Infra-sound Microphones

Normal measurement microphones have a very wide frequency range and cover most practical applications. There are however special situations where special microphones are required. One such application is the measurement of infra-sound. Normal measurement microphones have a low-frequency cut-off at about 3 Hz, but in some applications it is required to measure down to close to 0 Hz. Examples of such applications are the measurement of sonic booms and explosions (both chemical and nuclear), and noise generated by machinery such as diesel engines, wind turbines and specially designed mechanical transducers.

To achieve a very low low-frequency cut-off of down to 0.09 Hz, a special microphone combined with a special preamplifier and a low-frequency adapter is used. To account for pressure variations close to 0 Hz, a special ambient pressure equalization system with a very long settling time is used. For this reason, it is necessary to allow the microphone system sufficient time to settle if it has been subjected to fluctuations in ambient pressure, for example from changes in altitude, wind or a closing door. Microphone, preamplifier and low-frequency adapter are assembled and calibrated as a complete unit and should not be separated by the end-user.

A standard sensitivity calibration at 250 Hz can be performed using a Pistonphone. A low-frequency calibration requires special equipment and must be performed at our calibration laboratory.

GRAS infra-sound microphones are among the range of special microphones that furthermore includes 

• Array microphones
• Flush-mount microphones
• Intensity Microphones
• Intensity Probes
• Lownoise measuring systems
• Outdoor microphones
• Plate microphone kits
• Probe microphones
• QC microphones
• Surface microphones
• Turbulence Screen Microphones