Just like a motor. The impedance of an ordinary voice-coil speaker changes the more it moves and peaks at resonance(s). Because of back EMF, unless I have the term wrong.
Feedback from the speaker is the last great frontier - well, a great frontier, if not the last. Without feedback, you can't improve. And there's no feedback from the speakers. And today's best speakers perform as well as the best amps of 1950, on a good day.
As far as protecting speakers from being over-driven, gotta be a lot simpler ways than with radar.
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Your terminology seems to be correct, but what you're describing is simply Ringing:
http://en.wikipedia.org/wiki/Ringing_(signal)
The paramount question though, as far as I'm concerned, is how feedback (from the driver) could possibly help reduce ringing? That's a phenomenon that occurs simply by the very nature of the driver using an inductor. You really can't stop the tendency of an inductor to ring, you can only deal with it in some way. The "standard" solution seems to be a DC-coupled amplifier, sporting an extremely high damping factor, which can tightly control the amount of current within the resonant circuit comprised by the driver - the Crown K2 is a good example of a DC-coupled amp, with a damping factor of 7000 at the low end, IIRC.
Can someone point me to a thesis statement on this feedback stuff? What might one hope to do with the feedback data - maybe throw more capacitance into the network to counteract the ring? What's the net benefit? Am I off my rocker or what?
In the perfect Web world, posts which were top-filled with malarky would be prefaced with something like, "I think..." or "Possibly...." or as in silly olden days, "In my humble opinion..." That way, repliers ("replyers"?) would be sympathetic and will reply to misguided thoughts because the original poster was, at least, a modest person, if misguided.
Never the less, embracing the accepted, if dubious, rhetoric you find in anonymous testosterone forums in the audio (and, even worse, the motorcycle) worlds...
Look here (esp. at the download paper URL at the very bottom):
Tech
This is about capacitive motional feedback that I happen not to think highly of. But it illustrates pretty well about the topic and shows the measurements on frequency response and distortion.
Footnote: even with remote sensing to eliminate most of the speaker wire resistance (as in the Kenwood Sigma Drive feedback), you can never get help from DF over maybe 15 because the speaker voice coil DC resistance will always be in the circuit, I truly believe.
Remarkable of davygrvy not to believe you can control a loudspeaker by controlling the input to it. Remarkable, I truly believe.
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I forget the path of the USENET motorcycle forum, but their saying was "Live to flame, flame to live".
Anyways.. I would never consider a closed loop feedback system for the control of distortion using X-band radar for a number of reasons. Feedback systems can be quite fragile. The Velodyne is a fine example of such fragility.
I do like it for preventing distortion in front-loaded folded horn subs caused by only over-excursion in a PA setup where loudness is paramount because you have to run it all close to its point of death or you aren't getting the most from it.
Please describe for me the behavior of feedback at clipping? Not clipping of the amplifier, but the excursion limit of the driver.
A feedback system will just drive it harder into the damage zone. If you went the other way to reduce level rather than increase, you've gone in the correct direction for the distortion caused by over-excursion. I am controlling the input.
Ben, you have really got to get out more and make stuff.
Mix guides monitors meyer sound x-10 Field Test-Mix reviews the meyer sound x-10 linear control room monitor in mix guides monitors meyer's take on servo (microphone in the loop)
Given the rudeness and antagonism of so many posts in this thread (my own included), no decent person would want to contribute here. But since so many people have connected, I thought it might help if I provided some bit of summary and clarification.
1. First, some talk at cross purposes due to two different notions of "feedback." OP has in mind to protect his driver from over-excursion by using a $9.95 Mattel toy radar gun to measure excursion and detect when the cone has moved too far, provided this device of unknown abilities is sort of linear in the frequency region of interest.
2. The conventional sense of "feedback" steers the driver to reduce distortion. But "all bets are off" when the driver heads into over-excursion limiting, as the OP is interested in. So ordinary feedback is not useful outside the range of normal operation but then limiting is not useful to reduce distortion except at the extreme point.
3. While feedback back around the speaker is one of the last great frontiers of sound reproduction, substantial debate about the means of sensing speaker output. Or at least, sensing the motion of the cone dust cap or voice coil as the basic reference-datum. (I am convinced that only back-emf, VC-in-a-balanced-bridge, or direct generation from the voice coil or voice coils is best - and that toy radar is not a good R&D prospect.)
Other threads address motional and sound feedback with a modicum of civility.
1. First, some talk at cross purposes due to two different notions of "feedback." OP has in mind to protect his driver from over-excursion by using a $9.95 Mattel toy radar gun to measure excursion and detect when the cone has moved too far, provided this device of unknown abilities is sort of linear in the frequency region of interest.
2. The conventional sense of "feedback" steers the driver to reduce distortion. But "all bets are off" when the driver heads into over-excursion limiting, as the OP is interested in. So ordinary feedback is not useful outside the range of normal operation but then limiting is not useful to reduce distortion except at the extreme point.
3. While feedback back around the speaker is one of the last great frontiers of sound reproduction, substantial debate about the means of sensing speaker output. Or at least, sensing the motion of the cone dust cap or voice coil as the basic reference-datum. (I am convinced that only back-emf, VC-in-a-balanced-bridge, or direct generation from the voice coil or voice coils is best - and that toy radar is not a good R&D prospect.)
Other threads address motional and sound feedback with a modicum of civility.
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I was just interviewing Jason Kemmerer at Alpine. He contends that damping factor can indicate the amplifier has better "control" over the load. This is not in a sense of doing the math to see how much the additional tiny resistance changes overall circuit damping because you're right, it won't. But he says that an amp which is more robust and can for example better reject the huge back-EMF from monster subs normally has a much higher damping factor.
--> DF is not important for it's own sake, but can be an indicator of a better design.
This is in much the same way that we mostly worship amps with very wideband frequency response, very low noise floors and separation, and low distortion. The direct audibility of those specs is questionable; their usefulness is more in indicating "hey, this designer took a lot of care to make a more ideal device, so it probably sounds good." (Some devices like tube amps fail those conventional measures, yet stick around presumably because they do other nice things sonically which compensate).
Interesting thread despite the S/N ratio FWIW gold leaf is an easy to apply radar target. I would not knock using a cheap toy radar unit as a position sensor as long as the oscillator was stable enough to give a good clean phase signal from the mixer. It is actually quite smart using a long wavelength source like radar, as keeping track of phase shifts over multiple cycles is no fun.
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