xii CONTENTS 



Chapter Page 



G. Field Structures 171 



H. Horn Walls. Vibration and Absorption 171 



IX. MICROPHONES 



9.1 Introduction 172 



9.2 Pressure Microphones 172 



A. Carbon Microphones 172 



1. Single Button Carbon Microphone 172 



2. Double Button Carbon Microphone 175 



B. Condenser Microphone 177 



C. Piezoelectric (Crystal) Microphones 180 



1. Direct Actuated Crystal Microphone 182 



2. Diaphragm Actuated Crystal Microphone 182 



D. Moving Conductor Microphones 183 



1. Moving Coil Microphone (Dynamic Microphone) 183 



2. Inductor Microphone (Straight Line Conductor) 185 



3. Ribbon Type 186 



9.3 Velocity Microphones 189 



A. Pressure Gradient Microphone 189 



B. Velocity Microphone 194 



9.4 Unidirectional Microphones 203 



A. The Response of the Unidirectional Microphone as a Function of 



the Distance and the Frequency 204 



B. Efficiency of Energy Response to Random Sounds of the Unidi- 



rectional Microphone as a Function of the Relative Sensitivities 



of the Bidirectional and Nondirectional Microphones 206 



C. Efficiency of Energy Response to Random Sounds of a Unidirec- 



tional Microphone as a Function of the Phase Angle Between the 



two Units 207 



D. Distortion of the Directional Pattern in the Unidirectional Micro- 



phone 210 



E. Phase Shifting Unidirectional Microphones 210 



9.5 Miscellaneous Microphones 212 



A. Lapel Microphone 212 



B. Throat Microphone 212 



C. Hot Wire Microphone 212 



D. Battery less Telephone (Sound Power Telephone) 213 



9.6 Highly Directional Microphones 213 



A. Parabolic Reflector 213 



B. Line Microphones 214 



1. Line Microphone: Useful Directivity on the Line Axis. 



Simple Line 214 



2. Line Microphone: Useful Directivity on the Line Axis. Line 



with Progressive Delay 216 



