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Old 11th February 2004, 10:12 AM   #1
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Default Multiple driver sensitivity gain?

When 2 drivers are mounted near each other they gain 3db output sensitivity because of mutual coupling but isn,t this frequency dependent with them needing to be seperated by 1/3
waveleignth or less for this to happen? Would this be measured
from the center of one driver to the center of the other driver?

Thanks,

Woody
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Old 11th February 2004, 12:13 PM   #2
Svante is offline Svante  Sweden
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Seen straight in front of the speaker and in free space, the 3 dB gain is independent of frequency. As you may know the sensitivity gain originates from a doubled sound pressure (+6dB) for a doubled input power (+3dB), net +3dB. For low frequencies the sound pressures will add up in any direction since the delay between the two signals become negible compared to the period time. For higher frequencies there will be directions when the two signals actually cancel, and for high enough frequencies, and integrated over all directions the net efficiency gain will be 0 dB. (half of the directions cancel, half of the directions double on the linear scale)
But exactly straight in front of the speaker, the sensitivity gain is always +3dB.
Example:
10 cm distance between drivers, 7 kHz, speed of sound 345 m/s:
Wavelength is 345/7000=5 cm, half a wavelength is 2.5 cm. The first zero will occur at arcsin(2.5/10)=14 degrees off axis.

HTH
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Old 12th February 2004, 03:04 PM   #3
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Svante, If you use the term sensitivity correctly, then the sensitivity gain is in fact 6dB, as sensitivity is defined as sound pressure out for given voltage input, usually 2.83V. The impedance is not considered. The efficiency increase is of course 3dB. Everything else you say is well stated.

Andrew
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Old 12th February 2004, 03:24 PM   #4
Svante is offline Svante  Sweden
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Quote:
Originally posted by AndrewJ
Svante, If you use the term sensitivity correctly, then the sensitivity gain is in fact 6dB, as sensitivity is defined as sound pressure out for given voltage input, usually 2.83V. The impedance is not considered. The efficiency increase is of course 3dB. Everything else you say is well stated.

Andrew
Yes you are right, assuming that the drivers are connected in parallel.
I usually free myself mentally from the efficiency/sensitivity issue by thinking of four drivers in series/parallel, but obviously this was not the case now.

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