Quote:
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 first.
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.