On Axis/ Off Axis
All those who ever miked an amp know these two terms.
A microphone is “on axis” when it is directed at the speaker. The sound becomes trebly but at the same time there might appear the so-called “proximity effect” which leads to an increase in low frequencies response.
Arranging the microphone in a certain angle to the speaker is called “off axis”. The treble will now become less prominent and the whole sound will appear smoother.
The closer the mic is directed toward the cone of a speaker, the more trebly and direct the sound will be recorded. Aligned closer to the edge of the speaker the microphone will record a darker sound with more bass.
When you use several mics it makes sense to combine different positions to record various sound qualities and frequencies. Subsequently these sounds can be mixed.
Close –miked /Distance
The closer the microphone is to the speaker the more direct the sound will be. And because of the missing of room reflections the sound will be miked purely.
When you use more than one microphone in different distances to the speaker you might get phase cancellations. In this case it is necessary to shift the phase or to change the distance of the microphone that is further away from the speaker.
Furthermore there are different ways of positioning the room microphones that should clarify the spatial representation of the sound.
The XY and the AB positioning are common arrangements that are used in the studio but not on stage.
It can also be very interesting to mic the backsides of an open box to add more range to the sound. But in this case too you have to control the phase and adjust it if necessary.
The right speaker
When you use a 4X12 Box it makes sense to mic the different speaker in the studio and to compare them because every speaker sounds a little different. When you finally found your favorite one you should mark it for your next show so you can always mic this speaker. Otherwise the sound engineer will (in most cases) choose the speaker that is most close to his microphone stand.
The choice and the positioning of the microphones you can affect the sound and emphasize its strengths. It is worth it to deal more intensively with the advantages of your amplifier.