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Author Topic: Speakers in parallel and back EMF  (Read 1834 times)

David Trotter

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Speakers in parallel and back EMF
« on: January 17, 2005, 10:15:08 am »

sorry if this is a bit technical + dull, but i'm curious...

1) Talking to my lecturer today about connecting loudspeakers in parallel from a single amplifier channel. He attempted to point out a number of problems with doing this.

understand that all speakers incur a back emf caused by the cone moving back to its original position. This current/voltage flows back to the amplifier where it is dissipated as heat. The amplfiers damping factor is its ability to suppress this back-EMf and effectively "control" the motion of the cone. right?

So when you wire 2 or 4 speakers in parallel, surely you get problems with the back-EMF voltages circulating in the parallel circuits. Even if the drivers and boxes are the same, he said that you will still get interferance etc causing phase distortion which will result in the cones not moving in complete unison? The only way to get the cones moving exactly the same, it to have 1 amp per speaker, and to feed the output from each amp into a central controller and back to the inputs so they are always identical.

It this right? i've been looking all over but can't find anything written specifically on this problem. Perhaps this does occur, but the effects are just not worth worrying about as the human ear cant pick them up.

2) In the LAB sub, the 2 drivers are effectively coupled together via the air in the compression chamber. does this effect things in any way? Can you count them as a single large driver?

3) Is this the reasoning behind why Meyer have gone for powered speakers and why NEXO talk about special controllers which monitor the amplifiers output and the voice coil displacement?

From reading about all this, i don't think i shal be driving my 4 LABS of a single crown 5000 anymore. time to get some new amps with high DF.

-dave
bristol uni, uk




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John Roberts {JR}

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Re: Speakers in parallel and back EMF
« Reply #1 on: January 17, 2005, 10:34:24 am »

The parallel connection, as long as there is adequate drive capability is in fact preferred over series for precisely that reason. In parallel any back EMF is damped by the amplifier's output impedance which will be relatively low as indicated by damping factor. In series connection the back EMFs will superimpose on each other and can cause interesting interactions as the boxes/drivers vary. "Interesting" as in the Chinese proverb is not always good.

Of course, individual amps per box will be fine, but pricey.

JR
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