Another “instrument” with a wide range of characteristics is the loudspeaker. Anytime you are recording a guitar or bass cabinet, you are confronted with the acoustic nature of loudspeakers. A single loudspeaker is directional and displays different frequency characteristics at different angles and distances.
On-axis at the center of a speaker tends to produce the most “bite”, while off-axis or edge placement of the microphone produces a more “mellow” sound. A cabinet with multiple loudspeakers has an evenmore complex output, especially if it has different speakers for bass and treble. As with most acoustic instruments, the desired sound develops at some distance away from the speaker.
The most common approach is to close-mic an individual speaker. This is a habit people develop from viewing or doing live sound. In the live sound environment, most audio sources are close-miked to achieve the highest direct to ambient pickup ratios. Using unidirectional mics for close miking maximizes off-axis sound rejection as well. These elements lead to reduction of potential feedback opportunities. In the recording environment, the loudspeaker cabinet can be isolated and distant-mic techniques can be used to capture a more representative sound. Often, by using both a close and a distant (more than a few feet) mic placement at the same time, it is possible to record a sound which has a controllable balance between “presence” and “ambience”.
Placement of loudspeaker cabinets can also have a significant effect on their sound. Putting cabinets on carpets can reduce brightness, while raising them off the floor can reduce low end. Open-back cabinets can be miked from behind as well as from the front. The distance from the cabinet to walls or other objects can also vary the sound. Again, move the instrument and the mic(s) around until you achieve something that you like!