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In Reply to: Re: Silvaweld 6C33C OTLs posted by morricab on October 18, 2005 at 04:50:14:
Direct from the web: "Technically, the damping factor is the specified load impedance (in use, that'd be the speaker system) divided by the amplifier's output impedance."Damping factor is not independent of the load impedance. The load impedance = the speaker resistance at any given frequency. Thus since all speakers present a reactive load, damping factor is not independent of frequency, either. Most manufacturers will stipulate damping factor into an 8-ohm load, and few bother to tell you at what frequency, but 1kHz is a good guess. Anyway, the advertised damping factor of your amplifiers is likely to be incorrect for driving your Apogee ribbons, which have an impedance way lower than 8 ohms.
Follow Ups:
Lest I confuse you or someone else, when I wrote "the advertised damping factor of your amplifiers is likely to be incorrect for driving your Apogee ribbons", what I meant to convey is that if your amps have an advertised DF of 10, which is probably based on an 8-ohm speaker load, then they will actually function with a DF of 5 when driving your Apogees (as I stated above), assuming the Apogees have a real impedance of 4 ohms, but we know the impedance of the Apogee goes even lower than 4 ohms, further lowering the actual DF achieved in practise.I am not a big devote' of high damping factor (i.e., super low output impedance) amplifiers per se; my experience tells me that there is such a thing as "critical damping factor" which was defined and described long ago by Norman Crowhurst and others. However, when the ratio of the amplifier output Zo to the speaker Zi approaches one or certainly when it goes above one, which will happen if you turn off all your NFB, things do turn sour. Zeros are a must in that case.
Hi Lew,
Got those Silvaweld OTLs at home now. First I have been listening to them on my Acoustat 1+1 and the results thus far are very positive. I am going to check the frequency response is a couple of days to see how the speaker impedance is interacting with the amps but it doesn't sound really out of whack.Next up will be the Apogees. Here I expect less problems with frequency variations but perhaps more with ultimate power on tap. I still expect some beautiful sound though :). Really fine amps.
Hi Lew,
You are correct, my apologies. You are also correct about the change in damping factor with the lower impedance. Assumming a damping factor of 10 then into an 8 ohm load (at 1Khz or so) then the output impedance would be about 0.8 ohm. Therefore the damping factor into 4 ohms would indeed be 5. As to the Apogees I own, they do indeed measure quite flat in impedance from 3.2-4.6 ohms most resistive. There won't be much variation then in the frequency response. Besides 0.8 ohm is no worse than most tube amps on the market. Again, thanks for the correction, I should have verified what I was saying.
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