Condenser Microphone Cartridges - Types 4160 and 4180
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USES: 0 Laboratory standard microphones 0 Pressure and Free Field Reciprocity Calibrations 0 Coupler measurements FEATURES: 0 Well defined integral front cavities for coupler calibrations 0 Low hydrogen leakage from front cavity 0 Well-defined operating characteristics 0 Flat Frequency Pressure Responses up to: 4160: 8kHz 4180: 20 kHz 0 Artificially aged for long term stability 0 Low sensitivity to environmental changes 0 Standards: 4160: ANSI S1.12-1967, ANSI S1.l0-1966 (and revisions), IEC 327 and 402, JIS C 5515, and IEC draft standard for 1 " laboratory standard microphones type LS1 P 4180: IEC draft standard for 1/2” laboratory standard microphones type LS2aP Types 4160 and 4180 are high quality condenser microphones intended for use as laboratory standard microphones and in laboratory coupler applications where high accuracy and long-term stability are essential. One-inch diameter Type 4160 has become established as a laboratory standard microphone for use in the medium and low frequency ranges. Half-inch diameter Type 4180 has been developed as a laboratory standard microphone to meet the need for extended frequency calibrations. Both microphones are designed for coupler applications and can be used with couplers filled with gases other than air as they both feature very low gas leakage from the front cavity. Both microphones are of the external polarization type and operate on a polarization voltage of +200 Volts. The microphones are individually calibrated and pressure calibration data are provided with each microphone. s-- Types 4160 and 4180 are both high stability condenser microphones which find application as laboratory standards and in coupler measurements. Type 4160 has been used for some time in such applications and conforms to IEC 327 and 402, ANSI S1.12-1967 and ANSI Sl.lO-1966, JIS C 5515, and the current IEC draft standard for 1” laboratory standard microphones. It has become established as a high precision reference standard and is used in the medium frequency ranges and for measurements at low sound pressure levels. Type 4180 has been developed to meet a growing need for a laboratory standard 1 /2" microphone which enables measurements at higher frequencies and at higher sound pressure levels. Standard specifications for l/2” laboratory standard microphones are under consideration and the 4180 has been designed to comply with the most recent drafts of these standards. Types 4160 and 4180 are delivered in mahogany boxes with individual calibration charts. Description The high standards of design and construction of both microphones ensure a high quality laboratory microphone which is extremely reliable with respect to environmental factors and has an excellent long-term stability. The construction of Types 4180 and 4160 is similar to that of other Bruel & Kj^r condenser microphones but with the addition of well-defined front volumes to facilitate accurate mounting of calibration couplers. A feature of the front cavity of the 4180 is its shallow depth, only 0,5mm. Frequency Response Since Types 4160 and 4180 are designed mainly for use in pressure calibrations they have flat pressure response curves as can be seen in Fig.1. The 4160 has a flat response up to 8kHz and the 4180 exhibits a flat response up to 20 kHz. Measurements can be made at higher frequencies, up to 20 kHz for Type 4160, and up to 40 kHz for Type 4180, but with reduced sensitivity. Lower Limiting Frequency The pressure frequency response of Types 4160 and 4180 are not limited in the lower frequencies, since by the definition of pressure response the vent is not exposed to the sound field. However, when the microphones are used in measurements where the pressure equalization vent is exposed to the sound, for example in a free field, the sensitivity at low frequencies de-

creases. The lower frequency limit (-3dB), which is determined by the resistance of the pressure equalization vent, lies between 1 and 2Hz for the 4160 and between 1 and 3Hz for the 4180. Free Field Measurements Type 4180 may find application in free field and diffuse field measurements. It disturbs the sound field less than a 1” microphone and is less sensitive to angle of incidence. Dynamic Range The lower limit of the dynamic range for a condenser microphone system is determined by the diaphragm thermal noise and by the electronic noise in the preamplifier. For the 4160 connected to...

Fig. 3. Effect of temperature on microphone sensitivity (25OHz) oratory standard microphones be kept within a narrow temperature range. Changes in barometric pressure produce a change in air stiffness. Most of the microphone stiffness, however, is due to mechanical stiffness and the effect of small changes in atmospheric pressure is consequently minimized, see Fig. 4. In the absence of condensation, variations in relative humidity will have only a small effect on the microphone sensitivities due to a small variation in cavity air stiffness. For the full range of humidity, this effect is...

Coupler Adaptor Ring 1 "DB 0111 3PEN CIRCUIT SENSITIVITY* (250 Hz): -26,5dB + 1 dB re 1 V/Pa, 47mVIPa POLARIZATION VOLTAGE: +200 Volts FREQUENCY RESPONSE* (pressure): jp to 8kHz: ±1 dB (ref. to 250 Hz) PRESSURE EQUALIZATION SYSTEM: Back vented LOWER LIMITING FREQUENCY* (-3dB): 1 Hz to 2 Hz (vent exposed to sound) PRESSURE EQUALIZATION TIME CONSTANT: Range: 0,16to 0,08s DIAPHRAGM RESONANCE FREQUENCY (90” phase shift): 8,5 kHz (typ.) INSULATION RESISTANCE (at 85% RH): > 101S £> POLARIZED CAPACITY’ (250 Hz): 55 ± 3 pF CARTRIDGE THERMAL NOISE: 0,6 X 10~6Pa/\/Hz 9,5dB(A), 10dB(lin) UPPER...