keith_correa
Well-Known Member
+1.
Foam helps dissipate the energy of the driver back wave into heat through friction caused by offering resistance to the wave. So the energy of the wave when it emerges from the back of the foam [which is fixed to the wall] is reduced. But it is still present, and can excite the walls of the enclosure causing unwanted resonances - hence the use of damping material for the enclosure like bitumen sheets, rubber etc. which mass load and deaden the enclosure walls and prevent resonances. These waves are also reflected off the walls and interfere with the forward/backward movement of the speaker cone so all the more reason to decrease them.
You cannot use enclosure damping material [rubber sheets, bitumen etc.] interchangeably with foam, rockwool, glasswool etc. because they perform different functions though they complement each other. Unless of course you use something like NoRez which performs both functions.
The usage of polyfill for this particular application increases the perceived volume of the box changing the "Q" downwards from originally designed. But I think, room gain of ~+3dB to ~+9dB [depending on the frequency] kicks in thus making up for the change in "Q". But that is a function of your room and not of the speaker. So please experiment with no polyfill and putting in little amounts of polyfill and then freezing on the usage of polyfill.
Note: all this is as per my [limited] knowledge so feel free to correct me if I have misstated something.
