Is this a fluke?
default -- Sat, 04/18/2009 - 16:08
The other day I was comparing some amplifiers such as the McIntosh Lab's MC501, Pass Labs' X600.5 and Simaudio Moon W-7M. All are great amplifiers and can be used to drive a wide variety of speakers at any load. I was looking for the best amplifier, among these three, to be able to drive and control a difficult speaker such as the B&W 801D. According to their respective manufacturer's specification, the McIntosh MC501 has a damping factor of about 100; the X600.5 around 150 and the Moon W-7M a damping factor of at least 1600! While their rated output is fairly similar and all are great amplifiers, is it possible for the Simaudio to have a DF much higher than the other two? Does this mean the Simaudio is the best of the three to handle the 15" woofer driver on the 801D?
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An amplifier's damping factor is related to its output impedance—the higher the damping factor the lower the output impedance. Amplifier output impedance becomes significant when it is a substantial fraction of the loudspeaker's load impedance. When that happens, the amplifier's frequency response is changed by the loudspeaker, causing a tonal colorations. So long as the amplifier's output impedance is less than one-tenth the speaker's impedance, you won't have a problem.
I wouldn't make a purchasing decision based on this spec, unless the amplifier's output impedance were extremely high (more than one ohm).
See Dick Olsher's review of the Mystere IA21 integrated amplifier in Issue 189 (page 99), as well as the Manufacturer Comment, for more on this subject.
How did the various amplifiers sound in the bass?
I haven't had a chance to audition these amplifiers with the 801D, mostly because it's very difficult to find a dealer that carries all these brands. Nowadays, when you walk into a dealership, instead of hearing the products you want to hear, often you are persuaded to hear *alternatives* that the dealer carries. Also, when I was searching through manufacturers' websites, looking for specs that could differentiate one product to another, I found they are listed under different sets of specs. For example, I couldn't find the output impedance of the X600.5 on Pass' website. Nor could I find the same for the MC501 on McIntosh Labs' website (the specs for the Moon W-7m is very detailed though). This is when TAS comes in handy since you guys review thousands of equipments and can team them up and review them any way you want, even though you guys seem reluctant to directly compare the pros and cons of one against another.