Acoustic pressure field alongside a manikin’s head with a view towards i n s i t u hearing-aid tests

Abstract

The frequency responses of hearing aids measured in a free field differ from those measured on the head of a person or a manikin due to the scattering of the sound by the head and the torso. In order to compare and interpret the response of hearing aids located on the head at various frequencies it is necessary to know precisely the spatial pressure distribution. The amplitude and phase of the acoustic pressure were measured alongside a manikin's head in increments ranging from 2 to 5 mm with frontal sound incidence . The acoustic driver was located in front of the manikin at distances of 1.0 and 3.5 m from the ear-canal axis. The test frequencies were the octave band center frequencies from 0.5 to 4.0 kHz and the third-octave band center frequencies t•rom 4.0 to 8.0 kHz. The sound pressure level varies smoothly, as a function of position, alongside the head for frequencies equal to or less than 2.0 kHz. At frequencies equal to or greater than 4.0 kHz the pressure level changes rapidly with position. Particulary severe pressure minima were found to exist around the pinna at 6.3 and 8.0 kHz. The smoothing effect of test signals using pink noise of 6% and 29% bandwidth on the acoustic pressure variation alongside the head and behind the pinna is also shown.

Real Ear to Coupler Differences in Children and The Effects of Hearing and Microphone Location

“…The results showed an increase in sound pressure level at 1500 and 2000 Hz, and at frequencies above 7000 Hz , with large standard deviations at all frequencies. However, the results of this study show large inconsistencies with previous studies (Bentler, & Pavlovic, 1989;Madaffari, 1974;Kuhn & Burnett, 1977). There are several possible explanations for the inconsistencies.…”

“…Figure 8 shows a plot of the average hearing aid microphone location effect in dB as a function of frequency. The aid mic effect results from Kuhn & Burnett (1977) Figure 7. Mean real ear to coupler difference for 14 ears.…”

Adapting Hearing Devices to the Individual Ear Acoustics: Database and Target Response Correction Functions for Various Device Styles

“…Generic transfer functions can be derived from average data of human subjects or dummy head measurements. Bentler and Pavlovic (1989 , 1992 ) have compiled responses from the free and diffuse field to the eardrum and microphone locations of three standard hearing device styles (In-The-Canal, ITC; In-The-Ear, ITE; and Behind-The-Ear, BTE) that were pooled from a large number of separate measurements reported in the literature over several decades ( Killion, Berger, & Nuss, 1987 ; Kuhn, 1979 ; Kuhn & Burnett, 1977 ; Madaffari, 1974 ; Shaw, 1974 , 1980 ; Shaw & Vaillancourt, 1985 ; Wiener & Ross, 1946 ). More recently, directionally resolved Head-Related Transfer Function (HRTF) measurements on a dummy head with an ear simulator that included a pair of three-channel BTE hearing aids were presented by Kayser et al.…”

Cochlear Implants

“…The head has the greatest effect at all frequencies, the pinna affects the pressure differences at frequencies above 2500 Hz, and the torso has the least overall influence (Kuhn and Burnett 1977;Kuhn 1979;Gaunaurd and Kuhn 1980). Depending on the sound frequency, the attenuation of the velocity or pressure (intensity) due to the head can improve the SNR when the two are spatially separated.…”