Acoustics

What it means

Acoustics is the study of sound: of its generation, its propagation and its perception. For music it provides the physical basis of what the ear distinguishes as tone, sonority and noise. A tone arises when a body vibrates regularly and passes this vibration on to the air as a pressure wave; how fast it vibrates determines the pitch, how strongly, the loudness.

Musical use

Three connections are especially important for those who make music. First, the harmonic series: a vibrating body vibrates not only as a whole but at the same time in halves, thirds and further parts; the partials thus arising determine the tone colour and explain why the same A sounds different on the violin and the clarinet. Second, the simple numerical ratios: the octave, fifth and fourth correspond to the ratios 2:1, 3:2 and 4:3, and the simpler the ratio, the calmer the combined sound — on this rests the difference between consonance and dissonance. Third, the incompatibility of pure intervals: twelve perfect fifths and seven octaves do not yield the same note, and the difference is called the Pythagorean comma. Every tuning system is a way of dealing with this problem.

To this is added room acoustics, which decides how a sound reaches the listener: reverberation time, reflections and absorption alter balance and clarity often more strongly than many a subtlety of the performance.

For musicians three sub-fields are especially important. Room acoustics asks how reverberation, reflection and absorption form the sound in halls and churches. Instrument acoustics investigates how strings, air columns and membranes vibrate and why instruments sound different. Psychoacoustics, finally, describes how the hearing perceives pitch, loudness and tone colour. Added to these are applied fields such as building acoustics and electroacoustic transmission.

Performance practice

Use the overtones when intonating: when a combined sound is pure, the beats cease — this coming-to-rest is a more reliable criterion than any tuning device. In an ensemble tune by the sound, not only by the display. And adjust to the room: in a reverberant room fast passages need more clarity and less tempo, in a dry one more carrying power in the tone.