KIH #5: Power Over Sensibility

POS? To play with our ongoing 3-letter thematic, let this one momentarily mean power over sensibility to set the scene for today’s movie concept of Jane Austin meets Wladimir Klitschko. How much power must our amplifiers really deliver? Is the SET crowd off their collective rocker claiming a fistful of watts sufficient? How about shoppers of Musical Fidelity’s Tri-Vista kW monos of yore? According to Michael Fremer’s Stereophile review those were “rated at 1000W into 8 ohms, 1800 into 4 ohms and a speaker-boggling 3000W into 2 ohms. Instantaneous peak output is claimed to be a frightening 5000W, with a peak current potential of ±200 amps and output voltage of around 130 amps.” Did those amps embody the real truth to render their owners enlightened and in the full know?

Michael Fremer’s earlier review of MuFi’s 550K Supercharger monos explained that “how much power you need depends on how much realism you seek. If you want only background music or a pleasant but subdued version of the real thing, perhaps you don’t need that much power. However if you want a high degree of fidelity to the original event and the ability to reproduce the full dynamic majesty of a symphony orchestra, the concert SPLs of your favorite rock band or even the visceral drive of as expressive a solo pianist as Keith Jarrett, you may need more power than you think even in a room of small to medium size…The transient peaks in live music can reach high sound pressure levels. For example, John Atkinson sitting in a mid-hall seat in London’s Royal Festival Hal measured timpani thwacks at +106dB peak back in the early 1980s. Reproducing those peaks without clipping and thus generating ‘slam factor’ is what can make the difference between a system sounding ‘blah’ or ‘wow’, between ‘canned’ or ‘real’.”

Let’s disregard the stretch of equating playback of full symphonic forces in your living room with realism and doing it at concert-hall SPL desirable. Let’s first get a handle on actual figures. Owners of iDevices have a number of SPL meter apps at their disposal. I use Mint Muse’s Sound Level Meter Pro. It offers 5 different weighting schemes. I’m no android but such devices will have similar apps. There are always the Radio Shack types too.

On Kevin Seddiki & Bijan Chemirani’s Imaginarium album of intermingling guitar and zarb with some hand percussion at levels I’d run whilst writing a feature like this, I hit a ±50dB average with 58dB peaks. For serious sessions of the same purely acoustical very simple material in the hot seat I’d move the average up by about 6dB. If I wait long enough I’ll hit peaks of 70dB. With my 92.5dB speakers a good 3 meters from the seat and sound losing 6dB with each doubling of distance, let’s add 8dB to my peak figure. That still puts us about 15dB below the rating of my speakers to net <0.1 watts of listening power during peaks. Does that make me a bad audiophile and sissy listener? Nothing like a reality check to squash one’s macho notions of self worth.

From our trusty decibel chart we know that 20dB equal a 1:100 power ratio. Conveniently 20dB of dynamic range as measured by PureMusic’s peak-hold meter right inside my iMac’s playback software turns out to be high dynamic range for 95% of all my music. Most tunes show rather less. If I were to listen loud enough to make my speaker rating of 1 watt @ 1 meter = 92.5dB the very quietest level and thus 112.5dB the max peak figure, I’d need a 100-watt amplifier. But do I ever listen that loud?

Never! A constant 70dB level is about as loud as it gets before room pressurization turns ridiculous. Let’s build in an allowance of 20dB peaks above such an average rather than minimum figure to call it properly manly. On my soundkaos Wave 40 speakers I then really don’t ever move out of the 1st-watt gear. Pathetic, huh? Humiliating.

But it does mean that my posh $10.000/pr FirstWatt SIT-1 monos of 10/8w into 8/4Ω are perfectly suitable for my needs. They might well be underpowered for yours though. Take the Finnish Prime Loudspeakers Tone monitor I expected for delivery within a week of penning this. It would arrive with an 81dB sensitivity rating in tow. For proper headroom and the same 90dB peak figures at the same 3-meter ear distance, I now would want a 100-watt amplifier. Pursuing such painfully inefficient boxes comes at a price.

With that covered—you’ll do your own SPL metering to verify your situation—let’s lasso in a related argument I’m fond of. Low-power amplifiers can exploit single-ended operation and do so without paralleled output devices. With always-on outputs as is the case for class A operation there’s no zero-crossing distortion. One reason why low-power amps can sound so good is circuit simplicity. Fewer gain stages mean lower high-order distortion. Lower intrinsic distortion allows for zero or very low feedback. Non-paralleled output devices don’t muddy the picture with uneven behaviour between devices. That’s not trash-talking muscle amps. Excellent ones exist. It would simply seem to get disproportionately more expensive to do them right. The smart money might prefer not to go there.

The mantra of easy does it describes a playing field where the opposing players are team SPL and team speaker sensitivity. Core members of team SPL are room size and listening distance. The other team includes players like speaker impedance and amplifier ratings into lower impedances for the full picture. One you know your actual listening SPL– not imaginary figures, not hyped-up values proposed by pushers of muscle amps but actual in-seat measurements—you can quite easily figure out what your power needs are. If your room is of average size and you don’t listen unnaturally loud, chances are quite good that you’ll get by with a lot less than assumed. And that could open doors to amplifiers you never considered before. Having more rather than less options is a good thing…