How much power does it take to make loud sounds? A lot less than is commonly believed. How much does it take to avoid dynamic compression? It's here that the "power mongers" among 'philes gain powerful traction with their arguments. And that's how today's short essay began. "Hello Srajan, reading your review of the Melody 1688 preamp, I stumbled over your comment that 60 watts into a 101dB loudspeaker would be complete overkill. I respectfully dare to disagree: 60 watts on paper is almost 18dbW on paper, leading to a maximum sound pressure level of barely 119dB, on paper. Exactly this will give you the freedom of compression that you want to witness in musical dynamics! It should be a marriage made in heaven: No more thermal compression in high volume passages (as long as the speakers can handle 60 watts), no more tube amp "rounding off" phenomena, no more soft clipping.... it's just all the dynamics we want and then some! Enjoyed thoroughly the review, as well as I did enjoy the PrimaLuna ProLogue review, by the way! Best regards, Marcel Croese, Utrecht, NL, PrimaLuna electronics designer."
|Marcel Croese? Precisely he of 1990's Goldmund fame and later the Ah Tjoeb upsampler, i.e. a designer who knows his stuff to put it mildly. In a return e-mail, I pointed out that to my ears, 119dB peaks were rather loud. To which Marcel countered: "Sure it's loud and few people will ever play that loud...but that's not the point I tried to make. But what does a person interested in high quality audio playback want? Certainly not trade-offs. We've all grown accustomed to tradeoffs but it is our duty as designers, manufacturers -- and reviewers too -- to identify those tradeoffs and find a solution to them. One particular tradeoff we all take for granted is the lack of dynamic linearity. This may be caused by thermal compression in the voice coils of loudspeakers driven by high power amps, or by limited power outputs of small amplifiers that are driving high-efficiency loudspeakers. We all know 3wpc SET amps on 101dB horns or big Krells or Levinsons on Thiel or Wilson. Both suffer from lack of dynamic freedom when played loud. It certainly can sound very nice but big errors are common here and we all know it.
|Exactly these tradeoffs are taken care of when you assemble a system that uses high-efficiency loudspeakers that can at the same time handle a fair amount of power, and connect a healthy power amp to them that will not round off waveforms when you crank it up a bit. Here your 101dB speakers and 60-watt amp will do what neither of the above mentioned systems can. Now this is a system that can deal with real life dynamics. In this world of 24-bit resolution (actually we barely reach 20 bits but that's still over 123dB), we do not want the very last components in the audio chain to restrict the potential dynamic range that is available to us.
I'd like to stress the point that maybe the average level we are listening to is 90dB, but if we play healthy recordings a bit louder for fun, then dynamic peaks me well reach 20-30dB higher. One last point, not unimportant: a 60-watt amplifier on a 101dB loudspeaker under normal listening conditions is delivering only a couple of hundred mW, up to a couple of watts in peaks. The music signal will in its entirety be processed in the class A region of the amp and will not reach the point where it shifts into the region where crossover distortion is generated. This leaves the negative feedback very, very quiet. No crossover distortion products or amplitude peak roundoffs have to be fed back to the input stage for correction, so the original music signal will not be modified to carry the correction signal with it. Net result is cleaner sound. And when the occasional rims hot comes by, it may catch you by surprise and not be another predictable click in the musical pudding. Thanks for your original comment in the Melody 1688 review. I like it when a "simple" comment like this provokes a chain of thoughts that I can't keep to myself - Marcel."
The man's got a very valid point. He should - he's an engineer. His point does, however, hinge on recorded dynamic range. Anyone who's ever made compilations on CD recorders with meters for recording levels knows how pathetically compressed most modern recordings are. Many of them are lucky to make three bars of 3dB each flicker during the recording session. 20 to 30dB peaks of the kind Marcel references do routinely occur on classical music when well recorded. Take your average Pop recording equalized for radio broadcasts and car audio playback, however - now this type of dynamic range is pure theory. Still, Marcel was right to point out the error in my original 60-watt/101dB statement. It was incorrect because it lacked back story and qualification. Consider it rectified now by Marcel's expert explanation. Thanks, Marcel, for starting this exchange. It's all grist for the mill and we certainly don't wish to be guilty for perpetuating or promoting mythinformation.
For reference and as quoted from Thomas J. Glover's Pocket Ref [Second Edition, Sequoia Publishing], 80 decibels of sound intensity are called loud and equivalent to being inside a high-speed car, next to an electric shaver or exposed to a police whistle. The "very loud" range of 90 to 100dB encompasses a muffler-less truck, a symphony or band, a car horn at 5 meters, a home lawn mover or boiler factory. The Occupational Safety and Health Act of 1970 states that if two hours of daily exposure to 100dB levels are exceeded, then hearing protection must be worn. 110dB equates to close proximity with a passing train; 120dB to equivalent proximity to thunder or a diesel engine room; 130dB to propeller aircraft at 5 meters or a pneumatic rock drill plus instant ear damage and pain threshold. 140dB are delivered by artillery fire and jet aircraft, 194dB by 50 pounds of TNT at 10 meters.
To determine how much power you need for spirited sessions with orchestral reference material, consider that prolonged median 95dB of average playback levels measured at the listening seat are loud. This is something average loudspeaker sensitivities of 88dB/1w/1m will accomplish with less than 20 watts in an average room. To build in 20dB headroom above that median level for short-term peaks could require up to 2000 watts on paper since power proceeds in logarithmic function. Is that realistic - 2000 watts? If you're a commissioned salesman of high-power amplifiers, absolutely. If you're a listener like me who focuses on acoustic smaller-scale music in the global beat arena, I will tell you that 2 watts on 101dB speakers have never yet let me down or telegraphed that I'm suffering compression or clipping. So it all depends less on theory and far more on your actual listening habits and what the recorded dynamic range of your favorite music really is. One thing is beyond debate - a 100dB+ sensitive speaker of high power handling mated to a 50-watt amplifier should never run out of steam to induce dynamic limiting. Considering that the Croese co-designed PrimaLuna ProLogue 7 monos deliver 70 watts of ultralinear KT88 juice for all of $2,695/pr, the wisdom of high-sensitivity speakers becomes sensible not just sonically but financially as well. High sensitivity transforms affordable mid-power amps into Superman on Kryptonite. No need to spend more. Now where are all those clever affordable 100dB+ loudspeakers to complete this sensible equation?
Sensible and high-end audio? You gotta be kidding. We get giddy just reading about the Swedish Statement System with its $250K speakers. But that's precisely why Zu Cable has gotten the extensive coverage in our pages they have. Regardless of how you may personally feel about their house sound, there's no doubt that the industry has been bloody lazy to develop highly sensitive consumer speakers just as Detroit has been lazy to develop fuel cells to finish off our dependency on fossil fuels. When a new speaker outfit specializes in putting an end to this widespread laziness, it deserves our support. What we need is a return to sanity and practicality. With speakers at the very tail end of the audio chain, it's their sensitivity/efficiency quotient (acoustic power output for a given input voltage and load behavior) that determine the necessary expenditure of the preceding amplification. So where are the hordes of high-eff loudspeakers to abolish our dependency on expensive good-sounding high-power amplifiers while building in the dynamic headroom Marcel Croese reminds us is required for uncompromised musical satisfaction?