Re: [ATM] Voice coil actuators was: DC Motor for grinding machine question

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Many are asking questions about this.  I don't think Don is intending 
to drive the strokes of the tool with voice coils.  I believe what he 
intends to do is shake the tool a little bit with the coil actuator 
(or motor) in a pseudo-random way (using pseudo-random noise.  This 
"noise" will swamp out any periodic vibrations introduced by the 
bearings or driving motor/components.  Since is is nearly random, it 
won't introduce any periodic vibrations itself.

It's a neat idea.

Don believes these periodic vibrations might have an effect on the 
surface roughness of the mirror.  Personally, I don't, but I've been 
wrong before!

Mark Holm wrote:
> As I recall, most high end audio amps spec down to about 20Hz.  Below
> that, humans just hear the windows rattling.  The low C on a 32 foot
> organ stop has a fundamental frequency of about 16 Hz.  I hear that as
> more of a vibration than a tone.  (But what a vibration!)

Now a little off-topic for the audiophiles among us....

Audio amps can be AC-coupled (capacitor in series in the output, 
blocking DC), as tube amps often are, or DC-coupled (no capacitor in 
the output).  Those that are AC-coupled will roll off in the low 
frequencies until the response is zero at DC.

Good audio amps try to get down into the infrasonic range (below 20 
Hz) because that vibration is important in two ways - 1) It's fun to 
shake the walls, and 2) accurate reproduction of the low-frequency 
information is important in conveying the ambiance and acoustic 
properties of the recording venue.

	Mike Lockwood

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