I am not sure if this is the right forum to post this in, but have built servo amps using the Burr Brown OPA512 op amp chip which can deliver 10 amps from a 100 V supply into 8 ohms.
This IC is perfect for an closed loop speaker experiment.
If one can build into a driver, a position feedback device, and then uses this to provide closed- loop feedback into the op amp for error correction. This should really improve response linearity and reduce distortion. Has anyone ever seen this done? I am not having any luck doing a search.
It would be interesting to put an optical position sensitive feedback device with a fiber optic coupled LED and photodiode to get absolute cone position and use that to actively correct drive current. With sufficiently high power motors (low Qts, high BL drivers) the driver can overcome any distortion imposed externally by having the amp swing a higher correction current.
Theoretically, the distortion can be made to go to zero within the amplifier/driver actuation band width.
This IC is perfect for an closed loop speaker experiment.
If one can build into a driver, a position feedback device, and then uses this to provide closed- loop feedback into the op amp for error correction. This should really improve response linearity and reduce distortion. Has anyone ever seen this done? I am not having any luck doing a search.
It would be interesting to put an optical position sensitive feedback device with a fiber optic coupled LED and photodiode to get absolute cone position and use that to actively correct drive current. With sufficiently high power motors (low Qts, high BL drivers) the driver can overcome any distortion imposed externally by having the amp swing a higher correction current.
Theoretically, the distortion can be made to go to zero within the amplifier/driver actuation band width.
moved to planars/exotics.
Hi,
wouldn´t it be better moved to subwoofers? Where basically all other discussion about Motional Feedback take place?
jauu
Calvin
ps. "Theoretically, the distortion can be made to go to zero within the amplifier/driver actuation band width."
No, not even theoretically will the distortion become zero. ;-)
wouldn´t it be better moved to subwoofers? Where basically all other discussion about Motional Feedback take place?
jauu
Calvin
ps. "Theoretically, the distortion can be made to go to zero within the amplifier/driver actuation band width."
No, not even theoretically will the distortion become zero. ;-)
Yes and in fact I saw a thread just a short while ago --> http://www.diyaudio.com/forums/subw...-gain-servo-controlled-woofer-controller.html
XRK971 would you like it moved to subwoofers instead?
Tony.
XRK971 would you like it moved to subwoofers instead?
Tony.
Probably still better than just the woofer but it is something to address.
The response time of the positional sensor is also something to look at.
Slow response = power oscillator?
A few years ago I had a circuit for this and plotted the distance vs output.
I was trying for X of 1.5"
And found out that my dmm was giving me the voltage but when I put a scope on the output I found the cct was oscillating and the output was giving me more pulses vs distance. The poor dmm was just showing me what it could.
Got distracted with building something else and abandoned the project.
It is on the list...
🙂
Actually, you can make a superbly accurate linear positioning device. It's something I've thought about but never had time to work on, but it's used in some spectrometers with great success- use a laser with a beamsplitter, then recombine the beams. You get fringes which are perfectly periodic. You need a separate path to generate a quadrature signal so that you can tell if the cone is moving forward or backward.
additional difficulty comes from the cone usually being operated over the range of bending modes, "breakup" - it is a distributed system so the exact location of the motion sensor limits the knowledge of the cone's whole response, sound output
the mechanical phase shift, modes limits the amount of feedback that can be applied:
the mechanical phase shift, modes limits the amount of feedback that can be applied:
Scanning interferometry. Or for woofer how about just a microphone. Let the air do the averaging.
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I want to use this for full range drivers really but wanted people who know about amps and electronics to give input, which was why I posted it in amps forum at first. Lets keep it here in Exotics for now.
Thanks
X
Interferometric methods are way too complicated (expensive) and do not handle vibration or large motions well. A fiber optic proximity sensor with LED and photodiode has DC to hundred MHz bandwidth. The linearity can be handled optically with a mask on on scattering surface.
You're just counting fringes, so the linearity is immaterial. My first "real" project when I got out of school was designing a system like this for an FTIR system. The excursion of the voice coil coupled to the interferometer was 2cm or so. The difficulty with doing it cheaply back then was keeping the beam coherent over the travel length, but these days I would expect that you could pull it off with a laser diode and a few bits of optics. As mentioned by others, this won't account for cone breakup, but at least you can get the voice coil motion linearized.
Counting fringes...yes...I would like to see the circuit to convert that to a linear signal.
No, not sarcasm...I would really like to see the circuit.
Up/down counter and parallel input d-a? It would have to be fast and keep track of zero position.
I have some parts that could be used for this type of setup.
First surface mirrors and 50% transmission mirrors from cd/dvd drives.
Cone breakup...I would control close to the voice coil...cone breakup will happen with or without feedback.
laser doppler velocimetry is well developed - direction ambiguity, zero sensitivity is helped with frequency offset - Bragg Acousto-optic modulators are often used
then you have a (many) MHz FM signal to demodulate linearly
then you have a (many) MHz FM signal to demodulate linearly
Dug,
Good to hear from you in this forum. I used to do all this laser interferometry stuff in a past life. It's not the electronics that is hard as MHz counters are routine parts of many digital I/O cards, but what is tricky with interferometry is having a phase sensitive counter (two counters offset by known angle between 0 and 90 deg so you know direction of travel. Also the optics need to be really rugged and as someone else said, you can use diode lasers beam splitters etc. They will quickly grow in complexity and the speaker will be an optics experiment rather than a closed loop feedback experiment.
Regarding the cone breakup issue, I would use a very stiff cone and a motor with extra high modulation authority. Rely on the feedback loop to sledgehammer the cone movement to match the input signal.
I have built interferometers, spectrometers and fiber optic scattering proximity probes and I still think the best and most cost effective way is fiber optic coupled light scattering. I would put the dual fiber probe tip on the backside of the dust cap through the hole in the vented pole piece. It is nice and dark and you get direct movement of cone.
Good to hear from you in this forum. I used to do all this laser interferometry stuff in a past life. It's not the electronics that is hard as MHz counters are routine parts of many digital I/O cards, but what is tricky with interferometry is having a phase sensitive counter (two counters offset by known angle between 0 and 90 deg so you know direction of travel. Also the optics need to be really rugged and as someone else said, you can use diode lasers beam splitters etc. They will quickly grow in complexity and the speaker will be an optics experiment rather than a closed loop feedback experiment.
Regarding the cone breakup issue, I would use a very stiff cone and a motor with extra high modulation authority. Rely on the feedback loop to sledgehammer the cone movement to match the input signal.
I have built interferometers, spectrometers and fiber optic scattering proximity probes and I still think the best and most cost effective way is fiber optic coupled light scattering. I would put the dual fiber probe tip on the backside of the dust cap through the hole in the vented pole piece. It is nice and dark and you get direct movement of cone.
Greetings xrk
That is basically what I did with the failed positioning experiment...did not use optic cable on that one but I have some parts at work that I might be able to adapt to that.
One more thing on the list to try.
🙂
I have built several systems with a piezoelectric tweeter crystal as an accellerometer.
Works really good!
use two wery thin twisted wires to the basket where you place an OPamp buffer. from there you can have a pretty long feedback cable to the servo cirquit/power amp.
Works really good!
use two wery thin twisted wires to the basket where you place an OPamp buffer. from there you can have a pretty long feedback cable to the servo cirquit/power amp.
Esl63,
Neat idea to use accelerometer as sensor based on piezo crystal. Acceleration is two steps of integration away from position, which I think is the variable we want to use for feedback. Do you have any closed loop feedback applications you can share ?
Neat idea to use accelerometer as sensor based on piezo crystal. Acceleration is two steps of integration away from position, which I think is the variable we want to use for feedback. Do you have any closed loop feedback applications you can share ?
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