Multi-mic guitar phase, electric and acoustic

Two mics on a guitar is how you get a bigger, more finished sound than one mic can give you — a dynamic for the body and a ribbon for the smooth top on an electric cab, or a pair on an acoustic to cover the whole instrument. The catch is that the moment you have two mics on one source, you have a phase relationship, and if the capsules are even a few centimetres apart, some frequencies will cancel when you blend them.

The symptom is specific: each mic sounds good soloed, and the combination sounds thinner, boxier, or more hollow than you’d expect from adding them.

Electric cab

On a single speaker, a 57 up close and a ribbon a little further back hear the cone at slightly different times. That offset is a comb filter waiting to happen. If you’ve mic’d the back of an open cab as well, that mic is hearing the cone move away from it, so start by flipping its polarity.

Pick the mic that carries the core of the tone as your reference — usually the close dynamic — and bring the other into line with it, by timing where the offset is clean and by Phase Coherence correction where it isn’t.

Acoustic

An acoustic pair, say one mic around the 12th fret and one nearer the body, has the same issue over a wider spacing: the body mic hears the low end a moment later, and the two can hollow out the midrange when summed. A guitar plus a piezo or pickup blend behaves like the bass DI-and-amp case — the pickup is the early, direct copy and the mic is the later one.

Audio demo to add: a two-mic guitar (or cab) summed untreated, then corrected with PhaseLock — level-matched, same take, with a short methods note.

Keep what the distance gives you

Capsule distance is a tone tool, not only a problem. The space between two mics is part of why the sound is bigger than one mic, and a little phase interaction is part of that character. Correct the cancellation that’s thinning the tone or collapsing it in mono, and keep the width and depth the spacing was there to create in the first place. Sum to mono, trust your ears, and stop when the tone is full rather than when a meter says zero.