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OLD LYME, CONNECTICUT – MARCH 2009: The launch of the MO 2000 optical microphone expands Sennheiser’s microphone applications via a new type of transducer that processes acoustic signals on the basis of variations in light intensity. This new engineering feat makes the MO 2000 ideal for applications where other microphones are only partly suitable or cannot even be used at all. In addition, Sennheiser is also introducing the first – and currently the only – microphone in the market to be certified by EMI/EMC laboratories for use in potentially explosive atmospheres – the Sennheiser IAS MO 2000 SET.

“By implementing the optical principle, both the microphone head and the electronics can be located far away from each other,” noted David McNutt, industry team manager-installed sound. “And to insure functionality in demanding environments the microphone head is completely constructed of a plastic material that can withstand exposure to aggressive substances such as gases, salts and humidity. No electric current flows through the microphone head. All these features make this optical microphone the perfect candidate for applications in which communication or measurements are required under the most difficult conditions.”

MEDICAL APPLICATIONS In the medical field, for example, the optical microphone is ideally suited for use in magnetic resonance imaging (MRI) in order to maintain contact with the patient during MRI scans or to provide active noise cancellation. Due to its metal-free and current-free design, the microphone head does not interfere with the imaging process and is itself not influenced by the strong magnetic fields inside magnetic resonance imaging equipment.

MEASURING TECHNOLOGY The optical microphone also benefits from its metal-free and current-free design when used in measuring applications, as it does not influence the magnetic field. In EMI/EMC laboratories, for example, it functions like an “artificial ear” on a mobile phone without distorting the measurements.

POTENTIALLY EXPLOSIVE ATMOSPHERES A special version of the optical microphone is available for use in potentially explosive atmospheres and for outdoor applications. For example, the IAS MO 2000 SET can be employed for the acoustic monitoring of gas dehydration plants in natural gas production. In this case, the microphone can “hear” slow leaks that are otherwise too small to cause a pressure loss or to trigger an alarm message in other monitoring systems.

OPERATING PRINCIPLE OF THE OPTICAL MICROPHONE In the optical microphone, light from a light-emitting diode (LED) is directed onto a reflective diaphragm via a fiber optic cable (transmitter fiber optic cable). The diaphragm reflects part of the light into a receiver fiber optic cable. If the diaphragm is moved by sound signals, the reflected light beam is deflected, with the result that more or less light is coupled into the receiver fiber optic cable. At the end of the receiver fiber optic cable, a photodiode converts the light intensity variations into electrical signals.

OPTICAL MICROPHONE Versions and Areas of Application
MO 2000 Set: medical applications, measuring technology, industry
IAS MO 2000 SET*: potentially explosive atmospheres, outdoor applications

Polar pattern: omni-directional
Optical fibre: multimode 200/230 µm
Frequency response: 20Hz to 40kHz (±6dB)
Sensitivity: 15 mV/Pa
S/N related to 1 Pa sound pressure: >50dB(A)
Max. sound pressure: 134dB
Amplification: infinitely variable in the range +/-15dB, switchable in steps 0dB, +20dB, +40dB
AF output level: 15 mV/Pa (potentiometer in mid position, switch set to 0dB)
Output impedance: approx. 330 ohms asymmetrical, 660 ohms symmetrical
Current consumption: 120 mA
Operating temperature range: microphone: -10°C to +70°C; central unit: 0°C to 40°C

*The system IAS MO 2000 SET complies with the requirements regarding intrinsically safe optical radiation according to EN 60079-0:2004 and EN 60079-28:2007. It also meets the requirements of the ATEX Directive on explosion protection, which was documented with the Type Examination Certificate TÃœV 07 ATEX 553824 and TÃœV 07 ATEX 553825X. This certification allows the IAS MO 2000 SET to be used in potentially explosive atmospheres of Zone 1 (e.g. gas processing plants). The IAS MO 2000 SET has the degree of protection IP 54 (5=protection against dust deposits, 4=protection against splashing water from all directions) and is therefore suitable for outdoor applications.

ABOUT SENNHEISER Sennheiser is a world-leading manufacturer of microphones, headphones and wireless transmission systems. Established in 1945 in Wedemark, Germany, Sennheiser is now a global brand represented in 60 countries around the world with U.S. headquarters in Old Lyme, Connecticut. Sennheiser’s pioneering excellence in technology has rewarded the company with numerous awards and accolades including an Emmy, a Grammy, and the Scientific and Engineering Award of the Academy of Motion Picture Arts and Sciences.

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