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wrote:

"Arny Krueger" wrote in message
...
"Pooh Bear" wrote
in message

So what do you think it is that makes damping factor
*unimportant* ?

It's not that damping factor isn't important, its that it is an odd way to
express the underlying physical parameter which is amplifier source
impedance.

For openers, damping factor isn't an amplifier parameter, its a parameter
that is also strongly dependent on load impedance. Unfortunately the
underlying physical parameter remains pretty much unchanged, regardless of
load impedance.

With good modern amps, the amplifier's damping factor is generally so high
that it gets swamped by all sorts of things including voice coil DCR and
speaker wire DCR.

It means a lot more with tubed amps.

Which is probably why it was ever expressed as a value at all. When they
came up with it, tubes were dominant, then came good more accurate, less
volatile, transistors. :-)

Whether tube ( valve ) or transistor - damping factor ( a reciprocal measure of
amplifer output impedance ) is important.

A low damping factor means that an amplifier cannot adequately control speaker
resonances or the back emf caused by transients.

From the aspect of resonances - a 'poor' i.e. low damping factor will tend to
result in a possibly initially flattering bass rise around speaker resonance
with typical ported enclosures. This is well documented. The resulting bass is
also poorly controlled though leading to 'farty bass'.

The inability of an amplifier to control the back emf from the motor coil will
also result in signal degradation.

Note that the resistance of the cabling between amp and speaker affects damping
factor too. That's one reason why damping factor *in isolation* is misleading
perhaps. The resistance of the speaker cable appears in series with the
amplifier output impedance. This is why speaker wiring should be of the largest
practical gauge in order to reduce its resistance.

Having said that..... it was IME rare for tube amps to have better damping
factor than say ~ 15-20. Translating to an output impedance of maybe a few
hundred milliohms to an ohm. Likely the cable resistance made little difference.

Modern SS amps can have output impedances easily as low as in the tens of
milliohm region. This makes cable resistance much more critical in comparing one
with another ( along with bi-wiring etc... ).

Graham