Circumaural earphones provide improved coupling when compared with the standard supra-aural audiometric earphone (TDH 39, 49) [Kruger et al., J. Acoust. Soc. Am. 67, S91 (1980); Villchur, ibid. 48, 1387–1396 (1970); Erber, ibid. 44, 555–562 (1968); Shaw, ibid. 39, 471–479 (1966)]. The variability of real-ear responses of the TDH-49 earphone, audiometric circumaural earphones (Villchur-Telephonics Model 566, Beltone Auraldome & Audiocap), a hi-fi circumaural earphone (Sennheiser HD 430) and an insert phone (Knowles BP 1869) was assessed. Probe microphone frequency response measurements in the ear canal were used to evaluate intrasubject and intersubject variability with the above transducers (10Ss: 5♂, 5♀ 5 repetitions/condition: transducer, subject versus experimenter placement) and were referred to either the diffuse field or the tympanic membrane. Real-ear response variability is contrasted with KEMAR response variability [Kruger et al., (1980); Ciechanowski and Cooper, J. Am. Aud. Soc. 2, 88–94 (1976)] and with coupler calibration variability appropriate to the transducer (NBS 9-A coupler, Penn State flat plate coupler, Zwislocki coupler). The nature of the variations in real-ear responses with these supra-aural, circumaural, and insert earphones will be discussed in terms of calibration, probe microphone placement, coupling to the head, and earphone placement. [Work partially supported by AOS.]
Circumaural earphones have been shown to provide improved coupling when compared with the standard supra-aural audiometric earphone (TDH-39,49; calibrated with a standard NBS 9A coupler) [E. Villchur, J. Acoust. Soc. Am. 48, 1387–1396 (1970); N. P. Erber, J. Acoust. Sec. Am. 44, 555–562 (1968)]. A standard coupler is needed for circumaural carphone calibration. A flat-plate coupler has been designed for calibration of a circumaural earphone (Telephonics model 556) for hearing testing [P. L. Michael and G. R. Bienvenue, J. Acoust. Soc. Am. 66, 944–950 (1976)] and proposed as a standard coupler for circumaural calibration [J. Prout, ANSI S3.37, Working Group Draft (1979)]. The use of this flat-plate coupler for calibration of circumaural earphones for audiometry (Telephonics model 556, Beltone Auraldome and Audicup, and Phonic Ear) and for hi-fi listening (Sennheiser HD430, Koss VFR and HV1LC, and AKG 240) was studied systematically. Repeated intra and intertester comparisons, and control of earphone position suggested guidelines for reducing variations. The utility of this flat-plate coupler as a means of checking stability of earphone frequency response is supported. Differences in earphone responses, effects of leakage, and resonances will be demonstrated and discussed. [Work partially supported by AOS.]
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