Pegboard Helmholtz Resonator

[junkyardearl]

I noticed on john's site that a helmholtz resonator can be made using a piece of pegboard. I work at a retail chain and I was told to throw out a display made mostly of pegboard, needless to say I remembered John's hemlholtz article and put that piece of pegboard in my car. Now, I need some tips on building a helmholtz resonator using this chunk of pegboard and some lumber. I'm hoping you (john and the rest) can help me out here.

The piece of pegboard is 57 inches x 16 inches and is 1/4 inch deep. My plan is to cut this in half the long way, thus giving me two pieces each 28.5 inches long and 16 inches tall. I was then planning on building a frame that would be about two inches bigger than my pegboard on every side. A box would then be built around that frame with a depth of 12 or 16 inches. I was planning on covering the pegboard with a piece of fabric for apperence, and because I was going to affix insulation to the back of the pegboard as I believe John's plans state and I want something between my nose and the insulation, plus it will look cooler.

Now here's the questions. Is there an advantage to having the depth be 12, or 16 inches? What sort of wood should be used for the frame, and box? Is particle board ok for the back? Should insulation actually be put onto the back of the pegboard? Is there a certin kind of fabric that will work better than another? And finally is there any way to find out a frequency that I'm going to be cutting?

I know it's long winded, but I've never delt with building, or accoustic treatment before (minus the time brought a mattress into my hallway to cut echo). This seems to be the best forum, so I'm thinking I'll be getting plenty of help. Thanks in advance...

~james

[John Sayers]

Good thinking junkyardearl - yes you can make a resonator. Yes Particle board is OK for the back but if you seal it directly to the wall you don't need a back on it. You just need a box the same size as your board. As the depth increases the frequency gets lower. I'm not sure of the formula though - perhaps Jon T Gale knows??
The panel also acts as a panel absorber resonating to the resonate frequency of the board. Don't put the cloth directly over the board, lift it off 1/2" or so so that the holes are free to resonate like a bottle neck.

Good luck
Cheers
john

[junkyardearl]

Thanks a lot John! I took a trip to the good old home depot and found that my best option is probably going to be to make these puppies about 2 feet wide, 16 inches tall and a foot deep. As you say, the depth makes it go for the lower frequencies and I'm planning on making some of those tube absorbers mentioned in this forum about a week ago to catch those. I plan on putting a back on these, because my "studio" has to be totally portable. On any given day it could be at my house recording a singer/ songwriter with his or her accoustic guitar, or at the practice space of some young punk band. Basically I just want to have a bunch of tool to try to fix the room I'm in at the time as best as I can. This is most definately the best forum, so much to learn! Thanks again john and anyone who can give advice about getting the midrange out with this thing that would be great!

~james

[John Sayers]

junkyardearl - you could cut down the sheets even further say half again and make four boxes of varying depth. Put on a wall these would diffuse as well as absorb and the say 6" depth would work on the low mids leaving the lows for the Jon's tubes.

cheers
john