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control systems (maybe PID)

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qubits1

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I want to follow a 100 hz sine wave using some kind of control system. I looked at PID, but people said PID controllers are not fast enough. Can someone give me some pointers on what kind of a control system would be able to follow 100hz sine wave with a sensor lag of 1ms?
 
What exactly are you trying to do? Some details of this project would help.

Ron
 
Input come from a function generator and goes to an Amplifier that drives the speaker. The speaker is in a chamber. The sound bounces of the walls and creates harmonics. Now I want to keep sounds in this chamber at only the input frequency. So, I want to use the transducer(microphone) as a sensor in a feedback control system to drive the error between the input wave and sensor to zero. Essentially, it removes harmonics and noise.
 
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why wouldn't it be fast enough? the limiting factor would really be the gain-bandwidth product of the amplifier you would use.
 
How does an acoustic wave that bounces off a reflective surface cause harmonics? It takes a non-linear element to create harmonics. How is an acoustic wave bouncing off a surface non-linear?
 
The trick in any kind of feedback circuit such as this, is to prevent positive feedback and instability (the classic public address system squeal). The feedback phase will vary with frequency depending upon the size of the chamber, thus compensation could be rather complex. You would probably need to plot the gain and phase of the microphone output to speaker input versus frequency to determine the characteristics required of the compensation network to provide a stable feedback loop.

But as Mike asked, where are you getting harmonics? They are likely just from simple speaker distortion. Are you trying to generate high levels of sound?
 
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