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Old 7th June 2005, 03:07 PM   #1
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Default Voltage controlled output impedance matching servo

Describing this is not so easy...

I would like to phase-match the driver outputs going into 2 sepearate channels of subwoofer speakers - the "unpowered" type.

I think I will need to control somehow the "variable output impedance" of both driver amps with some kind of servo control scheme that will result in actually varying the phases of the two low frequency signals until they match by vaying at least one of the two driver's output resistance.

Let me try this again: Suppose one subwoofer has 4.10 ohms of reactance at 30Hz and the other has 3.9 ohms of reactance at 30Hz. One speaker will sound somewhat louder than the other and also there will be a phase difference compared to the other even if both driver amps had exactly the same output resistance.

But having the identical output impedances in 2 driver amps is also quite unlikely, so say the first driver's impedance varied in the worst possible direction while the other driver varied oppositely. Now we have a compounding of phase errors, potentially.

One solution to making a perfect phase matching or balance between the two channels would be to vary the output impedance of one side's driver until both channels were 100% in-phase. There would have to be a monitoring circuit of the opposite side's output phase and use a servo to voltage-control the monitored channel's output resistance until both channels were precisely in phase.

If anyone has ideas of how I can servo control the output impedance of one driver amp (in order to perform perfect phase matching), please help me out. Or, if you know where I might read up on someone's post, let me know. I would like to connect with someone who has tried this.




PS, hello SIL
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Old 7th June 2005, 05:31 PM   #2
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I would consider the problem you are trying to solve as a non-issue even with mono subs. With stereo subs, if you try to match them, balance wise, they would be mono.

If it's that important to you, why not just match impedance curves manually?
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Old 7th June 2005, 05:32 PM   #3
micb is offline micb  United Kingdom
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My question is why would you want to do all that?
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