Annex to Dartzeel NHB-108 review: Power Games...
2/2/2010
In this audiophile world of ours, each and every one is striving to reproduce an, already “packaged”, musical event as accurately, as possible. So, quite naturally, the crucial question arises: “How much power do I need to cater for this need”? And, to complicate things a bit more, this question is asked in tandem with another one: “How much quality power can I really get”?
Once more, the answers are never simple varying a lot, according to whom you are talking to. That is because it all depends mainly on what kind of music you fancy, your speakers of choice and the size of your room. The theory of “the all important first watt” -that we all know- is quite correct but the real problem is what happens, after you get this first one right! And let me tell you right from the start: All things being equal, you might never have enough power!
There is indeed a peculiar relationship between amplifier power and perceived loudness. This relationship is called "logarithmic", which means that a doubling of the amplifier power you are using, in watts, will result in just 3 dB more loudness. No big thing, if you just consider that 1 dB, is the smallest audible change that the average listener can detect! To double, now, the actual perceived loudness (10 dB more…) will require no less than 10 times more electrical power in watts. Another factor you should keep in mind, relates to the distance between you and the sound source. Speaker sensitivity, for example, is measured in dB SPL at 1 Watt, at 1 meter. A formula called the “inverse square law” indicates that each time this distance is doubled, the sound pressure weakens by 6 dB. Meaning that a speaker of, say, 94 dB real sensitivity (that’s 90 dB measured in an anechoic chamber, plus a 4 dB “bonus”, resulting from the -sound reinforcing- room reflections), will only be 82 dB sensitive at the, usual, 3m away from the source listening position…
Yes, but in stereo we have two speakers, don’t we? Of course we do, although another non-linear phenomenon comes at play: When one speaker is producing 82 dB, if you add a second speaker playing at the same level, it will only increase the overall loudness by 3 dB. Which, as we have already seen, is “peanuts”!
Let’s now come to real life: Not speaking of orchestras and choirs and rock venues, you should keep in mind that a single grand piano, can easily reach peak levels of 109 dB SPL. Going back to our previous example, we have 85 dB at the listening position, using 1 W of our, say, 50W amplifier. Going to 95 dB will require 10W, no big fuss! But you will surely need 100W to reach 105 dB and double again this power figure, to 115 dB…And for the correct reproduction of a rock venue peaking at 120 dB, how much power do you really need?
And a necessary clarification: Do not get fooled if your own experience (at a party, maybe…) can lead you to believe, i.e. that you can reach adequate levels with an underpowered amplifier. What really happens, here, is that you “push” your amplifier to produce distorted sound which – in turn – is perceived as (usually…painful) loudness. One more click of the volume control and you could be very well driving the amp into clipping and, eventually, say good bye to your speakers! Stepping down the party experience to the usual home auditions, it is still a fact that -in a “power hungry” system- we do hear distortions disguised as loudness and, as a result, we are often obliged to turn down the volume. It is when we try to remove these unwanted distortions and increase dynamic headroom, that we need the aforementioned amounts of sheer power. Finally, bear in mind that clean, undistorted sound is almost never “too loud”. Hearing is believing, here!
And a final statement: Although I have tried to give you an idea on how amplifiers interact with speakers, you should not consider the above analysis as being exhaustive. To really begin to frame this problem, one should also discuss speaker crossovers, amplifier power supplies and listening rooms. Maybe some other time…
Still, I stand by what I said in the beginning of this diatribe, i.e. that you might never have enough (quality…) power! The only thing I am asking you is to pay a little attention as to the magnitude of your endeavors, unless of course you like grand projects and you are ready to… suffer (financially)! I just thought about this Belgian audiophile who, in 1992, commissioned Charles van Oosterum to build the “Grand Enigma”. Which you will be able to examine by blowing-up the photo, accompanying this article.
The yields of this one-off project, permitted Charles to start his own speaker company: Kharma Loudspeakers…
Money matters aside, just notice the relationship between speaker sensitivity (at 5 m., no less) and amplifier power. Yes, good evening to you too!
Aristidis Coumpas
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