Microphones: Patterns, Placement and Proximity

A microphone converts moving air into voltage. In doing so it makes three decisions for you: which directions it listens to, which direction it is deaf in, and what it does to sound arriving from neither. All three are settled in the metalwork before you plug it in. Nothing downstream revisits them — by the time the signal hits a fader, what you wanted and what you did not are one signal.

Bands choose a microphone by how the front of it sounds, which is the least useful thing about it on a stage. A vocal mic spends the night surrounded by two wedges, a ride cymbal and a guitar cabinet. The channel reaching the console is therefore your singer plus a summary of the room, and how the mic treats that summary — not how it flatters the voice — decides whether an engineer can build a mix.

Three Ways to Turn Air Into Voltage, and Only One Has to Be Fed

A dynamic microphone is a generator. Its diaphragm carries a wire coil that sits in a magnet's gap, and a conductor moving through a magnetic field produces current all by itself — so the sound does the work and no power ever enters the microphone. The cost is that coil's mass. A heavier moving assembly starts late on a transient and runs out of top end sooner. That is why a snare reads blunter through a moving coil, and why the moving coil is still working ten years later.

A condenser suspends a very thin diaphragm a fraction of a millimetre from a fixed plate, forming a capacitor that changes value as the diaphragm moves. Almost no mass is in motion, so the top octave survives and attacks keep their edges. Two things follow. The capsule needs a standing charge to work at all, and its output is far too high-impedance to drive a cable — so every condenser carries a small built-in amplifier that also needs feeding.

A ribbon hangs a corrugated strip of foil, microns thick, loose in a magnetic gap. Both faces are open to the air. Pressure from the side pushes equally on each and moves nothing, which makes a classic ribbon a figure-of-eight by construction rather than by choice. Its moving mass is smaller than a coil's, and its top end tapers off rather than peaking — so ribbons civilise sources that read as harsh through a condenser.

That feeding is phantom power: direct current sent up the same two wires carrying audio back. IEC 61938 defines P48 as 48 volts give or take four, so anything from 44 to 52 qualifies. It arrives through matched 6.81 kilohm resistors, capped near 10 milliamps; the same standard covers 12 and 24 volt supplies. Identical voltage on both legs of a balanced pair means a dynamic mic on a correctly wired XLR never sees a difference across its coil. The old blanket warning about ribbons is half wrong now — active ribbons require phantom and passive ones survive it on good cable. What destroys a ribbon is a shorted or miswired cable, or a circuit patched while phantom is live.

What a Microphone Refuses to Hear Is the Spec You Are Buying

A polar pattern gets taught as where a microphone listens. Turn it around. Every pattern hears what is in front of it perfectly well, so the only part of the diagram that changes your night is where the deaf spot points — and an omni has none. It takes the wedge, the cymbals and the room at full strength.

The rejection figures differ more than the marketing suggests. A cardioid nulls dead behind and sits 6 dB down at each side. A supercardioid pulls its two nulls forward to roughly 126 degrees — about over each shoulder — and lets the rear back in around 12 dB down. A hypercardioid tightens the nulls to about 110 degrees and drops the sides 12 dB. Its rear lobe, though, climbs back to 6 dB down, so it hears behind itself about as well as beside itself. A figure-of-eight nulls at 90 degrees, the deepest side rejection going, and hears front and back alike.

The consequence is where the monitors go. A cardioid vocal mic wants its wedge dead behind it — but point a wedge at the back of a supercardioid or a hypercardioid and you have aimed it into a live lobe instead of a null. Those two want the box offset toward one shoulder, or a splayed pair either side of centre. Swapping in a more directional mic and leaving the monitors alone is how a stage gets worse.

Proximity Effect Is EQ That Moves With the Singer

Get close to a directional mic and the low end swells. The mechanism is worth knowing, because it tells you which mics do it. A directional capsule is open at the back as well as the front, and responds to the difference in pressure between its two faces. From a distance the arriving wavefront is essentially flat. What difference remains comes almost entirely from the extra centimetre the wave travels to reach the rear — a delay, which yields a bigger difference up high than down low, and which the capsule's design compensates for.

Up close the wavefront is still visibly curved. The back of the capsule can be almost twice as far from a mouth as the front, so the two faces genuinely see different loudnesses, and that gap is the same at every frequency. At 100Hz the delay-driven difference has shrunk to nearly nothing, leaving curvature as most of what remains — and the bass rises to meet it. Because it all comes from the gradient, the effect tracks how much gradient a pattern uses. Figure-of-eight shows the most, cardioid about half that, omnidirectional none whatsoever, since a sealed capsule reading absolute pressure has no second face to compare against.

That omni exemption is the fact people get wrong, and it is why a lapel mic clipped to a chest does not boom. With a pure gradient mic the rise becomes audible around a metre out and steepens fast. A cardioid handheld with lips on the grille, some 6 mm away, runs 6 to 10 dB up below 100Hz. Singers who work a mic are riding that curve — leaning in for a quiet verse, backing off a hand's width when the band arrives. It is also why a stage vocal mic sounds thin on a stand: the low end is rolled off by design, assuming a mouth will put it back.

Off-Axis Is Where a Cheap Microphone Gives Itself Away

Printed as one line, a polar pattern is a fiction, which is why data sheets publish a stack of them. Directivity slides toward omnidirectional as frequency falls; the outdoor lesson made that point about loudspeakers, and capsules do it too. It tightens up again at the top, once a wavelength shrinks to the same order as the diaphragm it is hitting — a 10kHz wave is about 3.4 cm long. So a sound arriving from the side is not simply quieter; it is quieter by a different amount at every frequency, which is a filter nobody designed and nobody can undo.

Live, that filter processes nearly everything, because almost nothing on a stage reaches a mic on axis. The hi-hat bleeding into the snare mic, the bass cab reaching the vocal, the room returning off the back wall — all of it lands in the same channel as the sound you wanted. A mic with an ugly off-axis response pours a honking version of the whole stage into every fader you own, which is what you are really fighting when a mix refuses to clear up. One that stays even off-axis gives you bleed that just sounds like a quieter room. A spec sheet shows you the axis nobody on your stage is standing on.

Distance Buys You a Ratio, Not a Level

Moving a mic changes two things at once, and loudness is the less interesting one. Direct sound obeys the open-field rule of 6 dB per doubling while the room's contribution barely shifts. Halve the gap to a source and you gain 6 dB of instrument relative to room — then hand the level straight back at the preamp. That ratio is why close-miking works on a loud stage, and the physics lesson already gives the spacing rule for the moment a second mic joins the first.

Pattern is the other lever on the same ratio. A directional capsule declines part of the diffuse field as well as the direct one. The feedback lesson gives the figure: a cardioid collects roughly a third of the diffuse energy an omni would. Restated as distance rather than decibels, that lets a cardioid sit about 1.7 times as far out as an omni for the same source-to-room balance, a supercardioid 1.9 times, a hypercardioid twice. That is the whole reach of a directional mic — not a telescope pulling a source closer, but a capsule refusing the room.

Working the Stage With What the Pattern Gives You

• Aim the null, not the mic — rejection is a direction you point on purpose, so find where the wedge sits before deciding where the mic ends up.
• Check the pattern before moving monitors — a supercardioid nulls near 126 degrees and a hypercardioid near 110, so neither one wants a wedge dead behind it.
• Reach for an omni when nothing needs rejecting — give up the null and you get back an even off-axis response, no proximity effect, and real tolerance of wind and popped consonants.
• Pick a working distance and hold it — proximity effect swings 6 to 10 dB of low end as a singer drifts, and nothing downstream untangles that afterwards.
• Audition a mic from the side — talk into its flank, and if your voice goes honky rather than merely quieter, every bit of stage bleed will arrive sounding that way.
• Switch phantom off before patching — the DC is harmless to a dynamic on sound cable, but a shorted or miswired one under live phantom is what destroys ribbons.