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audio controlled fan system ?

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freejazz

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I am planning to do an art piece in a warehose with fans that speed up and slow down based on the volume of an audio signal.

The audio signal will be prerecorded (not live) and has been made with 4 ocs. being controlled by a slow sine wave LFO. So the fans changing should be fairly obvious.

the fans will be moveing large tranceing paper stencils so huge shadows on the wall will be changing.

Thanks for any comments and suggestions.
 
There are a number of things to address in a project like this. I'll list some of them.

1. The air volume will be varying, based on your description. You will need to establish the minimum air volume and the maximum air volume to get the desired effects. Rather than volume you might establish fan motor rpm range. I don't know what kind of fans you have.

2. Worth mentioning, depending on the type of fan, you could vary the amount of air with a motorized damper. That might be simpler/cheaper that varying the fan speed. Again, not sure what you have or need so it's hard to say much more about this.

3. If you choose to vary the fan motor speed - the type of fan motor will determine the type of speed control. A universal AC motor can often be controlled more simply than most AC motors. Fan horsepower will usually govern the type of motor. If the motor isn't universal (or DC) then you'll need to use a Variable Frequency Drive to vary the speed.

4. Fan torque requirements matter. As the speed of a motor is reduced the ability of it to develop the necessary torque changes. If at any point the motor can't develop the torque the fan needs it will struggle and likely burn out. I can't cite any general rules of thumb because I don't know what kind of fan or what kind of motor you have - too many possibilities at this point.

5. You would need to characterize the response of your control system. Let's say you establish the min and max rpms for the fans. You need to know how to vary it in between. You want it to vary with the music but will it be a simple linear proportion - or something different. You'd likely establish this with some experimentation. I'd say you'd want some programmable system so that you can play with the response.

6. You would need some means to listen to the music and get some kind of output that is useful for controlling the air volume. It would seem that a fairly simple arrangement of filters would be sufficient.

I still keep trying to envision the magnitude of your project. I was working with someone who had this in mind for a large mall display. It would have been impressive but he had to abandon the project - just too expensive because of the size. It would seem that something small could be easily done with DC powered fans and relatively simple motor speed controls.

Anyway, sounds like fun.
 
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