Keis hit on another good point; however, his explanation negates the use of a good tube amp. Most tube amps will not double power as impedance is halved. Many only maintain power as impedance drops. In fact, some VERY good tube amps (mostly OTL's) will drop in power as the impedance drops, making them very sensitive to the speakers they drive. I think the most important aspect is "recovery", followed closely by "graceful clipping". Does the amp recover quickly from an instantaneous overload and does it clip (or distort) gracefully. Recovery: Let's not fool ourselves. Measuring a 95db peak at the listening position with a radioshack SPL meter does not even remotely represent the kind of load the amp is "seeing" at that instant. The peak is madeup of a variety of frequencys, each with a different impedance (on most real world speakers) and each with a different phase lag (worse on speakers with complex crossovers). Each factor requires the amp to provide more current than a simple calculation using impedance, voltage, and power would imply. How the power supply recovers from this instantaneous overdraw of current is a large factor in how the amp/speaker sounds before, during and after the peak. Even low level peaks on real music can put a big amp in "recovery". If this were all, however, Keis' Krells would be the way to go. Giant power supplies and the ability to provide rivers of current. Graceful clipping: This sounds like audiophile nonsense, but it really is not. Recovery and the harmonic content of the distortion are really closely tied, but not the same. For modern high end gear, how the output devices distort the waveform during these peaks determines the "sound" of the amp more than how much the output devices distort. Most solid state amps with FETs, MOSFETS, JFETS, Bipolar Transistors... tend to have a higher ratio of odd harmonic content of that distortion to even order harmonic content compared with that of a good tube amp. A low THD with more 5th, 7th, 9th order harmonics will usually sound harder and grainier than a higher THD comprised of a higher ratio of 2nd, 4th, 6th order harmonics. The Krells and Levinsons are excellent amps. I owned a 27.5 (also able to double power into halving of impedance down to 2 ohms) for 5 years and was very happy with it. However, I am getting far more realistic sound with my Avalons (in my system/room) with a pair of Manley Ref 250 mono tube amps than I ever got with my Levinson. They just behave better with the Avalon's more complex crossover and, IMHO I think distort more gracefully and recover faster. Power ratings and amp/speaker matching are NOT simple subjects. Excellent question Kvolk.
A "dumb" question about power ratings?
I'm no engineer, but I believe that our Revel Gem speakers have an impedance of 87db, which is whiy the dealers I talk with to recommend an amplifier that puts out at least 100 watts. If this is correct, does this mean that they are suggesting 100 TOTAL watts? Here's where I'm a little confused: The solid state amps I've looked at like the Levinson 334 or Ayre V-1 are "rated" in terms of total watts available. In this example 125 watts and 200 watts respectively. If that's right, then 1/2 of the total wattage is available to each speaker. A 200 watt amp provides about 100 watt per speaker - right? The reason I ask is that mono-block tube amps and the Pass 'class A' amps seem to be rated by the watts put out by each mono unit. If a mono-block tube amp is rated at 50 watts, then that means 50 watts for each speaker, or the equivalent of 100 total watts available in the system -- is this correct? Put simply, is a mono-block tube amp rated at 60 watts roughtly equal in power to a solid state amp rated at 120 watts? I find power ratings and figuring out how much amplifier power is optimum a bit confusing. I suspect this may be a dumb question, but I just want to make sure I understand the ratings correctly. Also, I'd love to know how to make the decision of how much power is enough. Is it simply a mathematical question dependent on how loud you want the speakers to play? Or do other sonic factors come into play? I've read about tube amps that only put out 15 watts, which seems miniscule to me. Would my Revel Gems even operate running off a low powered tube amp? What would they sound like? This is America, after all, isn't more power always better :-)? I will certainly appreciate your insights! Sincerely, Kurt