The Principle

In many acoustic measurement tasks, the local distribution and strength of sound sources is of interest. For such tasks, an acoustic camera is often used. This makes it possible to determine which part of a sound source causes which sound emission. An acoustic camera consists of a microphone array with an optical camera and a computer for evaluation. By using beamforming algorithms, a source map is obtained from the pressure signals recorded by the microphones.

Figure 1 shows the microphone array with 63 microphones and an optical camera, behind it the measurement electronics and the PC workstation.

Figure 1: Acoustic Camera (Total structure)

In beamforming algorithms, a measured sound field is compared with the simulated sound field of a point source. In the simulation, the location of the point source is varied over the geometric area in which the actual sound source is assumed to be (= sampling plane). If the assumed source position matches the actual source position, the result shows a higher value at this position than if there is no or only little match. Strong sources also have higher values than weak ones. The calculated source map is overlaid with the optical image and provides information about the location and intensity of the sound source(s) as an "acoustic image".

Figure 2 illustrates the beamforming principle and shows exemplary measurement results.

Figure 2: The beamforming principle

Application in Practice

Compared to the stationary system used in the laboratory, mobile acoustic cameras, some of which are pluggable, are often used in practice. A typical application is the

• Searching for sound sources in urban areas

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