From: paul@gaitlab1.waterloo.edu (paul j guy)
Subject: Re: Imped. Matching w/ Resistors?!
Keywords: damping amp
Organization: University of Waterloo, Waterloo,Ontario
Date: Wed, 15 Apr 1992 00:51:05 GMT

In article <1992Apr14.155623.7783@news.eng.convex.com> jgardner@convex.com (John B. Gardner) writes:
>
>I've seen this several times in this thread - that high damping is
>critical for accurate reproduction.  Well hold on just a second here,
>most tube amps, which "audiophiles" drool over and sell there Saabs
>to purchase (;-), have very LOW damping factors.  In fact, the
>Carver Silver Seven's which cost about $17,000 and are pretty much
>universally revered in the audiophile ranks, have a damping factor of 
>6!!!  Yes, that's 6!!! Compare this is to solid state amps which are
>typically >200.
>
>So, are we flapping our jaws in the electronic breeze, or could someone
>explain how an amp with a damping factor of 6 can sound good, despite
>what everyone is claming here.
>
 Well, this got my curiosity up, so I went and measured the DC resistance
of all the loudspeakers I could get my hands on, ranging from tweeters to
squawkers to woofers, high quality (Tannoy monitors), to mid-fi Japanese
stuff, to despicable little radio speakers. Surprise ! they all measured
between 60% to 100% of their rated impedance. In other words, there is
an effective PURE resistance in series with the 'part' that converts
electrical energy to sound. Measurements at DC will eliminate ANY reactive
(inductive or capacitive) component. Now, I have measured the AC component,
and it starts equal to the DC resistance at very low frequencies, hits
a peak (1.5 times or usually way more the nominal impedance), drops back
to the normal impedance, and then slowly climbs with frequency (all this
for a single speaker, it's a bit crazier with crossovers).
  If there is already about 60% of the nominal impedance in series with
the speaker, you raise a good point. Suppose I have an 8 ohm speaker.
Typically the speaker itself will contribute about 5 ohms series resistance.
A good cable will have a fraction of an ohm. With a damping factor of 6  
(@ 8 ohms) the amplifier will appear as .75 ohms (looking into the amp's
speaker output). What good is there having a damping factor of 100 when that
.08 ohms (looking back to the amp) is pretty well swamped by the 5 ohm
resistance of the speakers ?
  I suspect that the high damping factor is only good in that it gives
someone an idea of the huge amount of feedback in the amplifier. Now
whether thats a good point in respect to the sound quality is another issue.
Truly, it's really difficult to give a lot of feedback in a classic tube
output because of the hairy phase shifts in the output transformers. The
low-tech solution is to run triode output and get the inherent low output
resistance of triodes reflected through to the speakers, without excessive
feedback. I have always wondered what some of the exotic tube amps (like 
the Flutterman) sounded like, since they used no output transformer. These
monsters used a 6336 tube that was rated 1 amp plate current. (I'm
getting off the topic).
  The issue of 'parasitic' or extraneous resistances or reactances in relation
to amplifiers and cables also brings us close to the subject of many a 
cable war.......
  

-- 
-----------------------------------------------------------------------------
Paul J Guy			work phone:519-885-1211 ext 6371  
paul@gaitlab1.waterloo.edu	home/FAX/message:519-576-3090
pguy@watkin3.waterloo.edu	..remember...bullshit baffles brains...
Xref: sparky rec.audio:7389 rec.audio.pro:489