mono vs stereo vs quad

[4krow]

 Funny that I should ask, yet curiosity wins again. I get that a mono cartridge produces sound from a groove by moving up and down. I kinda get that stereo cartridge gets it's signal by moving side to side ( but what about crosstalk). Then, I will never understand how a quad cartridge can glean TWO more channels of info from a single groove! Anyone here know that story?

[fullheadofnothing]

What you get you got wrong:

Mono is horizontal (well, unless we're using Edison's hill-and-dale, but, so far as I know, there are no quadraphonic cylinders).

Stereo is horizontal AND vertical, or neither, depending on how you think about it (the grooves are cut 45

[Grainger49]

Ok, the three Quad systems I am familiar with are QS, SQ and DynaQuad.  DynaQuad used a single (mono) difference channel. 

Sansiu's QS was an encoding method.  It was great with Jimi Hendrix's EXP.  The guitar ran around in a circle.  Jimi must have known something that we all didn't know.

Sony's SQ was like FM multiplex.  It had a discriminator signal that told the decoder how to extract the rear, left and right, from the front left and right.

[4krow]

 FHON,
  The mono cartridge that escapes my memory is expensive(surprised me) and it sits in the cartridge without a cantilever, meaning that it can only move up and down. I am sure that this is the way a mono record is cut.
  Are you suggesting that a stereo groove uses the side to side, AND the 'hill and dale' for the channels' signals? Sorry, I should have gone to wikipedia before responding.

  G,

 I had never considered a carrier signal for Quad. Another ingenious idea.

[4krow]

Let me show where I got the idea that mono needle only moves up and down----

[fullheadofnothing]

What, exactly, is this proving? If there is a bump that pushes it to the left, it will move to the left. If it pushes up, it will move up. A three dimensional object can move in three directions. Mono records are horizontal, for literally over a century.

[Grainger49]

The stylus placement looks a lot like the old London Decca cartridge.  It was called a "positive tracing" cantilever.  It should still have room to move side to side in the hole.  I think the stylus was probably centered in the hole when it was made.

[4krow]

 Wow, hit a nerve eh? Was just showing what gave me the idea THATS all. No doubt I have a lot to learn. Not trying to prove my own theory.

[porcupunctis]

The channels are separated by the way the coils are arranged relative to the movement of the magnet.  Movement created by one side of the groove is optimized for one coil and (almost) unnoticed by the other.

If the magnet moves "to and away" from the coil, you will generate signal, but if it moves back and forth staying the same distance, then very little if any signal is generated.  So, they are offset by 90 degrees. 

That's a pretty simplistic explanation.  I'm sure there are more devils in the details than I would ever want to know.

Hope that helps.