Category: 8. Sound Intensity, Measurements and Determination of Sound Power, Noise Source Identification, and Transmission Loss

During the 1980s and early 1990s, extensive efforts were made in North America by an ANSI committee and in Europe by an ISO committee to develop a standard for the determination of the sound power of sources using sound intensity measurements. The ANSI Committee was concerned with developing an engineering grade standard to assist users…

It has been found that, in field determinations of sound power, the sound intensity method is superior to the sound pressure method because it is affected less by background noise and the measurement environment. This section describes real sound power measurements on an automated packaging machine using both sound intensity and sound pressure methods. Sound…

Some of the most common practical applications of sound intensity measurements are now discussed. In 1978, Chung and Pope demonstrated that using a two‐microphone probe that sound intensity could be measured both (i) at fixed points in the near field (2.5 cm) from a loudspeaker source and (ii) at 12 points on a hemisphere of 1 m radius…

The measurement of sound intensity is much more complicated than the measurement of sound pressure. In general, it requires the simultaneous measurement of sound pressure and particle velocity. This needs the use of at least two transducers. There are currently three main methods in use: The first p–p method is well established and has been in use…

As already discussed, in a one‐dimensional pure tone plane progressive wave the sound pressure and particle velocity are everywhere in phase for all values of time. The same situation exists far from idealized point sources of sound (monopoles, dipoles, quadrupoles, etc.) since the wave front curvature decreases and the surface becomes almost planar (flat) far…

Many different types of sound fields are encountered in practice. The sound field near to a simple point sound source has certain well‐known characteristics. However, sound fields generated by many simultaneously operating independent sources have much more complicated characteristics. A reverberant sound field, which is created when sources operate in spaces with hard wall surfaces,…

Sound fields are usually described in terms of sound pressure, which is the quantity we hear. However, sound fields are also energy fields, in which kinetic and potential acoustic energies are generated, transmitted, and dissipated. The acoustic energy in a sound field is not only of interest theoretically, but it is of practical importance as…

It is hard to realize that engineers and scientists have only been able to make quantitative acoustical field measurements with transducers for the last century. It is true that many scientists had previously been making qualitative acoustical studies. Osborne Reynolds describes the use of bells, the human voice and ear in his studies of acoustical…

Sound intensity is a measure of the magnitude and direction of the flow of sound energy. Although acousticians have attempted to measure sound intensity as long ago as the early 1870s, the first reliable measurement of sound intensity did not occur until over one hundred years later in the late 1970s. Then the convergence of…