Damping Factor?

[VINTAGEO]

Hi can anyone explain damping factor? I see all kinds of amps/receivers with different load capabilities 8,6,4,2 ohms etc. and then I see damping factors that are all over the place. I have a JVC AX-Z1010 amp 100 wpc which drives my AR-3A's no problem and it has a DF of 200!
I just purchased a beautiful Sansui (KING AMP) BA-5000 (300 WPC) which can handle loads below 2 ohms but has a DF of only 10!
This makes no sense to me, there has got to be more to it. I thought DF had to do with load capacity.

 

[DaveVoorhis]

A classic article on the subject: http://www.roger-russell.com/wire/damptoole.htm

A good summary: http://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response

 

[mhardy6647]

Damping factor (as it is recorded on most components' spec sheets) is no more, and no less, than the ratio of the load impedance to the output impedance of a power amplifier. Since the load impedance in the real world is almost-always frequency-dependent, it's among the most meaningless of all hifi "specifications", IMO.

If the load (loudspeaker plus cabling) has a nominal impedance of, say, 8 ohms, and the output impedance of the amplifier is 1 ohm (again nominal value), then the damping factor is 8.

All else being equal, the higher the output impedance of a power amplifier, the more it will "feel" the load impedance. This isn't necessarily bad -- but it does mean that the matching of load and amplifier will be more important with low DF for the best-sounding results. This is a fairly concrete case of that amorphous audiophile concept often termed synergy.

I use a transformer coupled, single-ended direct heated triode amplifier with zero applied negative feedback (DF ca.8 for an 8-ohm load); loudspeaker choice is fairly critical with an amplifier like this.

 

[mhardy6647]

That amplifier is output transformer (autoformer) coupled, isn't it? That's probably why the DF is low (cf the autoformer-coupled Macs).

EDIT: That's also probably why it's happy with a 2-ohm load. Within their limitations, a good output transformer or autoformer is a wonderful thing

 

[VINTAGEO]

Thanks for the replies, I think I got it..

 

[mhardy6647]

Just be aware: some folks think that the numerical damping factor is meaningful and important.
I am not one of those folks.

Note well, however: I am not saying that loudspeaker impedance curves, power transmission to loudspeakers, and amplifier output impedance are not important -- just that any correlation of a damping factor "spec" to the interrelationship of those parameter is random, or lucky, at best.

 

[twiiii]

Damping factor is a ratio of the internal impedance of an amplifier to the rated output impedance. If speakers were directly attached to amplifiers without passive crossovers using large speaker wire of the shortest distance possible high damping factors would really mean something. But as most speakers have passive crossovers with their own internal impedance, amps with very high factors are not always used to their biggest advantage. Tube amps with factors around 14 to 18 can be easily influenced by the crossover and speaker load varying the response of the amp as much as 6 db or more. Where amps such as yours might vary 1/2 of a DB, But by experience I would say with short runs with large wire; 50 or higher is more than adequate. Another thing to consider is the dynamics of the speaker itself. If the drivers use large magnets, with shorting rings in sealed boxas the woofers move ment is kept well under control and the amps needing to maintain absolute control is the primary concern. Where speakers that are ported, horn loaded or are mounted in very large enclosures depend heavly on the amp for control. So if youhad a Mcintosh ML or XR series speakers from the past a lower rating from tube amps would be no concern. But if you had a Klipsch, Altec, JBL or Bozak bi amped system, a high damping factor would be very desirable. AR use to recommend the AR-1 and AR-3 worked best with a damping factor of 1 from a Marantz Model 9. As the speaker system was controlled by the damping of the cone and the tight seal of the small enclosure.