Added More Dampening Material
Rick
The 1" thickness worked for me. The actual material I used is 1/4" F-13 felt from Mcmaster-Carr (P/N 8758K312). It's closer to 5/16" thick. I found by layering it up to ~1" thick I got the best sound reduction. See Pic. (I didn't realize it would still be available as the piece I used I've had for over 10 years. I've had good luck with Parts Express materials lately with speaker building and saw the adhesive backed product as a quick, readily available solution. Turns out Mcmaster.com still has the F-13 felt and it's only $15.90 for a 1' x 6' piece. I would recommend it instead.) I see restricting the airflow somewhat as a good thing and part of the solution as my unit had the compressor growling noise as well as significant air flow noise. We had the same idea with adding more material along the output "plenum". Here's what I did. See pic. This is the same 1/4" F-13 felt. I cut a paper pattern to fit along the top of fan outlet area. Then cut the felt and glued in with 3-M super 77 spray adhesive (applied glue to back of felt outside the TM). This gave me another dB or so of sound reduction. So now I'm measuring (with a Radio Shack SPL meter, C-weighted, slow response) 73dB at the table, 66dB on my pillow in back bed and 77dB at ear height at the sink in low cool mode. These are all 4-5 dB less than before modding. Definitely an improvement. Let us know what you end up with.
P.S. Don't try the Carbo-stat (P/N AC-337) air conditioner filter cloth/media from Home Depot. It's claim to fame is the thin layer of carbon impregnated cloth laminated to the electrostatic media. It's thin! 1/16", filtered extremely well but reduced the air flow too much and caused a very annoying whistle.
Troy
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