Acoustical Test Sources
audioXpress|January 2023
The choice of a sound source for acoustical testing and reporting is decisive and should be determined according to the applications. Let’s explore the characteristics and benefits of available sources for acoustical measurements.
Richard Honeycutt
Acoustical Test Sources

Acoustical testing can be classified according to the test setup: Response testing involves a sound-level meter (SLM) and/ or a real-time analyzer (RTA) to measure the sound level and/ or spectrum produced by a source. Stimulus-response testing incorporates an acoustical source whose sound output is known, and measurements of the resulting sound field are made in order to determine how a room or other enclosure affects the sound. Sound-system performance, reverberation, and echo testing exemplify this type of test.

The second type of testing requires a source with a certain directivity (polar response) and frequency response. The directivity of an acoustical source depends upon its physical characteristics and size.

A source that is small compared to the wavelength of the sound being investigated is called a point source and is omnidirectional. Directivity can be represented in any of several ways.

One way is a simple graph of the beamwidth plotted versus frequency. The directivity graph of an omnidirectional source would be very boring: a horizontal line showing a beamwidth of 360° at all frequencies. Another way is to represent the radiated sound field as a balloon whose shape and coloration represent the sound pressure level SPL) radiated in each direction.

The third way is a section drawing with a vertical or horizontal cut through the balloon. Such sections often show multiple lines, illustrating the variation in directivity with frequency.

Figure 2: The horizontal (upper) and the vertical (lower) directivity of the human voice vary with frequency; the standard deviation is indicated by the colored shading. (Image Source: Christoph Pörschmann, Johannes M. Arend: "Analyzing the Directivity Patterns of Human Speakers," www.researchgate.net/publication/343344151)

Source Directivity

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