May 1, 2003
Less Power to You
Curious about low-powered tube amps and high-efficiency speakers? Take a surf on the 'Net. There you will find megabytes of server memory devoted to the adulation of this relatively recent phenomenon in high-end audio. In such pages, self-styled tubeophile glitterati from all over the world will make you blush with suspiciously erotic terms such as "triode cream" and "velvety midrange." I have sometimes wondered whether my server administrator keeps track of my visits to sites like these, and whether I should take a shower or something afterwards. Such is the enthusiasm for low-powered sound that one may be reminded of the kind of breathless prose a foot-fetishist might indulge in when describing feet. Not that I have anything against feet. I have certainly come across some sturdy and symmetrically shaped pairs in my time. But honestly, are these weirdos on to something, or are they merely hedonistic asylum-escapees flogging their chosen hobbyhorse?
My first encounter with low-power audio could not have been further from the hype. It was five years ago, at a time when I was neither an audiophile nor aware of the existence of a low-power-versus-high-power controversy. My guide was Barry Falcon, the proprietor of Falcon Audio, a cluttered little electronic repair shop specializing in tube amplifiers located in a strip mall in North York, Toronto. My wife and I stopped by on a Sunday afternoon. We couldnt come on Saturday, as I recall, because Barry said that was the day "the wife and I do our shopping." Never mind that stores have opened on Sunday in Toronto for more than 15 years. Barry is an expatriate Englishman, you understand, and not given to wild excesses in scheduling. Hes the sort of Englishman who wears suspenders, not for reasons of fashion, but because they are a good way to hold your pants up.
We entered the shop through the back door, and took in rows and rows of metal shelving loaded from floor to ceiling with electronic bric-a-brac, much of it pre-World War II. In the narrow aisle along the side of the room was a pair of Medallion speakers. They were homebuilts, standing about five feet tall and a foot-and-a-half wide with a single Lowther driver and a back-loaded horn inside the cabinet. The horn opened to the room through a large port in the bottom third of the front panel. They were imposing, with nicely finished woodwork. Driving these was a pair of tiny, obviously do-it-yourself, 300B triode tube monoblocks with a Rega Planet CD player. The entire system probably cost less than $4000, not counting labor, but Lordy, did it sound good. Not perfect, of course. There was a nagging ringing noise in the extreme treble that Barry said he couldnt hear because of his high-frequency hearing loss (from his days in Her Majestys mortar brigade), but the bass was tight and fairly plentiful, and the midrange was soul-catching. When I found out you had to build the cabinets yourself, I balked. But I remember that audition much better than, say, my last wedding anniversary (sorry dear), and I thank Barry for putting me on the path.
What is it about low power that can sound so good? Can less really be more? Can yin be yang? Will this diatribe devolve into a series of irritating Bruce Lee aphorisms? Yes, no, and no. The "less is more" principle is founded on good common sense. You see, with good design and a bit of luck, all the components in a circuit do what they are supposed to do. Unfortunately, they also do things they are not supposed to do. Take capacitors, for example. Some are better than others, but none is ideal. In addition to the capacitive properties they are supposed to have, there are also what are called "parasitic" conductances -- resistance, induction, and unwanted or "stray" capacitance. Worse, the parasitics may vary with frequency, voltage, temperature, and mechanical vibration, producing distortions of various kinds. The same goes for resistors, transformers, wire, you name it. It is safe to say that, in general, the fewer components in the signal path, the simpler it may be to compensate for their flaws, and the less mangled the musical signal will hopefully be when it comes out the other side. This idea can be carried too far. The very simplest amplifier topologies are not always the best, but you get the idea.
Enter the tube amp. After the Gold Rush (sorry Neil) of "more is more" thinking with regard to transistor power, a few lonely, crazed tinkerers, many of them in Japan, began returning to Lee de Forests (Peace Be Upon Him) original triode vacuum-tube configuration, in designs with no feedback. The tetrode and the pentode, of course, were themselves the result of attempts to get more power out of a tube. These tinkerers rediscovered the notion that powerful sound could be had without megawatt amplification simply by using more efficient speakers. Todays regular-efficiency speakers at a sensitivity of, say, 80dB (that is, the speaker produces 80dB of sound pressure in response to a 1W sine wave at 1000Hz measured 1m from the speaker) are on the order of 1% efficient. By contrast, a 100dB-sensitive design is more like 40% efficient. That factor of 40 means your amp can be 40 times less powerful, have fewer components in the signal path, run single-ended rather than push-pull, and operate with no feedback.
But low power did not sweep the nation, as it were, partly because of the rarity of efficient speakers, and partly because of a pervasive cost-per-watt mentality in audio marketing. Then a curious thing happened. Conventional speaker manufacturers in search of better driver designs found that they could improve fidelity and dynamics by increasing cone stiffness and lightness, and decreasing magnet-gap tolerances. As a side effect, a category of real-world speakers arose that were also quite efficient, landing in the 94dB range. Speaker sensitivity, in the high-end marketplace at least, has now replaced power handling as the most-requested and most heavily marketed speaker specification. For me, this marks the first time in recent memory that a speaker specification which is actually useful has attained marketing-tool status. Speaking from personal experience, speakers that are 92dB sensitive or more may be satisfyingly driven by a triode of only 8W. So the gap is closing. These days, the best remaining justification for 100W-plus is the existence of unconventional speaker technologies such as electrostatics, ribbons, and ion tweeters. These more exotic transducers sometimes offer some spectacular sonic benefits, as well as a different set of trade-offs, but are notoriously difficult loads for an amplifier. Short of that, 100W amps also make very handy space heaters.
So fire up a computer where your boss cant see you, and delve into the wonderfully audio-erotic world of low power. Just dont say I didnt warn you when the heavy breathing starts.
Ultra Audio is part of the SoundStage! Network.