17 Mar
2014
17 Mar
'14
1:56 a.m.
On Sunday 16 March 2014 20:19:50 Lorenzo Sutton did opine:
On 16/03/14 19:39, Gene Heskett wrote:
An Altec M-21b, new in about 1955 or so, probably 40 years out of
production now has usable response beyond 20Khz. The PZM, a similar but
electret powered condenser mike, new in about 1985 IIRC also goes up into
that range.
On Sunday 16 March 2014 14:25:14 Ralf Mardorf did
opine:
Can anyone point out a commercially available microphone used in the
audio recording domain which will actually pic frequencies above 20 kHz?
On Sun, 2014-03-16 at 08:58 -0700, Len Ovens
wrote:
That I think is a personal call Ralf, primarily because at 48 Khz,
your anti-aliasing filters had better be very very good brick walls
by the time you get above 24Khz in input content I would mix the project at 48k or 96k
Why 96 KHz? 48 KHz doesn't cause any issues, but already provides
best sound quality. Likewise can anyone point out any commercially
available speaker used in
the audio reproduction domain which will actually reproduce frequencies
above 20 kHz?
Is the Altec Lansing 075 ring radiator tweeter still available? I once saw
some scope photos of the output of an M-21b, 3' away & on axis of the sound
output of the 075 driven by approximately a watt of a square wave at 25Khz.
The square wave was still recognizable. In the '50's we would set an 075
in the center pocket of the Cobra Horn of a JBL Hartsfield speaker, a huge
corner horn that was very good before we did that, and made it raise the
hair on the back of your head real if your eyes were closed and a 30ips
recording of the Dukes of Dixieland was playing from 10.5" reels on a
Berlant-Concertone tape deck. The only thing that gave it away was the
tape hiss, a good 68db down. There may yet be a few of those around, but
very few since it sold new in the 1950's for $750. That tweeter added
another 100 to the price.
The Hartsfield was fairly efficient too, better than the Voice at the time.
We could hit 130+db in the front room at Woodburn Sound Service in Iowa
City Iowa, with a 10 watt rated Fisher amplifier driving it. And I am
talking 130 very painful db's.
If the audio produced is made for fruition of humans
it makes absolutely
no sense to try and capture or reproduce anything above 20kHz, and for
average individuals 15kHz would probably more than enough.
And in case anyone is tempted to state that even if we don't hear them
frequencies above 20kHz influence the way we hear or 'perceive' music,
please also attach any _scientific_ study/paper/evidence (e.g.
large-scale blind tests etc. not anecdotal evidence) to such statement.
This is, according to your definition, anecdotal. I spent 2 years Chiefing
at a radio station in No. Kalipornia, who had one of those ultrasonic
motion detector burglar alarms. It wasn't working so the first thing I did
was fix it, dead battery. Then I had to rig it with a disabling switch to
shut off the power amp that drove the piezo speakers in it. I couldn't
hear it as such, but my ears would feel like I had just walked into a high
pressure chamber that yawning wouldn't fix, and in 5 minutes I had a
splitting headache. So it wound up with a switch that the owner could turn
on when he left for the day. To this day I can walk into a shop with one
of those things and tell them if its running right, surprising many a shop
owner who thought the installation was a secret even from his employees.
FWIW, they aren't worth it because of the false alarms they generate when
the wind is blowing against those huge plate glass front windows which can
move 1/2" or more in a good spring breeze. Sets them off every time. To
the LE people, they are the little boy crying wolf and are ignored.
Lorenzo.
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Cheers, Gene
--
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