Spectral changes in the tom-tom related to striking force

This study has investigated the question how the radiated spectra of a tom-tom changes with striking force. Five tom-toms of different size were recorded at four dynamic levels (pp, mp, mf and ff) and their averaged spectra analysed. It was observed that the number of modes excited increase with playing strength, seen in the radiated spectra as a characteristic change in slope for higher frequencies. At louder levels, there is also an initial frequency shift that causes the lower partials to gain width as well as amplitude. Measurements of the contact between drum stick and the drum head showed a decrease in contact time with increasing playing strength. * Summary of thesis work for the degree University Diploma in Electrical Engineering, Lower level, at KTH College of Engineering, Haninge. Introduction Research on drums is a wide field in which a few selected topics have been studied in detail, like the kettle, bass and snare drum (Fletcher & Rossing, 1991). The theoretical foundations of vibrating membranes are well known since long (Rayleigh, 1877), but many applied cases have still not been examined. An interesting question is whether the radiated spectra of drums change with excitation force like other traditional instruments. An increase in high-frequency content could be expected as it is a common behaviour of most traditional instruments, particularly well studied for the wind instruments and the piano. In this study, the radiated spectra of drums played at different dynamic levels are analysed. The type of drum examined has been the tomtom, a common part of the drumset and frequent in many music styles. Membranes, drums, and pitch The basic components of a drum are a shell and one or two membranes. The frequencies of the normal modes of vibration for an ideal membrane are given by