I have Rockboard...Now what?

[Moutee]

I recently purchased six sheets of Roxul Rockboard 60 from ATS Acoustics. After searching several forums and Google, I found various designs for "bass traps" or "acoustic panels." I've come up with a few questions as a result:

1) Are "bass traps" and "acoustic panels" the same thing; do they perform the same function and share the same design?

2) If they are different, which one suits my needs best?

I plan on placing the traps in a pretty small room (no less than 9'W x 13'L x 9'H) that has considerable slap echo and limited options for speaker placement. If any more information is needed to help me, I'll do my best to fill in the blanks. Thank you very much.

- Marc

 

[nibhaz]

1.) Acoustic panel is a generic term most often used to refer to a sound absorbing panel without any specific reference to frequencies range.
Bass traps are a form of acoustic panel whose design is geared towards abortion in the bass region of frequencies.

The most common design difference between a broad band absorber and a bass trap is increased thickness.


2.) The most correct answer would depend on what exactly you are trying to accomplish. I’ll assume that you have not measured the FR of your room, and thusly do not have a set of specific frequency you wish to address.

It is my understanding that Rockboard 60 performs more like OC 703, even though its density is closer to 705, so I’ll use the gas resistivity of 703 to model some boards using the porous absorber calculator.


The calculator only shows the absorption rate for one angle of incident but in an actual room sound would be hitting the panel at multiple angles so I’ve done the calculations for 0deg and 45deg to give you a frame to guesstimate a panel’s actual in room performance.

2” panel and 2” gap



2” panel and 4” gap



4” panel and 2” gap



4” panel and 4” gap



6” panel and 2”gap



As you can see the absorption rate in the bass region increases with panel thickness, and you can also see that substituting an air gap for actual material increase bass absorption.

Since you mentioned only flutter echo and only the six boards, I would probably construct 6 2” panels and mount them with a 2” air gap, focusing on 1st reflection points. If you need more bass absorbtion you could go to a 4" gap.

 

[bpape]

Agreed. One other possible placement. If the speakers are relatively close to the wall behind them, a 2" panel with an inch or so gap would do well behind the 2 front mains to help with SBIR.

Bryan

 

[Moutee]

Thanks for the prompt responses, guys. You're right; I have not done any measurements in the room, though I would like to. When you mention the 2-4" gap, is that part of the panel's construction? Examples below:

http://www.bobgolds.com/TrapMartin/home.htm (I assume this mounts flush to the wall)

vs.

http://www.youtube.com/watch?v=iyYUpkpL0gw (Gap behind the OC703)

 

[nibhaz]

Thanks for the prompt responses, guys. You're right; I have not done any measurements in the room, though I would like to. When you mention the 2-4" gap, is that part of the panel's construction? Examples below:

http://www.bobgolds.com/TrapMartin/home.htm (I assume this mounts flush to the wall)

vs.

http://www.youtube.com/watch?v=iyYUpkpL0gw (Gap behind the OC703)

The air gap behind the panel can either be part of the panel's physical construction, or it can be the product of your mounting method. It doesn’t really matter which way you get the air gap.

The second link that you posted will create a panel that has approximately a 1.5” air gap built in from the 1”x 2” (stock is usually smaller than spec) frame if you lay the wood like this:



You can then expand that 1.5” gap to 2” by placing something like this on the back of the panel.


On a panel the doesn’t have a gap built in, like the first link, you can use something like this to stand the panel off the wall or use different mounting methods such as: 1. 2. 3. or a variation of the last example where you place eye screws in the top of the panel and hang it from the brackets.


Hope this helps

 

[Moutee]

Thanks again; that was exactly the answer I needed. Off to the fabric store and Home Depot tomorrow!

Edit: Are there any free programs that I can download for measuring frequency response in a room?

 

[nibhaz]

REW is a free program that can be downloaded from here. You must register and login to the Home Theater Shack forum before downloading.

Further supporting documentation can be found here.

Good Luck

 

[Moutee]

That's exactly what I'm looking for. I'll try and use it in a week or so.