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From: michaelk@tekmdp.UUCP (Michael Kersenbrock)
Newsgroups: net.audio
Subject: Re: 75 Ohms at the amp ??
Message-ID: <2276@tekmdp.UUCP>
Date: Tue, 4-Oct-83 14:53:37 EDT
Article-I.D.: tekmdp.2276
Posted: Tue Oct  4 14:53:37 1983
Date-Received: Fri, 7-Oct-83 06:32:58 EDT
References: whuxk.284
Lines: 15

Your speaker cable does not start to show transmission line effects
until the the length of the cable approaches 0.05 wavelength (more or less) of
the highest frequencies transmitted down it.  The cable's "characteristic
impedance (e.g. 75 ohms for RG-59)" is of no significance until the
length is an appreciable fraction of the wavelength.  The wavelength
of 20Khz in coaxial cable (assuming a velocity factor of 0.66 which is
typical) is about ** 6 MILES **.  If your speaker cables are an apreciable
fraction of this length, you have other problems.
   The reason preamp leads use "coax" cable is for shielding of
low-level high-impedance circuits.  Speakers are high-level low-impedance
circuits (that are driven by a balanced cable anyway).

Mike Kersenbrock
Tektronix Microcomputer Development Products
Aloha, Oregon