Microphone Amplifier CMC 6 U
Variant Amplifier Versions
Special versions of the CMC 6 U are available with different gain (amplification factor) or extended frequency range. The CMC 6 U can be specially ordered, or retrofitted at the factory, to have a different (e.g. lower) low-frequency limit from the standard version (see, for example, the ”linear” version listed below).
CMC 6xt U – the 40 kHz version
This version is indicated by the letters ”xt” engraved on the microphone's output socket. It extends the frequency response of the axially addressed Colette capsules beyond 40 kHz.
On the pages of these capsules, the frequency response curves are shown with both, the standard CMC 6 U amplifier and the CMC 6 U xt.
CMC 6 U linear
The CMC 6 U microphone amplifier normally has a gradual rolloff in response below 20 Hz to guard against infrasonic disturbances from various sources such as air movement and vibration. However, when using pressure (omnidirectional) transducers, particularly with digital recording, it can be desirable to pick up frequencies below 20 Hz without attenuation. The special technology of the CMC 6 U linear microphone amplifiers makes this possible; on request we can deliver microphone amplifiers with response that is flat to as low as 3 Hz.
Caution must be advised with respect to infrasonics, however. Since pressure transducers can pick up very low frequencies, ventilation systems in large spaces (churches, concert halls) or traffic rumble can create a problem. With pressure gradient transducers the risk is even greater. They are far less sensitive to very low frequency sound, but respond much more strongly to low-frequency mechanical stimuli such as air currents and solid-borne noise. Such signals may be below the audible range of frequencies, but they can overload electronic circuitry and produce severe distortion, particularly in transformer-coupled circuitry.
CMC 6 U +5 dB”
The sensitivity of a microphone using this type of amplifier is 5 dB higher than with the standard version, but the equivalent noise level and maximum output voltage are not materially affected. Thus the highest sound pressure level which the microphone can accept without distortion is 5 dB lower than in the standard version, while the signal-to-noise ratio is essentially the same with either gain setting.
This version might be chosen in order to raise the microphone's signals above the noise level of the equipment to which it will be connected, and / or for working with sounds that occur mainly at low levels.