Notes on Tombak Acoustics

Shahin Mohajeri ©2003

Tombak follows the same basic rules as other goblet drums:

See also Matt Hannafin's article on Playing strokes and technique

Acoustics of striking the drum

• The width of the contact area determines the modes (in the tombak skin, not in air) that can be excited. Thus techniques with one fingure can excite higher vibrational modes than slaps(on the same region of drum).
• The length of time that the finger is in contact with tombak skin is important. Any mode with a period less than the contact time will be strongly damped. Thus hard part of finger or other hard things that strikes the skin or shell of tombak produce a higher tone color than soft part of finger.
• The player has some control over the duration of the contact by the way that he plays and so has extra control over the sound (by damping the sound of techniques very soon after striking).
• Putting a piece of cloth over the tombak skin dampen upper modes and so produce a lower, duller, sound.
• The player can also have control by hitting the drum at different locations:
  Striking Different locations on tombak skin will tend to excite some modes more than others. Remember that striking will most excite modes with anti-nodes near the strike point and least excite modes with nodes at that point. This is very important factor in
  Striking near the center and the center of the tombak skin (like the TOM technique) will emphasize the circle shaped modes, especially the fundamental. Since the center is a node for the non-circle modes and they will hardly be excited at all. The sound tends to be lower in tone color and duller when struck near the center.
• Hitting near the edge of the tombak will tend to excite the higher modes since they have anti-nodes out towards the edge. The tone color will be sharper and more percussive, with many upper partials. So, Pelang is a technique with sharp tone color in tombak. The more near the edge,the more sharpness of technique.
• If the pelang hits the rim of a tombak under the skin, it produces the sharpest tone color of tombak sound without changing its pitch.
• Tombak skin has an additional degree of freedom that we can not see in non-membranophonic 2 or 3-dimensional instruments. The player can alter the tension of the drumhead while playing the tombak to alter the modes and so the sound while the note is sounding.
• Tombak playing traditions involve altering the drumhead tension by pressing on the drumhead with some fingers while drumming with others. This changes the pitch of the sound of tombak and not muting it.
• The tombak player can also alter the sound of the instrument by lightly resting a finger on the head; this will force a node to appear where the finger rests. This will alter the sound by allowing only those modes to sound, which have a node at that point.
  The kind of skin used for tombak has a great effect on the sound timbre of it.
  

Tombak shell

• The shell of tombak plays a significant role in determining which modes contribute to the sound.
• 1) Simple drums with no body are called Frame Drums, example is the daf. If we delete the shell of tombak the acoustical behavior of the skin is like a frame drum.
  These produce pure drumhead modes with no modification from the body.
• 2) Next is a family of cylindrical drums with cylindrical bodies either open at the bottom or, more commonly, closed with a second drumhead. These include the snare drum, the tenor drum, and the bass drum.
  The body has broadly resonant normal modes that emphasize certain regions of the spectrum but the sound is basically the non-harmonic sound of a drumhead.
• 3) The Tympani have hemispherical bodies made of metal with a hole in the bottom.
  The metal bodies make the resonances much sharper than the wooden bodies of the tenor drum family. This means that the kettle plays a larger role in determining the sound structure. In addition, the hole in the bottom is chosen to offer significant resistance to air moving in and out of the drum at low frequencies. This damps the lowest mode of the drumhead and forces it to operate primarily in its upper modes. The interactions with the resonant cavity make the upper modes fairly harmonic and the Tympani have reasonably clear pitches.
• 4) There are lots of different kinds of drums with wooden or similar vegetable resonator bodies such as Conga drums, djembe drums, the tabla and mrdngam of India and Tombak.
• In these, the resonator is not as active as in the Tympani but does significantly determine the sound structure and give pitch to sound of instrument . The drums vary from strongly pitched to loosely pitched depending on the importance of the resonator.
  Tombak shell with its belled-neck (NAFIR) Is a Helmholtz resonator which produces a low pitch and hum like sound , when striking the center of tombak skin. The pitch of this hum sound depends on the length of nafir and its inner diameter. Small inner diameter of nafir produces hum sound with lower pitch.

Shahin Mohajeri

See also Matt Hannafin's article on Playing strokes and technique

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