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 Post subject: I thought damping factor was important in amps.
PostPosted: Sep Thu 16, 2021 5:14 pm 
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Was working on this McIntosh MC2100 amp and needed the service data. HiFi Engine had it, and the specs on this amp only shows a damping factor of 14! Is this what audiophiles mean by the "warm sound" output transformer amps have?! I was always told that the higher damping factor the better.


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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Thu 16, 2021 8:29 pm 
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That's one of the things that determines the sound of an amplifier. Yes, vacuum tube amplifiers tend to have lower damping factors than solid-state. Some speakers, especially acoustic-suspension, demand a high damping factor otherwise the base will be "liquid," another way of saying poorly damped. A bass transient will linger. Other speakers, such as bass-reflex or open-back, won't care.

-David


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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Thu 16, 2021 11:04 pm 
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IAW the "AUDIO CYCLOPEDIA", the practical damping factor depicted in amplifier specs is not realized, due to the resistance in the voice coil of the loudspeaker (and the resistance of the connecting cables). During the mid '50's, some companies, including McIntosh, had amplifiers with adjustable current feedback (or damping) to in theory, overcome this.

According to "AUDIO CYCLOPEDIA", the actual damping factor using an amplifier without "Variable Damping", was typically less than 1.33.

Charlie


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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Fri 17, 2021 1:48 am 
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Most speakers are designed to operate properly under these conditions since that is how they are usually used. You can mess up the damping by having too much resistance in the connecting wire, hence the usual recommendation to use heavy wire.

There were a few amplifiers made that had current output rather than voltage. Then the resistance of the connecting wire and voice coil didn't matter. But they had to be used with special speakers that were designed for this service. An ordinary speaker would be completely undamped electrically.

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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Fri 17, 2021 7:41 am 
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There are two explanation here:
Part 1:
THE DAMPING FACTOR DEBATE
by George L. Augspurger, James B. Lansing Sound Inc.
https://butleraudio.com/damping1.php

Part 2:
DEFINING "DAMPING FACTOR"
by John L. Murphy
Physicist/Audio Engineer
https://butleraudio.com/damping2.php

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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Fri 17, 2021 2:57 pm 
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Damping factor is the inverse of output impedance (an output impedance of one Ohm is a damping factor of 8 for an 8 Ohm speaker). The lower the output impedance, the less speaker impedance variations matter. Most speakers have a large variation in impedance vs. frequency, which would result in a large variation in output v. frequency with a high impedance source. And most speakers are designed to give the flattest response with a low source impedance. But how low? A damping factor of 10 will allow a variation of less than 1/2 dB on a speaker varying from 5 to 50 Ohms - probably not audible. Higher is "better", just like lowering distortion from .01% to .005% is "better" - only for bragging rights.

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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Fri 17, 2021 3:17 pm 
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I recommend looking at the PART 2 reference in the post above. I think that explains the significant bass difference heard from a large acoustic-suspension speaker system connected to a vacuum-tube amplifier and then a solid-state unit.

-David


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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Sat 18, 2021 9:26 am 
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dberman51 wrote:
I recommend looking at the PART 2 reference in the post above. I think that explains the significant bass difference heard from a large acoustic-suspension speaker system connected to a vacuum-tube amplifier and then a solid-state unit.

-David

It seems like the nature of any passive crossover networks placed between a given amplifier and the drivers in a loudspeaker will complicate the equation. Probably a good reason to use active crossover networks.

This makes me wonder now, what about servo controlled amp / loudspeakers, as are mainly used in woofer and subwoofer applications? Isn't this closer to actual damping control of cone travel, overshoot, ringing and so forth? How well does this approach work?
Seems to me it should work well (if properly applied engineering-wise).

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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Sat 18, 2021 9:53 am 
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dberman51 wrote:
That's one of the things that determines the sound of an amplifier. Yes, vacuum tube amplifiers tend to have lower damping factors than solid-state. Some speakers, especially acoustic-suspension, demand a high damping factor otherwise the base will be "liquid," another way of saying poorly damped. A bass transient will linger. Other speakers, such as bass-reflex or open-back, won't care.

-David

That is indeed very interesting. At one time I had one of the old Fisher tube amps with "variable damping" control. I'm guessing it was made in the mid to late 1950's.
I played around with it enough to conclude it didn't improve or degrade the sound to much extent. My loudspeakers were large ducted port bass reflex types. Now I know why, they didn't care.

So if variable damping in tube amps was the way to improve control of acoustic suspension woofers, did this feature fall out of favor due to the general improvements in amplifiers with time, or was their need displaced by higher power solid state types?

There are obviously late model tube amps manufactured, but the old Fisher and a few of its siblings are the only ones I have seen with variable damping control. So why did this feature mostly go away? Could be related to improvements in loudspeaker technology?

Or, a little bit of All The Above... ?

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 Post subject: Re: I thought damping factor was important in amps.
PostPosted: Sep Sat 18, 2021 6:07 pm 
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Location: Rochester NY USA
The term damping factor is misleading - since the speaker DC resistance is many times the output impedance of most amplifiers, cone motion damping won't change until damping factor approaches 1 so DF 10 vs 100 won't make a difference. The largest effect is the uneven frequency response due to the varying impedance of the speaker. Most speakers are designed for the flattest frequency response with a constant voltage (low impedance) source - or a high damping factor. If bass is "boomy"with low DF it's because the amplifier delivers more power into the higher impedance at the speaker's bass resonance. Same will occur at higher frequencies as the impedance increases due to its inductance. This is the main reason radios generally had a capacitor across the output transformer - the pentode amplifier has a high output impedance (DF <<1), so its output rises as impedance rises. Negative feedback lowers output impedance, but few radios used it until the '50s. Triodes have a lower output impedance (DF~3) and were the only choice for "hi fidelity" until negative feedback was widely used.

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