Jim Lesurf wrote:
In article , Nick Gorham
wrote:



I just tried the experiment on a few caps I have to hand. The ones that
produces a sound when driven by a sig gen were a BC 368WKT 220nf,
Acotronics MKP 47nf and a 2.2uf ClarityCap SA. Ones that I tried that
didn't prduce any sound I could hear were from Solen and Mundorf.


Not sure what you refer to as a 'name brand' but I would think at least
the BC would fit that decsription.


Though as expected the level was very low, at the 2vRMS 5kHz from my sig
gen, it needed the cap to be against the ear, but it was clearly there.


What is the o/p impedance of your sig gen? 2.2microF at 5kHz is about 15
Ohms if my fingers just pressed the correct buttons on my hand calculator.
Implies a reactive level of over a Watt if you really were applying 5v rms.

I just measured it, somewhere around 65R, off load it was giving 8v RMS.
I said with the cap in place, it was producing about 5v P/P on a scope
trace, or about 2v RMS.


If I understand the ClarityCap papers correctly, you'd need to find the
mechanical resonance of each cap to get a peak level of vibration. So 5k
might not give as large a response as some other frequency.


Yes, but I was just trying to test the assumption that no cap would
produce any noise, having found that some do under simple to achieve
conditions, there is scope to perform more detailed tests.

I wonder if something like a strain gauge attached to the cap would be
the best way to measure any vibration.

--
Nick