It is a spectacular performance at 0-60 degrees and more. There seems to be less difference between normal and other incidences with the thicker traps.

DD
Old 23rd March 2011
  #114
Well after reading sac's recommendation, Im starting to see that there is a vicious limit related to density (in a better way flow resisitivity) and thickness.

I imagine that in a sort of way, the sound can't travel very efficiently through it so the more material to go through the less friction is produced less absorption is achieved so thicker makes thing worst.


I've been using the calculator and found that just using the right air gap and the right thickness I can achieve very good results on very low freq in sacrifice of linearity.
I just hope that the calculator is giving an aptoximation and that is not giving a wrong information
Old 23rd March 2011
  #115
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Quote:
Originally Posted by Sebastian Vera View Post
Well after reading sac's recommendation, Im starting to see that there is a vicious limit related to density (in a better way flow resisitivity) and thickness.
Flow resistivity times thickness equals resistance. The two work together bearing in that the material has to be where there is particle velocity. Nothing vicious. heh

Innocuously,
Andre
Old 11th May 2011
  #116
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Great 3D.

It's not a good thing to leave it die.

Company products have standards. They can't produce a custom basstrap/panel for each client. So, I wonder, Why can't we reach a standard for the D.I.Y. too?

It would be nice to reach a standard of materials/thickness/density/airgap/size for
corner trap D.I.Y.
bass absorber D.I.Y.
RFZ panel D.I.Y.

That way we can run around these standards. Eventually retargeting the shoot for own specific needs.

Is it possible that after all amazing threads we can't reach standards?
Companies have standars. Why we don't have ones?

Best!
Old 11th May 2011
  #117
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According to various posts (DanDan, Jens, etc ...) there seems to be some generic recommended beasts.

- Superchunk 24"x 24" x 34" pink fluffy (Gas Flow Resistivity 5000) - All corners
- RFZ panel 24 x 48" x 4" rockwool 45Kg/m3 with 4" air , thickness meant to provide extra bass trapping - Ceiling and Side Walls, located using the mirror rule.

I'm not sure I understand what Bass Absorber is intended to mean and to be iinstalled ? Back Wall, Front Wall, elsewhere ?

If that's correct, may be this could be added to the new sticky (adding that measurements are recommended for best sizing and placement).
Old 11th May 2011
  #118
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Thank you mate. Really. Yes for absorber I meant front (behind monitors) and Back (behind listening point). -> also meant them as mobile bass absorber unit when you have to track your vocals.

Thank you really for summarizing. Really helpfull.

Than would be nice to add:

- good woods for the frames.
- good sheets for the "design".
->adding opinion if you whant to isolate rockwool with cellophane/kraft paper or just live it as they came.

Then we are done!



ps: excuse me. Are you sure that super chunck and Mega Corner Bass trap are the same stuff we are talking about?

I link you an example on what I meant with corner bass traps -> here -> just consider only the design and keep out his materials/density/etc for now.
Old 11th May 2011
  #119
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Better wait some of our experts validate what I wrote !!

Wood and Design are matter of taste, DIY expertise, budget, time to spend ...

Plus there are many room specificities, like power plug or air duct in the corners, etc ...
Old 11th May 2011
  #120
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DanDan's Avatar
SSC vs Corner Straddle

All the info you need on Corner Bass Traps is at studiotips.com
MegaTraps are similar to the large SSC but do have an 'extra'.
DD
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