TECH TALK
The perception of sound
In order to understand the acoustics of any installation, it’s important to understand how sound is perceived and calculated. Martin Altenbokum of Petra Engineering delves into the technical and mathematical science of sound.
A
sound source oscillates and causes small pressure fluctuations in the surrounding air – or gas or fluid – causing particles to start moving outwards. With the mass and compressibility of the air, the fluctuations are transmitted to the listener’s ear.
The pressure fluctuations are referred to as sound pressure p. The sound pressure is superimposed on the static atmospheric pressure p0
which depends on time and space. The sound source radiates a spatially distributed sound field with different instantaneous sound pressures at each moment. The observed sound incident at any point has two main distinguishing attributes - timbre and loudness.
The physical quantity for loudness (or amplitude) is sound pressure p, measured in N/m2
.
The physical quantity for timbre is frequency f, measured in Hertz (Hz) or cycles per second, 1Hz = 1/s.
Our human hearing range starts at about 16Hz and ranges up to 16000Hz or 16kHz. The ultrasound is above that frequency range and the infrasound below it, both of them being of technical interest, too.
A sound incident that can be described by a sine curve in the time-domain is called a pure or harmonic tone. A harmonic tone can only rarely be observed in natural sound conditions.
24 October 2019
www.acr-news.com
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