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Tabla is a musical instrument composed of two drums, the Bayan (left on picture) and the Dayan (right on picture).

tabla: bayan and dayan

A unique feature of the tabla is the tuning [black] paste called the gab, applied to the center of the dayan and off-center on the bayan. Typically when a membrane stretched over a resonating body is struck there is no clear sense of pitch because the sound produced is rich in inharmonic overtones. The gab when properly applied causes these inharmonic partials to be damped giving the dayan a clear sense of pitch when struck correctly.

(cited from this webpage; see also this Nature paper).

This explains why the black paste "gab" is added to the drum skins, however, it does not give any reasons why the Bayan's gab is off-centered on the Bayan. As it is always the case for Bayan and never for Dayan, I expect that the drum designers do it by purpose.

Q: Is there any physical reason to have the black load to be off-set on the Bayan? Theoretically, what would be the effect of this off-setting on the sound, if any?

Note that the skin of the largest one (Bayan) is far less stretched than the smallest one (Dayan) and the playing techniques are very different (for instance, see here for the largest drum and here for the smallest one).

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  • $\begingroup$ So have you analysed the vibrations of the output? Have you tested the sound waves produced by an ordinary drum and compared central hits to moving the hit point 1cm to the outer diameter each time? Of course you need a device to give the same input each time… $\endgroup$
    – Solar Mike
    Commented Jun 20, 2022 at 19:55
  • $\begingroup$ @SolarMike: this would require the drum designer to make "experimental" Bayan drums with black load at different positions. The location of the load is permanent, so it is not possible to test easily. Actually it is impossible if you are not a tabla maker. But could we guess the effect of the off-centering theoretically? $\endgroup$
    – Noil
    Commented Jun 20, 2022 at 20:05
  • $\begingroup$ What happened to "ordinary drum"?? $\endgroup$
    – Solar Mike
    Commented Jun 20, 2022 at 20:14

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Simply put, the blobs of paste act to damp out any vibrational modes which would have had mode maxima at that physical location. The energy applied to the drum then goes into other modes, presumably producing a desired sound.

This is roughly analogous to fingering a harmonic on a guitar string. When you pluck a string, the fundamental harmonic has minima at both ends and maximum at the half-way point. If you place a finger (gently, not a full stop) at that half-way point, the fundamental cannot excite so the energy goes into harmonic(s).

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