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½-inch Prepolarized, Free-field Microphone Type 40AE0 pages
7" Wide-frequency, Free-field Microphone Type 40AM 1/2 Product Data Typical Applications ■ Prcision acoustic measurements ■ Type 0 and 1 SPL measurements ■ Free-field measurements ■ Precision laboratory measurements The G.R.A.S. Microphone Type 40AM is a 7" wide-frequency, precision condenser microphone for laboratory work as well as for measurements in open acoustic fields. It is a pre-polarized free-field micro魭phone with a large dynamic range and an extended frequency response. As a free-field microphone, the Type 40AM is for measuring the sound pressure which existed before it was placed in the sound field, and pointing towards the sound source. The disturbing effects of its presence in the sound field are minimal at low frequencies (large wave-lengths compared with microphone size). At higher frequencies, the effects of reflections and diffractions generally lead to an increase in the measured sound pressure levels. Fig. 3 shows what these are in a free-field for vari-ous angles of incidence. The Type 40AM compenͭsates for this to provide a flat frequency response at an angle of 0° incidence in a free-field (see Fig. 2). Fig. 1 1A" Wide-frequency, Free-field Microphone Type 40AM G.R.A.S. CCP preamplifiers are also available for use with the Type 40AM, these are: ■ 7" Preamplifier Type 26CA ■ %" Preamplifier Type 26CB with the included adaptor GR0010 (see separate data sheets). 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: Dynamic range: 3.15 Hz - 31.5 kHz.......... ............+ 2.0 dB Upper limit (3 % distortion) 160 dB re. 20 liPa 5 Hz - 16 kHz ........... ............+ 1.0 dB Microphone thermal noise: 20 dBA re. 20 l Pa 3.15 Hz - 40 kHz........... ............+ 3.0 dB Capacitance: Nominal sensitivity: 17 pF 12.5 mV/Pa Temperature range: Polarization voltage: - 10 °C to + 50 °C ...continued overleaf o o I G . R . A . S. SOUND & VIBRATION Skovlytoften 33 2840 Holte, Denmark Tel +45 45 66 40 46 Fax +45 45 66 40 47 www.gras.dk gras@gras.dk
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