bass traps - depth vs density?

[Mr XY]

It seems that 6 inches is as deep as anyone seems to go with bass traps.

Is there a reason for this other than space and expense? - or is there a point of diminishing returns that means it is not really worth going much deeper?

For instance - what about building 1 ft deep traps with roxul fire batts (2.5 pcf) ? This would be cheaper than building a 6inch trap with oc 705 and would seem to be more effective as far as i can work out. Am i missing something here?

Any help greatly appreciated.

[SaSi_SiDi]

If "real estate" isn't too expensive or critical, then you can trade space for money.

In a smaller room people have trouble finding the space to space 2" traps another 2" from the walls.

[ciro]

Originally Posted by Mr XY

For instance - what about building 1 ft deep traps with roxul fire batts (2.5 pcf) ? This would be cheaper than building a 6inch trap with oc 705 and would seem to be more effective as far as i can work out. Am i missing something here?
Any help greatly appreciated.

Just to share what happens here (small and almost square room) I have some "standard" 4" 4pcf panels and also thicker traps (8" and more) that are 2 pcf in the front portion of room (ex:superchunks in the front wall and wall/ceiling) with excellent results below 100 hz.

Ciro

[Glenn Kuras]

Deeper is always better but most people just don't have the room. But yes if you can make them 1' deep do so. Keep in mind that it is also about coverage. It is always better to cover twice is much corner area with 4" vs covering half as much with 8".

[avare]

Originally Posted by Glenn Kuras

Deeper is always better but most people just don't have the room. But yes if you can make them 1' deep do so.

+1. thumbsup

One foot (30 cm) will give flat diffuse field absorption down to 50 Hz. Excellent response!

Andre

[Hypagen]

Originally Posted by avare

+1. thumbsup

One foot (30 cm) will give flat diffuse field absorption down to 50 Hz. Excellent response!

Andre

Hi everyone!

I have a 50Hz modal peak in my room at the listening position. When I open my door on the rear wall, the peak reduces by around 3db, which lead me to believe the modal peak is caused by reflections from the rear wall.

My room is 10ft long, does a 50Hz wave take around 5ft to do a full cycle and this is why I have a peak at 50Hz?

Would 18 inches depth of 60Kg Density Rockwool covering my entire back wall be the 'optimum' combination for absorbing down to 50Hz?

[Mr XY]

thanks for the responses guys! thumbsup gonna go with 1 ft of roxul then i think

[PaulP]

Originally Posted by Hypagen

I have a 50Hz modal peak in my room at the listening position. When I open my door on the rear wall, the peak reduces by around 3db, which lead me to believe the modal peak is caused by reflections from the rear wall.

My room is 10ft long, does a 50Hz wave take around 5ft to do a full cycle and this is why I have a peak at 50Hz?

That looks about right though the wavelength is twice the length of the
room, so 20 ft. Speed of sound divided by twice the length will give you
the frequency of the mode :

1125 ft/sec divided by 20 ft = 56 Hz (1/sec)

Paul P

[datune]

Isover (Isover, leader in thermal and acoustic insulation) told me that density does not affect absorption at all, is that true? ( I hope asking this question does not hijack your thread...)

[avare]

Originally Posted by datune

Isover (Isover, leader in thermal and acoustic insulation) told me that density does not affect absorption at all, is that true?

No. The effect is gradual over the densities used for acoustic purposes and depending on the thickness the density is quite important. If you want the skinny on this, and how density is NOT the important factor, read this:

GAs Flow Resisitivity thread.

Full of gas,
Andre

[Hypagen]

Originally Posted by PaulP

That looks about right though the wavelength is twice the length of the
room, so 20 ft. Speed of sound divided by twice the length will give you
the frequency of the mode :

1125 ft/sec divided by 20 ft = 56 Hz (1/sec)

Paul P

Cheers, I thought it was likely related, I must have had quarter the wavelength stuck in my mind for some reason, of course a 50Hz wavelength is 20ft (ha-ha!)

[Hypagen]

Originally Posted by avare

No. The effect is gradual over the densities used for acoustic purposes and depending on the thickness the density is quite important. If you want the skinny on this, and how density is NOT the important factor, read this:

GAs Flow Resisitivity thread.

Full of gas,
Andre

Good thread, I need to put some more thought into what I decide to do with the back wall of my room.

[datune]

Thanks Andre!