Bass trap....what's the truth?

[::XeS::]

Ok, yesterday I wrote a thread on Gearslutz about bass traps.
In my home depot I found only 2 kind of absorber:
- some kind of Isover panels, 2" thick, 145kg/m3 density
- big rolls of fiberglass, very soft, 1" thick, 40kg/m3 density

I asked wich one is better to build basstraps and broadband absorbers and they said me the less dense.
Said that they started explain me that a 2"-4" basstraps don't do anything below 100Hz. If I want some kind of absorbtion below 100Hz I need 20"+ basstraps O_O
Is it true or they are maniacs as usual?
I've never seen 20"+ basstraps (only if they are some corner traps).
Do you advice to use the less dense for basstraps and broadband absorbers?

 

[AntonioPetrole]

obviously 20 bass traps is a bit crazy for a smaller studio. 8 would be a solid number in my mind. 1 to each side of you, 1 in each corner, 1 above you, 1 or two behind your monitors. I don't have too much experience so take that like a grain of salt.

I don't go on gear slutz because they always answer everything with an infinite budget

 

[jipchen]

I'd go with superchunk basstraps for the corners.. they are obviously very effective in the low end.
And that's no gearslutz saying but the result of measurements (I agree the people on gearslutz are often exaggerating)..

2" is indeed very thin, most broadband absorbers I've seen are at least 10cm (about 4 inch) deep.
Imho the most competent people are on http://www.johnlsayers.com/phpBB2/index.php
There are huge threads about how to build them, how deep should they be, what's effective and what's blabla, etc.

edit:
Just an example of broadbandabsorbers:
http://www.mbakustik.de/dateien/BAB_Absorptionswerte.pdf
THE BAB50 is 5cm, BAB100 is 10cm and the BAB150 is 15cm deep. At 125 Hz a 5 cm absorber has an asborption factor of only 0,20..

 

[::XeS::]

obviously 20 bass traps is a bit crazy for a smaller studio. 8 would be a solid number in my mind. 1 to each side of you, 1 in each corner, 1 above you, 1 or two behind your monitors. I don't have too much experience so take that like a grain of salt.

I don't go on gear slutz because they always answer everything with an infinite budget

I was speaking about the depth (inches/cm) not about the number of the traps.
20"+ means something depth 50cm or more..

 

[jipchen]

Also, if you place them with a space between the wall and the actual absorber, it significantly increases its effectiveness.
(edit Actually, the common opinion on some forums is: if you cover the low end with effective bass traps (i.e. superchunks), the other acoustic panels are good with 2" plus 2" space from the wall.

 

[PhilTheBeard]

20 inch deep bass trap seem's a little retarded to me. I think 4 inch trap's would do you a world of good.

 

[::XeS::]

+1, that deep can only be reached with corner traps

 

[Jarkko Mattheiszen]

20 inch deep bass trap seem's a little retarded to me. I think 4 inch trap's would do you a world of good.

It's anything but retarded. Four inches of any material will only do you so much good. Otherwise any small cubicle could have perfectly tuned low-end just by slapping four inches of absorbing material on all surfaces. Obviously, that's not the case.

Seriously, read up on the John L. Sayers forum. There's some golden acoustics information there, both theoretical and practical.

 

[jipchen]

FWIW, my corner traps are between 50 and 100 cm deep (they're angled obviously) and the effect was HUGE by just building one of them. I'm super stoked for the remaining three. The improvement was instantly recognizable (also by other people), and I had lots of absorbers before that, the difference was never that big.

 

[PhilTheBeard]

It's anything but retarded. Four inches of any material will only do you so much good. Otherwise any small cubicle could have perfectly tuned low-end just by slapping four inches of absorbing material on all surfaces. Obviously, that's not the case.

Seriously, read up on the John L. Sayers forum. There's some golden acoustics information there, both theoretical and practical.

Hmm..... I'll def read up on this guy's stuff. But i know in the room i work in all we have is 4 inch trap's everywhere and it make's a huge difference in our room.

 

[Jarkko Mattheiszen]

Hmm..... I'll def read up on this guy's stuff. But i know in the room i work in all we have is 4 inch trap's everywhere and it make's a huge difference in our room.

Oh, I didn't mean 4" panels won't help, they definitely do, but only to an extent. I've got a combination of suprechunks, 4" bass traps and broadbands and 2" broad/highbands, and I could still use more

 

[::XeS::]

What about the density?

 

[jipchen]

What about the density?

I never dug that deep, so I personally can't help you there

But this should clear things up a bit:

absoprtion is not related to the destiny of a material, it is related to it`s flow resistivity.

It is important to have a optimal flow resistivity related to the absorber depth.
When you use some insulation with high length specific flow resistivity and make the absorber to deep, the soundwaves will be reflected, and don`t flow through the whole deepth of the absorber. When the absorber is thin, and you use insulation with a to low length specific flow resistivity, there is not enough resistivity to transform the sound energy into heat.

Remember, we talk about porous absorbers only.

The location of the absorber is as important as it`s porperties.

The destiny of rockwool, for example is nearly twice the destiniy of glasswool, with the same length specific flow resistivity.
The reason is it`s different porosity.


cheers
Mika

http://www.ultimatemetal.com/forum/9713230-post148.html
It's a quote taken from my studio construction thread.

 

[crillemannen]

My bass traps that are in front of me is about 50cm deep. And the one at the backwall is 70cm deep. And im in a 12m2 room (now when it is treated)
I also got panels made in MDF at the bottom of every basstrap. I don't think you can overdo it actually. But i always recommend consulting an acoustic architect before spending big money, that is what i did an my studio is awesome

 

[Soundlurker]

As mentioned, corner traps make a huuge difference in the low end. Regular 4-inch panels may remove some 100-150hz boominess, but good corner traps smooth out below that and they shorten the decay significantly. If you don't have any and your room is not of a more than decent size than you can be certain you have peaks and nulls of over a dozen or two decibels and the notes ring out too long making it even harder to judge what's going on.

 

[FloridaRolf]

What about the density?

Too dense materials may reflect (higher) frequencies

 

[sprack]

Certainly not cheap, but has anyone tried the Bag End E-trap?
It's an active trapping system.
http://www.bagend.com/bagend/ETrap.htm