x	CONTEKTS
CHAPTER		PAGE
A. The Relation between the Voice Coil Mass, the Load
Mechanical Resistance and the Initial Efficiency ......		213
B. The Effect of the Mass of the Vibrating System upon
the Efficiency ....................................		216
C. The Effect of the Air Chamber upon the Efficiency . . ..		218
D. The Effect of the Generator Electrical Impedance and
the Mechanical Impedance at the Throat of the Horn
upon the	Efficiency ...............................	220
E. The Effect of the Voice Coil Temperature upon the Ef­
ficiency	..........................................	221
F. The Effect of the Sound Radiation from the Unloaded
Side of the Diaphragm upon the Efficiency ..........		221

7.3DISTORTION •.•••••••••••••••.••••••••••••••••.•••••••• 223

	A. Distortion Due to Air Overload in the Horn .........						223
	B. Distortion Due to Variation in Volume of the Air
		Chamber ..	. . . . . . . . .	. . . . . . . . . . . . . .	. . . . . . . . . . . .	. ..	225
	C. Distortion Due to the Diaphragm Suspension System ..						226
	D. Distortion Due to a Nonuniform Magnetic Field in the
		Air Gap .........................................					227
	E. Subharmonic		Distortion ..........................				228
	F. Power Handling Capacity and the Voice Coil Tempera­
		ture .............................................					228
	G. Power Handling Capacity and the Amplitude of the
7.4		Diaphragm ..................		. . . . .	. . . . . . . . . . . .	. ..	229
	HORN LOUDSPEAKER SYSTEMS •••.•.•••.••••••••••••••.•						230
	A. Single Horn, Single Channel System				..............		230
	B. Multiple Horn, Multiple Channel System ............						233
	C. Compound Horn Loudspeaker ......................						237
	D. Multiple Horn, Single Channel System ..............						238
	E. Horn Loudspeaker for Personal Radio Receivers .... 239
	F. Folded Horns ....................................						240
	G. Horn Loudspeaker Mechanisms ....................						242
	H. Diaphragms and Voice Coils ......................						242
	1.	Field Structures ..................................					243
	J.	Horn Walls.	Vibration and Absorption ............				243
7.5	THROTTLED AIR FLOW LOUDSPEAKER •••...				••••••.••...	••.	243
7.6	IONOPHONE LOUDSPEAKER						244
VIII. MICROPHONES
8.1	INTRODUCTION						246
8.2	PRESSURE MICROPHONES ••••.••••.•......				•.••.•••••..	•..	246
	A. Carbon Microphones .............................					.	246
		1. Single Button Carbon Microphone ............				.	246
		2. Double Button Carbon Microphone ...........				.	251
	B. Condenser Microphone			(Electrostatic	Microphone) ..		253
	C. Piezoelectric		(Crystal)	Microphones ...............		.	257
		1. Direct Actuated Crystal Microphone ..........				.	259
		2. Diaphragm Actuated Crystal Microphone ......				.	260

			CONTENTS	Xl
CHAPTER			PAGE
3.	Diaphragm Actuated Barium Titanate Micro­
	phone		...... . ................................	260
D. Moving Conductor Microphones ...................				260
l. Moving Coil Microphone (Dynamic Microphone)				260
2.	Inductor Microphone (Straight Line Conductor)			263
3.	Ribbon		Microphone ..........................	264
4.	Probe		Microphone .................. . ...... . .	267
5.	Comparison of Electrodynamic Microphones. . . ..			268
E. Magnetic		Microphone .............................		270
F. Electronic		Microphone ............................		273

8.3VELOCITY MICROPHONES, FIRST ORDER GRADIENT MICRO­

PHONES ..• • •.•	..•...•.••••....	•••............... . ....	275
A. Pressure Gradient Microphone .....................			275
B. Velocity Microphone ..........................		. ...	279
8.4 UNIDIRECTIONAL	MICROPHONES .........	.. .... • ........ .	291
A. Combination Unidirectional Microphones ............			291
l. The Response of the Unidirectional Microphone as
a Function of the Distance and the Frequency . . ..			292

2.Efficiency of Energy Response to Random Sounds of the Unidirectional Microphone as a Function of

		the Relative Sensitivities of the Bidirectional and
		Nondirectional		Microphones ..................				293
	3.	Efficiency of Energy Response to Random Sounds
		of a Unidirectional Microphone as a Function of
		the Phase Angle Between the Two Units ........						295
	4. Distortion of the Directional Pattern					in the	Uni­
		directional Microphone .......................						297
	B. Single Element Unidirectional Microphones .........							297
	l.	Phase Shifting Unidirectional Microphone .... .						297
	2.	Polydirectional		Microphone ...................				298
	3.	Uniaxial Microphone .. . ..................					. ...	303
	4.	Uniphase Dynamic Microphone ................						305
	5.	Variable-Distance Unidirectional Microphon~ ..						307
	6.	Directional Condenser Microphone .............						307
	7.	Dipole Microphone ........			. ................		..	308
	8.	Differential Microphone.			Lip Microphone ......			310
8.5	HIGHER ORDER GRADIENT MICROPHONES ••......					••....	•...	311
	A. Second Order Gradient Microphones ...............							311
	B. Gradient Microphones of Any Order . ...					...........		311
	C. Noise Discrimination of Gradient Microphones .......							312
	D. Higher Order Unidirectional Grau: ~.lt Microphones ..							315
	E. Second Order Gradient Uniaxial Microphone ........							316
8.6	W AVE TYPE MICROPHONES • .........				• ........	• ..... ..	...	319
	A. Parabolic		Reflector	...............................				320
	B. Lens	Microphone ....		.. . . .........................				321
	C. Large Surface Microphone ........................							321
	D. Line	Microphones ..................			. .............			322
	l. Line Microphone: Useful				Directivity on the		Line
		Axis.	Simple Line .. . ........................					323