Quote:
Originally Posted by fatgaz  right ho,
I want to make some DIY acoustic treatment to damp the bass modes of my too-small listening room.
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I consider bass to be about 40 Hz to 160 Hz -ish, basically two octaves,
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SO should I be trying to make devices based on closed/restricted air chambers filled with absorber material such as helmhotz panels with slots / pegboard ? or damped membrane resonators ?
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Hey FG:
You can do the treatment you want without resort to resonating devices - some of the shortfalls of which are mentioned above.
The device described in the link below will work great for the range you are concerned with [though if your room is tiny you may well be braggin' to worry about 40 Hz
]:
http://forum.studiotips.com/viewtopic.php?t=535
punch in your dimensions here to find what the modal range of the room is:
http://www.bobgolds.com/Mode/RoomModes.htm
These simpler devices also will do the job and are a lot more efficient material cost wise than a SuperChunk... but won't work quite as well [you'll need to add a about 20 to 30% more linear feet of corner treatment with a 24' wide SCA to be equivalent to using 34" face width SuperChunks - utilize floor/wall and/or ceiling/wall corners as described above to place the additional treatment].
If you use the StudioTips Corner Absorber design, you can get a large boost in performance from +/- 60 to 120 Hz if you make sure you mount them so the rear edges touch both walls.
http://forum.studiotips.com/viewtopic.php?t=534
As explained correctly above, there is no need for boxes, frames, or panels. In fact all such additions will detract from the broadband characteristics. If you resist the urge to add such things you can use one of these designs together with wall and ceiling mounted first reflection point panels to do all your treatment, [low mids and highs]. In a small room - typically you will benefit from using all 4" thick panels [no need to focus on high frequencies - you'll benefit from the addition LF absorption and the additional cost to use all thick panels is small].
Just build a light weight rectangular wood frame the size of you mineral wool panels [maybe a cross brace or two] add at least 4" of mineral fiber [3 to 6 lbs fiberglass - or 5 to 8 lbs. rockwool are good choices] and upholster with a breathable fabric [literally something you can breath through] stapled to the frame on the backside. More on choosing mineral fiber and fabric here:
http://forum.studiotips.com/viewtopic.php?t=48
A nice list of various types of mineral wool and analogs that'll help you shop the local market:
http://www.bobgolds.com/AbsorptionCoefficients.htm
Good Luck!