[ARC5] zero

[Richard Knoppow]

----- Original Message ----- 
From: "J. Forster" <jfor at quikus.com>
To: <provero at ct.metrocast.net>
Cc: "Richard Knoppow" <1oldlens1 at ix.netcom.com>; "Bruce 
Long" <coolbrucelong at yahoo.com>; <kgordon2006 at frontier.com>; 
<arc5 at mailman.qth.net>
Sent: Friday, August 17, 2012 4:40 PM
Subject: Re: [ARC5] zero


> I've seen pics of a Japaneese sound detection machine like 
> an array of
> tubas on a truck body.
>
> Best,
>
> -John
>
     There were sound detectors developed during WW-1. I 
will try to find details but the microphones were of the 
hot-wire type which will respond to very low frequencies. 
They were used on large horns such as described above. The 
horns act both to increase the intensity of the sound and to 
make the detector directional.  At the time of the war about 
the only microphones which were known for the hot-wire also 
called a thermophone, used mostly for calibrating sound 
pressure intensity, carbon microphones, and early condenser 
microphones.  Carbon microphones are noisy and not suitable 
for reliable detection of low level sound but both 
thermophones and condenser microphones are.  Of the two the 
thermophone was probably the least finicky.
     These devices were used more for locating artillery 
than for finding aircraft.
     I know there is a fairly complete description in one of 
the books on acoustics I have but I can't remember exactly 
which one.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com