Sound Pressure Spectra of a Muted Cornet
James E. Ancell · The Journal of the Acoustical Society of America · 1960
Acoustic spectra of a cornet have been measured with the instrument equipped with several mutes of types used mainly in dance orchestras. Data are presented showing the sound pressure levels of the first 10–15 partials of the instrument when fitted with each of the mutes. The instrument was blown naturally by a cornetist, with an attempt to obtain a normal characteristic tone for each mute. The sound spectrum of the muted instrument is compared to that of the open or unmuted instrument. The mutes tend to exhibit the same formants for several different notes, indicating resonance phenomena in the acoustic networks. The measurements were made by playing the instrument in a dead room, and recording the sound on tape, with a condenser microphone and a magnetic tape recorder of professional quality. The sounds were then analyzed by playback through a heterodyne wave analyzer. Two of the mutes, the Harmon and the Solotone, are equipped with cylindrical aluminum tubes, open at both ends. The formants for these mutes display families of resonance peaks corresponding to the calculated open pipe frequencies. These resonances are also observed when the mutes are driven with an electroacoustic transducer. All of the mutes themselves act as Helmholtz resonators at 200 to 300 cps, which is, however, in the frequency range of considerably reduced output when fitted to the instrument.