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In Reply to: RE: Tube vs. Solid State for Planars posted by Taki888 on June 27, 2020 at 10:30:22
Damping is highly overrated. Basically it is the ratio of the speaker impedance divide by the amplifier output impedance. Assume you have a 4 ohm speaker and an amp with impedance of 0.01 ohm (SS). You would think the DF is 400 but because of the DCR of the cable and crossover needs to be added the actual DF might 4/2.01 or 2. With tube amps the output impedance 4,8,16 depending on the settings. So the actual DF of tube amps is about 1 - almost the same as an SS - and inconsequential.
If you want to get a higher DF, try vertical biamping so there is no crossover and the cable is short (placing the amp next to the speaker). Unfortunately the 1.7i can not be biamped because of the serial XO.
So the short answer to your question as to why DF is not frequently mentioned is that DF is immaterial.
FWIW I have always used (40 years) a tube pre with an SS amp. You should really look at a Class D, they work well with Maggies and over the last 10 years have improved. I am using a W4S ST-500 with my 3.7i.
I married the perfect woman - the downside is that everything that goes wrong is my fault.
Edits: 06/27/20 06/27/20Follow Ups:
The output impedance of a tube amp is not 4,8.16 depending upon the settings. :) Those are just transformer taps. The actual output impedance is lower than those numbers.Using an amplifier with significant output impedance, it's definitely possible to skew speaker frequency response looking into a varying impedance load of many loudspeakers.
The traditional way of defining "damping factor" was to include the speakers DC resistance in the denominator of the calculation. Thus you had a lower number than a simple speaker-impedance divided by amp output resistance calculation.
DF = Speaker impedance / (Amp output impedance + Speaker DC resistance)Dave.
Edits: 06/28/20 06/28/20
Thanks for the correction. However my point remains. A published high DF (normally 8 ohms divided by the output impedance) means very little in an actual setup. If this were not so, I doubt that many would prefer tube amps with their low DF over SS.
I married the perfect woman - the downside is that everything that goes wrong is my fault.
The point is.....most speaker systems are nowhere near a constant 8 ohm load. They have a varying impedance curve that can wobble all over the place owing to resonances, crossover alignment, driver inductance rise, etc, etc, etc.Damping Factor, per-se, is not the issue, but rather those varying impedance loads causing frequency shifts when using amplifiers with high-ish output resistance. This can be somewhat significant and this is what accounts (primarily) for subjective differences between various tube amplifiers relative to solid-state amps.
This is easy to experiment with. Just take your nice solid-state amp and add a 2 ohm resistor in series with the output. A sensitivity loss, obviously, but you will hear a tonal balance change as well.
Dave.
Edits: 06/29/20
The rule I've been working with for years is that any REAL value over maybe 50 is fine. That is going to include everything from amp to speaker / crossovers, cable and so forth.
An amp which is say.....500.... on the bench will never be so in a real system where it counts.
Too much is never enough
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