[TheForge] Acoustical baffling

[Steve Smith]

And another thing or two....

To absorb sound, you need an absorbent material and surface area. I have 
no idea if fiberglass insulation is any good at absorbing sound, but if 
it is, you still only have a flat surface. An anechoic chamber (kind of 
a spooky place to be--no echoes) has its walls covered with very long, 
skinny triangles (which takes up almost all the room). Not necessarily 
practical, but you get the idea. If you take the insulation and put 
ripples in it, it will absorb more sound.

Open cell foam is pretty good at absorbing sound, closed cell foam (what 
you get in insulation) is not nearly so good. I speak from personal 
experience. In college, we were having *severe* problems with the folks 
upstairs complaining about the noise. A housemate suggested putting foam 
on the ceiling. We bought 18 linear feet of foam for a 12' run of 
ceiling, looping it and nailing strips about every foot, so it was 
UUUUUU like that, with much more surface area. Nita went upstairs to her 
room, and we cranked Led Zepplin. After ten minutes or so, Nita came 
down and opened our door, quickly getting a very stunned expression. She 
wasn't sure we had started the test from upstairs. A year or two later, 
I was amazed to find that Ellen, an architecture student, thought that 
the loops of dirty white, ugly foam were art. She didn't realize it was 
functional. Not that it should be obvious, but I couldn't imagine anyone 
putting up something so ugly with only art as motivation.

If you have room, sending the sound into the stratosphere could be done 
with a slanted wall, with no roof that part only. Then you'd have to 
deal with the snow somehow, of course.

Steve

Steve Smith wrote:
> I've got a two stage compressor head that would normally be run by a 5HP 
> motor. Since I had a 3HP motor and didn't have a 5HP, I just slowed it 
> down proportionately (which seems to be right from the amps the motor 
> draws).
> 
> 1. Two stage makes it quieter than one stage.
> 2. Slowing it down makes it a fair bit quieter also.
> 3. I enclosed it on two sides only (plus roof), sending the sound down 
> toward the goat pasture. Baaah.
> 
> I have to listen really hard to hear it in my shop (it is outside and 
> about 10' down the building). I'm really not sure if I hear it or not 
> until I'm right next to it. No insulation, just 5/8 exterior plywood 
> weakly framed by 2x4's.
> 
> Mostly I'm reinforcing what others have said, with one addition: do you 
> really need that much air? If not, try a bigger pulley on the motor and 
> it will be quieter. Try slowing it to 2/3 speed and see if you have 
> enough air. It will be lots quieter.
> 
> Steve Smith
> 
> PlumDon at aol.com wrote:
> 
>> My 7.5 hp T-30 compressor is located outside my shop and under a roof 
>> but  not enclosed. But it is close (100') to a neighbor. It comes on 
>> frequently when  I am using the Old Blue hammer or sand blasting 
>> cabinet. I'm afraid it is  beginning to irritate them and I would like 
>> to head off any problems.  
>> I put up a 4' x 8' wall with T-111 and home insulation. Helps but 
>> still a  lot of noise going to the neighbors. I was thinking some kind 
>> of convenient  roll-up sound insulating blanket might be available 
>> that I could just drop down,  like a shade or curtain when in use. Any 
>> one have any experience or suggestions?  They would be greatly 
>> appreciated.  
>>  
>> Don  Plummer
>> Plummer Design Works
>> 392 Hallman Mill Road
>> Phoenixville, PA  19460
>> 610-495-5058
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