Sound source location using microphone arrays

Source localization using a ‘beamforming’ microphone array, sometimes called an acoustic camera, is now a standard measurement technique in the aircraft industry, where the measurements are used to provide information on sources of engine noise and airframe noise. 

Microphone array

A linear microphone array.
Two-dimensional arrays are also used.

Applications include engine test beds, wind tunnel tests on airframe components and measurements on aircraft in flight, where the method has the significant advantage that it provides a means of source identification for the aircraft operating under ‘real-world’, aerodynamic conditions.

There are many other potential applications of the method, including, for example, use in the automotive industry to track noise sources during a vehicle drive-by.  ISVR Consulting has the knowledge and experience to use the technique successfully for many other problems. Recent studies have included the identification of an unknown source of high-frequency tonal noise during a static aircraft test and a demonstration project to distinguish between motor noise and work-piece noise in a pillar drill (see below).

Other applications include leak detection in pressurised systems and localization of dominant noise sources around industrial plants.

 

Noise sources in a pillar drill

A pillar drill

A pillar drill

Separating the noise radiated by a workpiece from that of the machine itself is a common problem, sometimes necessitating intricate tests using sound intensity measurements, or temporary enclosures of parts of the machine, and so this is a potentially useful application of the array measurements.

The photograph on the left shows a typical bench-mounted pillar drill which is used in our workshop.

First, running the motor without drilling provides the first noise map presented below, which we have superimposed over the image of the drill.  This map is for the 6.3 kHz band. It is clear that the motor is generating the noise in this band.

Noise sources of the pillar drill - idling

Noise map around the pillar drill when motoring

Next, making a measurement while a small metal sheet is being drilled shows how the dominant noise in this frequency band is now radiated from the workpiece.

Noise sources of the pillar drill - drilling

Noise map around the pillar drill when drilling a metal workpiece

 

Publication:
Noise source identification using microphone arrays.  M.G.Smith, K.B.Kim and D.J.Thompson  reprinted from Proceedings of the Institute of Acoustics Vol. 29. Pt.5 2007 (pdf 450KB)