High Efficiency Speaker Asylum

Re: A fine point, but wiring drivers in parallel does not increase the system's efficiency...

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Bill Fitzmaurice

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In Reply to: A fine point, but wiring drivers in parallel does not increase the system's efficiency... posted by jeffreybehr on March 20, 2007 at 00:39:43:

Actually, it does. Efficiency is doubled, which results in a 3dB increase in sensitivity. The other 3dB comes from the halved impedance.

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Didn't read my note, huh? :-) It changes SENSITIVITY, not EFFICIENCY. The former is measured with 2.83VAC... - jeffreybehr 11:28:54 03/20/07 (2)
...measured into an 8-Ohm load resistor and then into the speaker, while the latter is measured with ONE WATT into the rated impedance of the speaker.
Of the 6dB increase in sensitivity, 3dB comes from drawing double the power out of the amp due to halved impedance, and 3dB comes from doubling the cone area. THAT's the 'theoretical amount' I mentioned in my note.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
- Re: Didn't read my note, huh? :-) It changes SENSITIVITY, not EFFICIENCY. The former is measured with 2.83VAC... - Bill Fitzmaurice 13:03:56 03/20/07 (1)
  Efficiency is acoustic power out versus electrical power in, expressed as a percentage. Mutual coupling of two identical drivers (what you refer to as doubling the cone area) doubles the radiating efficiency of the system, which results in a 3dB increase in the voltage sensitivity. The phenomenon is frequency limited, and total efficiency with direct radiators cannot exceed approximately 25% (D.B.Keele, 91st AES convention, AES preprint #3193).
  - Yes and no. EFFICIENCY is increased 3dB and SENSITIVITY is increased a further 3dB. - jeffreybehr 18:51:27 03/20/07 (0)
    Yes, output increases (6dB) when you parallel the 2nd driver, but now you've driving it with TWO Watts. When one decreases the Voltage to reduce power to 1 Watt, output decreases 3dB but the output is still 3dB higher than it was before we started.
    So when we parallel an identical driver, efficiency increases 3dB and sensitivity increases a further 3dB.
    -------------------------------------------------------
    Tin-eared audiofool and obsessed landscape fotografer.
    http://community.webshots.com/user/jeffreybehr

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