Dryer Vent Accoustics

Problem: Our house in the city shares a common wall with our neighbor. At the back of the house, our dryer vent is positioned about 8 feet from this common wall. Nothing is wrong with the dryer according to a repair- person and anyone's casual observation. The vent pipe is not obstructed at any point. The exhaust vent fan (or dryer blower?) does make a typical "whirring" noise which escapes from the vent and resonates in a way which disturbs the neighbor. As crazy as it seems, I now believe it's a legitimate problem for them due to the configuration of the buildings and back yard.
Considerations: -- I could possibly re-route and add to length of vent (limited by dryer spec, of course), but would prefer not to. Besides, I'm not sure it would help much by itself. -- This is actually a dispute between our tenant and our neighbor, so I'd like to keep them both as happy as possible. It's also been a long-term problem.
Proposal: My idea is to build a "sound-absorbing" box (approx 2' x 2') which simply attaches to the building, over the existing dryer vent. I don't want to restrict air-flow in any way, so the box would have to have to have an appropriate opening for the air to escape. I'm envisioning a simple box [a] lined with some sort of thick, sound- absorbing foam, [b] having a hinged door to allow any cleaning/lint removal, and [c] having a sufficient design to allow for adequate air- flow.
Questions: 1. I know acoustics is a complex area. However, could something like this actually mitigate the "whirring" sound of a clothes dryer as it exits at the vent? 2. I've researched acoustic foams on the web. Any thoughts on what types might work best for this application? 3. Would the placement of the air-flow exit hole(s) within the box impact the efficiency of any foam? 4. Any other design elements (or other suggestions) which I should consider?
Thanks!!!
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On Jun 30, 1:05?pm, snipped-for-privacy@yahoo.com wrote:

first try sitting a box or something several feet from the vent, and large enough to block the noise, see if this helps.
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On Sat, 30 Jun 2007 10:05:04 -0700, snipped-for-privacy@yahoo.com wrote:

I don't think so either.

I think any box, even without a lining woudl do a lot if it stood in between the noise and the people listenign. But a lining would be good too. Any lining would be good, an old shirt, an old flannel shirt, part of an old blanket. That's assuming the open end points down and it won't get wet.
I think you can just omit one side of the box, a side that doesn't point to any people, and that will make cleaning easy, and assembly quicker.

There must be an acoustics newsgroup (or a music one) or yahoo list, or even a web list of some sort.
You shoudl be able to pin down all the places where the noise is coming from by using an automotive stethoscope, which JCWhitney and maybe Harbor Freight has sold very cheaply, under 5 dollars. But if you don't have one of those, you can use a stick. Even a wood ruler or a yard stick. Two feet is a convenient length. Touch it to the various spots and hold it near your ear, and you'll hear things that only owls and leopards could hear without the stick.
Narrow down whether it is the air coming out of the pipe that has the noise (You need something else to hear the air**, but if nothing else is making noise, it's the air, I think.) or the end of the pipe, or the louvers there or whatever.

I don't think you need best. Any foam, including the left over peed-on mattress from the crib, will do 75% of what the best foam will do. Anything that's not hard, whether foam or not, will do 60%. These are just my guesses.

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Thanks, mm. Appreciate the thoughtful reply. Much appreciated.
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Armaflex. You can get it at an HVAC supplier, but noise is a very subjective problem. If you think you hear it, you will.
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Agreed. From experience, I know that noise is very subjective. Many thanks for the reply. I'll look into it.
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If the pipe is actually RESONATING as you described, then changing the length may detune it and may have a big impact. It's easy enough to try.
Mark
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Yeah, I'm not certain to what degree the pipe amplifies the noise originating from the dryer. I've taken the pipe off the dryer, and I can hear the same "frequency" (coming from a non-expert). But, perhaps the pipe is actually amplifying it. Currently, the pipe (flexible aluminum) is only about 6' in length from the vent fixture (which is a simple hood/flap).
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Maybe.
Then wouldn't there be even easier things, like tying a belt or blanket around a part of it? (I'm assuming it gets nowhere near hot enough to set fire to a blanket, or you could use leather or tie a piece of wood or steel to it.) Or tying a rope around part of it and tying the other end to some place fixed. The rope around the pipe shouldn't be at the middle, or at an even third, quarter, fifth, etc, but somewhere that would interfered with the frequency one is hearing. I guess just tie it up and move it a quarter inch at a time.

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itself, like an organ pipe, the pipe itself does not vibrate, just the air inside... Mark
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snipped-for-privacy@yahoo.com wrote:

In the interests of comity, can you negotiate a drying schedule acceptable to all parties? Something like Tue/Thur/Sat, noon to five?
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