Is there a way to calculate the damping factor of an amp/receiver, when it's not listed?

[triode17]

Damping factor is a rather useless term because it is measured at the speaker terminals. Once you add speaker wire, even the best wire, the damping factor drops considerably. Like from 300 to 30.

 

[Gibsonian]

Some of us use oversized speaker cable and avoid passive components and retain much of the published DF for our bass drivers.

Technique makes for articulate and tight bass.

 

[nj pheonix]

After reading this article, i tend to question just how important damping factor really is
http://www.roger-russell.com/wire/damptoole.htm

 

[damacman]

After reading this article, i tend to question just how important damping factor really is
http://www.roger-russell.com/wire/damptoole.htm

Written by none other than Floyd E. Toole. Problem is that the science he uses to prove his findings contradicts the conjecture surrounding the topic ...

 

[damacman]

Some of us use oversized speaker cable and avoid passive components and retain much of the published DF for our bass drivers.

Technique makes for articulate and tight bass.

Read the article two posts above ...

 

[Gibsonian]

Read the article two posts above ...

I've already read those and digest several others. It's a simple thing, and can easily be calculated on anyone's system. I also have EE on my team that helped me understand this simple concept.

 

[gadget73]

Tube amps with output transformers don't like having the load removed.

which is why I specifically said to not do it on a tube amp

Working this out on a tube amp can be a little more difficult just because of how loading works on one. If you load it lightly vs loading it properly and check for voltage difference, you're not only measuring damping, but the results of changing the effective load on the output tubes. Smarter people than me probably know an accurate way of doing it, but considering most tube amps rarely cross too far into the double digit range anyway I doubt it matters all that much.

 

[wyn palmer]

which is why I specifically said to not do it on a tube amp

Working this out on a tube amp can be a little more difficult just because of how loading works on one. If you load it lightly vs loading it properly and check for voltage difference, you're not only measuring damping, but the results of changing the effective load on the output tubes. Smarter people than me probably know an accurate way of doing it, but considering most tube amps rarely cross too far into the double digit range anyway I doubt it matters all that much.

Yes, I understand. I was just adding an explanation as to why it was the case- it's not generally understood, believe me- and offering a way around so that measurements can be made.
I also don't know why the measurement thing is tricky- essentially you want to know the output impedance of the amp- and that, I believe is essentially independent of the load- even for a tube amp.
The results of changes in damping factor have been analyzed before.
https://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response
This really just deals with the mechanical aspects, and shows time constants for various possible speaker parameters- and shows decay times of, I believe, c. 7 time constants- which is about 60dB of decay- or below audibility. The decay times are 40ms and above, but only change by a factor of 2 with damping factor.
For the back emf case- the opposing voltage produced obeys Lenz's law (V=-Ldi/dt)
A typical sub woofer has c. 2.5mH of inductance I believe, so for a 1 ohm source resistance the opposing voltage decays with a TC of 2.5ms, 7 TCs are c. 20ms so the normal decay of the loudspeaker dominates.
I hope that this helps to quantify the effect of damping factor.

 

[gadget73]

The way of measuring it seems like it would have to be different. For an SS amp I'd set the output to some level with no load, then connect a load and measure it. The difference in voltage would lead me to output impedance from some simple Ohm's law math. With a tube amp you can't do that. Unloaded is it's own problem, but if you load it at say 100 ohms, take a reading, then load to 8, the resulting voltage change isn't just the output impedance of the amp. You're also changing the plate to plate load on the output tubes, and that may throw a wrench into it. I don't know that it really matters if you aren't checking anywhere near max output but it just seems like it adds another variable into the mix. I've never measured any of my own, and I'm reasonably sure none of them have a published DF or output Z to check my measurements against to see if the method works out.

 

[BinaryMike]

The way of measuring it seems like it would have to be different.

Different, but not terribly complex. Just load the amp with, say, nine ohms, measure load voltage, then add a parallel resistor to bring load resistance down to, say, seven ohms, then measure load voltage again. Calculate delta E over delta I, and you've got the amp's Z internal. You do need an accurate AC voltmeter for this test, but for tube amps, the need isn't extreme.