By far, the most popular mic on the market today is the dynamic cardioid mic, so that's as good a place as any to start. "How does it work, what exactly is a cardioid, and how and where would you use it" will be our focus today. Let's look inside one and see what we find:
Well, it has a cone (like a small speaker), a voice coil (like a small speaker), and it sits in a magnetic gap (like a small speaker), so isn't it just a small speaker in reverse? Yes, and no. The operating principle is the same, but the execution is very different. When's the last time you saw a 3/4" speaker that went down to 30 or 40 Hz? Here's how it's done:
The system resonance is chosen for a mid band frequency. By itself, the capsule's response looks something like this (the black line):
...just one big resonant peak, with the response falling off rapidly on each side of the peak. Now you can tame that peak by putting in a resonant chamber that's tuned to that peak, which will give you two smaller peaks on either side, like this (
the red line):
And if you add two more resonant chambers, tuned for each or those peaks, and, if you make the chambers a little more broad band, the response starts to really flatten out (the blue line, and finally the green line):
...but remember, it's still a lot like a bunch of tuned coca cola bottles inside there.
Now ya gotta do all of this stuff JUST to get the response usable - never mind about the mic pattern yet!
A lot more to come!! Everybody still with me at this point? Any questions?
