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In Reply to: RE: No Such thing as a "98 dB efficiency" loudspeaker posted by Thom_M on May 07, 2008 at 19:36:57
But let's temporarily ignore that measure of a speaker's ability to convert electrical energy into acoustic energy and concentrate on the traditional uses of Efficiency and Sensitivity as applied to measuring speaker output.
In the decades of tubed amps, we measured Efficiency as the SPL delivered 1 meter from the speaker with the speaker driven with 1 Watt of power. That '1 Watt' was just that--whatever Voltage into the speaker's rated impedance that was required for 1 Watt of power*.
When solidstate amps and low-impedance speakers started becoming popular, the industry started measuring Sensitivity. That's the SAME measurement method as Efficiency except the drive Voltage is always 2.83VAC...regardless of the speaker's rated impedance. Of course the 4-Ohm speaker will be drawing TWO Watts from the SS amp and the 16-Ohm speaker will be drawing only 1/2 Watt, but the measurement is still valid as long as we understand how it's measured.
I believe the proper way for a manufacturer to present its speaker's Sensitivity is to state it something like '2.83V/8Ohms/1M/1K (or whatever frequency is used), but not many are that specific.
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* Into 4 Ohms that's 2 Volts RMS, into 8 it's 2.83VAC, and into 16 it's 4 VAC.
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