The Endevco. microphone model EM40BE is a ¼-inch precision condenser microphone for general purpose measurements in open acoustic fields. It is a prepolarized free-field microphone with a large dynamic range and a wide frequency response. As a free-field microphone, the model EM40BE is for measuring the sound pressure which existed before it was placed in the sound field pointing towards the sound source. The disturbing effects of its presence in the sound field are minimal for most of its frequency range because of its small dimensions. At higher frequencies, the effects of reflections and diffractions generally lead to an increase in the measured sound pressure levels. Fig.2 shows what these are in a free-field for various angles of incidence. The model EM40BE compensates for this to provide a flat frequency response at an angle of 0° incidence in a free field (see Fig.1). Endevco Isotron preamplifiers are also available for use with the model EM40BE, these are: • ¼-inch Preamplifier model EM26CB Endevco microphones comply with the specifications of IEC 1094: Measurement Microphones, Part 4: Specifications for working standard microphones. Non-corrosive, stainless materials are used in manufacturing these microphones to enable them to withstand rough handling and corrosive environments. All Endevco microphones are guaranteed for 5 years and are individually checked and calibrated before leaving the factory. An individual calibration chart is supplied with each microphone. Applications • High frequency measurements • High level measurements • Acoustic transient measurements • Use with Endevco Isotron® preamplifiers • Repairable Endevco® model EM40BE ¼-inch Prepolarized free-field microphone Description cmyk

Endevco® model EM40BE ¼-inch Prepolarized free-field microphone Specifications Frequency response: 10 Hz–40 kHz: ± 1 dB 4 Hz–80 kHz: ± 2 dB 4 Hz–100 kHz: ± 3 dB Nominal open circuit sensitivity: at 250 Hz: 4 mV/Pa Polarization voltage: 0 V Upper limit (3% distortion): 166 dB re. 20 ìPa Microphone thermal noise: 30 dBA re. 20 ìPa Nominal cartridge capacitance: Polarized: 5.2 pF Resonant frequency: 90° Phase shift: 100 kHz Effective front volume: Nominal at 250 Hz: 0.6 mm3 Static-pressure coefficient: 250 Hz at 25°C –0.014 dB / kPa Influence of axial vibration, 1 m/s2: 60 dB re. 20 ìPa Temperature:...