Basstrap thickness

[Erluf]

Hi!

In all the tutorials I have seen, people always make these huge traps that looks very thick and takes up a lot of space. Why do they do that? Several sites I've browsed states that a 100mm rigid rockwool or rigid fiberglass plate has an absorption coefficient close to 1 down to at least 125Hz. Havent found any sites displaying the coefficient lower than that.

I'm making a couple of these traps myself and I'm wandering if i can get away with just using one 100mm. My room is not that big and 20cm thick traps would make it a lot smaller.

Thanks in advance for any input

[avare]

Because 125 Hertz the absorption is high for random incidence, not normal incidence, and with bass traps we are interested in absorption BELOW 125 Hertz.

That is the Reader's Digest version. If you want something the full story, start with BBC RD 1992-11.

Andre

edit: I just noticed this:

Havent found any sites displaying the coefficient lower than that

Look at the tests of scores of 4" materials at Bob Gold's excellent absorption site.

[EricF]

Small rooms actually do better with MORE trapping and absorption per square foot than a larger room.

Here's how I handled my little corner:
With the partition removed...

Partition in place (right side of the rack). Everything actually feels very comfortable this way...

[jeremycox]

10cm traps should be fine

[Erluf]

That looks pretty good EricF! How thick are your traps?

[Glenn Kuras]

Originally Posted by EricF

Small rooms actually do better with MORE trapping and absorbtion per square foot than a larger room.

Here's how I handled my little corner...

Great job Eric!!!!!!!!

Glenn

[SixAndChange]

Those are lookin' nice!



I have a question Glenn (or anyone really).

I've heard it said many times that you should space the traps away from the wall approx. the same thickness of the trap. I have also heard you say that spacing a 2" trap off of the wall two-inches would do just as much as flush mounting a 4 inch trap.

Now would you say that if you wanted to save material on a first reflection absorber, you could get away with just doing that, using one sheet of OC703 2" and spacing it two inches? Or would you recommend actually getting 4" and spacing it four inches off the wall?

[avare]

Originally Posted by SixAndChange

I've heard it said many times that you should space the traps away from the wall approx. the same thickness of the trap. I have also heard you say that spacing a 2" trap off of the wall two-inches would do just as much as flush mounting a 4 inch trap.

Now would you say that if you wanted to save material on a first reflection absorber, you could get away with just doing that, using one sheet of OC703 2" and spacing it two inches? Or would you recommend actually getting 4" and spacing it four inches off the wall?

Gapping is done at the home level to save money on material. The following is from a post I wrote many moths ago an keep on quoting

In my part of world, 4” 703 is $3.85 per square foot . Roxul Safe n Sound (2.5 pounds per square foot and 3.5” thick) is 27 cents per square foot. A little off on the density but ONE TWELTH the price!

An interesting effect of the pricing is that gapping becomes a non issue. People at times consider having an air gap between the material to increase low frequency absorption. If a gap is used, their has to be some way to keep the material from falling into the gap. Typically this done with chicken fencing and strapping to which it is attached. The chicken fencing costs 50 cents per square foot here. Putting a 3.5” gap behind the Safe N Sound would be over twice as expensive as filling the entire space!

In other words, if you effective a material selection, gapping is more expensive than filing the entire space!

Full of it,
Andre

[Andreas G]

Originally Posted by Erluf

In all the tutorials I have seen, people always make these huge traps that looks very thick and takes up a lot of space. Why do they do that?

It has to do with the wavelength, or better said with 1/4 of the wavelenght of the frequency you want to absorb. The thicker your rockwool or rigid fiberglass plate is, the lower the absorbtion of the frequencies goes. I think in a small room it's not a bad idea to know where your modal-ringings are (in a rectangle room it's not so difficult to discover them), to know what absorbtion is needed. E.g. if your room is 3m x 6m you'll probably have some problems at around 30Hz, 60Hz, 120HZ, 180Hz, 360Hz ... so if your absorbtion goes only down to 125Hz you might still have problems with the lower frequencies and their harmonics. There are also other bass-trap solutions for lower frequencies which might be more space- and sabine-co-efficient – efficient (huh... english, what a tongue twister :-)

Good luck, Andreas

[EricF]

Originally Posted by Erluf

That looks pretty good EricF! How thick are your traps?

Thanks, Erluf and Glenn!

The panels on the wall in front of the desk are 2" thick. Everything else is 4" thick. Due to some severe space limitations I had to make some compromises, but the improvement in all apsects of my monitoring is dramatic.