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Best way to absorb below 100Hz
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Protone
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#1
29th December 2012
Old 29th December 2012
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Best way to absorb below 100Hz

Hi,

I have a well treated room, but the decay time from 100Hz down is still a bit too long. The modes have been dealt with, succcesfully, but the overall decay time at low end could still be better.

I have "free" space at the rear wall, and I would like to find a best way to use that space. Height: 1200mm, Width: 2800mm, Depth: up to 400mm.

So far I have used Porous Absorber Calculator to find best resistivity/air gap combination to use with simple Porous Absorber. Seems to me like the best combination in my case (below 100Hz) is to fill all of the space using something with very low resistivity. Correct?

But since I know so little about different bass trap designs, I´d like to ask if there is better way to use that given space than using Porous absorber? Like I said, I only need to focus below 100Hz, above that I think the room is as good as it gets.
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29th December 2012
Old 29th December 2012
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Built in Slat design (Scattering/Diffusion) on all Bass Traps click here
#3
29th December 2012
Old 29th December 2012
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Using any absorber may affect the "as good as it gets" part. Using a porous absorber of any resistance will significantly affect the overall response/decay times unless a NE style room (which is unlikely).

There are some great threads that may help you here which discuss Helmholtz / Pressure Based absorbers. These types of absorbers or even some kind of hybrid may have less of an impact on the decay times above 100Hz.
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29th December 2012
Old 29th December 2012
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VPR

A deep fibre back wall with a layer of wood laths in front would work well and look good. Use Newells 543 pattern or boggy's numbers for the laths/gaps.
This is easy to do, cheap, guaranteed to work well.
There are more space efficient Bass traps which are not critically tuned, i.e. safe for DIY. If you can get hold of the correct materials, i.e. Caruso Isobond and Steel, then the VPR design is worth considering.
Perforated Panel with Porous Absorber trap
DD
Protone
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29th December 2012
Old 29th December 2012
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Thanks guys, all very informative replies! I´ll check those links.
Protone
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2nd February 2013
Old 2nd February 2013
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Hi!

after doing some research I decided to go with insulation covered with wood laths, like DanDan suggested.

I just have one question about the insulation. There are no air flow resistivity specs available for most of the insulation products here in Finland, so I´m not sure what to get.

Most "fluffy" one I have found so far is Isover KL37. I think it´s 14kg/m3. The other one I already happen to have is Paroc Extra, 30kg/m3. But I don´t know how that diffence effects the air flow resistivity, and the absorbtion charasteristics of my 400mm thick wall.

So the question is, is 14kg/m3 noticeably better below 100Hz than 30kg/m3, when the thickness of the wall is 400mm (16")?
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2nd February 2013
Old 2nd February 2013
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Quote:
Originally Posted by Protone View Post
Hi!

after doing some research I decided to go with insulation covered with wood laths, like DanDan suggested.

I just have one question about the insulation. There are no air flow resistivity specs available for most of the insulation products here in Finland, so I´m not sure what to get.

Most "fluffy" one I have found so far is Isover KL37. I think it´s 14kg/m3. The other one I already happen to have is Paroc Extra, 30kg/m3. But I don´t know how that diffence effects the air flow resistivity, and the absorbtion charasteristics of my 400mm thick wall.

So the question is, is 14kg/m3 noticeably better below 100Hz than 30kg/m3, when the thickness of the wall is 400mm (16")?
Don't forget to show before and after measurement when choosing the treatment. If there isin't any changes then it don't work.

Without any measurements we can only guess!
#8
2nd February 2013
Old 2nd February 2013
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