The MO 2000 Set from Sennheiser is a specialty measurement microphone that can go where other microphones fear to tread. The microphone uses a light from an LED that is directed onto a reflective diaphragm. As the diaphragm is moved by sound signals, a displacement of the reflected light is read by a receiver waveguide, which in turn activates a photodiode that converts the light intensity variations into electric signals.
The advantage of this system is that microphone head and the electronics can be located far away from each other. Additionally, the component parts of the MO 2000 H acoustic-optical microphone head are made of a plastic material that is suitable for use in areas with aggressive substances, such as gases, and salts, or areas of high humidity and radiation. All components of the microphone head, including the optical waveguides, are free of metal with no electric current flow.