Pickup Patterns

The microphones used for live sound typically range from cardioid to hyper-cardioid pickup patterns. These directional characteristics have become synonymous with concert sound mics. They are not the only polar patterns that work on the concert stage. Figure-eight, omnidirectional and a variety of stereo mic patterns can also pickup excellent sound and achieve good gain-before-feedback. Everything depends on the situation and the available selection of mics.

There are many excellent cardioid and hyper/super-cardioid microphones. These patterns are the mainstay of live sound because they provide predictable results and offer some selectivity in determining which sounds are picked up and which are rejected. Unfortunately, the rejection of unwanted sound is only relative and not absolute. The best directional microphones offer very smooth frequency response both on-axis and off-axis. The off-axis response is critical to achieving the highest gain-before-feedback, as peaks in the response are the first frequencies that ring. These peaks will also vary with angle and make careful monitor equalization moot when the mic/monitor relationship changes. (Of course, floor monitors have their own variations in frequency response at different angles, especially if more than one are in close proximity.)

The mic's off-axis response is also responsible for the way leakage of sound from other instruments is picked up. It is not unusual for a highly directional mic used to pickup sound from a relatively quiet instrument, such as an acoustic guitar, is also picking up the snare drum. However, the combination of acoustic guitar EQ and the off-axis response of the mic can make a mess of what was a good snare sound. Even a perfect directional mic cannot reject all the leakage from other instruments because some of this leakage is reflected from the face of the instrument/vocalist and into the front of the mic. Acoustic guitars, with that big flat surface, are one of the obvious offenders (hence the interest in not-so-acoustic pickups).

A good omni-directional mic can have better gain-before-feedback than you might expect, simply because it has a very flat frequency response in all directions. It also can be placed very close to the instrument without the buildup of low frequency common to directional mics. This combination (flatter/closer) can give excellent results in situations where there are lots of sound sources, such as percussion, and allow the distance to determine relative volume without changing the tone of the instrument.

Figure-eight patterns offer the flattest off-axis response of any pickup pattern and also have the highest rejection (theoretically infinite) of sound sources located 90 degrees off-axis. This allows you to be very selective in the direct sounds the mic picks up. I have used figure-eight mics (such as a U87) on rack and floor toms. A balance between cymbals and toms is created by positioning the mic. The rejection of adjacent toms/cymbals is excellent and the on-axis sound is very natural. This is much trickier when picking up the sound from moving targets, such as vocalists, horn players or percussionists, as they may move into the absolute rejection at the sides of the mic just as they hit their cue.

Stereo microphones can also provide excellent results when used appropriately. There are so many good pickup formats (X/Y cardioid, X/Y figure-eight, M/S, spaced-omni pairs, spaced-omni trios, ORTF, binaural pinnae, binaural ITE, and many others), and each has its advantages and disadvantages. On stage, leakage can make the use of stereo mic techniques more challenging but there are situations where it also offers the best sound. Large sound sources, such as a choir, can be picked up using three spaced-omni mics and panned appropriately (this is most effective in Left/Centre/Right FOH configurations) to create the size and spaciousness that choral performance can demand. An X/Y stereo mic (on a drum overhead or in a grand piano) can provide a solid stereo image that can be panned just enough to achieve some spread in the FOH but not so much that the overall balance changes in seats on the sides of the venue. The X/Y pickup has less destructive interference (due to the physical proximity of the capsules) when not panned hard left/right. The result is little tonal change between slight panning and hard panning. Especially useful in shows where the ballad needs the big piano sound but the rest of the show needs a smaller rhythm-section piano sound.

The next time you are selecting mics, check to see if there are a few "other" patterns to try. Even the lowly omni lavalier mic can produce excellent sound in the right situation. You may find solutions to problems that had been unfixable with your stock cardioid mics. You may even find places where one mic can do the work of two. All it takes to experiment is the mic, a few extra minutes in sound check and an extra mic line in the snake to FOH. Yeah, I know, not on this tour!

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