Audio Tech Talk: Damping Factor

[Sarong1]

Some one asked me recently a relevant question on damping factor, here is one article that explain it in a more layman manner. Abstracted from http://www.crownaudio.com/pdf/amps/damping_factor.pdf

UNDERSTANDING DAMPING FACTOR

[/left]

Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They

keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing."

In other words, the speaker produces sound waves that are not part of the original signal.

Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope.

When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its

suspension. So that nice, snappy kick drum turns into a boomy throb.

Fortunately, a power amplifier can exert control over the loudspeaker and prevent ringing. Damping is the

ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor, which is load

impedance divided by amplifier output impedance. Let's explain.

If the speaker impedance is 8 ohms, and the amplifier output impedance is 0.01 ohms, the damping factor

is 800. That's a simplication. Since the speaker impedance and amplifier output impedance vary with fre-

quency, so does the damping factor. Also, the impedance of the speaker cable affects damping. Thick

cables (with low AWG) allow more damping than thin cables with (high AWG).

The lower the amplifier's output impedance, the higher the damping factor, and the tighter the sound is. A

damping factor of 1000 or greater is considered high. High damping factor equals tight bass.

How It Works

How does an amplifier control speaker motion? When the loudspeaker cone vibrates, it acts like a micro-

phone, generating a signal from its voice coil. This signal generated by the speaker is called back EMF

(back Electro Motive Force). It travels through the speaker cable back into the amplifier output, then

returns to the speaker. Since back EMF is in opposite polarity with the speaker's motion, back EMF

impedes or damps the speaker's ringing.

The smaller the amp's output impedance, the greater is the effect of back EMF on the speaker's motion.

An amplifier with low output impedance does not impede the back EMF, so the back EMF drives the loud-

speaker with a relatively strong signal that works against the speaker's motion. When the speaker cone

moves out, the back EMF pulls the speaker in, and vice versa.

In short, the loudspeaker damps itself through the amplifier output circuitry. The lower the impedance of

that output circuitry, the more the back EMF can control the speaker's ringing.

To prove it to yourself, take a woofer that is not connected to anything. Put your ear next to the cone and

tap on it. You might hear a low-pitched "bongggg" if the speaker itself is poorly damped. Now short the

speaker terminals and tap again. You should hear a tighter thump.

Damping factor varies with frequency. As you might suspect, damping factor is most important at low fre-

quencies, say 10 Hz to 400 Hz.

Edited December 22, 2006 by Sarong1

[Slonez]

This is what the designer (Steven Mantz) of your amplifier has to say (see attached).

I suspect what he said is true cos no/very few manufacturers nowadays emphasis high damping factor as a good design criteria.

High damping factor was the "IN THING" a decade ago where you find many amps with damping factor of 1000 or 2000.

Steven Mantz happens to be a renown amplifier designer for those of you who do not know.

Cheers!

Edited December 22, 2006 by Slonez

[Sarong1]

This is what the designer (Steven Mantz) of your amplifier has to say (see attached).

I suspect what he said is true cos no/very few manufacturers nowadays emphasis high damping factor as a good design criteria.

High damping factor was the "IN THING" a decade ago where you find many amps with damping factor of 1000 or 2000.

Steven Mantz happens to be a renown amplifier designer for those of you who do not know.

 

Yes you are right, once in a while, I will flip back what was written in the manual that came with the amp. But that was a bit too technical for some newbies to digest, and the someone that posed me the same question, happened to be a newbie as well.

 

No wonder I don't see so much of the manufacturer mentioning about damping factors nowadays. Thanks bro.

[Coolbreeze90]

Think this is a really good article on the damping factor...

 

Really explains it in the most simplest terms...

 

Maybe the administrators can think of coming up with a sub folder for audio tech talk??

 

it can be a good reference for newbs like mua to do some reading??

[Kermit]

ya ya...more audio tech talk pls...should have such discussions long time ago...many such parameters are seldom understood, which is maybe why many amp manufacturers don't even bother to tell you such things, THD, S/N ratio blah blah blah. Tell u also dun understand, bring you there too far...

 

Let's keep educating ourselves with such tech discussion!!! kudos.

[Bluemice]

the top part too cheem ...

 

OT a bit: the para on the RMS seems quite off, imo. the ( Root of 4)^2 example is way off...

as both parameters are of different units, can just write off in such simplistic manner.

 

any PE in electrical can comment ?

 

mice

[Sarong1]

More will come, I hope the moderator can keep a subfolder under "Audio Tech Talk" as sticky so that folks including me can continue to contribute and the knowledge wouldn't be lost.

[Ukexports]

alot of useful info ther

[Ractis]

I belong more towards the school of thought that damping factor isnt a really important metric of sound quality.

 

Anyway, another good article here talking about DF, when applied to passive vs active crossover network. In summary, it is saying that DF is greatly reduced when applied to passive x-over networks, hence it is advocating active x-overs.

 

http://sound.westhost.com/biamp-vs-passive.htm

 

Also, tube amps and class D amps tend to have lower DF, if this means anything at all :)

Edited January 21, 2007 by Ractis

[Kermit]

Bro, maybe you like to explain a bit more on why you believe DF isn't a really important metric of SQ? Perhaps we can gain some insights? You may have valid grounds to think so...interesting.

[Ractis]

The article bro slonez posted above explains it rather nicely. From theory, actual effective DF depends more significantly on the speaker/crossover resistance, so much so that an amplifier with DF of 20 or 2000 wouldnt make much difference

 

Practically, I have heard from tube amps to class D and class T amps that control the bass very well, hence I really do not think a high DF is a must for better control of the speakers.

 

For amplifiers, I personally would look at the s/n ratio, wattage at 1% thd and reliability features (fault protection, noise/turn on-off pop rejection, good heat management)

[Kermit]

oic. You're talking about the DF of amplifiers...fair enough. I tot u're saying in general that DF isn't really affecting SQ...got a scare...thanks for clarifying. Of cos, given a choice, amp with good DF is a good to have lah.