Corner Bass Traps - Always beneficial?

[edorr]

Attached is a picture of my current room. I have somewhat randomly dumped some absorbtion panels on the walls. The two panels behind my speakers are 4" bass traps. I will take possesion of a pair of Evolution Acoustics MM3 tomorrow and have sold the two subs in the picture.

http://forum.audiogon.com/cgi-bin/fr...ome&1285196540

My question is twofold. With the subs gone, I have now space for "top to bottom" triangular corner bass traps behind the speakers. Is this always a good idea, or are (REW or other) measurements required to assess if this will beneficial in my room? Should I set up and measure the new speakers first before spending some money (not soo much), on traps? Note: I also have a Trinnov room correction system to address bass issues.

If I end up buying the corner traps, what would be the best position to put the 24 x 48 panels? The ceiling would be the most obvious location. Apologies for my ignorance - I feel like a true amateur among the pro's hanging around here.

[Bruce B]

Bass traps are always good at room boundries. Just play some music with bass content. Now get up and walk over to the corner or up against the back wall.... you can hear the bass build-up.
I'd put bass traps in every corner of the room!

[amirm]

First things first. You don't have a bass trap! A 4 inch absorber is a broadband absorber that starts at a few hundred hertz and goes up. I Just simulated a 4 inch fiberglass absorber. Here is what it looks like:



As you see the response drops like a rock 300 Hz or so and by bass frequencies below 80 Hz there is no absorption. This is because these panels are put on walls where the velocity is essentially zero so their effectiveness goes away. If you put 4 inch air gap behind them and get them further out where the velocity is higher, then they work a lot better but still, even then, absorption is only 0.3 at 65 Hz.

Best thing to do is measure with REW and find the peaks and pull them down with a DSP. That will get rid of boominess. Filling in the gaps can be done with better placement of speakers or addition of subs.

Edit: I noticed you have trinnov. Let it optimize the bass. Corner bass traps are not a whole lot more efficient than above because again, they are working against the laws of physics.

[edorr]

First things first. You don't have a bass trap! A 4 inch absorber is a broadband absorber that starts at a few hundred hertz and goes up. I Just simulated a 4 inch fiberglass absorber. Here is what it looks like:



As you see the response drops like a rock 300 Hz or so and by bass frequencies below 80 Hz there is no absorption. This is because these panels are put on walls where the velocity is essentially zero so their effectiveness goes away. If you put 4 inch air gap behind them and get them further out where the velocity is higher, then they work a lot better but still, even then, absorption is only 0.3 at 65 Hz.

Best thing to do is measure with REW and find the peaks and pull them down with a DSP. That will get rid of boominess. Filling in the gaps can be done with better placement of speakers or addition of subs.

Edit: I noticed you have trinnov. Let it optimize the bass. Corner bass traps are not a whole lot more efficient than above because again, they are working against the laws of physics.

Sounds plausible and I cannot argue with the laws of physics, but the upshot would be the entire "bass trap industry" is selling snake oil, because no bass is actually being trapped. I find this hard to believe, but thenagain many commentators say the same about the high-end cabling market. What do I do - Tough call. May be I'll take the 48" x 24" x 4" panels from the wall and put them diagonally in the corner to simulate the triangular traps I was thinking of getting, and hear/measure what this does for in room bass response.

[DonH50]

Uh, Amir old chap, the absorption is really a flat line at zero if there is an air gap? Methinks thee should check the variables on that graph again...

Seriously, it depends upon the material, of course, and how much of it, etc. I do a little better with a lot of absorbers, including several 6" and 12", all spaced a few inches off the wall (which increases the absorption a bit and also their effective surface area slightly).

The real point of this post: Amir, what program did you use to simulate that? I want it.

Thanks - Don (the ever-curious)

[amirm]

Uh, Amir old chap, the absorption is really a flat line at zero if there is an air gap? Methinks thee should check the variables on that graph again...

No, that is just the way the simulator works if you set the air gap to 0. I didn't want to show both and have one confused with the other. Here it is with 4 inch air gap:

The real point of this post: Amir, what program did you use to simulate that? I want it.

It is a free template that runs inside excel! Here it is: http://www.whealy.com/acoustics/Porous.html

[amirm]

Sounds plausible and I cannot argue with the laws of physics, but the upshot would be the entire "bass trap industry" is selling snake oil, because no bass is actually being trapped.

Sadly it is true. From Dr. Toole's CEDIA presentation:

""Sometimes these (modular bass absorbers) are called "bass traps." The problem with the name is that some of them don't "trap" much of anything excpet cash from unwiiting purchasers."

I find this hard to believe, but thenagain many commentators say the same about the high-end cabling market. What do I do - Tough call. May be I'll take the 48" x 24" x 4" panels from the wall and put them diagonally in the corner to simulate the triangular traps I was thinking of getting, and hear/measure what this does for in room bass response.

Yes, that is a good way to test them. Recently someone tested corner traps he built before and after on AVS.

Here is before:



After adding "superchunks"



Needless to say, he was very unhappy with the results. Here is how he built them: "The superchunks are about 5.5' tall, a few inches off the floor (to match my wall panels), to about a foot from the ceiling. They are 36" faced and filled with pink fluffy insulation"

[MylesBAstor]

What about these panels Amir that I use in my room?

http://www.ultrasystem.com/usfeature...sTechInfo.html

I've had people over and hear an inch or two in placement makes a world of difference.

[AudioExplorations]

Best thing to do is measure with REW and find the peaks and pull them down with a DSP. That will get rid of boominess. Filling in the gaps can be done with better placement of speakers or addition of subs.

This is how I currently address my room issues and it is VERY effective. In the future when I move to a dedicated listening room I would like to get rid of the DSP and address bass issues with acoustic treatment. The material properties are of utmost importance (specifically the resistance to airflow). The 'pink foam' used in the example is likely the reason why there is so little improvement. Also, I believe it may be best to address specific room issues with tuned narrow range bass trapping along the relevant XYZ dimensions of the problematic modes.

[bblue]

What about these panels Amir that I use in my room?

http://www.ultrasystem.com/usfeature...sTechInfo.html

I've had people over and hear an inch or two in placement makes a world of difference.

I've wondered about those. The claims seem to be too effective! Have you done any measurements with and without, or moved from point A to point B?

--Bill