you will have to read foreverbumpins tutorial, its kinda complicated.... the chamber of it area wise has to be the same area as the subs cone, then depending on the subs Fs, u get the lengts. mine is 40, so, 1130[speed of sound or something] 1130/40, 28.25, this the wavelength in ft, then divide by 4 to get quarter wave[length], so a chamber 7.0625 ft long. confusing, i know.