Negative impedance

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Poormanq45

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Posted: March 15, 2005 at 10:19 PM / IP Logged

What are the pros and cons of Negative vs. Positive Impedance?

auex

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Posted: March 15, 2005 at 10:33 PM / IP Logged

You sure ask alot of discussion questions don't you?

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Poormanq45

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Posted: March 15, 2005 at 10:42 PM / IP Logged

yep, I like starting technical discussions about stuff.

Steven Kephart

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Posted: March 16, 2005 at 1:19 AM / IP Logged

Could you provide an example to put your question into a practical medium. That should help us answer your question.

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DYohn

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Posted: March 16, 2005 at 8:29 AM / IP Logged

"Negative impedence" is an term used to describe an amplifier condition where the output voltage increases as load increases. It leads to unstable amplifier operation and is in general a bad idea except for very specific and specialized applications (usually in broadcast amplifiers.) In audio it is something to be avoided. Impedence as we normally use the term on this board, meaning the combination of resistance, inductance and capacitance caused by AC current flow in loudspeakers, cables, etc. is neither "negative" nor "positive".

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Steven Kephart

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Posted: March 16, 2005 at 11:14 AM / IP Logged

DYohn wrote:

Impedence as we normally use the term on this board, meaning the combination of resistance, inductance and capacitance caused by AC current flow in loudspeakers, cables, etc. is neither "negative" nor "positive".

Thanks Dyohn. That's what I figured, which is why I was looking for a "for instance".

Steven Kephart

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Poormanq45

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Posted: March 16, 2005 at 1:02 PM / IP Logged

Ok, I think I figured out what negative impedance actually means in audio terms.

Basically it is a measurement of the difference between the output impedance from an amplifier and the return impedance signal. As we know, a voice coil changes temperature, and the impedance also changes. So from what I've read, this changing impedance can be compensated for by the amplifier.

Also, as the impedance changes, the drivers ability to acurately reproduce the signal from the amplifier can change significantly.

Poormanq45

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Posted: March 16, 2005 at 1:08 PM / IP Logged

Also, IIRC, this negative impedance circuitry combined with a sensitive microphone can be used to tune a system to a uniform sound in almost any environment.

I think this is what Bose and Yamaha are currently using.

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Negative impedance

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