Measuring headphones (Al Bregman )

Subject: Measuring headphones
From:    Al Bregman  <BREGMAN(at)HEBB.PSYCH.MCGILL.CA>
Date:    Sat, 5 Feb 2000 15:48:55 -0500

Dear List, A colleague of mine, Andr=E9 Achim, at the University of Quebec in Montr= eal is doing a project studying the interfering effects of tinnitus on hearin= g. He asked me about how to calibrate headphones with the precision acceptab= le to audiology journals. He is. If anyone has advice on this, rather than replying to me would you kindly e-mail him at the following address: : achim.andre(at) Thanks, Al -------------------------------------------------------------------------= --- ----------- Is a surrogate head required to calibrate an auditory threshold evaluations system, and why? I am setting up a system to assess and compare auditory threshold to pure tones modulated by different amplitude envelopes for frequencies up = to 16 kHz. My PC-based system implements a Von B=E9k=E9sy audiograph using t= he DirectX technology. I selected Sennheiser HD-615 circumaural dynamic headphones, rated for -3= dB from 10 to 30000 Hz, and am about to calibrate the whole system in SPL units. I understand that the interest is in the pressure received at the ear drum and that a flat plate coupler [used by Al Bregman] would miss th= e resonance characteristics of the ear canal. I do not have a realistic artificial head coupler. My question is: Wouldn't it be quite satisfactory to calibrate the system with a flat plate coupler and than correct this calibration for the resonance characteristics of a representative ear canal? I presume that = the required correction would simply be a difference curve, in dB, previously obtained in calibrating the same earphones with a flat plate and with a h= ead model. If this is reasonable, can anyone provide me with the gain characteristic of the ear canal as a function of frequency (i.e. the difference curve between calibrations with the two coupler types) for a fairly wide range of frequencies? If this appears unreliable, can anyone explain why this approach should be avoided, and what approach to use with my Sennheiser circumaural headphones? Please reply to: achim.andre(at) -------------------------------------------------------------------------= --- ---- Albert S. Bregman Emeritus Professor Dept of Psychology McGill University Montreal, QC Canada H3A 1B1 Tel: +1 (514) 398-6103 Fax: +1 (514) 398-4896

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