Closed-Loop Amplification with Driver Cone Position Fedback - Page 3 - diyAudio
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Old 1st July 2013, 11:32 PM   #21
jcx is offline jcx  United States
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depending on radiation condition velocity or accel are more nearly proportional to SPL

both near/far field and intentional cone breakup/frequency proportional decrease in radiating area are in play

but position isn't important to sound production - just keep the average centered in the gap
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Old 1st July 2013, 11:56 PM   #22
xrk971 is offline xrk971  United States
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So a soundwave that a mic records and what we want the amp and driver to reproduce are not dependent on position? I argue that position x(t)=function of time is the fundamental parameter to measure because amplifier current drives voice coil position - I think they are a linear relationship and it is their nonlinearity that produces distortion. From position as function of time we can get velocity or acceleration. So we are trying to correct for the distortion by measuring position for error correction.
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Old 2nd July 2013, 12:56 AM   #23
DUG is offline DUG  Canada
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Originally Posted by xrk971 View Post

...

So we are trying to correct for the distortion by measuring position for error correction.
I would think so.

I rejected using an accelerometer for sensing because of the integration(s) required to get position.

It would be fine for sine wave vibration testing (which I did for 12 years in a test lab) but not for music! (IMHO)

I would like to see the results using a "burst" waveform using an accelerometer as feedback.

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Old 2nd July 2013, 01:18 PM   #24
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http://www2.ece.ohio-state.edu/~schn.../subwoofer.pdf

I have built several as i stated before... its working wery well!
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Old 2nd July 2013, 02:12 PM   #25
xrk971 is offline xrk971  United States
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Originally Posted by esl 63 View Post
http://www2.ece.ohio-state.edu/~schn.../subwoofer.pdf

I have built several as i stated before... its working wery well!
ESL,
Very nice paper - nice work man! Ohio State has some good stuff! My google search did not catch this and I am glad you pointed it out. This is exactly the info I was looking for. I am really surprised by how well the piezo accelerometer output tracks with SPL (Fig 3.3.1). What is the mass of the piezo element and can it be made small enough to work with a 4 inch full range driver with a typical Mms of 4 grams?
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X
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Old 2nd July 2013, 02:29 PM   #26
tyu is offline tyu  United States
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Thanks esl 63 for posting the bass sevo paper........Can you say what res.an cap was used in the Zobel??
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Old 2nd July 2013, 03:11 PM   #27
SY is offline SY  United States
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Originally Posted by DUG View Post
Counting fringes...yes...I would like to see the circuit to convert that to a linear signal.
It's a lot more convenient to process things digitally, then output the "final" analog version. In 1985, this took several large boards in a rack, these days, it's easily done in real time with a microcontroller and ADC/DAC.
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Old 3rd July 2013, 06:34 PM   #28
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You can use one extra voice coil as well...
But my experience is that a piezo tweeter works really really good!
http://www.macaulayaudio.co.uk/roaring%20sub.pdf

student project with accellerometer:
http://www.ti.com/corp/docs/landing/...ch_LaBella.pdf


Here is a study which is interesting.
Well i have some circuit design to share that works really good.
send me a PM
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Old 3rd July 2013, 06:35 PM   #29
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Sorry here was the link...
http://cogsys.imm.dtu.dk/nonlincomp/Klippel.pdf
esl 63
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Old 4th July 2013, 02:25 AM   #30
xrk971 is offline xrk971  United States
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ESL,
Thanks for the link on the dual voice coil technique with one serving as the transducer. Very clever, but it only gives signal when there is motion - kind of like the accelerometer. It is nice because it is easy to fit an extra sensing coil in a driver as the sensing one doesn't need to have as many windings to produce drive power. I am surprised that there is not a commercial implementation of this yet. Or is there and I am not aware of it?
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