Dynamic range is the range of volume of an instrument from its softest to its loudest level.
The dynamic range of an instrument determines the specifications for sensitivity and maximum input capability of the intended microphone. Loud instruments such as drums, brass and amplified guitars are handled well by dynamic microphones which can withstand high sound levels and have moderate sensitivity. Softer instruments such as flutes and harpsichords can benefit from the higher sensitivity of condensers. Of course, the farther the microphone is placed from the instrument the lower the level of sound reaching the microphone.
In the context of a live performance, the relative dynamic range of each instrument determines how much sound reinforcement may be required. If all of the instruments are fairly loud, and the venue is of moderate size with good acoustics, no reinforcement may be necessary.
On the other hand, if the performance is in a very large hall or outdoors, even amplified instruments may need to be further reinforced. Finally, if there is a substantial difference in dynamic range among the instruments, such as an acoustic guitar in a loud rock band, the microphone techniques (and the sound system) must accommodate those differences. Often, the maximum volume of the overall sound system is limited by the maximum gain-before- feedback of the softest instrument.
Intensity Level in Decibels (at distance of 10 feet).
An understanding of the frequency output, directional output, and dynamic range characteristics of musical instruments can help significantly in choosing suitable microphones, placing them for best pickup of the desired sound and minimizing feedback or other undesired sounds.
Another instrument with a wide range of characteristics is the loudspeaker. Anytime you are placing microphones to pick up the sound of a guitar or bass cabinet you are confronted with the acoustic nature of loudspeakers. Each individual loudspeaker type is directional and displays different frequency characteristics at different angles and distances. The sound from a loudspeaker tends to be almost omnidirectional at low frequencies but becomes very directional at high frequencies.
Thus, the sound on-axis at the center of a speaker usually has the most “bite” or high-end, while the sound produced off-axis or at the edge of the speaker is more “mellow” or bassy. A cabinet with multiple loudspeakers has an even more complex output, especially if it has different speakers for bass and treble. As with most acoustic instruments the desired sound only develops at some distance from the speaker.
Sound reinforcement situations typically require a close-mic approach. A unidirectional dynamic microphone is a good first choice here: it can handle the high level and provide good sound and isolation. Keep in mind the proximity effect when using a uni close to the speaker: some bass boost will be likely.
If the cabinet has only one speaker a single microphone should pick up a suitable sound with a little experimentation. If the cabinet has multiple speakers of the same type it is typically easiest to place the microphone to pick up just one speaker. Placing the microphone between speakers can result in strong phase effects though this may be desirable to achieve a particular tone. However, if the cabinet is stereo or has separate bass and treble speakers multiple microphones may be required.
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, experiment with the microphone(s) and placement until you have the sound that you like!
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