Acoustic wall panels - air gap or thicker panel?...
Old 8th December 2012
  #1
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Acoustic wall panels - air gap or thicker panel?...

I have some 50mm thick fibreglass panels to go on my walls.

I have been told that fitting these with a 50mm air gap behind will increase their performance. That I understand.

However, when I asked whether simply fitting a 100mm thick panel - without an air gap - would give me even better performance, I was told "no". The figures from the manufacturer say otherwise though... EQ Acoustics

What are your thoughts - 50mm with air gap, or 100mm without?...
Old 8th December 2012
  #2
Rockwool = thick is good and a bit of air is good

50 mm x 2 or 100 mm = happier life

one 50 mm = not enough
Old 8th December 2012
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It's a small room, so I can't really afford more than 100mm away from the wall total.

So you'd say 100mm panel, no air?
Old 8th December 2012
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Quote:
Originally Posted by Gadget13769 View Post

So you'd say 100mm panel, no air?
Assuming you use OC703, 100mm panel and no air gap will be more effective below about 350Hz than 50mm panel and 50mm air, based on this:

Porous Absorber Calculator - Results

Play around there with "Amend Parameters
Old 8th December 2012
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Hmmm, thanks - looks like 100mm may be the way to go then.
Old 8th December 2012
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For sure. Have a look at what happens with 100mm panels AND a 50mm air gap though just out of curiosity, and also see what happens with a 100mm air gap:

Porous Absorber Calculator - Results

Well worth pulling them out as much as you can, up to their own depth or a bit more. Much ore than that (~200mm+) makes them even better at lower freq. (below ~100Hz) but less useful above that.
Old 8th December 2012
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That's an intriguing graph.

Whilst 100mm will obviously extend my absorption lower, it isn't necessarily as capable as the 50mm plus air gap and 100mm no air gap in the 250hz - 800hz frequency range.
Old 8th December 2012
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Right you are, it's all a compromise

The lowest room modes are always the biggest problem in my opinion though so generally I think the more absorption you can get down low the better. I admit that it is just a generalization though.

However, maybe you might need more absorption in the 250 - 800 Hz range than down lower.

It's best to measure then treat accordingly even though it's a hassle at first.
Old 8th December 2012
  #9
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Yeah, I think I'm going to have to measure.
Old 8th December 2012
  #10
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Yep that's a good idea, good luck!

Steve.
Old 8th December 2012
  #11
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Quote:
Originally Posted by Gadget13769 View Post
That's an intriguing graph.

Whilst 100mm will obviously extend my absorption lower, it isn't necessarily as capable as the 50mm plus air gap and 100mm no air gap in the 250hz - 800hz frequency range.
???

Andre
Old 8th December 2012
  #12
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Quote:
Originally Posted by avare View Post
???

Andre
I guess if you need lots of absorption at 500Hz, you would be best to use 50mm OC703 and a 50mm air gap, compared to the other options on this graph I made?

Porous Absorber Calculator - Results
Old 8th December 2012
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Quote:
Originally Posted by stevenkelby View Post
I guess if you need lots of absorption at 500Hz, you would be best to use 50mm OC703 and a 50mm air gap, compared to the other options on this graph I made?

Porous Absorber Calculator - Results
Yes - thanks.
Old 8th December 2012
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Quote:
Originally Posted by avare View Post
???

Andre
Sorry, we're referring to the graph linked in stevenkelby's posts...
Old 8th December 2012
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Quote:
Originally Posted by stevenkelby View Post
I guess if you need lots of absorption at 500Hz, you would be best to use 50mm OC703 and a 50mm air gap, compared to the other options on this graph I made?
I see what you are referring to now. Reality is that the upper range bumps and the gradual slope at the high end, implying .9 @ 1 kHz does not occur. Also for frequencies above low order room modes, random incidence is appropriate.

Lest you take the above as rather terse, the work you did in putting together that graph is great!

More than theoretical,
Andre
Old 9th December 2012
  #16
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Thanks for the info Andre, I still have a lot to learn!

Up to what frequency (approx) are the traps effective then? How can you tell, can it be calculated or is it a rule of thumb?

Here is the graphs with random incidence ticked, I have to read about what that means now!:

http://www.stanleyhallstudios.co.uk/...&s42=1&d42=100

It looks like the thicker panels with more air gap are more effective at all frequencies then, with no down sides apart from the size/cost. Is that right?

Thanks,

Steve.
Old 9th December 2012
  #17
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From that latest plot, I reckon 100mm solid might be my best compromise.

I don't really have room to go more than 100mm total from the walls, and 100mm solid seems to have an obviously better performance than 50mm panel + 50mm air.
Old 9th December 2012
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Quote:
Originally Posted by stevenkelby View Post
Thanks for the info Andre, I still have a lot to learn!
You are welcome!

Quote:
Up to what frequency (approx) are the traps effective then? How can you tell, can it be calculated or is it a rule of thumb?
For high frequency absorption, look at absorption tests. Bob Golcs has a fantastic list of them.

Quote:
It looks like the thicker panels with more air gap are more effective at all frequencies then, with no down sides apart from the size/cost. Is that right?
Thicker panels are better at low end. As panels get thicker, the best materials are lighter, with ~12" and thicker being best with regular insulation, dirt cheap compared to 703 etc. The downside is the size.

Welcome to the world of acoustics, where aspirin is drug of choice for learning!

Andre
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Old 9th December 2012
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Quote:
Originally Posted by Gadget13769 View Post
From that latest plot, I reckon 100mm solid might be my best compromise.

I don't really have room to go more than 100mm total from the walls, and 100mm solid seems to have an obviously better performance than 50mm panel + 50mm air.
IF 100 mm is the depth you can use, then solid of ~64 kg/m3 mineral wool type material IS BEST. Not a compromise.

Good luck!

Andre
Old 13th December 2012
  #20
Quote:
Originally Posted by avare View Post
IF 100 mm is the depth you can use, then solid of ~64 kg/m3 mineral wool type material IS BEST. Not a compromise.

Good luck!

Andre
Roxul Safe and Sound is 72 kg/m³. Would that be considered good material for 4" bass trap?
Old 13th December 2012
  #21
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Quote:
Originally Posted by solarplexus311 View Post
Roxul Safe and Sound is 72 kg/m³. Would that be considered good material for 4" bass trap?
My recollection is that Safe n Sound is 40 kg/m³.

Andre

Last edited by avare; 14th December 2012 at 06:16 PM.. Reason: Corrected spelling error.
Old 13th December 2012
  #22
Quote:
Originally Posted by avare View Post
My recolelction is that Safe n Sound is 40 kg/m³.

Andre
On their website it is posted 72 kg/m³.
Old 13th December 2012
  #23
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Quote:
Originally Posted by solarplexus311 View Post
On their website it is posted 72 kg/m³.
This is interesting. The datasheet which I just D/Led (attached) indicates 40 kg/m³. This value is consitent with the acoustic absorption characteristics of the material.

Interestingly,
Andre
Attached Files
File Type: pdf SafenSound.pdf (25.2 KB, 63 views)
Old 13th December 2012
  #24
Quote:
Originally Posted by avare View Post
This is interesting. The datasheet which I just D/Led (attached) indicates 40 kg/m³. This value is consitent with the acoustic absorption characteristics of the material.

Interestingly,
Andre
Ok, they should update their website then. So Safe 'n Sound no good then?
Old 14th December 2012
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Quote:
Originally Posted by solarplexus311 View Post
Ok, they should update their website then. So Safe 'n Sound no good then?
Did you tell Roxul about the error so that it can be corrected?

It is good, 703 is better AT 4" depth.

Andre
Old 14th December 2012
  #26
Thanks Andre. Any suppliers in Canada for 703?
Old 14th December 2012
  #27
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Quote:
Originally Posted by solarplexus311 View Post
Thanks Andre. Any suppliers in Canada for 703?
All across the country. Look under HVAC suppliers and insulation in the phone book. 703 is a generic term in the studio acoustics field for 48 kg/ft³ fiberglass and 64 kg/m³ mineral wool. Many companies make and sell such products.

Good luck!

Andre
Old 17th December 2012
  #28
I can't find anything that is of 64 kg/m³ mineral wool anywhere around my home. The only other thing I found was this Roxul AFB:

Roxul AFB®

Please help me find something!
Old 17th December 2012
  #29
I found some Knauf Insulation Rigid Plenum Liner with ECOSE® Technology in 1" and 2". It has a PCF of 3.0 on the website (but the salesman told me it was 1.5, I think maybe he is mistaken). Is it a good product for insulation?
Old 17th December 2012
  #30
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Quote:
Originally Posted by solarplexus311 View Post
I can't find anything that is of 64 kg/m³ mineral wool anywhere around my home. The only other thing I found was this Roxul AFB:

Roxul AFB®

Please help me find something!
The AFB is acsoutically equivalent to 703. Call the 800 numbers that Owens-Corning, Roxul and otheres have on their websites and ask for the dealers in your area witht he rpoducts you are interested in.

Andre
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