New measurement microphones for aggressive environments and extremely low actual sound situations

The Microtech Gefell MMS 212 1/2" – Precise, stable and reliable measurements under varios harsh environment conditions

The new developed Microtech Gefell MMS 212 1/2" measurement microphone was designed to be very robust to extreme environment conditions like  temperatures up -40 °C to +125 °C, vibration high moisture and dust.

In combination with the new capsule MKS 221 Rugged design and the preamplifier MV 212 the MMS 212 is ideal for measurements in harsh industrial or R&D environments.

This opens up a wide range of applications in areas such as R&D, industry, e.g. in the automotive sector. For example in brake dyno testings. This type of test is often run for weeks with a wide range of temperatures and humidity.

The innovative, special protected measurement microphone MMS 212 allows during acousting testings  for consistent data quality in wide-ranging rugged, hazardous and difficult environments.

The extended frequency range of the free field response, from 3,5Hz to 20kHz, combines with a 50 mV/Pa sensitivity, 15dBA of inherent noise, and tolerates SPL peaks up to 139 dB (136 dB RMS) for 3% THD at 1 kHz.
The  robustness is achieved by a special designed protection grid, pressure compensation opening and BNC plug connector with Integrated Electronics Piezo-Electric (IEPE) power supply.

The new MMS 212 is an IP67 rated solution and can be calibrated with a standard 1/2" sound calibrator, offering TEDS for increased accuracy.

An integrated power-on indicator in the MMS 212  permanently indicates that the microphone is working as intended, and helps to ensure reliable measurements in unique, sometimes unrepeatable situations.

A substantial component of the MMS 212 is the special developed new measuring capsule MKS 221.

½“ Microphone Capsule – MKS 221 Rugged Design

The MKS 221 Rugged Design has a special headgrill with an additional protection grid in front of the membrane against mechanical  damage in harsh and aggressive like humidity or Dust  .

This new capsule has a free-field response and is therefore optimized for correct acoustic measurements under free-field conditions with 0 degree incidence.

The equalization of the static air pressure is by means of a capillary to the preamplifier (rearvented). The microphone capsule is suitable for sound level meters of Type 1 acc. IEC 61672.

MKS 221 – An important difference

The difference to the competitors is the standard 1/2-inch and it doesn’t need a special calibrator-adaptor with another diameter.

MV 212 – 1/2“ Microphone preamplifier for rugged environment

The MV 212 is a microphone preamplifier for externally polarized microphone capsules.

The thread for the microphone capsule complies with the international standard IEC 61094-4.

The electrical connection is via a BNC cable to devices with IEPE supply. The microphone preamplifier internally generates a 200 V polarization voltage for externally polarized microphone capsules.

The MV 212 is very robust to extreme temperature, humidity, dust and vibration and therefore designed for applications in rugged environments. An integrated power-on indicator permanently shows the correct function and ensures reliable measurements.

The microphone preamplifier is suitable for sound level meters of IEC Type 1acc. IEC 61672.

MMS 214 – The special microphon designed for acoustic measurements of very low sound pressure levels

Many measurement situations where the actual sounds are extremely low, requires totally different measurement microphones.

For this reason Microtech Gefell designed a completely new measurement microphone – the MMS 214 model. It  offerings a particularly low inherent noise level, which enables acoustic measurements of very low sound pressure levels.

The electrical connection is via BNC cables to measuring channels with IEPE supply.

The polarisation voltage for the externally polarised measuring microphone capsule is generated in the measuring microphone preamplifier.

The measuring microphone is equipped with a built-in memory for microphone identification (TEDS according to IEEE 1451).

A key part of the MMS 212 is the special developed new measuring capsule MKS 225.

MKS 225 – ½“ Microphone Capsule for low inherent noise mics

The 1/2" measuring microphone capsule MKS 225 achieves a particularly low self-noise in conjunction with a suitable measuring microphone preamplifier, such as the MMS 214 or MV 240.

It is designed especially for acoustic measurements of very low sound pressure levels in research, development and industry. The special construction and design concept of the microphone capsule guarantee a high temporal constancy of the electroacoustic parameters. All important parts are made of stainless steel.

The protective cap protects the diaphragm from mechanical damage and can be exchanged for a protective cap with integrated electrostatic excitation electrode for calibration.

The static pressure equalisation between the inner cavity and the atmosphere is ensured via a capillary to the downstream preamplifier. This allows the use of a dry adapter. The MKS 225 measuring microphone capsule is suitable for class 1 sound level meters according to IEC 61672.

All new measurement microphones are complemented with an extended range of accessories from simple adaptors, cables and windscreens, all the way to specialized supports and conditioning modules.

New Preamplifier – MV 240 digital

Extending the vast catalog of Microtech Gefell’s measurement microphone innovations, the new MV 240 digital is a 1/2" preamplifier that combines a high-impedance transducer with an analog-to-digital 24-bit converter.

The output signal of the measurement microphone capsule is optimally adjusted to the dynamic range of the analog-to-digital converter by an impedance converter and a pre-amplifier with a very low noise level and THD. One channel of a 24 bit analog-to-digital converter converts the lower level range of the capsule signal and the other channel the upper level range. A following processor combines these two level ranges to the one-channel 32 bit output signal, that represents calibrated sound pressure levels. The MV 240 digital converts sound pressure levels from 7 dB to 160 dB – more than the complete dynamic range of a typical 1/2“ measurement microphone capsule. The pre-amplifier supports the sample frequencies 48 kHz, 96 kHz and 192 kHz. Measurements up to 80 kHz are possible with 1/4“ measurement microphone capsules.

Customer benefits of the new MV 240:  

• Only one measuring range for the entire dynamic range, i.e. no range switching necessary,
• Direct digital sound pressure conversion (with exact sensor-ADU adjustment to exclude common sources of error),
• Sampling frequency up to 192kHz is supported,
• No measurable/audible USB artifacts, USB class compatible (USB 2/3), no additional driver necessary,
• User independence from special manufacturer software, possibility of using commercially free available measurement software,
• Internally generated capsule polarization voltage 200V,
• Minimal inherent noise due to optimum adaptation of the measuring capsule to the AD converter,
• Compatible with all common OS, such as Windows®(XP,Vista, 7, 8, 8.1, 10),Linux, Mac OS®, ioS®),
• Electrical voltage in the system is irrelevant to the user due to direct digital sound pressure conversion.

      (Direct Digital Sound Pressure Transformation/DDST, based on a new definition:

       1µPa ≙ Integer value 1 in LSB.)

Another major advantage is a test generator integrated in the microphone, which checks both the complete transmission and evaluation of a 32-bit data stream from the microphone via the interface to the measurement software on the PC, as well as a further integrated test generator, which generates a signal corresponding to the sound pressure of 1 Pascal to show the reference point in the respective measurement software.