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¼-inch Free-fi eld Microphone Type 40BF0 pages
%-inch Free-field Microphone Type 40BF Product Data and Spcifications Typical applications ■ Sound pressure measurements ■ High frequency measurements ■ High level measurements ■ Acoustic transient measurements The G.R.A.S. Microphone Type 40BF is a %-inch precision condenser microphone for general purpose measurements in open acoustic fields. It is an exter-nally polarized free-field microphone with a large dynamic range and a wide frequency response. As a free-field microphone, the Type 40BF 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 (see Fig. 1 inset). At higher frequencies, the effects of reflections and diffractions generally lead to an increase in the meas-ured sound pressure levels. Fig. 3 shows what these are in a free-field for various angles of incidence. The Type 40BF compensates for this to provide a flat frequency response at an angle of 0° incidence in a free-field (see Fig. 2). Fig. 1 V-inch Free-field Microphone Type 40BF (inset shows true size) G.R.A.S. %-inch preamplifiers (see data sheet for Types 26AA, 26AB, 26AC and 26AL) are also available for use with the Type 40BF. The mount-ing thread (5.7 mm - 60 UNS-2) is compatible with other available makes of similar microphone pream魭plifiers. All G.R.A.S. microphones comply with the specifications of IEC 1094: Measurement Microphones, Part 4: Specifications for working standard microͭphones. Non-corrosive, stainless materials are used in manu-facturing these microphones to enable them to with-stand rough handling and corrosive environments. All G.R.A.S. 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. Specifications Frequency response: Microphone thermal noise: 4 Hz - 100 kHz............ ...........± 2.0 dB 30 dBA re. 20 u, Pa 10 Hz - 40 kHz............ ..........± 1.0 dB Capacitance: Nominal sensitivity: 7 pF 4 mV/Pa Effective front volume: Polarization voltage: Nominal at 250 Hz:....... ........... 0.6 mm 3 200 V Temperature: Upper limit (3 % distortion): Range:................. . . . - 40 °C to + 150 °C 166 dB re. 20 u, Pa ...continued overleaf o s > G.R.A.S. Sound & Vibration Skovlytoften 33 2840 Holte, Denmark Tel +45 45 66 40 46 Fax +45 45 66 40 47 e-mail: gras@gras.dk www.gras.dk
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