Importance of high Damping Factor in high-end power amp?

[bordeno]

I'm sure this has been discussed before, but I'd like some info/ opinions here.

First off, what exactly IS "Damping Factor?" I know it has to do with woofer control, thus it affects the perception of the bass in your system, but how? Also a high damping factor is supposedly better, but how important is that spec when you're comparing power amps? What do manufacturers do to a power amp to give it a high damping factor?

Most Japanese receivers/ amps from the '70s did not have high damping factor, with numbers like 60 or so.

Many separate amps boast of high DFs; apparently some don't attach alot of importance to it, for example the Yamaha MX 600 I have only has a 70 damping factor but its still a nice amp.

Start waxing eloquent, comrades...

 

[mhardy6647]

Damping factor is the ratio of the (nominal) speaker/load impedance to the output impedance of the power amplifier.

(Donning Nomex suit): The magnitude of the damping factor (as long as it's more than about 10) it is largely superfluous.

Very high DF is "generally" indicative of large (maybe excessive) amounts of negative feedback in the amplifier.

caveat emptor. Try before you buy.

 

[the-real-mandak]

Read here: http://www.classic-audio.com/marantz/mdampingfactor.html

 

[motorstereo]

I just swapped amps that have very similar power ratings to drive my big polks. An adcom gfa555ll to a bose 1800. The bose has a damping factor of 40 the adcom has a much higher damping factor of 800. The bose 1800 has a much nicer sound than the adcom driving my multiple driver speakers. I thought this was an area that the extra damping factor would be a bonus but I was sorely mistaken. The adcom sounded lifeless to me; very sterile and not enjoyable at all to listen to. Thankfully the older bose unit sounds very nice indeed. Hence I'm not a fan of high damping factors anymore. I believe mac units have low damping factors also and not many people complain about them not sounding good.

 

[jimfet]

That's some good reading mandak has there. But if it is a little to technical, let me put it like this.
A spkr, when it makes a note, natually acts like a pendulum, or say a bell. After the note, it wants to move back and forth till it stops. Now imagine how that would sound while making a bunch of notes. Not to good. The damping factor is the ability of the amp to stop the spkr from going back and forth. The higher the factor the faster it can stop the spkr. But granted you can probably not hear the difference between 100 or a 1000 damping factor. Plus there is alot more to make an amp sound good other than the DF.

 

[bordeno]

MOtorstereo....there must be more to the difference in sound than the DF, I'm just guessing though. I do agree about the sound of Adcom I had a 5500 for about two weeks and sold it on eBay as the sound just didn't do much to impress me. Some people love 'em though, sold for a profit.

Thanks for the responses!

 

[bully]

A higher DF does improve an amps' "grip" on the woofer, but I've read that 50 is about all you need. Much higher DF doesn't hurt, though.
A spec that all of a sudden became "important" as makers touted their models.

 

[wineslob]

DF is also speaker dependent. Most dynamic speakers from the era of low DF amps were high compliance (very stiff suspensions, I think I have this right?) and dident need the amp to control the woofer. With newer designs, woofers have LARGE peak to peak swing capability (subs), and with the advent of ribbon systems, amps needed to have better control of the speaker. The Apogees I have are a good example. With low DF amps the bass is "flabby". With higher DF amps (200+) it becomes tuneful, quick, and more detailed.

 

[mhardy6647]

high compliance (very stiff suspensions, I think I have this right?)

The old-time speakers were low-compliance, with relatively stiff suspensions that supplied restorative force like a spring. AR more or less invented the high-compliance woofer, which could use the restorative force of a fixed volume of air behind the driver (acoustic suspension). The AR woofer in its enclosure was highly damped (i.e., Qtc was fairly low... maybe near the "ideal" 0.707, but I am not sure!)

When you're trying to understand the (mathematically literally) complex interaction of an amplifier and a nonideal, reactive load such as a loudspeaker, don't forget the back-EMF generated by the voicecoil, which is (I believe) maximal at resonance. I think much of the "control" dogma revolves around the magnitude of Q (resonance peak) of the woofer in question in situ in the speaker in question (i.e., the Qtc).

EDIT: Here's a reasonable treatise on what I was yammering about above, written by someone who actually knows what he's talking about (Thomas Dunker)!
http://melhuish.org/audio/article5.html

and, slightly less technically, here:
http://www.webervst.com/spterm.html#damp