The hook
The mic cabinet has two kinds of microphones in it. One kind gets handed to every singer without a second thought. The other kind lives in a padded case, and the one time you plugged it in, it was silent. Then someone pressed a mysterious button labeled +48V, and suddenly it was the most detailed microphone you'd ever heard. Also, someone immediately warned you never to press that button "wrong."
Two kinds of mic, one scary button. Ten minutes from now, none of it will be mysterious.
The lesson
Every microphone does the same job: pressure wave in, voltage copy out (lesson 1.4). What separates the two big families is how they pull it off, and the how determines everything: toughness, sound, and whether they need that button.
Dynamic mics: the electric generator.
Inside a dynamic mic, the diaphragm (the thin membrane the sound hits) is glued to a coil of wire suspended in a magnet's field. Sound moves the diaphragm, the diaphragm moves the coil, and a wire moving through a magnetic field generates voltage. That's it. A dynamic mic is a tiny electrical generator powered by sound itself.
Consequences of that design:
- No power needed. It generates its own signal.
- Nearly indestructible. A coil and a magnet survive drops, spit, drum hits, and being used as a hammer (don't).
- Loves loud. Point it at a snare drum or a screaming guitar amp; it cannot be overloaded by any sound a stage can make.
- Slightly slow. The coil has mass, and mass resists fast movement. The very quickest details (the airy top end, the finest transients) get smoothed over. Dynamics typically roll off before the highest frequencies.
The classic stage vocal mics you already know are dynamics. They're the default for loud, close, rough-service duty: stage vocals, snare, toms, guitar amps.
Condenser mics: the measuring instrument.
A condenser replaces the coil with two plates, one fixed, one a feather-light metallized diaphragm, separated by a hair's width of air and holding an electrical charge between them. Sound flutters the light plate, the spacing changes, and the changing spacing produces the voltage. Almost no moving mass at all.
Consequences:
- Exquisitely fast and detailed. With nearly nothing to move, the diaphragm follows every flicker of the sound: full frequency range, crisp transients, the "expensive" sound.
- More sensitive. Higher output, hears quieter sounds and sounds farther away. (On a loud stage that's a mixed blessing: it hears the drums from across the platform too.)
- Needs electricity. The plates must be charged and the tiny signal buffered by electronics inside the mic. No power, no output. Enter the button.
- More delicate. Not glassware, but not a hammer either.
Condensers are the choice when detail matters more than durability: acoustic instruments, choirs and ambient pickup, cymbals/overheads, studio vocals, and most headset and lavalier mics (their tiny capsules are almost always condensers).
The elegance of phantom power is that it needs no extra cable: the console pushes 48 V up both signal conductors of the balanced line equally, and because balanced inputs only listen to the difference between the wires (lesson 2.3), a voltage that's identical on both is inaudible. The condenser sips power off the line; the audio rides on top.
And the fear around the button is mostly — mostly — overblown:
- Dynamics don't care. A healthy dynamic mic on a proper balanced cable simply ignores phantom; the identical voltage on both wires produces no current through the coil. Leaving +48 on across a dynamic won't hurt it.
- The real dangers are specific: vintage ribbon mics (a rare, delicate breed; if your church owns one, you'd know) can be damaged by phantom, especially with a faulty cable; and anything connected through a damaged or miswired cable can get the 48 volts where it doesn't belong. Consumer gear plugged into mic inputs (laptop adapters, wireless receivers that specifically say no phantom) can also object.
- The everyday danger is your speakers and ears: switching phantom on or off sends a loud POP down the line.
Which yields the two habits that make you phantom-safe forever: know which inputs have +48 on and why (per-channel on many boards, global on some older ones; know which you own), and mute the channel (or master) before toggling phantom or plugging/unplugging a phantom-powered line.
One more spec you'll meet on every mic box: we'll cover polar patterns (which directions a mic hears) in the next lesson. It deserves its own session because placement plus pattern is where feedback is won and lost.
Go deeperoptional
Dynamic mic physics is Faraday's law in a can: output EMF V = B·l·v, flux density times wire length times velocity of the coil. Note the v: a moving-coil mic is a velocity-sensing transducer, and its output rides on how fast the diaphragm moves, not just how far. The moving mass (diaphragm + coil, tens of milligrams) with the suspension forms a resonant system typically tuned in the 1–5 kHz presence region. The familiar "presence bump" of stage vocal mics is a designed-in consequence of the physics, not an accident. Above resonance, mass reactance rolls the response off, which is the honest reason dynamics fade past ~8–12 kHz.
The condenser is a capacitor with C = εA/d. Hold charge Q nearly constant (via a gigohm-order bias resistor: the RC time constant vastly exceeds audio periods), and since V = Q/C = Q·d/(εA), voltage tracks plate spacing linearly. The diaphragm can be metallized mylar a few microns thick with sub-milligram moving mass, two to three orders of magnitude lighter than a dynamic's coil assembly. Hence the transient fidelity and extension to 20 kHz and beyond. The catch is impedance: the capsule's source impedance at audio frequencies is gigohms, unusable directly, so an impedance-converter FET or tube sits millimeters behind the capsule. That electronics stage is what phantom actually feeds (in true condensers it may also generate the polarizing voltage; electrets carry a permanently charged layer and use phantom only for the buffer).
Phantom's implementation is a study in balanced-line thinking: +48 V DC is applied to pins 2 and 3 through two 6.81 kΩ resistors matched to ±0.4%, with pin 1 as the return. Because both signal legs sit at identical DC potential, a differential input sees zero volts of it; capacitors (or the input transformer) block the DC from the preamp's audio path. The tight resistor matching isn't pedantry: any mismatch unbalances the line's source impedances and degrades CMRR, converting mains hum from "cancelled" to "audible" for that channel. This is also precisely why phantom is harmless to healthy dynamics (equal potential on both ends of the coil → no current) and why a damaged cable is the actual hazard: short pin 2 to ground while pin 3 holds 48 V and current now flows somewhere unintended, through a ribbon, if one is attached. (Modern ribbon mics increasingly include protective transformers or active electronics; the "phantom kills ribbons" rule is really "phantom plus a fault kills ribbons," but the safe habit is the same.)
Two spec-sheet numbers worth decoding on any mic: sensitivity (mV/Pa, output at 94 dB SPL; condensers commonly 8–30 mV/Pa, dynamics 1–3 mV/Pa, which is why condensers need ~15–20 dB less preamp gain) and self-noise (dBA, the capsule electronics' own hiss; excellent large-diaphragm condensers reach 5–7 dBA, while dynamics have effectively none of their own but demand more gain, which surfaces the preamp's noise instead: the corridor logic of lesson 2.2 again, one level down).
Remember
- Dynamic = coil + magnet: self-powered, tough, loves loud, slightly soft on top. The stage-vocal and drum default.
- Condenser = charged plates + feather diaphragm: detailed, fast, sensitive, and needs phantom power to work.
- Phantom is 48 V sent invisibly up the mic cable. Harmless to healthy dynamics; hazardous mainly via ribbons and faulty cables.
- Mute before toggling phantom or plugging any powered line. Every time.
- Choose by job: armor (dynamic) for loud/close/rough, lens (condenser) for detail/distance/air.
Your turn
- Sort your mic cabinet into dynamics and condensers, and label the case or shelf.
- Determine whether your console's phantom is per-channel or global, and audit which channels have it on right now.
- Practice the reflex until it's automatic: mute, plug, unmute.
- Pick one source you currently mic with a dynamic (acoustic guitar, piano) and try a condenser on it at rehearsal. Listen for what the lens sees that the armor missed.