How to measure turntable suspension?

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YNWOAN

Can any body tell me a definite way of measuring what frequency my turntable suspension is operating at? A friend of mine is using four 'power balls' (small, very bouncy 'rubber' balls) in his suspension and tells me he believes the suspension to be operating at 3Hz. I have also experimented with these balls (3 or 4 balls and a variety of loads) but just can't see how anything like 3Hz can be achieved. I also want to experiment with magnetic isolation so any help regarding the measurement of turntable suspension frequency would be enormously appreciated.

sreten

Hi,

If it operating at circa 3Hz it will bounce up and less than twice
for every single rotation of an LP which goes round at ~ 2Hz.
This should be easy enough to see by inspection.

Another way of doing it is getting a rhythm in your head that matches
the apparent rate an then timing typically 8 bars for a 4 note rhythm.
This should be ~ 10 seconds, (or 5 if your counting up and down).

On spring suspended subchassis turntables the main vertical mode
can be estimated this way, though lateral, rocking and twisting
modes may be higher in frequency, resolve to the bounce.

FWIW 3Hz to 4Hz is typical of heavy platter sprung subchassis
turntables and it is hard to imagine balls working at this point
without being on the verge of total collapse / instability.

Small wheel bicycle innertubes between two layers can get
this low. I have not seen a magnetic schema that works
in all planes, usually horizontal is severely compromised.

/sreten.

edit : the easiest method is a calibrated stroboscope .....

YNWOAN

Hi sreten, could you just clarify "If it operating at circa 3Hz it will bounce up and less than twice
for every single rotation of an LP", did you mean to type 'up and down'?

I thought I had read somewhere that 3Hz would equate to 3 cycles per second i.e. up,down,up,down,up,down per second?

sreten

Hi,

If your only counting the ups (ignoring the downs) then your counting cycles.
If your counting up, down, up, down, up, etc you are counting half cycles.

/sreten.

Don Bunce

If you have a metronome,set it to one click per bounce,and divide the BPM reading by 60 to determine the freq,ie:180 bpm =3 hz.

YNWOAN

Thanks Conrad, that is indeed pretty much exactly what I was looking for

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