Can anyone tell me what this is?

[clk]

http://www.youtube.com/watch?feature=player_detailpage&v=tPfZDO3uHIE#t=134

At 2:14 there is a circular foam like thing that comes with the packaging and is cut out exactly like a mosquito coil. What is it?

[MONGO]

thats a gasket for the back of the speaker frame.

It has adhesive on one side to stick to the frame.

[clk]

Oh thanks. Now to think of it, I've seen it used on the frame of very few boxes, but I've also pulled out many a subwoofer from its box and there was no gasket. Is it always necessary for it to be installed?

[MONGO]

it is not always necessary, some subs have the rubber gaskets around but can be used without also with no air leakage.