!"#$%&'()*+$#$*,(-.,+*/+( 0$#1(2""'$%&#$*,+($,(-./3*( 4..56&%7(-860**9./( :*,#/*'( ( ( ( ( ( ( ( 4;(2,#*,$*(<.5/&,*( <.5$&(2/#+(&,5(=.%1,*'*>?()/*>/&@( A,$3./+$#?(*9(:&'$9*/,$&B(-&,#&(C&/6&/&( 4.6/8&/?(DEB(FGGH( =&6'.(*9(:*,#.,#+( TABLE OF CONTENTS ....................................................................................................................................2 TABLE OF FIGURES.........................................................................................................................................3 ABSTRACT ..........................................................................................................................................................4 INTRODUCTION................................................................................................................................................5 DESIGN GOALS: A WOOFER FOR ELECTROSTATIC SPEAKERS...........................................................................5 WOOFER SERVO FEEDBACK OVERVIEW...........................................................................................................5 DESIGN REQUIREMENTS ....................................................................................................................................6 OPTICAL SPEAKER POSITION SENSING APPROACHES ......................................................................................7 Point Source, Point Receiver.......................................................................................................................8 Point Source, Linear Receiver.....................................................................................................................9 Linear Light Source, Linear Receiver.......................................................................................................10 Linear Optical Encoders............................................................................................................................11 SPEAKER POSITION SENSORS..................................................................................................................12 INFRARED POINT SENSORS – PACKAGED AND DISCRETE ..............................................................................12 POSITION SENSING DETECTORS (PSDS) WITH LEDS AND LASER DIODES ...................................................15 LINEAR SENSORS – FIBER OPTICS (SEND AND RECEIVE) ..............................................................................20 LINEAR RECEIVERS – PHOTODIODES ..............................................................................................................22 LINEAR SOURCES – LED ARRAYS..................................................................................................................23 LINEAR SOURCES – ELECTROLUMINESCENT WIRE ........................................................................................24 LINEAR SOURCES – LINEAR LASERS...............................................................................................................25 LINEAR SOURCES – COLD CATHODE FLUORESCENT LAMPS (CCFLS) .........................................................26 FEEDBACK SPEAKER DESIGN AND PROTOTYPING........................................................................28 PROOF OF CONCEPT – LINEARITY TESTING....................................................................................................28 FIRST PROTOTYPE – OPEN BAFFLE.................................................................................................................30 Sensor Mounting Design............................................................................................................................30 Position Sensing Verification ....................................................................................................................32 SECOND PROTOTYPE – INFINITE BAFFLE........................................................................................................33 FEEDBACK CIRCUITRY.....................................................................................................................................34 Power Amplifier Modifications .................................................................................................................34 Feedback Circuit Design ...........................................................................................................................35 SPEAKER TESTING AND DISTORTION MEASUREMENTS .............................................................36 METHODOLOGY ...............................................................................................................................................36 RESULTS AND ANALYSIS .................................................................................................................................36 Open Loop - No Feedback.........................................................................................................................36 Closed Loop – With Feedback...................................................................................................................37 Voice Coil Movement vs. Speaker Movement...........................................................................................37 CONCLUSIONS AND FUTURE WORK......................................................................................................40 ACKNOWLEDGEMENTS..............................................................................................................................41 APPENDIX 1 – FEEDBACK CIRCUIT DIAGRAM ..................................................................................42 REFERENCES ...................................................................................................................................................43 ( 2 =&6'.(*9(4$>8/.+( FIGURE 1 - THE COMPONENTS OF A SPEAKER (NOT TO SCALE).............................................................................7 FIGURE 2 - POINT LIGHT SOURCE, POINT RECEIVER ............................................................................................8 FIGURE 3 – PSD AND NARROW BEAM LIGHT SOURCE POSITION DETECTION .......................................................9 FIGURE 4 – PSD OUTPUT VARIES WITH LASER POSITION......................................................................................9 FIGURE 5 – LINEAR LIGHT SOURCE POSITION MEASUREMENT............................................................................10 FIGURE 6 – LIGHT SENSED CHANGES WITH SPEAKER POSITION..........................................................................10 FIGURE 7 – SPEAKER POSITION SENSING WITH A LINEAR OPTICAL ENCODER ....................................................11 FIGURE 8 - SHARP GP2D120 ANALOG IR POSITION SENSOR ............................................................................12 FIGURE 9 - SHARP GP2D120 OUTPUT VOLTAGE VS. DISTANCE TO OBJECT.......................................................13 FIGURE 10 - SHARP GP2D120 TIMING CHART ...................................................................................................13 FIGURE 11 - IR EMITTER AND RECEIVER MOUNTED TO THE MEASURING DEVICE .............................................14 FIGURE 12 - THE MIRROR HEIGHT IS ADJUSTED BY ADDING OR REMOVING WASHERS......................................14 FIGURE 13 - DISCRETE IR SENSOR OUTPUT VOLTAGE VS. DISTANCE.................................................................15 FIGURE 14 - ONE DIMENSIONAL PSD SECTIONAL VIEW .....................................................................................16 FIGURE 15 - PSD CONFIGURATIONS WITH CONSTANT LIGHT PATH DISTANCES ................................................17 FIGURE 16 - A SELECTION OF 1-DIMENSIONAL PSDS .........................................................................................17 FIGURE 17 - PSD LINEARITY WITH FOCUSED LED LIGHT SOURCE. ...................................................................18 FIGURE 18 - PSD LINEARITY WITH LASER DIODE LIGHT SOURCE.......................................................................19 FIGURE 19 - LED FIBER OPTIC LIGHT SOURCE ....................................................................................................20 FIGURE 20 - INCANDESCENT FIBER OPTIC LIGHT SOURCE...................................................................................21 FIGURE 21 - ADVANCED PHOTONIX SILICON PIN PHOTODIODE (PDB-V612-2)..............................................22 FIGURE 22 – LED LIGHT BAR (LEFT) & LED ARRAYS (CENTER AND RIGHT). (NOT TO SCALE) ......................23 FIGURE 23 - ILLUMINATED ELECTROLUMINESCENT WIRE ..................................................................................24 FIGURE 24 - LINE LASER DIODE MODULE ............................................................................................................25 FIGURE 25 - LINE LASER DIODE INTENSITY PROFILE...........................................................................................25 FIGURE 26 - CCFL'S IN VARIOUS SHAPES AND SIZES ..........................................................................................26 FIGURE 27 – LINEARITY PROOF OF CONCEPT SETUP ...........................................................................................28 FIGURE 28 - LINEARITY PROOF OF CONCEPT SETUP WITH CCFL LIT .................................................................29 FIGURE 29 - CCFL AND SOLAR CELL LINEARITY MEASUREMENTS....................................................................29