Acoustical behavior of a bass drum
Thomas D. Rossing · The Journal of the Acoustical Society of America · 1987
The bass drum is one of the loudest instruments in the orchestra. Its two large membranes may be set to equal tension, but more often the batter head is tuned to a higher tension. The sound spectrum contains many peaks that can be related to the vibration modes of a membrane. The low tension of the heads plus the strong coupling via the enclosed air lead to a large frequency difference (about 112 octave) between the two (01) modes associated with in-phase and out-of-phase motion of the heads. Sound decay rates for most modes are slightly greater when the two heads are at the same tension.