Fleisher & Fastl
Fell, Kessel und Gestell der Orchesterpauke *
HEAD, KETTLE AND STAND OF THE ORCHESTRAL TIMPANI
Beside the head of the timpani, its non-active components such as the kettle, stand and additional parts are in the focus of the considerations. In continuation of former studies the mechanical vibrations of these parts of the timpani were investigated. First of all, the actual source of the timpani sound was identified. It was found that the sound originates exclusively from the head and not from the kettle of the timpani. This finding is based on intensity measurements and numerical computations. Nevertheless, it has to be kept in mind that the kettle plays an important passive role. It acts on the acoustic radiation and on the fine-tuning of the intervals of the head’s vibration frequencies.
Experiments as well as computer simulations using Finite Elements and coupled Finite Elements/Boundary Elements have shown that the kettle is vibratory, but to a much less extent than the head. Further experiments have confirmed that the same holds for the stand and the remaining components of the instrument. The vibrations of these parts do not constructively contribute to the generation of the timpani sound. On the contrary, there are indications that they can downgrade the acoustic signal by shortening the sustain of partial tones. Within narrow frequency regions, the main tone, quint or octave happen to decay much faster than defined by the radiation resistance as the only damping mechanism.
It is suspected that resonances of distinct parts of the instrument stand can convert vibration energy into heat which, in consequence, is no longer available to the generation of sound. It could be detected that the quint and octave decay irregularly fast when a resonance of the kettle edge is excited by the vibrating head. Future experiments are to show if the timpani sound sustains longer and more uniformly when resonance effects of non-active components of the timpani are avoided.