G.R.A.S. 40AF 1/2" Ext. Polarized Free-field Microphone

Freq range: 3.15 Hz to 20 kHz
Dyn range: 14 dBA to 149 dB
Sensitivity: 50 mV/Pa
  • 40AF 1/2

Introduction

G.R.A.S. 40AF is a high-precision condenser microphone made according to IEC 61094-4 requirements. The 40AF’s design is based on the original reference ½” pressure microphone, but optimized for free-field measurements with a 12 dB increase of the sensitivity. The result is a nominal sensitivity of 50 mV/Pa, slightly longer microphone housing, and a natural reduced dynamic range.

It can be used for Type 0 and Type 1 measurements.

40AF is the perfect free-field complement to the G.R.A.S. 40AP ½” Ext. Polarized Pressure Microphone. 

40AF is individually factory-calibrated and delivered with a calibration chart stating its specific open-circuit sensitivity, pressure, and corrected free-field frequency responses. 

Typical applications and use

The properties and robust design make 40AF the natural choice for an all-round free-field, high sensitive microphone suitable for both field-work and laboratory measurements.

The high sensitivity and reliability has made 40AF the preferred measurement microphone for sound level meters/analyzers with 200 V polarization voltage option and, as such, enables IEC 61672 Class 1 measurements.

Compatibility

The 40AF requires a standardized ½” or ¼” LEMO preamplifier and an input module that supports this technology with a 7-pin LEMO connector.

System verification

For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. 42AB Sound Level Calibrator.

For proper sensitivity calibration, we recommend using a pistonphone like G.R.A.S. 42AP Intelligent Pistonphone.

Quality and warranty

All G.R.A.S. microphones are made of high-quality materials that will ensure life-long stability and robustness. The microphones are all assembled in verified clean-room environments by skilled and dedicated operators with many years of expertise in this field.

The microphone diaphragm, body, and improved protection grid are made of high-grade stainless steel, which makes the microphone resistant to physical damage, as well as corrosion caused by aggressive air or gasses.

This, combined with the reinforced gold-plated microphone terminal which guarantees a highly reliable connection, enables G.R.A.S. to offer 5 years warranty against defective materials and workmanship.

Service

If you accidentally damage the diaphragm on a G.R.A.S. microphone, we can — in most cases — replace it at a very reasonable cost and with a short turn-around time. This not only protects your investment, but also pleases your quality assurance department because you don’t have to worry about new serial numbers, etc.

Calibration

Before leaving the factory, all G.R.A.S. microphones are calibrated in a controlled laboratory environment using traceable calibration equipment.

Depending on the use, measurement environment, and internal quality control programs, we recommend recalibrating the microphone at least once a year.

TYPE (Microphone features) FF
Frequency range (±1 dB) Hz 5 to 10 k
Frequency range (±2 dB) Hz 3.15 to 20 k
Dynamic range lower limit (microphone thermal noise) dB(A) 14
Dynamic range lower limit with G.R.A.S. preamplifier dB(A) 17.0
Dynamic range upper limit dB 149
Dynamic range upper limit with G.R.A.S. preamplifier @ +28 V / ±14 V power supply dB 142
Dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply dB 149
Open-circuit sensitivity @ 250 Hz (±2 dB) mV/Pa 50
Open-circuit sensitivity @ 250 Hz (±2 dB) dB re 1V/Pa -26
Resonance frequency kHz 14
Microphone cartridge capacitance, typ. pF 18
Microphone venting Rear
IEC 61094-4 Compliance WS2F
Temperature range, operation °C / °F -40 to 150 / -40 to 302
Temperature range, storage °C / °F -40 to 85 / -40 to 185
Temperature coefficient @250 Hz dB/°C / dB/°F -0.01 / -0.006
Static pressure coefficient @250 Hz dB/kPa -0.011
Humidity range non condensing % RH 0 to 100
Humidity coefficient @250 Hz dB/% RH -0.001
Influence of axial vibration @1 m/s² dB re 20 µPa 62
CE/RoHS compliant/WEEE registered Yes / Yes, Yes
Weight g / oz 6.5 / 0.229

Typical frequency response. Upper curve shows free-field response for 0°, lower curve shows pressure response.

Free-field corrections for different angles of incidence

Optional

G.R.A.S. AF0008 Adapter for ¼” preamplifier and ½” microphone
G.R.A.S. GR0010 Adapter for ¼” preamplifier and ½” microphone
G.R.A.S. RA0001 Right-angled (90°) adapter for ½” microphone and ¼” preamplifier
G.R.A.S. RA0003 Adapter for ¼” preamplifier and ½” microphone
G.R.A.S. RA0016 20 dB Attenuator for externally polarized ½” microphones