G.R.A.S. 40SA Probe Microphone

Freq range: 2 Hz to 8 kHz
Dyn range: 40 dB(A) to 166 dB
Sensitivity: 3 mV/Pa

Typical applications and use

  • Acoustic-impedance measurements
  • Exhaust-system measurements
  • Near-field measurements
  • Measurements at high temperatures
  • Pressure-distribution measurements in smallenclosures


The G.R.A.S. 40SA is constructed with detachable stainless-steel probes tubes which guide the acoustic signal to a microphone inside the housing of the 40SA. After being sensed by the microphone, the acoustic signal is passed on to an impedance matching wave guide which eliminates unwanted internal reflections. The result is a smooth frequency-response ranging from 2 Hz up to 20 kHz. The internal microphone is connected to a low-noise preamplifier with a high dynamic range; ensuring a measurement range from approximately 40 dB to 166 dB re. 20 μ Pa. The data sheet shows the preamplifier’s connections via its LEMO plug.

The G.R.A.S. 40SA Probe Microphone is internally compensated to equalize the internal pressure of the microphone with the static pressure at the probe’s tip . The static pressure within the Type 40SA will therefore adjust itself to the static pressure existing at the probe’s tip; which it does with a time constant of approximately 0.1 s.

The 40SA can be used with various probe lengths and is delivered with four standard probe lengths, i.e.: 20 mm, 40 mm, 80 mm and 160 mm. Intermediate lengths can be made by cutting these standard lengths. Also, the stainless steel tubes can be bent to a radius as low as 5 mm without downgrading the system’s acoustics. A exible probe tube is also provided for use in measurements where stiff stainless-steel tubes are not practical. This does, however, slightly downgrade the system’s acousticperformance.

The right angled design of the 40SA makes it particularly well suited for measurements on exhaust-gas systems and other machinery in general as well as for scanning vibrating surfaces such as loudspeaker diaphragms and cabinets.

The compact size, low weight and all-stainless-steel construction of the 40SA make it robust, easy to handle and easy to mount.

Frequency range (±3 dB) Hz 2 to 8 k
Dynamic range lower limit (microphone thermal noise) dB(A) 40
Dynamic range upper limit dB 166
Set sensitivity @ 250 Hz (±2 dB) mV/Pa 3
Polarization voltage V 200 V / Traditional
Power supply, single V 120 to 28
Output impedance Ω 55
Temperature range, operation °C / °F -25 to 700 / -13 to 1292
Temperature range, storage °C / °F -40 to 85 / -40 to 185
Temperature range with G.R.A.S. preamplifier, operation °C / °F -25 to 70 / -13 to 158
TEDS UTID (IEEE 1451.4) 27 v. 1.0
Connector type 3 m 7-pin LEMO
CE/RoHS compliant/WEEE registered Yes/Yes/Yes
Weight g / oz 40 / 1.4110

Pressure-equalization time constant: Internal to tip static pressure: typically 0.1 s

Typical frequency response with a 40 mm probe tip


G.R.A.S. GR0265 Pistonphone adaptor for 1.25 mm
G.R.A.S. GR0266 Pistonphone adaptor for 1.6 mm
G.R.A.S. GR0267 Heatsink and tool
G.R.A.S. GR0275 Calibration coupler
G.R.A.S. GR0263 1.3 mm pin for calibration coupler
G.R.A.S. GR0263 1.6 mm pin for calibration coupler
G.R.A.S. YY0004 Pair of pliers
G.R.A.S. YY0005 File
G.R.A.S. MI0016 Silicone grease
G.R.A.S. EK0018 Teon tubing (L: 0.5 m Dia: 1.6 mm)
G.R.A.S. GR0258 20 mm Probe tube
G.R.A.S. GR0259 40 mm Probe tube
G.R.A.S. GR0260 80 mm Probe tube
G.R.A.S. GR0261 160 mm Probe tube
G.R.A.S. GR0401 Flexible Probe tube


G.R.A.S. AA0008 Extension cable 3 m
G.R.A.S. 12AA Power modules
G.R.A.S. 42AA Pistonphone