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From: John Woodgate
Subject: Re: audio line specifications
Date: Sun, 8 Dec 2002 05:48:44 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sun, 8 Dec 2002 06:29:37 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Vlad wrote (in
<email@example.com>) about 'audio line
specifications', on Sat, 7 Dec 2002:
>The source impedance affects harmonic distortion, intermodulation and
>response the same way it does to a speaker . The ratio between the
>impedance of a speaker or a headphone and the source impedance is
>called "damping factor"
This does NOT apply to headphones. The moving system is *resistance
controlled* - it is damped up to the hilt mechanically and needs no
>A pair of headphones or speakers connected to a an impedance of the
>same value . Example a 8 ohms speaker connected to an amplifier with
>an output impedance of 8 ohms has a damping factor of 1 and that is
>consider a very low quality system by today's standards.
>You only find that on low quality devices were maximum transfer of
>energy or spurious low frequency resonance is desired
You don't find it AT ALL. Your 'maximum transfer of energy' is way off
beam. That would mean half the power dissipated in the source and half
in the load.
>A good system today has a damping factor close to 100 .
>Yes, the output impedance of the amplifier is 100 times lower then the
>impedance of the speaker or in this case the headphones that in the
>majority of the cases are only miniature speakers.
This is not at all correct. A damping factor, which doesn't apply to
headphones at all, of 100 means that the source impedance (amplifier
output source impedance) is 1/100th of the voice-coil resistance, ***so
that the electrical damping is controlled very nearly by the voice-coil
resistance alone***. In other words, a damping factor of 100 gives a
damping resistance of 8.08 ohms. negligible difference from a damping
factor of 50, say, giving a damping resistance of 8.16 ohms.
This 'damping factor' scam has been exposed here several times. It was
first agreed as debunked by the person who invented it - Fritz Langford-
Smith, in 1947! Would you like a copy of his text?
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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