R&D Report 1954-32 : The Labor Tube microphone Type MD3 Studio. W.I. Manson, J. Nash The Labour type MD 3 Studio microphone is a moving-coil instrument in which the sound is transmitted to the diaphragm through a telescopic tube several feet long; the microphone is used occasionally for special purposes in television transmissions. Measurements of frequency response, sensitivity, impedance and susceptibility to interference from alternating magnetic fields have been made on a single specimen and the variation in characteristics with extension of the telescopic tube has been investigated. The microphone has a relatively low sensitivity and is suitable for use only at close range.