What happens if we listen from a distance of, say, 2 meters instead of 1? The sound is quieter (duh!), but by how much? In “free space” (outdoors) sound pressure falls of at the inverse of the distance-the sound is 3 dB softer for a doubling of listening-distance, or 6 dB softer for quadrupling it. You can check the Test Bench box in our speaker reviews for a statement of each loudspeaker model’s sensitivity that is consistently derived, and easy to compare, across all products. One caveat, and it’s a biggie: due to measurement techniques, environments, and plain old manufacturer mendacity, spec-sheet sensitivity ratings can be extraordinarily variable, so take claimed differences with a double shake of salt. But if you’re torn between two similar-price speaker models you love equally, choose the higher-sensitivity one. Let me underscore that speaker sensitivity has nothing whatsoever to do with speaker quality, sonic or otherwise it’s a simple quantification of how-loud-per-watt. But if you’re torn between two similar-price speakers, choose the one with higher sensitivity. Speaker sensitivity has nothing to do with speaker quality, sonic or otherwise. Choose instead a speaker of 90 dB SPL/1 watt/1 meter sensitivity and you just made the equivalent change in perceived volume as doubling your amplifier power without increasing your actual amp power by so much as a milliwatt, or your amplifier budget by so much as a dime. A typical consumer speaker given 1 watt and measured via a microphone placed 1 meter away will produce about 87 dB sound pressure level or SPL (“how loud,” in decibel terms). Two different loudspeakers served identical 1-watt signals will play louder or softer depending on their sensitivity (sometimes referred to as "efficiency," though that term is less technically correct in this instance). (If we’re talking stereo, with two identically powered channels driving two identical speakers, we get about 3 dB more loudness (or dynamic potential) off the baseline thanks to the laws of acoustics). All this presupposes one amplifier channel driving one loudspeaker, just to keep it simple. (That’s like saying that Emilia Clarke is “twice as hot” as Mila Kunis.” But I digress.) That’s right: you must double power to effect any meaningful difference at all in perceived volume, and you must times-ten it to make things really, solidly, usefully louder. A 10 dB change is characterized by the general populace as “twice as loud,” whatever that means. Great! What do “only” and “mere” mean? In real-world terms, a 3 dB loudness increment is quite small-in fact, it’s the smallest change in loudness most untrained listeners will call noticeable. Mercifully, logarithms simply multiply their ratios, so 30 dBw, for example, equals 1,000 watts (10 dB more than 100 watts or 10x20 dBw, which is 10x100 watts.) Stay with me now, here’s the nub: this means that doubling amplifier power yields only a 3 dB gain in “how-loud-ness,” while increasing power ten-fold yields a mere 10 dB increase. Ten watts is 10 dBw, and 100 watts is 20 dBw. In the dBw case the standard is 1 watt.) For mathematical reasons I ain’t going into here, 2 watts equals 3 dBw, and 4 watts 6 dBw. (Remember, all decibel expressions are always at their core expressing a ratio: comparisons, usually to a standardized reference. That is, relative to 1 watt, 1 watt is precisely zero greater or smaller (duh!). We call an output of 1 watt, connected to a loudspeaker-like test-load of 8 ohms (effectively 2.83 volts from the amplifier,) “zero dB-watts,” or 0 dBw. The dB watt’s key value is this: Assuming reasonably linear loudspeaker behavior, dBw translate more or less one-for-one to the increase in useful loudness you can expect from a given loudspeaker in a given setup. Yet it’s a superbly useful and far more meaningful way to describe amplifier capabilities-and once you get the basics, you can roughly convert spec-sheet wattages to dB watts easily enough. A decade or so back, a movement to make the “dB watt”-decibels in reference to 1 watt-a spec-sheet staple enjoyed brief traction, but today the abbreviation “dBw” is rarely seen. To hold a meaningful conversation we must talk amplifier power in terms of decibels, a scale that expresses power comparisons the way we hear: logarithmically. Well-audio power, anyway.įirst, foremost, and forever, the diabolical decibel (dB). I can, however, arm you with a few concepts to think about, concepts that, if mastered, hold the key to all power. What’s the Number One question demanded of self-styled audio experts like me? “How much power do I need?”īut expert or not, I can’t answer it: not without knowing the details of your speakers, your room’s size, layout, and furnishings, your listening habits, musical tastes, boxers-or-briefs, and a dozen other details.
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