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Содержание 2604

Страница 1: ...e built in rectifier and meter circuit can be switched to measure either the arithmetic average the true r m s or the peak value of the input signal The instrument also contains the inter nationally standardized weighting networks for sound level measurements Connections for Cond enser Microphone and Level Recorder Nrerum Denmark 80 05 00 BRUKJA Copenhagen Telex 5316 88 2604 ...

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Страница 3: ...Microphone Amplifier Type 2604 October 1965 ...

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Страница 5: ...nals etc 19 3 Operation 22 Voltage Measurements 22 Calibration 22 Measuring 22 Sound Level Measurements 23 Setting up 23 Calibration 24 Measuring 2 5 Recording of Sound Level 27 Calibration by Means of a Calibrated Sound Source 28 Influence of Background Noise 30 4 Accessories 32 External Filters 32 Condenser Microphones 35 The Two Channel Microphone Selector Type 4408 37 Response Test Unit Type 4...

Страница 6: ...6 Measurement of Acoustic Absorption Coefficients 48 Recording of the Frequency Response of Sound Projectors 49 Directional Characteristics of Projectors 50 Recording of Frequency Response of Hydrophones 53 C Mechanical Measurements 54 Vibration Measurements 54 Recording the Frequency Response of Accelerometers 56 Measurement of Microphony in Tubes 58 Appendix 60 Specification 62 ...

Страница 7: ...e defined as the auditory sensation evoked when such vibrations normally in air impinge upon the ear As an auditory sensation sound is limited to frequencies in the range from about 20 Hz to 20ooo Hz Pressure fluctuations outside this range will not generally produce the sensation of sound The Decibel Scale Acoustical instruments for measuring pressure variations are usually cali brated in dB deci...

Страница 8: ...0 114 dB T Loud automobile horn dist 1 m ubar 110 Trnside airliner DC 6 100 Trnside 10 94dB subway train New York tbar 90 Trnside motor bus 80 T Average traffic on street corner 74dB bar 70 Tconversational speech 60 o 1 54 dB T Typical business office ubar 50 T Living room suburban area 40 o 01 34 dB TLibrary tbar T 30 T Bedroom at night I 20 0 001 14 dB T Broadcasting studio ubar I 10 T Threshold...

Страница 9: ...arious frequencies are judged by the average human being to sound equally loud Other sets of equal loudness contours which deviate from these curves in certain respects have been published by various investigators but the curves shown in Fig 0 2 have been recommended as standard by the International Organization for Standardization ISO R 226 1961 E The reference level is usually set up at 1ooo Hz ...

Страница 10: ...r effect Noise control Man s sensitivity to vibration is extremely limited especially for the higher frequencies so that measuring instruments are needed in order to determine accurately the vibrations in question By substituting an accelero meter for the microphone a sound level meter can usually be adapted to measure vibration instead of sound level and thus serve a dual purpose in the fight aga...

Страница 11: ...ed in the unit G which is the acceleration derived from the gravitational force of attraction of the earth As the gravity alters with latitude and altitude a standard gravity is chosen to G 9 80665 m sec 2 32 1739 ft sec 2 9 ...

Страница 12: ...y characteristic in the range 10 Hz 200 kHz is obtained If a frequency analysis is required external filters such as the Band Pass Filter Set Type 1612 can be inserted between the amplifier sections The set up will then be similar to the Audio Frequency Spectrometer Type 2112 In the case of vibration measurements the Preamplifier Type 1606 or Cathode Follower 2612 2613 2614 or 2615 with Accelerome...

Страница 13: ... for the B K Condenser Microphones and Preamplifiers The other input socket accommodates a 14 mm coaxial plug and can be connected to the input circuit of the amplifier either directly or via a variable potentiometer for relative measurements A three position INPUT SWITCH marked Condenser Microphone Direct and Input Potentiometer gives individual selection of these three input facilities When the ...

Страница 14: ...ith negative feed back the amount of which may be varied by two potentiometers The sensitivity of the apparatus can then be adjusted and thereby calibrated the reference voltage being used as calibration voltage One of the potentio meters is in circuit when the INPUT SWITCH is in position Condenser Microphone the other when the switch is in either of the two positions Direct or Input Potentiometer...

Страница 15: ... 4 5 10 At low frequencies the meter pointer will start to fluctuate when the METER SWITCH is in the position Fast When the fluctuation due to the low frequency is too large the r m s value read is no longer the correct value and the METER SWITCH should therefore be set in position Slow The lower limiting frequency in position Fast is approximately 20 Hz sine wave Arithmetical Average Measurements...

Страница 16: ...uch circumstances the peak value read on the meter is thus not the maximum that occurs A 60228 Fig 1 2 Electrical circuit of peak rectifier further limitation of the peak indication is due to phase distortion in the amplifiers and is discussed in the Appendix As indicated in Fig 1 2 the output resistance of the output stage is approx imately 50 Q which is the charge resistance for C1 and C2 The di...

Страница 17: ...ifier For use of the scales concerning the Standing Wave Apparatus reference should be made to the Instruction Book for this apparatus Overall Performance of the Instrument Signal to Noise Ratio When the RANGE MULTIPLIER switch is in position X 1 0 dB the signal to noise ratio for full scale deflection on the meter is better than 55 dB for any setting of the METER RANGE switch see also Fig 1 4 By ...

Страница 18: ...ave to contain a certain energy to be indicated When for example measurements are made on noise signals with Gaussian distribution the indicator will only react for noise peaks which are lower than approximately 2 5 times the r m s value i e fc lower than 2 5 To be able to check on how far the input amplifier is driven in making selective measurements the FREQUENCY RESPONSE SWITCH of the Micro 16 ...

Страница 19: ...Linear 10 200ooo typical frequency and phase response curves are shown in Fig 1 5 The two curves shown in the high frequency range of the phase response characteristic indicate the lowest and highest typical phase distortion Amplification i_ 20 30 40 50 60 uri 10Hz 200000 Hz lo n I C lo lj I I v I li 1 2 5 10 2 0 200 000 800 600 00 200 0 200 00 60 ao 00 2 r Meter switch r Off I Peak r b f r RM r A...

Страница 20: ...reamplifiers via the CON DENSER MICROPHONE input socket The third rectifier supplies the necessary anode voltages for the amplifiers and the polarization voltage for the microphone cartridge of a Condenser Microphone when used These two voltages are stabilized with the aid of two neon tubes A socket marked POLARIZATION VOLTAGE on the front panel of the apparatus makes it possible to measure the po...

Страница 21: ...itivity Adjustment Amplifier Input Frequency Response Switch Fig 2 1 Drawing of Type 2604 with control knob identification Refer Fig 2 1 OVERLOAD INDICATOR POLARIZATION VOLTAGE Red light indicating that the input amplifier is overdriven 4 5 volts peak at the output of the input amplifier For measurement of the microphone polarization voltage The measurement should be carried out with a DC voltmete...

Страница 22: ...ER For connection of external filter e g the Band Pass Filter Set Type 1612 DENSER MICROPHONE A screwdriver adjusted potentiometer for adjust ment of sensitivity when the input CONDENSER MICROPHONE is used METER RANGE FREQUENCY RESPONSE SWITCH SENSITIVITY AMPLIFIER INPUT POWER METER SWITCH 20 A stepped attenuator 20 dB for attenuation of input signal For the selection of linear amplification in th...

Страница 23: ...disconnected RECORDER Output terminal for connection to monitoring in struments such as the Level Recorder Type 2305 RANGE MULTIPLIER Stepped attenuator 10 dB for attenuation of the signal level between filter outputs and the output amplifier EXTERNAL FILTER OUTPUT For use when utilizing external filter 21 ...

Страница 24: ...ER RANGE Ref FREQUENCY RESPONSE SWITCH Linear 10 200ooo METER SWITCH RMS fast RANGE MULTIPLIER X 1 0 dB The control knobs not mentioned can be in any position 5 The meter deflection should now be 16 dB red mark on the scale If not adjust to the correct value by means of the screwdriver operated potentiometer SENSITIVITY AMPLIFIER INPUT on the front panel Measuring The Microphone Amplifier has now ...

Страница 25: ... X o 3 Full scale deflection is found to be 10 mV X o 3 3 mV i e the 0 31 5 volts scale must be used The voltage measured can be recorded on a level recorder such as the Type 2305 which should then be connected to the output socket marked RE CORDER Other monitoring instruments such as oscilloscopes tape recorders or even high impedance loudspeakers can be used utilizing the RECORDER socket which i...

Страница 26: ...one Amplifier Condenser Microphone proceed as outlined in the following tables Microphone 4131 or 4132 Microphone 4133 or 4134 1 Check the microphone polarization voltage 1 Check the microphone polariza tion voltage 2 Set the control knobs in the fol lowing positions 2 Set the control knobs in the following positions INPUT SWITCH Condenser Microphone INPUT SWITCH Condenser Microphone n 2110 o a eo...

Страница 27: ...rew driver until the meter pointer deflects to the red mark For sound level measurements the control knobs should be in the following positions INPUT SWITCH Condenser Microphone METER RANGE 160 dB SL FREQUENCY RESPONSE SWITCH Linear Weighting curves A B and C or External Filter as desired RANGE MULTIPLIER 0 dB METER SWITCH RMS fast or other positions as desired The control knobs not mentioned can ...

Страница 28: ... the number of dB SL in dicated by METER RANGE the number of dB indiCated by RANGE MULTIPLIER the correction facfor K in dB K being the correction factor for the microphone Example 1 Deflection of the meter 15 dB Position of METER RANGE 100 dB SL Position of RANGE MULTIPLIER 10 dB Position of FREQUENCY RESPONSE SWITCH C Correction Factor K 11 dB Sound level 15 dB 100 dB 10 dB 11 dB 116 dB C Exampl...

Страница 29: ...ng calibration and operating procedure is recommended for this arrangement Connect the RECORDER output of the Amplifier to the Level Recorder input and supply the Recorder with a 50 dB Range Potentiometer Refer Level Recorder Manual if necessary 1 Measure the sound level referring to the preceding passage Sound Level Measurements 2 Next set the control knobs of the Level Recorder Type 2305 as foll...

Страница 30: ... Means of a Calibrated Sound Source An easy way to calibrate or check a measuring arrangement for sound in vestigation is offered by the employment of the B K Pistonphone Type 4220 or Noise Source Type 4240 respectively I Pistonphone The Pistonphone is a compact battery operated easily portable device de signed for the calibration of microphones and measuring set ups It is very accurate and the ca...

Страница 31: ...n here II Noise Source The Noise Source is designed to give a quick check on measuring arrangements set up for sound investigation The Source is a cartridge in which steel balls generate the noise level Further information is given in the manual or data sheet for this device 1 The procedure for employing the apparatus is similar to that given for the Pistonphone with the exception that the control...

Страница 32: ...using 107 dB The correction factor K of the Mi crophone 13 3 dB The indicating meter should then de flect to 107 80 13 3 13 7 dB If it is required to measure the sound emitted from a particular piece of equipment e g an electric motor best results would be obtained by removing the motor and do the measurements in an anechoic room with no disturbing background noise However this is not always possi...

Страница 33: ...background noise A graph is given above of the dB value to be subtracted from the total reading for different values of background sound level When the difference between total reading and background level is more than 2 3 dB this method is accurate enough for most purposes However when smaller differences are measured the motor noise must be measured in an anechoic room or the background sound le...

Страница 34: ...r details concerning the use of the Band Pass Filter Set the reader is referred to the Instruction Book for the Set If filters other than the Type 1612 are used in conjunction with the Micro phone Amplifier care should be taken to ensure proper matching The output impedance of the input amplifier section of Type 2604 is approximately 12 Q and in most cases a series resistor must therefore be added...

Страница 35: ...ge is an instrument designed for selective attenuation of any frequency within the range 20 20ooo Hz It consists of a parallel T network the resistance components of which are continuously variable within each of six frequency ranges selected by a Lin 0 dB Frequency F _I Lin d i Distortit 2bt ll 50 60 70 80 90 100 110 0 1 0 2 0 3 0 4 o s 1 f fo 2 3 4 5 10 20 120 i915f Fig 4 2 Frequency characteris...

Страница 36: ... o 5 can be obtained in one operation In part Application of this book a measuring arrangement is described using the Frequency and Distortion Measuring Bridge for distortion measurements It should be noticed that the combination consisting of the Bridge and the Microphone Amplifier is equivalent to the Frequency Analyzer Type 2107 when this is in position Frequency Rejection Psophometer Filter ZS...

Страница 37: ...characteristics within the tolerances permitted in the standards Condenser Microphones Condenser Microphones When employing one of the B K Condenser Microphones in conjunction with a Microphone Amplifier Type 2 604 a complete equipment for high precision measuring and analyzing of sound is produced The B K Condenser Micro phone program is very extensive and is constantly progressing The pre domina...

Страница 38: ...bar 1 V ubar Dynamic Range re 2 X 10 4 ubar 15 146 dB 32 160 dB 64 174 dB 70 180 dB A weighted to 4 distortion Maximum Safe Sound Pressure 165 dB 180 dB 185 dB re 2 X 10 4 ubar Temperature Less than o 01 dB per C Coefficient Construction Cylindrical Out 23 77 mm o 936 13 2 mm o 52 7 4 mm o 29 side diameter Ambient Pressure Coefficient 100 mm Hg pressure o 2 dB o 1 dB Less than o 1 dB decrease equa...

Страница 39: ...h dummy cartridges and placed in a 130 dB Sound Sound Fields Field the Cathode Follower output is 50 dB below normal microphone output Working Temperature 2612 2613 2614 2615 From below 40 C to above From below From below 100 c 40 C to 40 C to above 150 C above 100 C above 250 C intermittent To give an impression of the area of application some of the most important accessories are mentioned Artif...

Страница 40: ...e two anodes Still it is reduced by more than 80 dB at 20 Hz When the Selector is operated manually the toggle switch is employed This switch then operates the relay which in turn switches the output from the Type 4408 to one or the other of the two inputs The Selector may also be remotely controlled The toggle switch must then be in position 2 and the external control switch is connected by means...

Страница 41: ...uencies and for tone arm resonance investigations It is intended for pick up design work and also for general purpose checks in combination with the gliding frequency records when curve plotting equipment is not available The espouse Test Unit Type 4409 consists of three sections the channel selector the equalizing filter section and the synchro starter The channel selector is a low noise relay dr...

Страница 42: ... all constructed in such a way that they are in accordance with International Standards Hearing Aid Test Box Type 4212 In measuring the free field response and distortion of complete hearing aids and small microphones the Hearing Aid Test Box is an indispensable equip ment The Test Box is portable and consists of a small anechoic chamber with a built in loudspeaker and regulating microphone as wel...

Страница 43: ...hen the Microphone Amplifier is utilized in vibration measurements a pre amplifier for the B K Accelerometers is a necessity Therefore the Vibration Pick up Preamplifier has been designed It is connected to the CONDENSER MICROPHONE input from where the necessary power to the Preamplifier is also supplied A measuring arrangement built up of one of the B K Accelerometers the Preamplifier and the Mic...

Страница 44: ...T IMP The impedances are 20 kohms and 600 lJ A third position of the switch allows a grounded middle point of the INPUT to be utilized Vide Fig 4 9 Fig 4 8 Input Transformer TI 0001 To give a flat frequency response 10 20ooo Hz o 2 dB the OUTPUT of the Transformer should be properly loaded First to ensure that a low capacity is connected to the OUTPUT of the Transformer the special low capacity ca...

Страница 45: ...hen the Transformer has an open INPUT terminal and is located in the most unfavourable position in the field Input Fig 4 9 Schematic diagram of Input Transformer The transformer ratio 1 1 can if necessary be adjusted by a potentiometer ADJUSTMENT accessible at the bottom The Transformer is correctly pre adjusted at the factory 43 ...

Страница 46: ...nes suitable for the measurements in question For information concerning these and other instruments used in the described applications reference should be made to part Accessories in this book or to the respective leaflets and manuals A ELECTRICAL MEASUREMENTS Distortion Measurements The non linear distortion in four terminal networks is normally expressed by means of the formula d 100 B F O i i ...

Страница 47: ...ectly in from the Micro phone Amplifier meter provided that the meter circuit is switched to measure the r m s value of the signal The B F O itself has a distortion factor of o l in the middle frequency range when unloaded It therefore allows measure ment of distortion factors down to around o 5 which is sufficient in most practical cases Automatic Recording of Electrical Impedance By using the Au...

Страница 48: ...imilar set up In this case the connection to the Level Recorder and the COMPRESSOR INPUT have to be interchanged This method is very convenient for a quick and easy check of the frequency dependance of an unknown impedance B ACOUSTICAL MEASUREMENTS Checking of Hearing Aids An arrangement for the checking of hearing aids is illustrated in Fig 5 3 This set up makes it possible to automatically recor...

Страница 49: ... combination enables the sound pressure level on the hearing aid to be kept constant without in fluencing the practically free sound field conditions The B F O Type 1022 supplies the required power for the loudspeaker in the chamber while a B K Condenser Microphone which is placed in the Artificial Ear is used for the measurement of the acoustical output from the hearing aid The microphone is conn...

Страница 50: ...1612 and setting the filter switch of the Band Pass Filter Set so that it runs ahead of the frequency scanning of the B F O the selected frequency difference being in accordance with the harmonic which is going to be measured Measurement of Acoustic Absorption Coefficients Small samples can be tested for their acoustical absorption by means of the Standing Wave Apparatus Type 4002 as shown in Fig ...

Страница 51: ...Standing Wave Apparatus Type 4002 is equipped with two measuring tubes covering two frequency ranges 95 to 1800 Hz and 800 to 6500 Hz Acoustic materials with absorption coefficients in the range 4 to 100 can be measured with the apparatus Additional information can be found in the Instruction Book for Type 4002 The absorption measurements can if necessary be made selective by adding the Band Pass ...

Страница 52: ... 15 z _p_ Sp _l_20 10 L LJo F 2 Q QJioc No _ _ p 5 0 o __10 5 Wr Sp 20 Q SI9n Roct F Scolo o o OoO 1000 2000 10000 20000 50000 100000 boa QP 0123 1000 10000 100000 Hz 161777 Fig 5 7 Recording taken with the set up in Fig 5 6 Directional Characteristics of Projectors The directional characteristics of an echo sounder projector may be meas ured by the combination shown in Fig 5 8 A projector and a h...

Страница 53: ...er I I I I ___________________ J 2804 AOOOlL Fig 5 8 Measuring arrangement for automatic recording of the directional characteristics of projectors Fig 5 9 Typical directional characteristic of a projector Clevite Research Center AX209 51 ...

Страница 54: ...y controlling the Turntable from the Level Recorder it is possible to run it in synchronism with the paper drive motor As the projector rotates the sound pressure at the hydrophone will vary in accordance with the directiona properties of the projector and when picked up by a hydrophone it will 6 0 0 iii 2604 2604 14 Standard Hydrophone Water Hydrophone Projector 161780 Fig 5 10 Measuring arrangem...

Страница 55: ... reference sound pressure level at the symmetrically placed hydrophones If the standard hydrophone has a linear free field response in the measured frequency interval the recording will immediately show the free field response of the unknown hydrophone Due to the use of the compressor arrangement the delay time i e the time needed for the sound to travel the distance from the projector to the hydr...

Страница 56: ...mentioned the necessary voltages for the opera tion of th e Preamplifier are supplied from the Microphone Amplifier The INPUT SWITCH of the 2 604 should be set to position Condenser Micro phone and the FREQUENCY RESPONSE SWITCH to position Linear 10 200ooo Information as to calibration of the set up is given in the manual for the Preamplifier 1606 If desired the vibration can be recorded on a Leve...

Страница 57: ... a recording obtained from measurements carried out on a system as shown in Fig 5 12 The dominating frequency here is approximately 50 Hz but some higher frequencies are also present This can be seen by comparing the levels recorded for the various D characteristics with the level of the acceleration and by employing the curves shown in Fig 5 13 The determination of the dominating frequencies in t...

Страница 58: ... this way a constant acceleration level is maintained at the vibrating unit The accelerometer under test is placed on top of the vibrating table The signal from the test object is via another amplifier Type 2604 fed to the Level Recorder Type 2305 The Level Recorder is mechanically coupled to the B F O by means of a flexible shaft Thereby the frequency variation of the B F O can be syn chronized w...

Страница 59: ...erometers C llbreHMChef tfcw t cu Type4JM Serial no 111 762 8 l r s o 2 C C W C t 10 6 PP I 50 2 a s 5 1 2 Mia 1Mhullnlcaltla J 02 0 pl _ _ 10 0 3 _ 0 1 _ Mtlwel _ 49 5 h l fis r _ 20 HoMetGhmaat o HO OOifiMO a v aii _V Iue ty _ lwlt O i _ J nw M tiO IINP c rlo 200 MOhalf l llleaJ otfiii Uietlftfol ll laUon lnaVvO Iollbook olo eooatfl I C a 10000 Hz 21111 c u 264 Fig 5 16 Typical calibration curve...

Страница 60: ...nerator by means of a similar circuit to that which is described in Frequency Response Recording of Accelerometers By this means the vibrating force acting on the tube is kept constant In Fig 5 18 is shown a diagram of a circuit which is used in the measure ments on a Philips tube ECC82 The AC voltage developed across the anode load is fed to the input of the Level Recorder section of the Type 330...

Страница 61: ...diagram for measuring the microphony of a Philips Type ECC 82 tube oooocoocoooooooooococoooococccoooocoooooooooooooooo lrG I _ _ _ r bY llibrator at I G I MIAL 3 L 51 700 __ _ o io QP 0123 10 10000 I Fig 5 19 Recording of the measurements carried out on the ECC 82 59 ...

Страница 62: ...E m V r 1 2 dt Finally it is sometimes desired to know the max value that the signal may reach within a certain time interval a period and this value is known as the peak value of the signal In Fig A l the significance of the above definitions with regard to a periodic signal of period T is indicated e t t T r 58089 Fig A t Example of a periodic signal with indication of the peak r m s and arithme...

Страница 63: ...hase distortion When the amplitude vs frequency characteristics of the amplifier is practically straight in the range of the signal frequency contents the number of harmonics and their original amplitude relationships are unchanged in the phase distorted signal at the output of the amplifier If this signal is measured on the amplifier output by the r m s average and peak to peak measuring indicati...

Страница 64: ...s is incorporated Attenuators METER RANGE Variable in steps of 20 dB Accuracy within o 15 dB relative to position 10 mV and 1ooo Hz RANGE MULTIPLIER Variable in steps of 10 dB Accuracy within o l dB relative to position X o 01 and 1ooo Hz Meter Meter Rectifier Circuits Accuracy R M S o 3 dB of the read value for crest factors up to 4 o 5 dB for crest factors from 4 to 5 0 dB for sine wave Average ...

Страница 65: ...l Amplifier Stability Better than o 3 dB for a deviation of 10 of power supply voltage Polarization Voltage The polarization voltage for the Condenser Microphone Cartridges can be adjusted about 200 volts Power Supply 100 115 127 150 220 240 volts AC 50 400 Hz Power consumption is approx 50 watts Cabinets With the mechanical design of all B K apparatus it is very easy to interchange the instrument...

Страница 66: ...als and knobs Height Type 2604 A I 38cm 15 inches Type 2604 B 40 5 em 16 inches Type 2604 C 44 2 em 17inches Accessories Included 4 screened plugs JP 0018 Fuses and lamps 64 Width 38cm 15 inches 40 5 em 16 inches 48 2 em 19 inches Depth I Weight 20cm 12 5 kg 8 inches 27 6lbs 27 3 em 16 5 kg 11 inches 36 5lbs 20cm 12 5lbs 8 inches 27 6lbs ...

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Страница 68: ...B K Orboe Print Copenhagen October 1965 ...

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