Re: Were there any 'high quality' early headphones ?
The headphones for audiometers were generally calibrated by coupling them into a capacitance microphone (made by B&K) in a soundproof box, then to a B&K signal level meter to ensure the actual audio output across the full range of audio frequency signals was standardized. The driver circuitry in the audiometer, could be adjusted, to compensate for the actual frequency response of the headphones so that the sound pressure level was correct at all audio frequencies. B&K also made suitable headphones. They must have had a reasonably flat response or else massive drive level adjustments would have been required across the audio frequency range, as I recall that was not the case.
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