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Brüel & Kjær 4131/32, Instruction & Application, Page: 28 / 44

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Summary of Contents for 4131/32

Page 1: ...essories Precision condenser microphones for measurement purpose Each microphone is individually cali brated Frequency range of calibration 20 20ooo c s The 4132 fulfils the requirements of the Americ...

Page 2: ...I...

Page 3: ...One inch Condenser Microphones AUGUST 1962...

Page 4: ...ation Voltage 19 9 Temperature 20 10 Static Ambient Pressure 21 11 Magnetic Fields 22 12 Vibrations 22 13 Humidity 23 Modification of the pressure equalization 24 Comparison Type 4132 Type WE 640 AA 2...

Page 5: ...ng the microphone connecting plug Stabilized plate and heater voltages for the cathode follower and polarization voltage for the cartridge are avail able on this seven poled socket The microphones may...

Page 6: ...into an AC voltage component if a constant charge is present between the electrodes The charge is obtained by means of a stabilized DC polari zation voltage and it remains constant as long as the char...

Page 7: ...d Re in order to obtain a satis factory low limiting frequency Dia Back plate Hole for static pressure equalization Fig 3 Schematic construction of a condenser microphone cartridge Mechanical iH Cartr...

Page 8: ...ee field and Pressure Response At higher frequencies the diffractions of the sound waves on the microphone produce an appreciable change in the resulting sound pressure acting on the microphone diaphr...

Page 9: ...signed devices instead of the protective grid see Accessories the respnose may be made practically independent of the angle of incidence in an extended frequency range The free field and diffuse field...

Page 10: ...one is 10 cis The mechanical construction of the cartridges is shown on Fig 6 The choice of the materials and th design of the suspensions of the different parts are made principally with a view to ob...

Page 11: ...the transducer to a 750 Q output impedance They are electrically identical units The mechanical construction however is different in that the Cathode Follower Type 2612 is fitted to a flexible goose n...

Page 12: ...cis The output signal is at any fr equency more than 50 db below that obtained with the microphone cartridge in P lace 130 db where the microphony is measured within the frequency range of 20 20ooo c...

Page 13: ...0 10 8 10 s 100 i s 1m 3 33 feet 3 4 6 8 llOOS s 2 3 4 6 8 tlK 7 s 2 3 4 5 6 8 100K 7 s 2 3 4 0 1 6 8 1000KCfs 1 59215 Fig 9 Graph of cathode follower high frequency performance with different lengths...

Page 14: ...ds and may al so be suspended by means of its own cable The power supplies necessary to operate the cathode followers arc provided by the amplifier via the multi socket at the front panel qr by a Micr...

Page 15: ...73496 J 2 t O Hr andwlU 200V r r i Lr i n r at 4 68 mY whr 46 6 db N V ba r C a trldra o pecn e i ul tHnaltlrit af 5 37 mV I b r 45 4db Y l bar car i J o 11 t l 0 t0 6 C utyat l k c a wllh200V pola rl...

Page 16: ...0 0 0 0 0 0 0 0 0 0 0 0 BrUel KJcar BrUel KJcar 1SQO Gl 12oog roc e soon Gl 30 j 0 50 0 0 100 o 8 o o 500 0 0 2000 5000 10000 C 1 20000 OI IIon 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 159209 0 0 0 0...

Page 17: ...gm resonance 90 phase angle which is approximately critically damped occurs at about 7 5 kc s 4 Free field Corrections The pressure increase which is caused by the reflections of free field sound wave...

Page 18: ...0 180 15 Free field corrections for db Type 4131 and Type 4132 with protecting grid 10 5 I I I I I db 7 1 L I 10 r 1k 3 I I I ol I 1 I I I 300 V I I i I I I v I i i I I j I I vv 1 I v v 1 i I I I I I...

Page 19: ...hprotectilggid With protecting grid Withprotectmg gnd Fig 15 Typical directional characteristics for the microphones grid is substituted by a Random Incidence Corrector UA 0055 see Fig 30 or a Nose Co...

Page 20: ...per limit of the dynamic range is set by the harmonic distortion and is approximately 146 db for 4 total harmonic distortion See Fig 16 No damage will be caused to the cartridge if a sound pressure of...

Page 21: ...ization Voltage The condenser microphone cartridges have been designed to operate with a polarization voltage of 200 volts They are not tested above 260 volts The polarization voltage supplied from th...

Page 22: ...nsula tion material used in the connecting cables of the cathode followers 2612 and 2613 should not be exposed to higher temperatures than 100 C 212 F db 11111 M111111 11111 M 40 20 0 20 40 60 80 100...

Page 23: ...0 00000000000 0 BrOe CIIr l l l l 1 tl o ol c l 25 G 15 e 5 7 Yffi fJ31 p r atmospherjc pressLRs _ _ _ ___3__ t LA F _1Q__ _ Na 11 _ __2 5_ _ Il 5 8 W s 1 tQ0__ 0 0 0 0 II II o o o o o o o o o o o o o...

Page 24: ...magnetic shielding should also cover completely the goose neck O DD O ODDOOOOOOODDOODDOOOOOOOOOD D D OO OOOOOOOO O OOOOOOO O 1 f1vWtrggMg3e 50 Gauss 50 cts magnetic field follower 2613 n JJiiJY g 15 n...

Page 25: ...In Fig 25 is shown the sensitivity to vibration of varying frequencies The aweep covers the frequency range from 10 c s to 2ooo c s The slight increase towards the higher frequencies is due to the dif...

Page 26: ...ridge is ready for use again By removing the wire completely the time constant will be approx 8 msec corresponding to a low frequency cut off of 50 c s NOTE During the modification the cartridge shoul...

Page 27: ...ler adaptor DB 0111 is illustrated on Fig 27a The resulting change in frequency characteristiCs is seen in Fig 27b The ada ptor DB 0111 is included in the Couplers Type DB 0160 and DB 0161 see Accesso...

Page 28: ...dence above 3 4 kc s The normal incidence sensitivity is in particular well above the random incidence sensitivity e g 6 db greater at 10 kc s This is a certain source of error when for example measur...

Page 29: ...to 10 kc s Fig 31 If better omnidirectional properties are wanted the B K Half inch Type 4133 34 or Quarter inch Type 4135 36 microphone cartridges should be used at the expense of a lower sensitivit...

Page 30: ...Screen UA 0050 Total length 28 em The Nose Cone UA 0051 is designed to substitute the protection grid of the Microphone Type 4131 The Nose Cone is extremely useful for measurements in wind tunnels duc...

Page 31: ...ncidence for Microphone Type 4131 fitted with Nose Cone UA 0051 10 Free field corrections for type 4131 I QO f and 4132 with Nose Cone UA 51 r db f Pressure Response Odb oo 1 5 180 v t LL_V JQO I r K...

Page 32: ...UA 51 4131 3kcJ i 30 UA 51 4131 10 k cjs Fig 36 Directional patterns of the condenser microphone Type 4131 equipped with a nose cone UA 0051 instead of the protecting grid 6051f...

Page 33: ...ell remote from the associated in truments an extension cable must be used to make the connection Several standard lengths of extension cables are available for this purpose Extension Cable AO 0027 is...

Page 34: ...ard ring system of the cathode follower Note The low frequency cut off of the combination 4133 34 2612 13 is around 25 30 c s Fig 38 Adapter UA 0030 Flexible Extension Rod UA 0039 This adaptor introdu...

Page 35: ...oupler It is mounted in the same manner as the DB 0160 Further information about the couplers will be found in the B K Technical Review No 4 1961 DB 0160 DB 0161 Fig 40 Sectional view of the 6 cm3 cou...

Page 36: ...switch Fig 4 1 The Two Channel Microphone Selector Type 4 408 NB The heater supply wiring in the 4408 provides for series connection of the cathode follower heaters and one cathode follower cannot th...

Page 37: ...hree small mercury cells The external diameter of the housing varies from 23 77 mm o 936 to 25 4 mm l and its total length is 27 em 11 A small moving coil voltmeter is also included for checking the b...

Page 38: ...fe with 8 hours service periods 20 hours Weight with batteries and 3 meters cable o 6 kg Tube CK 512 AX Transistors 2 X 2N2374 60pF H 4 ffi Ei 3 2 000 Load 106 1l 1 61 388 Fig 44 Diagram showing the 2...

Page 39: ...3 16 V is equivalent to 130 db S L when using a 4131 microphone cartridg e at the input The B K standard screened cahle AC 0002 present a capacity of 100 pF m Fig 45b Part Numbers of the battery drive...

Page 40: ...0 22 o 22 o 45 db and the probability of obtaining larger errors than o 8 db is less than o l Microphone Calibration Equipment If a better accuracy is wanted the most practical and reliable solution i...

Page 41: ...s of the Micro pllone Calibration Apparatus Type 4142 utilizing the reciprocity technique which is the method retained by the American Standard Association Z 24 4 1949 Screened cable f Socket marked B...

Page 42: ...ntact the periphery of the cartridge diaphragm in order to obtain an accurate definition of the spacing between actuator grid and diaphragm By applying an AC voltage between the grid and the diaphragm...

Page 43: ...Cathode Followers 2612 2613 Part Numbers 41...

Page 44: ...B K Auguat 1961...

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