Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!decvax!decwrl!glacier!mips!sjc From: sjc@mips.UUCP Newsgroups: net.analog,net.audio Subject: Re: Cables Message-ID: <568@mips.UUCP> Date: Tue, 22-Jul-86 00:31:01 EDT Article-I.D.: mips.568 Posted: Tue Jul 22 00:31:01 1986 Date-Received: Wed, 23-Jul-86 00:17:59 EDT References: <1383@voder.UUCP> <126@druxo.UUCP> Distribution: na Organization: MIPS Computer Systems, Sunnyvale, CA Lines: 65 Xref: decwrl net.analog:990 net.audio:3105 > If Mark will forgive me, I have re-posted his article on impedence vs. > frequency differences. This is an interesting article from the perspective > of the amount of flames it DIDN'T receive: when it was demonstrated that > skin effect was insignificant at audio frequencies there were a flurry > of "told-you-so, cables don't make a difference" articles posted. I am > awaiting the responses from these folks disputing Marks measurements. > > OK tech weenies, here are some MEASURED impedances vs frequencies for some > > real audio cables on the market... > > > 2 Meter Interconnects (Impedance in ohms) > > Brand 5khz 10khz 15khz 20khz > > Randall .012 .040 .067 .114 ... > > > 10 foot speaker cables (Impedance in ohms) > > Brand 5khz 10khz 15khz 20khz > > MIT MH-750 .025 .074 .122 .162 ... My memory of EE100 is so rusty it would be presumptuous for me to claim to be a tech weenie, but when I read the original posting I thought the author was throwing in the towel! The numbers are so darned small (except for the "off chart" readings, which I can't judge without seeing the chart) that they suggest that if there _are_ audible differences among these interconnects, they're due to something other than the magnitude of series impedance. Seriously, 1. If the input of your well-designed amplifier presents a uniform impedance across the audio spectrum, then the magnitude of series interconnect impedance is less important than its uniformity with respect to frequency. An interconnect whose impedance is a uniform 100 ohms would not affect the frequency response, but the Randalls (the worst shown), whose impedance varies from .012 to .114 ohms, would: given a typical amplifier input on the order of 1e4 ohms, the perturbation would be (ignoring phase, which the posting has regrettably not provided for us) roughly 20*log10(1e4/((1e4)+(1e-1))) = -0.00009 dB. 2. Assuming a 1-ohm speaker, then the .1 ohm variation in impedance for the MIT cables (the worst shown) could perturb the frequency response on the order of 20*log10(1/(1+.1))= -0.8 dB, which may well be audible. That's a good argument for using 16 gauge zipcord, which will not exhibit this problem. 3. To claim that "cables can't make a difference" is to climb out on a shaky limb. One can surely concoct a cable having sufficiently weird reactive properties to make an audible difference. A less shaky limb is "a cable can sound different from 10 feet of 16 gauge zipcord only by being worse". > > ...Some quotes in the literature: "Cables tend to accentuate the > > portion of the spectrum where their impedance begins to rise, while > > higher frequencies are attenuated...Note that deviation of series > > impedance is caused by skin effect and inductance." This literature contradicts itself. Never mind that Kirchoff's voltage law suggests that rising cable impedance should attenuate rather than accentuate; assume that this literature is right. Then skin effect (which raises the series impedance) would _accentuate_ the highs. -- ...decwrl!mips!sjc Steve Correll