Originally Posted by Sebg
Adhoc - I see the graph now but I did not see it earlier on when I made my post. Thanks very much. That link to your construction was great as well. edit: the photographs seem out of sequence but I think from your written description it is possible to see what you did.
I wonder if the grade of the rubber makes much difference? Do you have a link or some physical properties of the rubber sheet? Natural rubber is around 1,000kg/m^3 so 3mm thick = 3kg/m^2 but I wonder what Duro (hardness) it is.
KAsmira - the rubber sheet was fixed and sealed on 4 sides to make the enclosed volume airtight - it was just a brief discussion about how tight the membrane should be when it is fixed.
My pictures out of sequence? No way man!
Didn´t you see them as most people would: To reach this goal
, you first have to do this
, but before that you need to do this
, which of course means you have to start with this
The important thing for the absorber and its target frequency is a correct air space behind membrane versus its actual measured
weight / area unit. I personally would not trust any catalogue figures on density, always measure the stuff you use. Wrong density entered => incorrect results from calculations.
Natural rubber sheeting, like Trelleborg #2645, #510 or #61490, has a stated density of 1000 kg/m², hardness is 40 +/-5 Shore A (= very soft , like a common rubber band). I hand picked some EPDM rubber and other synthetic rubber with higher density. Reason: With a higher surface weight I could use a smaller air space behind which saved me about 160 mm / 6,5" in room width and length. Hardness was 70 +/- 5 Shore A = very common for rubber gaskets in nitrile, EPDM etc but the hardness itself shouldn´t be an important point in this case.