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Re: Do multiple drivers have to be paralled to increase sensitivity?

Posted by AndrewG on June 2, 2000 at 22:27:04

In Reply to: Do multiple drivers have to be paralled to increase sensitivity? posted by Jon L on June 2, 2000 at 18:17:05:

1. When you wire two drivers in series, the total impedance of the circuit doubles.
2. The voltage-drop across EACH driver halves (The voltage-drop across the PAIR is the same as across the original single driver).
3. The SPL output of each driver halves (ie drops by 6dB - we are talking SPL, not power output).
4. If you assume that the sound output from the drivers adds in perfect phase, then the sum of two driver SPL's is 6dB greater than that of each separate driver.
5. First you lost 6dB, then you gained 6dB, whaddya got? 0dB change!

In fact, there is probably a bit of loss due to the physical distance between drivers and individual driver variation leading to less than exact in-phase summing of output. If the outputs were in random phase relation (eg pink noise from two non-phase-correlated sources), then the SPL's would sum as RMS values (ie 0.707 of their peak) and the total SPL for the pair would be 3dB greater than the output of each driver.
The real situation would probably be closer to the in-phase sum (+6dB) than the RMS sum (+3dB); ie close to no change, maybe a slight loss.

You would be passing the signal through twice as much voice-coil wire and voice-coil inductance (inductances in series sum together). At first glance, this looks like a bad idea, but the doubling of power-handling, halving of cone excursions and the opportunity to use D'Appolito design without halving the impedance seen by the amplifier might be worth it.

Andrew.

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