Phono preamp headroom - why?

[MaxwellsEq]

I would understand the logic of A weighting if the only thing that mattered is whether humans can hear pure turntable rumble. But there's so much going on below 30Hz, including arm-cartridge resonance and downstream electronic and speaker sensitivity to low frequency perturbations that I thing it should be an absolute value.

 

[sergeauckland]

Regarding rumble, every rumble measurement I've seen uses the IEC curves, which were identical to earlier British Standard and DIN curves, rather than A weighting. A weighting has been applied to broadband noise, not to rumble.

There used to be rumble meters available from audio test equipment manufacturers, but as none of mine have the rumble filters, I've created the filters in Audacity which works as well as it can, given the LPs available.

As to making measurements, I've never found it satisfactory using test LPs, as the noise from the LP masks the actual turntable rumble. The best way is using a rumble bridge, which is now virtually unobtainable, and I wish I had one.

I've never seen any figures for the rumble on the cutting lathe, and I would like to know how that's measured, whether with a bridge, or from a cutting. I would expect the numbers to be rather different.

S.