Many people say a mic spec sheet is useless, it can't tell you how a mic will sound, whether good or bad, on any particular source or any source at all. While that is true, that's not what the spec sheet is for. It's more to save us time in not bothering to try out mics that are completely inappropriate for our intended source and the rest of our gear.

As I imagine you might know, mics come in two basic flavors (with some unusual others I'll ignore for this article): dynamic and condenser. Ribbons are dynamic. Some strange Europeans call condenser microphones "capacitor microphones". (then again they call apartments "flats" and car trunks "boots".) Condenser is an old word for capacitor, so take your pick. And there! That's the first spec: microphone type; sometimes called operating principle.

Within that same spec, you might also see a reference to polar pattern, perhaps in an oblique way: "pressure" or "pressure gradient".  In simple words, a pure pressure mic is omnidirectional, and a pure pressure gradient mic is bidirectional, or figure-8.

Also, you might learn some more information about the type of mic. For example, condenser mics are further subdivided into two categories, electret and externally biased (or polarized). The latter are sometimes called "true" condenser mics, but an electret mic capsule is just as much a capacitor, so I think that's prejudiced!  OK, I'm "biased" too... (sorry for the pun!) And, finally sometimes the diameter of the capsule diaphragm is stated. "Small" and "large" are the usual descriptors, but sometimes the'll be kind enough to specify the actual diameter in millimeters or inches.

So what have we learned about this mic so far? Whether it's a dynamic or condenser style mic, it's pressure gradient or polar pattern and it's capsule size. What does that all mean to us?

well, dynamic mics and condenser mics have very different applications. Broadly generalizing (with many exceptions), condenser mics tend to have better transient and high-frequency response. They also tend to be much more sensitive (We'll talk more about sensitivity when it appears further down the spec sheet.).

Diaphragm size can affect those specs as well, though there is some disagreement as to how much.

We also know one important item: condenser mics need power. This power is usually supplied via "phantom power" supplied by the preamp, although an external power supply or an internal battery are two other possibilities. Dynamic mics do not need phantom power, except for some recent ribbon designs that have an internal preamp. Furthermore, the voltage required often differs by type; externally biased condensers often want a full 48V, but electrets are frequently happy with anything from 12V to 48V. How much power does our mic want, though?  Usually for condenser mics you'll see a spec for current, in mA, instead of volts. The maximum possible under the phantom power standard is 10mA, but most mics use far less. 2mA to 5mA is typical. If you see much more than that on a mic spec sheet, be a little careful. Not all preamps can provide the full 10mA defined in the phantom power standard, and as we shall see in a couple of weeks, preamp manufacturers are very bad about admitting that.

Next up is polar pattern. I have already mentioned the two extremes; all other polar patterns are in between: subcardioid, cardioid, hypercardioid, and even more in between patterns. Different polar patterns are generally selected for their pickup and/or rejection of sources at various angles, or more artistically, for the characteristic frequency response they offer. Usually along with the pattern, you'll get a polar response graph, at least at 1kHz, but often at a range of different frequencies.

You can see a lot from this latter type; if a mic has a consistent off-axis response at a range of frequencies, it might be a better choice for use in a stereo pair than a mic that has all kinds of crazy things going on at diffeent frequencies. That one you'd probably want to save for on-axis use. Just keep in mind that, because of the nature of sound itself, all polar patterns are somewhat omni at low frequencies, and somewhat directional at high frequencies.

Naturally, next on our spec sheet is the frequency response. Don't flip out over the hard numbers you see here. You don't necessarily want every mic you use to have 20Hz-20kHz response.  That, by itself, doesn't make a mic "better". Microphones aren't studio monitors! What does that numeric range mean, anyway? Most manufacturers will list the "corner" frequencies of the mic's response at the extremes; that is, the 3dB or maybe 6dB down points at the high and low end. So a mic like the Shure SM81, for example, is listed as 20Hz-20kHz, whereas the SM58 is 50Hz-15kHz. Does that mean the SM58 has no response at all below 50Hz?  Such that if you use it on bass cab, the low E will magically disappear?  No, of course not.  It's a smooth downward falling curve, so maybe -8dB at 40Hz. (Also, there is proximity effect, which causes directional mics like the SM58 (and SM81) to have increased bass response when the source is within a fcouple of inches. Better to look at the actual frequency response curve graph.

So next we look at the frequency response curve. Some will say these are notoriously inaccurate. From a measurement microphone perspective, that is probably true. If you take any one example of a microphone, you might get a fair amount of deviation from the published curve, which is typically an average of 10 or more units. Put simply, no two microphones, even of the same make and model, will have identical curves to each other, let alone ientical to the one printed on the spec sheet. That graph is not intended to represent precision; it's main puropse is to represent overall character.

So instead of reading every nook and cranny of the wiggle on that graph, instead look for broad patterns. How fast does the high end rolloff? Are there peaks in the presence range for a tailored response, or is this a relatively flat-response mic? Or is the thing just really dark? Unfortunately, the manufacturer won't tell you if those presence peaks sound like audio crack cocaine or nails on a chalkboard. But it might keep you from buying a mic for a totally inappropriate purpose.

Next time: math and mics.