So I've been reading and thinking lately... perhaps falling into that category "the guy reads a few articles off the web and thinks he's an expert, but he don't know shit."
Fundamentally, there is (a) the omni pressure transducer, (b) the figure 8 pressure gradient transducer, and (c) the baffle approach to turn a figure 8 into a directional mic by delaying the sound wave a tiny bit. The omni is simple enough that even I can understand it, no questions there.
First question... if I understand ribbon mics correctly, there is a ribbon hanging in space fixed at one end, with a magnetic field trying to hold the other end in place. When sound pressure hits the ribbon, there is a small lateral excursion, which tugs the magnet on the end, and that generates a tiny voltage. It seems to me if pressure comes from the front of the mic, or the back of the mic, it will generate the same magnitude excursion, and tug on the magnetic field the same amount, which generates the same little voltage. The magnetic fields doesn't care if the ribbon is being pushed left or right. If that's true, the same sound pressure impulse coming from the front or back should generate the signal voltage, no phase inversion when coming from the back side. Yet "everyone knows" the back side of the mic is out of phase with the front. Is the voltage generated from the ribbon swinging like a pendulum? I assumed it was a linear motion, like a solenoid. What am I missing?
I'm probably explaining it terribly, but I think I understand the fundamental idea behind directional (such as cardioid) mics. There is a baffle system or passage ways, and the sound pressure wave coming from the back of the mic has to run through a maze, which delays it a tiny bit, just enough so the same sound pressure hits the front of the diaphragm at the same time, canceling each other out. If I think about that, it's absolutely amazing that it works as well as it does, right up there with internal combustion engines and making a computer out of a bunch of transistors. Multi-pattern LDC's (like AKG414) have 2 of these modified pressure gradient transducers facing in opposite directions. Sum the voltages from the 2 cap in different ways, and you have yourself multi-patterns. OK, I think I understand that. My question is... in cardioid mode the back capsule is just not used at all, right? But it's this big set of flat plates, it's got to be "in the way". I would think a fixed card cap (my ADK-TC) would sound a hell of a lot better than double cap mics in cardioid mode (my TL's) but that doesn't seem to make a big difference. What am I missing? It's just all in the design of baffling I suppose.
Second question... a Schoeps MK8 is a single diaphragm condenser, intended to be very close to the "primary" figure 8 pattern, no doubling up on bastardized card caps here. So how do they do that? I'm guessing the backing plate is quite open and airy, which allows free air flow as much as possible, while still having enough meat left for capacitance. I'm sure those Schoeps engineers are pretty sharp guys, and it took them a while to get it right, so why doesn't every other company make one like it? Is it just because there isn't a big market? I suppose most people don't understand philosophically that it is very cool to have this pure and simple primary figure 8... most people would rather have a multi-pattern. Still I would think there would be more examples out there, including a bunch of cheap Chinese copy cat models. What am I missing?