• Array Microphones : used in situations where concurrent measurements are required at several points.

• Environmental microphones : for long-term unattended noise surveillance.

• Free-field microphones: designed to measure the sound pressure in a sound field and compensate for the influence of its presence in the sound field.

• Pressure microphones: designed to measure the sound pressure that actually exists in front of its diaphragm.

• Outdoor microphones: for permanent outdoor use and are encased in stainless steel units that can withstand all weathers year after year

• Low-noise level microphone systems: to measure noise levels below the threshold of human hearing, e.g. from disk drives, computer equipment in general and in quiet rooms.

• Probe microphones: specially designed for difficult measurement situations, for example in high temperatures or airflow.
  
  

• Random-incidence microphones: designed essentially to measure sound pressure levels in a diffuse sound field as they existed before the microphone was introduced into the diffuse sound field

• Window microphones: for measuring community noise striking the facades of, say, hospitals, offices and dwellings.
  
  

• Surface microphones: for use in places where sound measurements are performed in the presence of air flow, e.g. on the external surfaces of vehicles either in motion or in wind tunnels.

• TEDS Plug and Play. A TEDS contains the critical information needed by an instrument or measurement system to identify, characterise, interface, and properly use the signal from an analogue sensor. The TEDS resides in embedded memory, typically an EEPROM, within the analogue transducer, as defined in the IEEE P1451.4 standard.

• Constant Current (CCP) : “Constant Current Powerâ€?. Describes G.R.A.S. power supplies that maintain a constant level of current for driving CCP transducers. Only a co-axial cable is needed for connecting the transducer to the power supply and subsequent analyzer.

• Constant voltage: Measurement microphones and preamplifiers require special voltages for supply and polarisation. Standard externally-polarised condenser microphones require a stable polarisation voltage of 200 V DC for proper operation. This may be turned off in the power modules for use with prepolarised microphones.

• Low Noise Power Modules
• Constant voltage and CCP

Powerful tool for locating sound sources, order rank them and determine the emitted sound power. The method is based on the simultaneous determination of sound pressure and particle velocity by two closely spaced microphones. The sound intensity probe must ensure a well-defined acoustic spacing between the microphones as well as minimise disturbances to the sound field.

To ensure maximum measurement accuracy, the spacing between the micro-phones must be optimised for the given measurement conditions. At low frequencies, in highly reverberant conditions, this spacing must be large, whereas for measurements at high frequencies, it must be small.

• Intensity probes (50AI)
• Special intensity probes:
  • Vector intentisity probe Type 50VI
  • Wide-band intensity probe Type 50VI-3
  • X-Y-Z Intensity probe Type 50VX

The Telephone Test Head Type 45AA is a tailor-made fixture for testing the acoustic performance of telephone handsets in accordance with international standards and recommendations.

The design of the Type 45AA combines precision with a robust construction to ensure stability and reproducible test results with a minimum of acoustic interference.

Four different, detachable precision brackets are provided for mounting the Mouth Simulator according to the standardised positions shown in the table for speaking into a telephone. These positions are maintained to within an accuracy of 1 mm. Reference gauges are available for verifying this.