--- In Walter Knapp <>
wrote:
>As one who has done hearing tests on many thousand young adults
>(military recruits and draftees from the central valley of
California) I
>can say this is a very simplified view of what folks hear.
...
Of course, the hearing threshold is not the same for all
frequencies. The minimum threshold of about 0dB is restricted to the
frequency range of our speech between about 500 Hz and 6 kHz.
Nevertheless, the sound level units are based on the average hearing
threshold (0dB corresponds to 20=B5Pa). It is obvious, that our
hearing thresholds may also vary in the short term. A very loud rock
concert or an extreme bang may also shift the hearing threshold
temporarily. Surprisingly, the self-noise level of many microphones
is frequency-depended too. The MKH series microphones match the
human hearing threshold curve very well (there is an increase of the
self-noise outside the speech range).
>Mother nature may have designed very good 'microphones', but they
are
>very easily damaged. I also believe that they are not
omnidirectional.
Sure, a single ear is not an ideal omnidirectional 'microphone'.
Perhaps, the directional characteristic of a single ear is similar
to something like a cardioid. But both ears together should be more
or less omnidirectional. This is of course simplified, but it would
be impossible always to cite the associated textbooks when
discussing a certain issue ;-). At least the ears are not comparable
to shotgun microphones (which have the lowest available self-noise
of around 5 dBA). Even the omnidirectional MKH 20 is not really
omnidirectional for all frequencies. Its getting more directional at
higher frequencies. Our ears seem to behave in the same way. It is
this frequency-dependency which also helps us to locate sounds
(despite of the time-of-arrival or phase differences between the two
ears and other effects as defraction around our head).
Raimund
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