In response to our WFTD, Hangover and Damping Factor, inSync reader Tom D adds some of his experience from working with a major amplifier manufacturer. Don’t worry if you don’t understand the what he says, or the jargon he uses. The point that is clear from this, and one I preach frequently, is that gear specs aren’t always what they seem. They should be measured against practical experience, which is a big reason to be talking to the sales crew at Sweetwater for purchases, because they all have extensive experience. Here goes:
“Damping factor is an interesting buzzword, created by amp manufacturer marketing departments, that has limited practical value. The equivalent circuit for a power amp to loudspeaker circuit includes a set of small resistances (amp and, hopefully, cabling) and a large resistance, all in series. The ability of an amplifier to selectively separate out series resistances, for the sake of servo-style “damping,” is greatly exaggerated. Any damping factor number beyond 10 is created (invented) in the lab and has no practical effect on loudspeaker movement. At high frequencies, the major component is, usually, series inductance. Amp damping has no effect on that component, either.
I was a QSC engineer for a near-decade and our “damping” calculation illustrated the “meaningless numbers” value of this parameter. We measured the RMS voltage of a no-load amp output. Applied an 8 ohm resistive load and noted the decrease in the output voltage. Using the known output resistance and the voltage drop, we calculated (and advertised) “damping.” God knows how some other manufacturers did their calculation, since their advertised numbers didn’t even come close to any measurable value. It doesn’t take much speaker cable resistance to wreak big damping factor numbers.”