Is it nessesary to use foam/insulation when building a subwoofer box?
insulation or polyfill is normally used in sealed boxes that are smaller than the manufacturer of the sub recommends. The reason we use it is to diffuse the backwaves so that the soundwaves don’t bounce back off the inside of the box and hit the back of the speaker cone. When this happens it causes the cone to vibrate and distorts or partially cancels out the sound. If the sealed side of your bandpass box is smaller than the recommended size for the sub, filling the sealed side will help. I never use polyfill in ported boxes, it is not necessary.
