The Use of Intensity Techniques for Noise Source Identification in Small Machinery

Intensity techniques are now widely used for two purposes: sound power determination and source identification. The work described in this presentation illustrates an application of the latter type. As part of a noise control program for a small domestic appliance, a narrow‐band intensity measurement system was developed based on a face‐to‐face microphone probe, a two‐channel FFT analyzer, and a personal computer. The probe was used to measure the nearfield normal intensity on planes parallel to the device\u27s major surfaces. Graphical display of these data allowed the radiated sound field to be visualized at any desired frequency. Further, it was possible to distinguish between various types of component sources by examining the field in detail. For example, airborne sound that is generated within the device and radiates to the exterior through apertures or “leaks” was plainly visible. Radiation from the exterior surface of the device resulting from direct vibrational excitation of the surface and from structure‐borne vibration could also be identified. Knowledge of this type was used to advantage to guide the noise control treatment program. Nearfield surveys conducted after these modifications yielded a particularly vivid indication of the effects and benefits of the individual modifications