What are the origins of the theory that timpani bowls are harmonic cavity resonators? The misconception of the bowl being a true air cavity resonator perhaps started innocently enough as many the early instrument developers and musicians did not have an understanding of musical acoustics and assumed through deduction that the timpani bowl served the same function as that of the body of many instruments. It wasn’t until 1877 that Lord Rayleigh properly identified and documented the function of the bowl as it related to the acoustic properties of timpani.
The sound quality of the early instruments has been documented as being less than desirable so any new innovation was heralded as a triumph. Sebastian Virdung, Musica getutscht (1511) refered to kettledrums as “monstrous rattletraps” (Ungeheure Rumpelfässer) and “the ruination of all sweet melodies and of all music.” Curt Sachs, in his The History of Musical Instruments, translates this phrase as “rumbling barrels.”27 As with the evolution of any instrument, timpani have seen many changes through the centuries.
Early in the seventeenth century as the pairing of timpani and trumpets began being utilized more regularly in indoor concert music, there was a growing desire to acquire more pitch, resonance and musical sensitivity from the instruments. Most iconographic evidence (open to speculation) suggests that for outdoor playing, the drums were generally struck dead or slightly off-center. This method of producing pitch (striking the drum dead/off center) is in fact how noted musicologists Edmund Bowles 53 and John Michael Cooper 29 believe timpani produced pitch until the very end of the 18th century. This purportedly yeilded a sound with a very percussive attack with a quick decay, and little discernible pitch.
Fine for voluminous and percussive outdoor playing where only a relative sense of pitch was needed, but not practical for the concert hall. It would seem logical that a different playing spot (i.e. near the edge as done today) might have solved the problem, but that was not the characteristic sound of the instrument at that time. Why?
Generally, poor mechanical tolerances of the bowl and tensioning system along with inconsistent membrane thicknesses made it impossible to adjust the instrument in a manner where the drum was able to produce a clear and sustained sense of pitch. By striking the drum near the edge, the player excites the preferred diametric modes, which when aligned correctly, can produce a sustained sense of pitch. For an instrument where the principal tone and upper partials were not able to be uniformly adjusted because the membrane did not vibrate evenly, when struck near the edge, the sound produced would be extremely discordant. An alternative was to strike closer to the center or slightly off center, which would still excite mode 1,1 to some extent, but not the upper preferred modes. The result was a sound with a slight sense of pitch, but little or no sustain or resonance.
One solution to the lack of resonance was to insert a sound-bell inside of the drum, which would vibrate as well as collect and focus the vibrations of the head and funnel them through to an opening in the bottom of the drum. The appendage to the inside of the bowl first appeared in the German-speaking regions of Europe in the early seventeenth century and was called Schalltrichter, literally sound-bell. The funnel-shaped bell was intended to increase the resonance of the drums. It was clearly established as an essential part of the instrument by the mid-eighteenth century because J.P. Eisel’s Musicus autodidactos (1738), states that when the drum is hit, the Schalltrichter vibrates back and forth, helping to create a “resonant reverberance” (saussenden Nachklang). It apparently was a continued success because according to Ben Harms, “They were a common feature in timpani fabricated in Germany for close to 300 years, ca. 1600-1880.”28
Schalltrichter Removed from Timpani
courtesy of The National Music Museum
Schalltrichter Inside of Timpani
courtesy of The National Music Museum