Is this enough?!

[DanDan]

Gap good. Enough?....No.
DD

[paulpod]

Cheers for you reply, how thick would you recommend? I could double them up to get 60mm?

[DanDan]

Paul, how long is a piece of string?
Broadly speaking many of us agree that 100mm with a 100mm airgap is a good shot for side and overhead reflections.
See studiotips.com for devices that attempt to go lower. For real bass action take a look at Modex, MaxTraps, Monster and Mega Traps. The large SuperChunks are a decent DIY solution.
Go to RealTraps and GIK for room treatment articles.
Everybody goes through the first steps of the learning curve, little point in rehearsing it over and over here.
DD

[SörenHjalmarsson]

Hi Paul,

Originally Posted by paulpod

Hi there,.
In terms of thickness, is 30mm (1.18 inches) thick enough?

It would be enough if you were only trying to attenuate those frequencies whose 1/4 wavelengths falls within the depth of a 1.18" trap (which would be down to about ~2900Hz).

I plan to leave a gap between the rockwool and the walls, as i heard that this improves bass absorption - is this correct?

Leaving an airgap behind the panel increase the effective absorption coefficient of the insulation. i.e. you get some extra absorbtion, free of charge. A 100mm thick trap with a 100mm airgap behind will give you almost as much absorbtion as a 200mm thick trap would...


MVH

[Jens Eklund]

Originally Posted by SörenHjalmarsson

It would be enough if you were only trying to attenuate those frequencies whose 1/4 wavelengths falls within the depth of a 1.18" trap (which would be down to about ~290Hz).

You lost a zero, 2900 Hz.

[DanDan]

Cox/D'Antonio quote significant absorption at frequencies where the fibre is 1/10 of the wavelength. For Random Incidence, Concert Halls and such, it is often considered at 1/15 or even 1/20. See Q4Avare.

DD

[Jens Eklund]

Originally Posted by DanDan

Cox/D'Antonio quote significant absorption at frequencies where the fibre is 1/10 of the wavelength.

I think Sören was referring to the depth related to maximum absorption. Yes, absorption will take place for lover frequencies as well but less than for those equal or shorter than ¼ wavelength.

[Max Dread]

Originally Posted by Jens Eklund

lover frequencies

Thanks Jens

My girlfriend read this and now she's all jealous and says she's leaving me.....

[DanDan]

Well, it appears size does matter, or is it sighs matters......
DD

[SörenHjalmarsson]

Originally Posted by Jens Eklund

You lost a zero,

Whoops! Sorry, good catch Jens. It would absorb down to 2861Hz (i changed it in my OP to avoid confusion...)

Originally Posted by Jens Eklund

I think Sören was referring to the depth related to maximum absorption. Yes, absorption will take place for lover frequencies as well but less than for those equal or shorter than ¼ wavelength.

Precisely!


Sören

[DanDan]

It is possible to over or under, state the absorption, depending on what one means by significant, and whether one relies soley on prediction, or one takes on board real world measurements.
However I believe most here will go along with Cox when he states 'significant' absorption at 1/10 of the wavelength.
30mm x 10= 300mm. Significant absorption down to 1KHz.

I would also point out the approximate doubling of absorption measured in tests, as opposed to the predictions, where the material is distributed.
Furthermore, in tests, we see significant absorption at a full octave below predicted.
I am not sure if these factors are included in Cox or not.

I am not advocating miracles here, but I must say that fibrous absorption does perform way better and lower in frequency than the worst case scenario (the Whealy default 0 degress) predicts.

DD

[Jens Eklund]

Originally Posted by DanDan

I am not advocating miracles here, but I must say that fibrous absorption does perform way better and lower in frequency than the worst case scenario (the Whealy default 0 degress) predicts.

Above the Schroeder frequency; yes.