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Sennheiser launches optical microphone

The launch of Sennheiser’s new MO 2000 optical microphone offers an entirely new type of transducer that processes acoustic signals on the basis of variations in light intensity. This engineering feat makes the MO 2000 ideal for applications where other microphones cannot even be used. Sennheiser also has released the IAS MO 2000 SET, certified by EMI/EMC laboratories for use in potentially explosive atmospheres.

In the optical microphone, light from an LED is directed onto a reflective diaphragm via a fiber-optic cable, which reflects part of the light into a receiver fiber-optic cable. The reflected light beam is moved by sound signals, modulating the amount of light entering the receiver fiber-optic cable. At the (remotely located) end of the receiver fiber-optic cable, a photodiode converts the light intensity variations into electrical signals.

Using an optical transducer, the microphone head and the electronics can be kept separate. Because there is no electrical current flowing in the metal-free capsule design, the mic can withstand environments that conventional mics cannot. This makes the MO 2000 useful for communication with patients within an MRI machine, where the presence of metallic objects is dangerous. In potentially explosive atmospheres, the IAS MO 2000 SET can perform acoustic monitoring of gas dehydration plants. The microphone can “hear” slow leaks that are otherwise too small to detect with conventional monitoring systems.

With a frequency response of 20Hz-40kHz and immunity from a wide range of environmental conditions, Sennheiser’s optical microphone offers the potential for application in many situations previously dismissed as impractical.