Damping Factor and Transient Response

[Verdinut]

Thoughts on an Amplifier Damping Factor and Transient Response of Speaker



Some say that an amplifier's damping factor is irrelevant for all purposes. I beg to disagree.



An amplifier's output impedance, that is damping factor, can have an effect on how a speaker's moving mass responds faithfully to the program material fed to it. Please bear in mind that, at 4 ohms, the damping factor is also divided by two as compared to the published specification which is usually based on an 8 ohm speaker load. The amplifier's damping factor is obtained by dividing the speaker impedance by the internal output impedance of the amplifier.



The transient response of a speaker cone depends on several factors. These are:

1. The Qts of the speaker: This is affected mainly by the ratio of the coercivity of the magnet to the moving mass of the transducer. With a set moving mass, the stronger the magnet, the lower is the Qts figure, and this situation favors an excellent transient response. In a closed enclosure, this figure is not as important as in a vented one, because of the entrapped air pressure which acts as a damper.

But if you drive a speaker with a high moving mass to magnet coercivity ratio in a bass-reflex enclosure, with a tube amplifier, or even a McIntosh solid state amplifier designed with an output transformer (added resistance), those amplifiers having a high output impedance, you risk obtaining a very poor transient response.

2. Use of an inductance in series with the speaker in a passive crossover. The resistance of the inductor is added to the internal resistance of the amplifier and there goes most of the original damping factor. The use of two power amplifiers, one for the woofer and one for the high frequency drivers preserves a good part of the low resistance of the amplifier, provided that the cable connected between that amplifier and the woofer has a low resistance. This configuration is called bi-amping and an active crossover is required between the preamplifier and the two power amplifiers to divide the frequencies among the transducers. Another advantage of the bi- amplification is that you have a more efficient woofer (less resistance in series).

3. Resistance of the speaker cable. This factor depends of course on the size of the wire (AWG 14 as an example) and the length. For serious audiophile listening, one should use no smaller than gauge 14 and preferably use a bigger wire, at least gauge 10, when driving a 4 ohm woofer, because of the higher currents necessary to drive such driver.

NOTE: IMHO, THERE IS NOT MUCH POINT IN BI-WIRING SPEAKERS. Should you suspect a poor transient response, you would get quite better results by just attaching both cables together in parallel and connecting them to only one speaker terminal. That way, you might get a noticeable advantage with half the cable resistance, more so since your speakers use passive crossovers.

 

[TheWarrior]

Damping, Damping Factor, and Damn Nonsense
by Floyd Toole

 

[Verdinut]

Your comment just shows that you know nothing about the mechanics of a loudspeaker!

 

[Swerd]

Your comment just shows that you know nothing about the mechanics of a loudspeaker!

Welcome to Audioholics Verdinut.

I have to say that your comments above reveal far more about you than it does about amps or speakers.

 

[mtrycrafts]

Your comment just shows that you know nothing about the mechanics of a loudspeaker!

No, It shows that DF is irrelevant, period. Better people that you, it seems have shown this to be true.
You'd have to have a DF of about 10 or less to matter and probably closer to about 4.

You better have some hard facts here not just conjectures. You have evidence that it matters?

Here is another reference for you to ponder:

http://cartchunk.org:8080/audiotopics/DampingFactor.pdf

 

[TheWarrior]

Welcome to Audioholics Verdinut.

I have to say that your comments above reveal far more about you than it does about amps or speakers.

No, he's right, I misspelled Damping.... was just too focused on the Damn Nonsense

 

[slipperybidness]

Your comment just shows that you know nothing about the mechanics of a loudspeaker!

For MODERN Solid State Amps, the damping factor is pretty much the most useless spec on the spec sheet. It can safely be ignored by the end user.

If you are talking about Tube Amp technology, then the DF may become relevant to the conversation.

I can provide literature references from Amplifier Construction Books if needed.

 

[PENG]

Damping, Damping Factor, and Damn Nonsense
by Floyd Toole

Crown used to make a big deal about this but since they became part of Harman they might have changed that tune, or at least tone it down.

 

[TheWarrior]

Crown used to make a big deal about this but since they became part of Harman they might have changed that tune, or at least tone it down.

That's funny, I was not aware of that! From a casual glance, it looks like they make no mention of damping factor anywhere. Guess they decided to be professional!

 

[PENG]

That's funny, I was not aware of that! From a casual glance, it looks like they make no mention of damping factor anywhere. Guess they decided to be professional!

I guess they cleaned things up on their website so you won't find anything easily now. If you are curious about what they used to say, you could probably find something in the manuals for the older models, or some tone down stuff hosted by 3rd parties such as this one

 

[Chu Gai]

Here's an older article on DF by Richard Pierce with some math. In general, amps with low output impedance like SET's or OTL'S, when hooked up to a speaker will have a frequency response that mirrors to some extent the impedance profile of the speakers.

 

[mtrycrafts]

Here's an older article on DF by Richard Pierce with some math. In general, amps with low output impedance like SET's or OTL'S, when hooked up to a speaker will have a frequency response that mirrors to some extent the impedance profile of the speakers.

That's even a better article than one of his others.
So far 0.1 dB has not been shown to be audible and 0.2 only under very special circumstances.
So, around DF20 and less, maybe.

And, a thought came to me that DF varies over the frequency band of the speaker beyond the nominal impedance. So, that change RP was talking about is more difficult to hear over a narrower band.

 

[PENG]

To be clear, I linked one of Crown's article just to show how Harman might have influenced them, as it would seem that Crown no longer advocates the need for their exceptionally high DF on their website; and it is difficult to find related articles from their previous publications.

 

[mtrycrafts]

To be clear, I linked one of Crown's article just to show how Harman might have influenced them, as it would seem that Crown no longer advocates the need for their exceptionally high DF on their website; and it is difficult to find related articles from their previous publications.

Yep, I think it was clear enough.