Artificial Mastoid Calibration System at NIM, China ZHONG Bo zhongbo@nim.ac.cn
Contents 1 General Introduction 2 Application of Artificial Mastoid 3 Artificial Mastoid Calibration System 2
1 General Introduction Vibration Signal Acoustical Signal Vibration Signal 3
1 General Introduction Bone-conduction Products (1) Bone-conduction Audiometry Pure Tone Audiometer Air-conduction Audiometry 4
1 General Introduction Bone-conduction Products (2) Bone-conduction Headphone 5
1 General Introduction Bone-conduction Products (3) Bone Anchored Hearing-aids Bone-conduction Hearing-aids 6
1 General introduction Vibration Signal Bone Vibrators Vibrator Alternating Force Signal Too big Uncomfortable Force Signal How to measure the force??? Too small Unable to hear 7
Contents 1 General Introduction 2 Application of Artificial Mastoid 3 Artificial Mastoid Calibration System 8
2 Application of Artificial Mastoid Vibration Signal Sound Pa V Acoustical Signal Artificial Ear Vibration Analyzer Vibration Signal F v V Artificial Mastoid 9
2 Application of Artificial Mastoid Force Artificial Mastoid Charge Amplifier wire Force Charge Charge Amplifier Voltage Analyzer Force Charge Capacitor Voltage Analyzer 10
2 Application of Artificial Mastoid Force Charge Capacitor Voltage Analyzer pc/n nf mv (x N) (a pc/n) / (b nf) (a/ b)mv/n Force Sensitivity cmv/n 11
2 Application of Artificial Mastoid Force Charge Charge Amplifier Voltage Analyzer pc/n g mv/pc mv (x N) (a pc/n) (g mv/pc) (a g)mv/n Force Measurement Chain Sensitivity dmv/n 12
2 Application of Artificial Mastoid So, when use artificial mastoid, these two sensitivities should be known: 1) Force Sensitivity (including cable); 2) Force Measurement Chain Sensitivity (including charge amplifier) Artificial Mastoid Calibration is important!!! PTB CMCs 13
2 Application of Artificial Mastoid 2.1 Audiometer Calibration Bone-conduction: FL = HL + RETFL FL(Force Level): Measured by Artificial Mastoid (db, re: 1 un); db = 20*log (F/ F 0 ); Example:20 * log(1 mn/ 1 un)= 60 db. HL(Hearing Level): Describe hearing loss (db); 0 db----no hearing loss; 100 db----terrible hearing loss. RETFL(Zero Level): Average Hearing Threshold Level, from ISO standards. 14
2 Application of Artificial Mastoid 2.2 Characteristics Measurement of Vibrators Measurement Parameters includes: Frequency Response; Resonance Frequency; Distortion; Maximum Force; Electric-Force Sensitivity; Frequency Response Curves 15
2 Application of Artificial Mastoid 2.3 Hearing-aids Evaluation Hearing-aids Standards: IEC 60118-0, IEC 60118-7, IEC 60118-9. Evaluation Parameters includes: Saturation Force Level; Output force level frequency response curve for an input SPL of 90 db (OFL 90 curve); Basic force level frequency response; Non-linear distortion; Acoustical-mechanical sensitivity level; Internal noise from the hearing aid; 16
2 Application of Artificial Mastoid 2.3 Hearing-aids Evaluation Evaluation set-up for bone-conduction hearing-aid 17
Contents 1 General Introduction 2 Application of Artificial Mastoid 3 Artificial Mastoid Calibration System 18
3.1 Brief Introduction Old calibration system was built in 1986; Some instruments had problems, stopped working since 2003. In 2009, a new calibration system was bought from B&K. 19
3.2 Mechanical Assembly 20
3.2 Mechanical Assembly 21
3.2 Mechanical Assembly 22
3.2 Measurement Hardware Acoustical Analyzer Type 3560C 5 Channels Input; (using 3 channels with CCLD supply) 1 Channel output; (generating sine and white noise signal) CPB tool. Charge Amplifier Type 2647 Converting charge signal to CCLD gain: 1 GV/C or 10 GV/C 23
3.2 Measurement Hardware Impedance Head Type 8001 Measuring point mechanical mobility and impedance; a piezoelectric accelerometer and also a force gauge; Up to 10 khz. Force Gauge Accelerometer 24
3.2 Measurement Hardware Power Amplifier Type 2718 40 db voltage gain; Continuously variable current limit from 1A to 5A; Low distortion and wide frequency range. Exciter Type 4810 Frequency range: DC ~ 18 khz; Maximum bare table acceleration 550 m/s 2 25
3.2 Measurement Hardware Accelerometer Calibrator Type 4294 Standard Acceleration of 10 m/s 2 ; Load: 0 ~ 70 g; Mechanical Filter Type 0553 26
3.3 Measurement Software (a pulse VBA program) 27
3.4 Measurement Procedure 3.4.1 Pre-Setup 28
3.4 Measurement Procedure 3.4.1 Pre-Setup Set nominal acceleration sensitivity for impedance head; Set nominal force sensitivity for impedance head; Set nominal gain for charge amplifier. 29
3.4 Measurement Procedure 3.4.2 Accelerometer Calibration (simple method) Using 4294 to correct acceleration sensitivity for impedance head; 30
3.4 Measurement Procedure 3.4.3 Force Calibration (simple method) Using 4294 and mechanical filters to correct force sensitivity for impedance head; 31
3.4 Measurement Procedure 3.4.4 Charge Calibration (simple method) Output 1V voltage; 1V * 1 nf= 1 nc; 1 nc??? 32
3.4 Measurement Procedure 3.4.5 Mass Compensation Measuring little mass below the force gauge; using white noise as exciting signal. 33
3.4 Measurement Procedure 3.4.5 Mass Compensation Point mechanical impedance (magnitude) Point mechanical impedance (phase) Point effective mass Point stiffness 34
3.4 Measurement Procedure 3.4.6 5.4 N Measurement 5.4 N is a static force condition on which artificial mastoid works; 550 g * 9.8 m/s 2 5.4 N. 35
3.4 Measurement Procedure 3.4.6 5.4 N Measurement Point mechanical impedance (magnitude) Point mechanical impedance (phase) Point effective mass Point stiffness 36
3.4 Measurement Procedure 3.4.6 5.4 N Measurement Point mechanical impedance (5.4 N) Point mechanical impedance (mass compensation) Artificial Mastoid Mechanical Impedance (5.4 N) Artificial Mastoid Force Sensitivity (5.4 N) 37
3.4 Measurement Procedure 3.4.7 2.5 N Measurement 2.5 N is a static force condition on which artificial mastoid works; 255 g * 9.8 m/s 2 2.5 N. 38
3.4 Measurement Procedure 3.4.7 2.5 N Measurement Point mechanical impedance (magnitude) Point mechanical impedance (phase) Point effective mass Point stiffness 39
3.4 Measurement Procedure 3.4.7 2.5 N Measurement Point mechanical impedance (2.5 N) Point mechanical impedance (mass compensation) Artificial Mastoid Mechanical Impedance (2.5 N) Artificial Mastoid Force Sensitivity (2.5 N) 40
3.4 Measurement Procedure 3.4.8 Export the results 41
3.4 Measurement Procedure 3.4.8 Export the results 42
3.4 Measurement Procedure 3.4.8 Export the results 43
3.4 Measurement Procedure 3.4.8 Export the results 44
3.4 Measurement Procedure 3.4.8 Export the results 45
3.5 Discussion Impedance head calibration needs further research; Uncertainty evaluation needs more discussion; deviation of white noise exciting or sine exciting needs more experiments; more further work should be done in future. 46
Thank You for Your Attention! 47