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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: What happens to back EMF with a feedback amplifier? posted by morricab on August 17, 2006 at 05:01:34:
Imagine a perfect amplifier with NF, ie a zero output impedance.With a resistive load it is easy to see that the output stages will source whatever current is necessary (source current with positive output v, sink with negative output v) to maintain the output voltage at Vin x gain. In a good simple classic design, the feedback mechanism is "faster" than the output amplifier (and the input bandwidth is limited) such that control is always maintained.
When the load becomes reactive (= vector sum of crossover plus speaker engine coil) things can get very interesting!
After a speaker excursion there is indeed a back-emf as the speaker becomes a generator and wants to dump its potential energy (from its displacement) somewhere.
If the amplifier is still in control, the output stage will have to sink _current_ for a postive input etc to maintain the target output voltage, ie absorb the energy.
So the design of the output stage has to accomodate this, and there may well be an abberation in the feedback mechanism until the loop regains control. This may be during the driver stage slewing from sourcing to sinking levels within the amplifer. This is not forever, unless the amp has locked up or is oscillating.
A so called "difficult" speaker load with low impedance and a lot of motor energy can easily play havoc with an amplifer that measures well with a rssistive load.Add the complex impedance and _phase response_ of a crossover explains why there is a lot of subtlety in amp and speaker design.
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Follow Ups
- Perhaps a better way of visualising it? - clifff 07:20:50 08/17/06 (6)
- Definitely a better way of visualising it !!!!!!! - Soundmind 06:42:33 08/18/06 (3)
- Re: Definitely a better way of visualising it !!!!!!! - morricab 11:36:20 08/18/06 (2)
- Re: Definitely a better way of visualising it !!!!!!! - morricab 11:53:36 08/18/06 (0)
- Morricab...stick to chemicals...preferably water, it's safer nt - Soundmind 11:42:04 08/18/06 (0)
- Re: Perhaps a better way of visualising it? - morricab 09:56:06 08/17/06 (1)
- Rate of change! - clifff 10:24:03 08/17/06 (0)
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