Eir'KEClS Or .AKlAIlGr* Oir S «*©... VOLTAGE ON THE SENSITIVITY OF THE BL MICROPHONE The attached graph shows the effect of supply voltage (V ) on BL microphone output over the voltage range 0.9 to 20.0 volts d.c. S The "nominal" line illustrates the performance of the "average" BL microphone coming off of our production lines. Please note, however, that variability in components and assemblies yield a range of possible sensitivity changes for each supply voltage. This chart is referenced to our standard speci fication of a 1.3 volts d.c. supply voltage and indicates the possible change of output for any single BL microphone as compared to its 1.3 volts sensi t i v i t y. As an example, changing Vg from 1.3 volts to 3.0 volts will increase the lKHz output voltage by 0.3 dB to 2.4 dB for 99% of the BL microphones pre sently produced. However, 65% to 70% of the product will change only be tween 0.4 dB and 1.5 dB for this same V„ change. If the BL microphone is to be used at a lower supply voltage, 0.9 volts for example, the output loss (relative to the 1.3 volt output) could range from 0.5 to 6.5 dB (normally 1.5 dB) for 65% to 70% of-our production, and the loss could exceed 10 dB for about 12% to 15% of our present production. We guarantee, by 100% testing, that all BL microphones will not exhibit more than a 3 dB loss at 1.1 volts dc compared to the 1.3 volts output for that unit. f IMPORTANT NOTE: The graph is useable only for general application perspective and must not be used to generate specifications or limits. KNOWLES ELECTRONICS. INC. 3100 N. MANNHEIM ROAD • FRANKLIN PARK. ILL. 60131 » U.S.A. TELEPHONES (312) 455-3600 • CABLE - KNOLEC CHICAGO • TELEX-25-3387 101 NEW TELEX NUMBER 72-8397 BL-5 EFFECTS Or vAaiAHOM Uj: dvf?LY JlL mim^B VOLTAGE ON THE SENSITIVITY OF THE BL MICROPHONE 1 KHz SENSITIVITY CHANGE VS. DC SUPPLY VOLTAGE For All BL Models (Data Based on Random Sampling) +*•*> 4-3-0 .«99% T of BL Product Nominal w70% of BL -f*.o > +/.o ■U •H Product m C a) w >w u P i cn 0) •J 4-1 a o m -/.o -X..O —3.0 -^.o— G.O — -J— *-£.& e* 0 s «o <o Vs DC SUPPLY VOLTAGE (Logarithmic Scale) KNOWLES ELECTRONICS, INC. 3100 N. MANNHEIM ROAD • FRANKLIN PARK, ILL. 60131 • U.S.A. TELEPHONES (312) 455-3600 • CABLE — KNOLEC CHICAGO • TELEX-25-3387 NEW TELEX NUMBER 72-8397 S-083-566 101 BL-5 <^FF APPLICATION NOTES BL Series Microphones General Description; A line of subminiature, piezoelectric microphones with i n t e g r a l a m p l i fi e r s t a g e f o r a p p l i c a t i o n s r e q u i r i n g h i g h s e n s i t i v i t y, w i d e frequency range, small size, and high mechanical shock resistance. The sen sitivity of these microphones is high enough so that a transistor stage can be omitted in some applications. Typical Dimensions; (in inches) BL-1670 Series BL-1680 Series Length .312 max. .312 max. Width .220 max. .220 max. Thickness .163 max. .090 max. Nominal Sensitivity at 1000 Hertz re; 1 Volt/microbar with a Supply Voltage of 1.3 Volts DC: BL-1670 BL-1671 BL-1672 -55.0dB -54.5dB -54.5dB BL-1680 BL-1681 BL-1682 -57.5dB -57.5dB -57.5dB Note: A change from 1.3 to 1.1 Volts DC shall cause not more than a 3.0d3 decrease in 1 KHz output. Nominal Impedance at 1000 Hertz: 13,000 ohms. (Range: 8,000 to 22,000 ohms.) Battery Drain at 1.3 Volts DC: 50 microamps maximum. DC Voltage at Output Terminals (See Fig. 1): Negative Terminal Common - 0.2 to 0.9 Volts DC Positive Terminal Common - -0.4 to -1.1 Volts DC © model number and date code on this side Figure 1 (Negative Terminal Common) Case Grounding; No greater than 100 ohms DC resistance between case and negative terminal. KNOWLES ELECTRONICS. INC. 3100 N. MANNHEIM ROAD • FRANKLIN PARK, ILL. 60131 • U.S.A. TELEPHONES (312) 455-3600 • CABLE - KNOLEC CHICAGO • TELEX-25-3387 NEW TELEX NUMBER 72-8397 171 BL-7 APPLICATION NOTES j> ■' IJX BL Series Microphones Application; The circuit of Figure 2 will allow these units to be connected in place of most two-wire microphones. A load resistor %, may be necessary to reduce the sensitivity to a suitable level, and will produce a DC current path for those circuits which presently depend on one through the microphone. Table 1 below provides a rough guide to the value of %, required for a given reduction in sensitivity for all models. Low frequency response may be reduced by using coupling capacitor values of less than 1 mfd. _ . , Ta b l e 1 Approximate Sensitivity Reduction (dB) \ (ohms) -=Jr--1.3Volts To A m p l i fi e r Input *L Figure 2 oo 0 5 10 15 20 15K 7K 3K 1.5K Since the microphone will be connected to the power supply, a portion of any alternating voltage present on the power supply (fed back from the amplifier) will appear at the output terminal of the microphone. This power supply feedthrough should be taken into account in the design of the amplifier, as it may affect the frequency response and stability of the amplifier. Range of power supply feedthrough (e0/e^n) in Figure 3: Negative Terminal Common: -17dB to -6dB .... . . ... Positive Te r m i n a l Common: - ldB to - 6dB -J^ 1.3Volts rti Sj'| ein = lOmV lap Figure 3 An RC decoupling network in series with the positive lead can be used to attenuate this effect. The suggested maximum value of R is 2000 ohms (to avoid excessive voltage drop at the BL terminals). The appropriate value of C can be determined experimentally. KNOWLES ELECTRONICS. INC. 3100 N. MANNHEIM ROAD • FRANKLIN PARK, ILL. 60131 • U.S.A. TELEPHONES (312) 455-3600 • CABLE - KNOLEC CHICAGO • TELEX-25-3387 171 WY NEW TELEX NU.