Eddy current damping

[dqswim]

There seems to be much interest in reducing audio vibrations but I have seen no use of eddy current damping.

As an example Eddy current damping works when a copper plate is moved through a strong magnetic field. The magnetic field induces an opposing charge in the copper plate which acts as an efficent way to dampen vibrations.

I guess for this to work the audio component(s) of interest would have to be floating or suspended by springs. I'm sure I've seen mention of this, at which point taking the next step to dampen the vibrations would be easy with a few rare earth magnets and a copper plate.

At the moment I don't have plans for testing this at home, maybe over the summer

If anyone has gone to such lengths to deaden vibrations I would like to hear about it.

-dave

 

[Francis_Vaughan]

I think you would want to provide a good story about exactly which vibrations you wish to dampen. Eddy current damping has seen use - in particular in tone arms. But it's efficacy requires movement so that the dominant dimension of the conducting mass is the one moving and cutting the magnetic lines of force. Fine if a plate is moving along the plane of the plate, but useless if you are trying to dampen tangential vibration, which is the usual mode. For other vibrations you may need to show they actually exist, and then that they are important. Mounting an item of audio equipment in springs would appear to be making a problem to solve, rather than the converse.

Simple lossy mechanical dampening typically has much greater loss, and will be preferred, except when there is a need for a very well controlled contactless damping. A lump of rubber is an astoundingly good damping material.

For damping a vibrating plate you really only have constrained layer damping, which can also work very well.

Calculations to show the energy loss in the system would a good idea too, then you could relate them to equivalent mechanical resistance. Or, closer to home, model the system as an equivalent RLC, and see what it gets you.

 

[dqswim]

Thanks for the reply, I'll have to look into their use in tonearms.

I admit that my knowldege of the vibrations associated with audio equipment is lacking. Maybe I need to find some way to get and hook up an accelerometer to my amplifiers and my speakers and then I would know what needs to be done.

I just though of the idea because I had seen it mentioned on the wilson audio site that david wilson suspended his turntable from rubber bands and I though that damping in such a case might work well.

The rubber plates would definetly be easier to impliment and they do a good job at many frequencies. I think the benifit of the eddy current damping would come in is lower frequence vibrations. On that note I am interested in some of the calculations of vibration damping and associated energy loss, do you have any suggestions or references to get me started?

 

[Francis_Vaughan]

The Dynavector DV505 is a good example of eddy current damping of a tonearm. What a classic beast that was.

Hanging a turntable from rubber bands is simply an extreme example of any suspended chassis turntable. It forms a mass/spring low pass filter. With long rubber bands the spring constant of the bands would be very low, and so the frequency very low too. One would have to worry about the issue of picking up additional air borne energy if the chassis was too high up - although the propensity to pick up lower frequencies may actually be further diminished. Adding an eddy current damper to such a beast might be rather a good thing - you would want some damping, and the lack of contact would help avoid conduction of higher frequencies through the damping mechanism.

Look at just about any junior level undergraduate mechanical engineering textbook for a good start. But the easiest way to work with simple ideas is to translate them into electrical equivalents.

So far, nothing above on amplifiers, let alone solid state amplifiers. So to keep us honest ... No doubt glowing bottles can gain from good vibration isolation. There are certainly some claims about microphonics in solid state designs too. However, as always, some numbers wouldn't go astray. I find some of the lunatic fringe stuff with, so called, vibration isolation, damping, or control, quite off the edge.