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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: re: Sensitivity and Efficiency posted by mhardy6647 on February 17, 2007 at 12:51:16:
Well I think we have the same understanding but not necessarily the same usage of terms.To get really precise, "efficiency" is indeed a raw percentage. The convention is to use this percentage in prosound, but not in home audio. Most home speakers are less than 1/2% efficient.
You wrote: "Sensitivity is defined dB per watt (or, generally, at 2.83VAC, which is indeed 1W at 8 ohm but 2W at 4 ohm) at some fixed distance..."
In my opinion, using the term "sensitivity" to describe BOTH the 1 watt/1 meter AND the 2.83 volt/1 meter SPL rating is confusing. Likewise, interchangeably using the term "efficiency" to describe both is also confusing. As you point out, the voltage-based SPL spec changes as the impedance of the load changes - but the wattage-based SPL does not! That's because it's really power (watts) that drives a speaker, NOT volts!
The explanations of "efficiency" and "sensitivity" at the link you provided in your "scoop" post is very good, by the way. First describing the basis of 1 watt/1 meter specifications:
"The manufacturer measures the sound pressure level (SPL) that a speaker produces with one watt of power at a distance of one meter. But this measurement is actually a measure of a speaker's EFFICIENCY, and NOT its sensitivity." [emphasis Duke's]
And next, the basis for 2.83 volt/1 meter specifications:
"The manufacturer measures the SPL a speaker produces at 1 meter on 2.83V of input power. Today's solid-state amps do a pretty good job of maintaining their output voltage in comparison to older, tube-style amps. So the measurement of a speaker's voltage SENSITIVITY is considered a more accurate measurement." [emphasis Duke's]
My point being, it is appropriate to use the term "efficiency" when referencing a 1 watt input, and the term "sensitivity" when referencing a 2.83 volt input. If there's another convention the industry would like to use that doesn't promote confusion, that would be fine with me.
The confusion probably first arose when marketing departments for manufacturers of 4-ohm speakers realized they could hike their numbers by 3 dB just by switching from a wattage-based specification to a voltage-based one. Few people would dig deep enough to find out exactly what the impressively high "efficiency" or "sensitivity" specification was based on, especially if the terms are used as if they're interchangeabe. (Now some manufacturers are using "in-room" specs, inflated by yet another 3-6 dB!).
I maintain that since power (acoustic watts) is what comes out of a speaker, power (electrical watts) is the more appropriate measurement of what goes into it. Note that it is power (watts) that heats up voice coils. You don't see "voltage handling" specs - you see "power handling" specs, in good old-fashioned watts.
Getting back to efficiency as a percentage, if you know the percentage efficiency and the wattage input, you can easily calculate the SPL output (ignoring power compression). However, if you know the percentage efficiency and the voltage input you cannot reliably calculate the SPL output. You must also have the impedance of the load. Once you have the voltage and the impedance you can convert to watts and calculate the SPL output. So focusing on voltage this or voltage that is to a certain extent a distraction from what really drives speakers - which is watts. That tells us what the speaker can do. If the amp's power doubles into a four ohm load, fine - let that be part of the amp's specs, not the speaker's.
Just my $.02 - not enough to buy a cigar.
Duke
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Follow Ups
- Sensitivity and Efficiency - not interchangeable terms (also anti-voltage rant) - Duke 14:20:05 02/17/07 (0)
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