International Standard Reference Zero for Audiometers

Abstract

This is a detailed report on the technical activities of ISO's Technical Committee on Acoustics No. 43, Working Group on Threshold of Hearing, which led to the ISO Recommendation R389, "Standard Reference Zero for the Calibration of Pure-Tone Audiometers," November 1964. The activities described are the determinations of the transfer factors from loudness balancing experiments between the five earphonecoupler combinations in R389, the incorporation of the transfer data into the computation of the reference equivalent threshold sound-pressure levels (RETSPL) in R389, and the details of the weighting of the original threshold determinations. A statistical analysis estimates the average standard deviation of the RETSPL in R389 to be 2 dB due in large part to the variance in the transfer factors. The present USASI standards are definitely outside the ISO uncertainty limits at all frequencies. The standard deviation of the differences between adjacent columns in R389 (or the equivalence of the RETSPL for the different earphonecoupler combinations) was estimated to be 2.5 dB. To improve accuracy in audiometry, it is suggested that the variance due to the transfer factors be eliminated by agreement on one standard earphone type. ForewordThe working Group No. 1 on Threshold of Hearing, of ISO/TC43 on Acoustics, constituted itself as a body of technical experts in 1955 to arrive at a best value for an international threshold reference level for the measurement of hearing. The six members, all associated with laboratories carrying on researches into audiometry and the measurement of hearing threshold, were from Europe and the United States of America. They agreed early in their deliberations (1) to examine carefully all available published data from various laboratories on threshold levels expressed in physical terms, (2) to make additional threshold measurements to resolve any outstanding differences between laboratories, and (3) to carry on any measurements needed to place all the data on a common basis, such measurements to be made in the members' respective laboratories. Completion of these monumental tasks culminated in ISO Recommendation R389.The details of their efforts are recorded in Mrs. Weissler's paper. Each of the several members, some now retired, had an opportunity to comment on the paper in draft form. Chairman Ltischer aptly remarked: "Es geht daraus die grosse Grfindlichkeit der ISO-Untersuchung hervor, so dass an der Richtigkeit des vorgeschlagenen Standards nicht zu zweifeln ist." R•c•Am• K. Coo•:, Member

Equivalent threshold sound pressure levels (ETSPL) for Interacoustics DD 45 supra-aural audiometric earphones

“…For details see references [2] to [5] in the Bibliography ' . These references are (Cox & Bilger, 1960;Whittle & Delany, 1966;Weissler, 1968;Michael & Bienvenue, 1980). Thus it seems that the 5-dB ' error ' that is often seen with TDH 39 stems from this loudness balance equivalence and not from an uncertainty in real hearing threshold determinations.…”

An active free-field equalizer for headphones used in functional magnetic resonance imaging

“…Pure tones in third octave intervals between 63 Hz and 10 kHz were used as stimuli. This method is also similar to the loudness balancing procedure employed to compare different headphones during development of ISO 389 [10], as described by Weissler [11].…”

Development and Pilot Testing of Smartphone-Based Hearing Test Application

“…The results of hearing tests are quantified as the hearing level (HL) in decibels for each test frequency. HL is for a given ear at a specified frequency using a transducer, measured with an audiometer calibrated to reference equivalent threshold level (RETSPL) for air conduction [ 31 , 32 ]. For the calibration of audiometric equipment, its RETSPLs should be known to translate output sound level measured in units of dB SPL into dB HL.…”