Phase response of intensity microphones: Generally speaking, one can say that the intensity technique measures the direction of the sound wave by detecting differences in arrival time at two microphone positions.
 

If the sound wave arrives at microphone A first and then, slightly later, at microphone B, the sound wave must be travelling in the direction from A to B. If, on the other hand, the sound arrives at microphone B first, then it must be travelling in the opposite direction. If the sound wave arrives at the two microphones at the same time, the sound wave must be travelling perpendicular to the microphone pair.
 

The ability of the microphones to determine accurately small timing differences can be expressed as the phase difference between the two microphones. Therefore, phase-matching is an all-important parameter for intensity microphones.
 

Click on images for details:

Intensity-Microphones and Calibrator   : :   G.R.A.S.
	¼" Intensity-Micr. Pair		½" Intensity-Micr. Pair		½" Pre-polarised Intensity-Micr. Pair		Intensity-Microphone Calibrator
	Type 40BI   Dynamic Range:           40 - 168 dB re. 20µPa    Sensitivity:           3 mV/Pa    Frequency response:           IEC 60651 Type 0    Phase response:           IEC 1043 Class 1    Polarisation voltage:           200 V   Comment:           Complete set of two phase-           matched ¼" intensity           microphones, solid spacers           and adapters for ¼"           Preamplifiers (Type 26AA)            For measuring very high           intensity levels where the           dynamic range of the ½"           Sound-intensity Pair Type           40AI is insufficient, or in           situations where the small           size of the Type 40BI is           necessary		Types 40 AI and 40AK   Dynamic Range:           21 - 152 dB re. 20µPa    Sensitivity:           25 mV/Pa    Frequency response:           IEC 60651 Type 0    Phase response:           IEC 1043 Class 1    Polarisation voltage:           200 V   Comment:           Complete set of two phase-           matched ½" intensity           microphones, solid spacers           and adapters for a pair of ¼"           Preamplifiers (Type 26AA)            The microphones have a free           field response optimised for           use in face-to-face           configuration intensity           probes and have a high           sensitivity to enable low-level           measurements            Type 40AK: as above but           does not include spacers and           adapters for ¼" preamplifiers		Types 40GI and 40GK   Dynamic Range:           20 - 160 dB re. 20µPa           (< 1% THD at 100 Hz)    Sensitivity:           12.5 mV/Pa    Frequency response:           IEC 60651 Type 0    Phase response:           IEC 1043 Class 1    Polarisation voltage:           0 V   Comment:           Complete set of two phase-           matched ½" pre-polarised           intensity microphones, solid           spacers and adapters for a           pair of ¼" Preamplifiers           (Type 26CB)            The microphones have a free           field response optimised for           use in face-to-face           configuration intensity probes           and have high a sensitivity to           enable low-level           measurements.            The 40GK also includes one           straight and two right-angled           adapters to connect the           microphones with a pair of ¼"           Preamplifiers such as the Type           26CB            Type 40GI: A pair of phase-           matched ½" intensity           microphones similar to the           Type 40GK but without           spacers and adapters for ¼"           preamplifiers		Type 51AB   Input Connection:           BNC socket    Maximum input signal:           50 Hz - 6.3 kHz    Frequency-intensity index:           >27 dB (nominal microphone           spacing 25 mm)    SPL difference b/n channels:           <0.1 dB    Operating temperature range:           +5 °C to +40 &de;C    Comment:           Coupler for calibrating the           phase response of           microphone pairs used for           measuring sound intensity,           e.g. the Type 40AI and           Type 40BI            Includes a calibrated acoustic           resistance to enable the           computation of particle           velocity and intensity levels            The Type 51AB complies with           the standards of IEC 1043

 
Want to learn more or place an order?     Contact us.
 

Other G.R.A.S. Sound and Vibration products

• Easy selection Microphone Sets 
• Microphones
• Preamplifiers
• Power Modules
• Simulators:
  • Couplers
  • Artificial Ears and Ear Simulators
  • Mouth & Pinna Simulators
  • KEMAR Head & Torso Simulator
  • ANSI/ASA S12.42 test fixture
  • Telephone Test Head
  • Hearing-protector Test Fixture
• Pistonphones and Calibration equipment  
• Intensity microphones and calibrators
• Intensity Probes
• Accessories