The measurement microphone set have been combined so they fulfil our users’ typical measurement needs. Independently of your measurement system and application you should be able to find a set that suits your needs. The microphone sets can be connected directly to all professional measurement systems and as indicated they are available for both CCP and 7-pin LEMO inputs.
If your measurement platform supports intelligent transducers according to IEEE 1451.4 (TEDS) you can simply plug in the microphones and they will identify themselves with their specific properties, types and calibration data. A feature especially appreciated by multi-channel users.
The CCP sets use high-quality coaxial cables, whereas the LEMO sets use a special, soft type of multicore shielded cable. If extended cables are to be used you should consider the possible influence on the upper frequency and dynamic ranges.
All microphone sets are delivered as a unit and are calibrated accordingly. The sets are delivered with calibration charts including sensitivity values and frequency response curves for the complete set. The sensitivity value can therefore be used directly in your system setup.
For frequent verification of the measurement chain a sound source will be required. G.R.A.S. supplies a 114 dB sound calibrator for this purpose. Depending on the use and your internal quality control requirements we recommend that the sets are recalibrated at least every second year. For a more accurate verification we recommend calibration with a pistonphone. G.R.A.S. supplies 114dB and 134dB pistonphones. Further, we recommend calibration of the sound sources against an extreme reliable reference. G.R.A.S. offers such a service and recommends this calibration every second year.
Special microphones are often required for applications where there are particular requirements regarding the methods of measurements and configurations.
The G.R.A.S. hemispheres are compliant with the ISO 3744, 3745 and 3746 (ANSI S12.54, S12.55, S12.56) standards and accommodate for 4, 10 and 20 positions. These are clearly marked to ease the mounting and maintain measurement repeatability. Two hemisphere structures are available; a 1 m measurement radius and a 2 m measurement radius.
Head & Torso Simulators
Audio design is becoming a vital part of the development of a lot of daily products like automobiles, computers, hearing aids, mobile phones etc. Either to improve on its basic function, or to optimize the clients’ experience with the product.
KEMAR was initially invented in collaboration with the audiological industry for the use of hearing aid development, and is still the defacto standard for this industry – however since then the usage of KEMAR has spread into a multitude of other industries like: telecommunications, hearing protection test, automotive development etc.
The major difference between KEMAR and the standard head and torso simulators (HATS) on the market is that KEMAR is built on a large statistical research of the average human body – meaning the KEMAR HATS has the same acoustical properties as an average human, including distinct facial features.
Through the years G.R.A.S. has developed a range of accessories and special versions of KEMAR – allowing you to design a test setup that can allow you to research in your specific industry, whether this is for development of the next generation mobil phones or the next super car.
KEMAR meets the international standards that are specified by ISO, IEC as well as ANSI.
The KEMAR manikin is the recognised industry-standard for in-situ anthropomorphic testing in the fields of:
- Hearing conservation
- Noise abatement
- Sound recording and sound-quality evaluation.
An externally polarized condenser measurement microphone cannot work on its own. It needs to be connected to hardware that can act as an interface between the raw signal output and the data acquisition unit or measurement device. The Power Module is such an interface that improves the performance and reliability of the measurement chain.
- It provides polarization voltage for the transducer, ensuring that the microphone gets the charging voltage it needs.
- It provides supply voltage for the microphone preamplifier. The preamplifier acts as a unity gain impedance converter. It provides a certain amount of line drive capability by providing a low output impedance and output current, making it possible to transmit the signal from the transducer to the Power Module without significant degradation.
- A power module can provide amplification or attenuation to the signal, thus making it possible to fine tune the measurement chain to the signals being measured and the hardware being used.
- Selectable filters make it possible to exclude unwanted noise from the measurement, e.g. wind induced noise from outdoor measurements.
- Overload detection makes it possible to validate the measurements and is a useful tool in monitoring setups.
- When a Power Module with gain is used, you can use longer cables because of the power module’s ability to deliver current.
- A Power module introduces electrical isolation.
Calibration is an essential step in every precision measurement. It establishes the relationship between the sound pressure and the electrical output of the microphone.
Calibration can be performed at either 250 Hz or at 1 kHz. Both frequencies have their advantages and disadvantages.
250 Hz is in the frequency range where the frequency response of almost all microphones is flat and will therefore give the most accurate calibration.
If, however, the microphone is used in connection with measuring equipment with weighting filters, for example a sound level meter with A-weighting, the 250 Hz signal will be attenuated by the weighting network. In this case it might be advantageous to use a 1 kHz calibration frequency.
At 1 kHz, the weighting filters have 0 dB attenuation and will therefore not affect the calibration.
On the other hand, since the frequency response of the microphone is not flat, a small error could be introduced.
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