Recent times have seen the introduction of small spherical arrays whose usefulness as sound intensity probes is the focus of this paper. The presented probe consists of a spherical shell, 30 mm in diameter, housing four 14 in. microphones arranged in a regular tetrahedral configuration. Classical formulae may be used to estimate the sound intensity vector, as may methods based on spherical harmonics decomposition. Results are shown to be comparable to those obtained from classical sound intensity probes. The existence of an analytical model for a plane wave's diffraction about a sphere provides a means for adopting common optimization techniques for potentially improving the intensity vector estimate, however. This paper examines the validity of non-linear least squares optimization in conjunction with the proposed spherical sound intensity probe when placed in the following sound fields: (1) a simple plane wave; (2) a plane wave corrupted by noise; and (3) multiple incident plane waves. Under certain conditions, the probe is shown to greatly extend the operational frequency range of classical sound intensity probes. The optimization algorithm is found to lack robustness against deviations from plane wave conditions, however.

The international standard IEC 60318-4 specifies an occluded ear simulator for testing headphones, earphones, hearing protectors, hearing aids etc. The standard specifies a specific microphone type which limits the dynamic range of the coupler, such that it is not possible to measure very low levels or very high levels. Additionally, the standard 711 coupler is often interfaced to a pinna simulator incorporated in a Head and Torso simulator as per IEC 60318-7. This interface has traditionally been implemented as a cylindrical, straight ear canal simulator. This makes the fit of many modern in-ear headphones and hearing protectors problematic and unrealistic. By using low noise microphones instead of the standard microphones, the coupler can be used for measuring extremely low sound pressure levels such as noise floor, low level distortion or microphonics. Conversely, by using low sensitivity microphones, the coupler can be used for extremely high level measurements—useful for testing active and passive attenuation ratings of hearing protectors. Moreover, using a vast database of 3D human ear canal scans, a new pinna and ear canal simulator is proposed that will greatly improve measurement accuracy and repeatability on products going on or in the ear.