Ceramic Cartridges and RIAA Equalization, Plus: Sneak preview of Knowzy samples page Options

[Knowzy]

The upcoming page* showcasing the USB turntables samples I've been posting put a renewed focus on ceramic cartridges. This caused me to update the case against ceramic carts in the turntable guide.

I added a new section on RIAA equalization and would appreciate a review for technically accuracy. In particular, I would like you to pick apart this declaration:

Ceramic cartridges don't require a pre-amplifier yet still approximate the RIAA curve. You might say that ceramic cartridges equalize the audio signal organically: They rely on their chemical composition to implement the RIAA curve.

Am I over simplifying? Are there capacitors or other components down the line that also affect the equalization of the signal or is it truly all in the cart itself?

As always, I appreciate your insights.

-Jeff

* Sneak preview. This is the only link on the Internet leading to that page.

[Knowzy]

Actually Clive and I agree. The ceramic cartridge inherently rolls of the treble with a -6 dB/octave roll-off because it responds to the amplitude of the music in the groove, not the velocity.

I'm still pretty fuzzy on the difference between constant-amplitude and constant-velocity (I even went as far as asking the EE forum on PhysicsForum.com to define and contrast the terms- no takers yet).

My fuzziness aside, does this mean my declaration stands up, particularly if we replace my uber-Californian adverb "organically" with "mechanically?"

[cliveb]

I'm still pretty fuzzy on the difference between constant-amplitude and constant-velocity (I even went as far as asking the EE forum on PhysicsForum.com to define and contrast the terms- no takers yet).

Consider an LP groove with a frequency of X. In order for the stylus to trace this groove for a certain time period, it needs to travel a distance proportional to X. Now double the frequency to 2X. The groove wiggles back and forth twice as many times in a given period of time, and therefore the stylus must necessarily travel twice as far. Given that it must do so in the same period of time, it therfore follows that its speed is doubled. And if its output is proportional to velocity (a magnetic cartridge), the signal level also doubles. (Twice the signal level = 6.02dB, and twice the frequency = 1 octave, hence Arny's statements about 6dB/octave). But if its output is proportional to amplitude (a ceramic cartridge), the signal level depends only on the size of the sideways deflection.

My fuzziness aside, does this mean my declaration stands up, particularly if we replace my uber-Californian adverb "organically" with "mechanically?"

The difference between constant-velocity and constant-amplitude is down to simple geometry. I suppose the analysis of geometrical changes with respect to time is the area of mathematics we call "mechanics", so you could use that term. But it's important not to confuse this term with what a lot of people think of when you say "mechanical" (like how machines work).

The reason why a magnetic cartridge is constant-velocity is due to the laws of electromagnetics. If you move a magnet next to a coil, you induce a current that is proportional to the speed at which the magnet moves (all other things such as strength of magnet, turns on the coil, etc. being equal, of course).

A ceramic cartridge is a constant-amplitude device because the nature of the piezo-electric effect is such that the generated voltage is proportional to the pressure applied.