The hook
Two churches again. In one, the choir mics sound like a choir. In the other (same brand of mics, same size choir) the sound is thin and strangely hollow, like the singers are at the bottom of a well, and the system feeds back the moment the volume creeps up.
Nobody in church two bought bad gear. They put good gear in the wrong places. Placement is the highest-leverage skill in all of live audio: it costs nothing, it's decided before the first fader moves, and no amount of EQ later can fully undo a bad choice here. An engineer with cheap mics in the right spots beats expensive mics in the wrong ones, every time.
The lesson
Three ideas run this lesson: which directions a mic hears, what closeness does to tone, and what happens when mics gang up.
Idea one: every mic has a deaf side. Aim it.
A mic's polar pattern is the map of which directions it hears. The ones you'll actually meet:
- Cardioid. Hears the front, ignores the rear. The pattern is heart-shaped (hence the name), with its deaf spot directly behind the mic. This is the overwhelming default for live work, and the reason is one word: feedback. From lesson 0.4, feedback is the loop mic → speaker → mic. A cardioid lets you break the loop geometrically, by pointing its deaf rear at whatever must not be heard.
- Supercardioid / hypercardioid. Tighter at the front, better rejection at the sides, but with a catch: a small hearing lobe pokes out directly behind, and the true deaf spots move to the rear diagonals (roughly 120–130 degrees off the front). Great isolation on loud stages if you respect the new null positions.
- Omnidirectional. Hears equally in all directions. No deaf side at all, so nearly useless near loudspeakers, but it has hidden virtues (flat, natural tone, and no proximity boominess) that make it common in lavaliers.
- Figure-8. Hears front and back, deaf at both sides. Rare on stage; a studio and ribbon-mic specialty.
Here's the move that makes this practical. Everyone thinks about where a mic points. Engineers think just as hard about where its null points. The most valuable real estate on stage is a mic's deaf side:
- Vocal mic with a floor monitor? A cardioid's null faces straight back, so the monitor goes directly behind the mic, straight down the handle.
- Using supercardioids? Straight behind is now the worst place for a wedge (that rear lobe hears it). The wedge belongs off to the rear diagonal, in the null. Same stage, different mic, opposite right answer. Mixing this up is one of the most common feedback causes in upgraded systems.
Idea two: distance is a tone control.
Directional mics (everything above except omni) share a quirk called proximity effect: the closer the mic gets to the source, the more bass it adds. At a few inches, a cardioid can pile on a serious low-end boost.
Used well, it's free warmth: the classic "radio voice" is a presenter working a cardioid close. Used blindly, it's mud: the singer who eats the mic on every song gets boomier and boomier, and the volunteer at the board responds with volume when the actual fix is EQ or an inch of distance. Know the lever exists and it starts working for you: back a boomy vocalist off slightly, or lean a thin-voiced reader in.
Distance has a second effect: the further away the mic, the more room it hears relative to the source, and the more gain you need, which brings feedback closer (that's lesson 0.4's "get close to the mic" advice, now with its full mechanism). Close means direct, dry, and feedback-resistant. Far means natural, roomy, and riskier. Every placement is a spot on that slider, chosen on purpose.
Idea three: mics gang up badly. The 3:1 rule keeps the peace.
Now the hollow choir from the hook. When two open mics both hear the same source (singer A's voice arriving at mic A directly, and at mic B a split-second later), the console adds both copies together. Two copies of one sound, slightly out of step, partially cancel each other at a whole comb of frequencies (remember wavelength from lesson 1.1: at some frequencies the delayed copy arrives exactly upside down). The result is that unmistakable thin, phasey, bottom-of-a-well sound. Not broken. Interfering.
You can't stop mics from overhearing each other entirely. You can make the overheard copy too quiet to matter. That's the 3:1 rule:
For any two open mics, the distance between them should be at least three times the distance from each mic to its own source.
Choir singer 2 feet from their section mic? The next section mic should be at least 6 feet away. Two podium mics each 1 foot from their readers? Keep the mics 3+ feet apart. At three-to-one, the leaked copy arrives enough quieter (distance costs level, lesson 1.2) that the cancellation becomes inaudible.
And the companion habit, worth more than any rule: close unused mics. Every open mic adds leakage, room rumble, and another path to feedback. The pastor's headset during the full-band opener, the choir mics during the sermon: mute them. Fewest open microphones wins; it's such a reliable principle that old broadcast engineers treated it as law.
Go deeperoptional
Polar patterns come from one elegant recipe. There are two primitive capsule behaviors: pressure operation (diaphragm sealed on one side, responds to pressure alone: omnidirectional) and pressure-gradient operation (both sides exposed, responds to the pressure difference across the diaphragm: figure-8, with response proportional to cos θ). Every first-order pattern is a weighted blend: R(θ) = A + B·cos θ, with A + B = 1. Cardioid is the even split (0.5 + 0.5·cos θ), which nulls exactly at θ = 180°. Supercardioid (≈0.37 + 0.63·cos θ) nulls at ±126°; hypercardioid (0.25 + 0.75·cos θ) at ±110°, buying narrower front pickup at the cost of a growing rear lobe (−12 dB for super, −6 dB for hyper). Handheld cardioids implement the gradient component acoustically, via rear entry ports and an internal labyrinth that delays rear-arriving sound so it self-cancels at the diaphragm. That is precisely why cupping the ports collapses the pattern to omni.
Proximity effect falls out of the same physics. A gradient capsule's driving force combines two terms: the phase difference between front and rear (which scales with frequency) and the amplitude difference from inverse-square spreading (which scales with 1/r and is frequency-independent). Far away, the phase term dominates and the response is flat. Close in, the amplitude term (relatively strongest at low frequencies, where the phase term is weakest) takes over and tilts the response upward at the bottom. The boost can reach +16 dB at 100 Hz at kissing distance. Pure pressure (omni) capsules have no gradient term, hence no proximity effect. That's one reason omni lavaliers sound so consistent as a speaker's head moves.
The comb filter, quantified: sum a signal with a copy delayed by τ and cancellation notches appear at f = (2k+1)/2τ, spaced 1/τ apart: a 1 ms path difference (about 1.1 ft) notches at 500 Hz, 1.5 kHz, 2.5 kHz... With equal-level copies the notches are theoretically infinite; the audible damage tracks the level ratio between copies. At a 3:1 distance ratio, inverse-square gives the leaked copy roughly −9.5 dB relative to the direct one, which caps comb ripple near ±3 dB, about the threshold where it stops reading as "hollow" and disappears into ordinary response variation. That's all the 3:1 rule is: geometry chosen so the interference ripple falls below audibility. It assumes roughly similar source levels into both mics; a quiet reader next to a loud singer needs more generous spacing (or, better, a muted channel).
Note what the rule does not fix: a single source deliberately captured by two mics (two mics on one guitar cab, stereo pairs). There you manage phase by alignment rather than distance: coincident placement (capsules as close as possible, per XY technique) or measured/nudged delay. The 3:1 rule is for separate sources with separate mics; stereo miking has its own geometry, which arrives with the recording lessons in Level 8.
Remember
- Every directional mic has a deaf side. The engineer's move is aiming the null, not just the front: cardioid nulls straight back; supercardioid nulls at the rear diagonals, with a small lobe straight behind.
- Cupping the grille destroys the pattern and invites feedback. Teach the band.
- Proximity effect: closer = bassier, on every directional mic. It's a tone control. Use it, or at least stop being used by it.
- Close = dry and feedback-resistant; far = natural and risky. Choose the distance on purpose.
- Two open mics hearing one source cancel into hollowness. Keep mic-to-mic distance at least 3x the mic-to-source distance, and mute every mic not in use.
Your turn
- Look up (or test) the pattern of your main vocal mics, cardioid or supercardioid, and verify each wedge sits in the actual null.
- Do the proximity demo on yourself: talk into a vocal mic at fist distance, then at an inch. Hear the bass arrive.
- Measure your choir or podium mic spacing against 3:1 and move whatever fails.
- Count how many channels are open during a typical sermon. Mute everything that isn't working. Notice the room get cleaner.