Xref: utzoo sci.electronics:10671 misc.legal:15916 misc.misc:9366
Path: utzoo!attcan!uunet!dino!ceres!zaphod.mps.ohio-state.edu!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics,misc.legal,misc.misc
Subject: Re: Phone Harassment
Summary: Utter nonsense about inflicting sound injury through the telephone
Message-ID: <3666@kitty.UUCP>
Date: 17 Mar 90 16:12:06 GMT
References: <21849@watdragon.waterloo.edu> <13746@watcgl.waterloo.edu> <1990Mar16.001210.27602@ddsw1.MCS.COM>
Distribution: na
Organization: Recognition Research Corp., Clarence, NY
Lines: 42

In article <1990Mar16.001210.27602@ddsw1.MCS.COM>, benfeen@ddsw1.MCS.COM (Ben Feen) writes:
> I saw an interesting method of getting back at phone harrassers - It
> involves a car battery, a large capacitor, and some wiring thru your phone.
> I'm not gonna go into it, but if you go through a certain sequence, you can
> send a surge through Ma Bell's wires, straight into the offender's
> handset..........

	The above reference is utter nonsense.  At best, the discharge of
a capacitor into a telephone line will provide a *mild* click at the far
end.

	500-type or equivalent telephone sets which employ a passive network
all have a varistor across the receiver element, with such varistor being
specificically designed to suppress clicks.  Telephone sets employing
electronic networks attenuate clicks using a combination of amplifier
limiting with varistors and/or diodes.

	A continuous sound above a certain level will also be limited at
the receiving telephone by the above means.

	The auditory threshhold of pain is generally considered to be
140 dB SPL (Sound Pressure Level), which is approximately equivalent to
2,000 microbar (dyne/cm^2 for CGS fans).  Since the volume of air between
the eardrum and the receiver diaphragm is "considerable", since there
is considerable air "leakage" between the ear and a telephone handset,
and since the diaphragm displacement in a receiver element is rather
small, it is virtually impossible to achieve 140 dB SPL even if the
receiver element were directly driven by a power amplifier (obviously
not found in a telephone).

	Furthermore, there is NO WAY for sufficient energy to be transmitted
through the switched telephone network into a loop-powered telephone set
with a handset to create such a sound pressure level.

	While one can no doubt create a sound which will make *some* people
at the receiving end *uncomfortable*, it is improbable that any pain, let
alone auditory damage, can be inflicted.

<> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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