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Sound Isolation

4-1

Section

4

Microphone Devices and Systems

Every electronic system has a starting point, and in the case of audio, that point is usually a
microphone. The source origination equipment available for a well-equipped audio studio range
from traditional mics to special-purpose devices intended to capture sounds in difficult environ-
ments. Microphones are transducers—nothing more, nothing less.  No matter how large or small,
elaborate or simple, expensive or economical a microphone might be, it has only one basic func-
tion: to convert acoustical energy to electrical energy.

With this fundamental point clearly established, you might wonder why microphones exist in

such a mind-boggling array of sizes, shapes, frequency response characteristics, and element
types.  The answer is simple.  Although the basic function of all microphones is the same, they
have to work in many different applications and under various conditions.

Choosing the right microphone for a particular application might seem as easy as falling off a

log, but it is a decision that deserves considerable thought.  Just as no two production sessions
are alike, the microphone requirements are varied also.

Microphone manufacturers offer a selection of units to match almost any application.  With a

good working knowledge of the various microphone designs, choosing the right mic for the job
becomes a much simpler task.  The education process begins with a look at some of the micro-
phones commonly in use today.

In This Section:

Chapter 4.1: Microphones

4-7

Introduction

4-7

Pressure Microphones

4-7

Piezoelectric Microphone

4-9

Electrostatic (Condenser) Microphones

4-10

Electret Microphone

4-12

Boundary Microphone

4-14

Electrodynamic Microphones

4-15

Pressure-Gradient (Velocity) Microphones

4-17

Combination Pressure and Pressure-Gradient Microphones

4-20

Frequency Response as a Function of Distance

4-21

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Source: Standard Handbook of Audio and Radio Engineering

4-2 Section Four

Dual-Diaphragm Condenser Polydirectional Microphone

4-21

Twin-Cardioid-Element Polydirectional Condenser Microphone

4-23

Single-Element Unidirectional Microphones

4-24

Unidirectional Condenser Microphone

4-26

Moving-Coil Unidirectional Microphone

4-27

Variable-Distance Unidirectional Microphone

4-27

Ultra-Directional Microphones

4-29

Line Microphone

4-29

Wave Microphones

4-31

Miscellaneous Types of Microphones

4-31

Sound-Field Microphone

4-31

Lavaliere Microphone

4-33

Wireless Microphone

4-33

Selecting Microphone Types

4-33

References

4-34

Bibliography

4-35

Chapter 4.2: Stereophonic Techniques

4-37

Introduction

4-37

Two-Microphone Coincident Techniques

4-37

XY Cardioids and Hypercardioids

4-37

Blumlein

4-38

MS Stereo

4-39

Two-Microphone Near-Coincident Techniques

4-40

Two-Microphone Spaced Techniques

4-41

Spaced Omnidirectional Microphones

4-43

Spaced Cardioid Microphones

4-43

Spaced Bidirectional Microphones

4-44

Spaced Hypercardioid Microphones

4-44

Performance Considerations

4-44

References

4-45

Chapter 4.3: Low Power Amplifiers

4-47

Introduction

4-47

Single-Stage Transistor or FET Amplifier

4-47

DC Conditions

4-47

Input and Output Impedance, Voltage, and Current Gain

4-49

AC Gain

4-49

Common-Base or Common-Gate Connection

4-50

Common-Collector or Common-Drain Connection

4-51

Bias and Large Signals

4-52

Multistage Amplifiers

4-53

DC-Coupled Multistage Amplifiers

4-53

Cascaded Transistors

4-55

Parallel-Connected Devices for High Currents

4-56

Series-Connected Devices for High Voltage

4-57

AC-Coupled Multistage Amplifiers

4-57

Power Output Stages

4-58

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Microphone Devices and Systems

Microphone Devices and Systems 4-3

Single-Ended Amplifiers

4-58

Push-Pull Amplifiers

4-58

Parallel-DC, Series-AC Amplifiers

4-59

Series-DC, Parallel-AC Amplifiers

4-59

Full-Bridge Amplifiers

4-60

Classes of Amplifiers

4-60

Gain Block and the Operational Amplifier

4-62

Feedback and Feed Forward

4-63

Linear Feedback

4-64

Feed Forward

4-65

Nonlinear Feedback

4-65

Voltage Feedback

4-65

Current Feedback

4-66

Output and Input Impedance

4-66

Feed Forward and Correction of Estimated Errors

4-67

Differential Amplifier

4-67

References

4-68

Bibliography

4-68

Reference Documents for this Section:

“A Phased Array,” Hi Fi News Record Rev., July 1981.

Bevan, W. R., R. B. Schulein, and C. E. Seeler: “Design of a Studio-Quality Condenser Micro-

phone Using Electret Technology,” J. Audio Eng Soc. (Engineering Reports), vol. 26, pp.
947–957, December 1978.

Black, H. S.: U.S. Patent 2,102,671.

Blumlein, A.: British Patent 394,325, December 14, 1931; reprinted in J. Audio Eng. Soc., vol. 6,

April 1958.

Dooley, W. L., and R. D. Streicher: “M-S Stereo: A Powerful Technique for Working in Stereo,”

J. Audio Eng. Soc., vol. 30, pp. 707–718, October 1982.

Eargle, J.: Sound Recording, Van Nostrand Reinhold, New York, 1976.

Eargle, J.: The Microphone Handbook, Elar Publishing, Plainview, N.Y., 1981.

Fewer, D. R.: “Design Principles for Junction Transistor Audio Power Amplifiers,” Trans. IRE

PGA, AU-3(6), November–December 1955.

Fredericksen, E., N. Firby, and H. Mathiasen: “Prepolarized Condenser Microphones for Mea-

surement Purposes,” Tech. Rev., Bruel & Kjaer, Copenhagen, no.4, 1979.

Garner, L. H.: “High-Power Solid State Amplifiers,” Trans. IRE PGA, 15(4), December 1967.

Gordon, J.: “Recording in 2 and 4 Channels,” Audio, pp. 36–38, December 1973.

Harper, C. A. (ed.): Handbook of Components for Electronics, McGraw-Hill, New York, N.Y.,

1977.

Instruction Book for RCA BK-16A Dynamic Microphone, IB-24898, Radio Corporation of

America, Camden, N.J.

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Microphone Devices and Systems

4-4 Section Four

Killion, M. C., and E. V. Carlson: “A Subminiature Electret-Condenser Microphone of New

Design,” J. Audio Eng. Soc., vol. 22, pg. 237–243, May 1974.

Kirchner, R. J.: “Properties of Junction Transistors,” Trans. IRE PGA, AU-3(4), July-August

1955.

Kishi, K., N. Tsuchiya, and K. Shimura: “Unidirectional Microphone,” U.S. Patent 3,581,012,

May 25, 1971.

Kubota, H.: “Back Electret Microphones,” presented at the 55th Convention of the Audio Engi-

neering Society, J. Audio Eng. Soc. (Abstracts), vol. 24, no. 862, preprint 1157, December
1976.

Lipshitz, S. P.: “Stereo Microphone Techniques: Are the Purists Wrong?” presented at the 78th

Convention of the Audio Engineering Society, J. Audio Eng. Soc. (Abstracts), vol. 33, pg.
594, preprint 2261, July-August 1985.

Long, E. M., and R. J. Wickersham: “Pressure Recording Process and Device,” U.S. Patent

4,361,736, November 30, 1982.

Lynn, D. K., C. S. Meyer, and D. C. Hamilton (eds.): Analysis and Design of Integrated Circuits,

McGraw-Hill, New York, N.Y., 1967.

Microphones—Anthology, Audio Engineering Society, New York, 1979.

“Miking with the 3-Point System,” Audio, pp. 28–36, December 1975.

Nisbett, A.: The Technique of the Sound Studio, Hastings House, New York, N.Y., 1974.

Olson, H. F.: Acoustical Engineering, Van Nostrand, Princeton, N.J., 1957.

Olson, H. F.: “Directional Electrostatic Microphone,” U.S. Patent 3,007,012, October 31, 1961.

Olson, H. F. (ed.): McGraw-Hill Encyclopedia of Science and Technology, 5th ed., vol. 18,

McGraw-Hill, New York, N.Y., pg. 506, 1982.

Olson, H. F.: Music, Physics, and Engineering, 2d ed., Dover, New York, N.Y., 1967.

Olson, H. F.: “Ribbon Velocity Microphones,” J. Audio Eng. Soc., vol. 18, pp. 263–268, June

1970.

Petersen, A., and D. B. Sinclair: “A Singled-Ended Push-Pull Audio Amplifier,” Proc. IRE, vol.

40, January 1952.

Rasmussen, G.: “A New Condenser Microphone,” Tech. Rev., Bruel & Kjaer, Copenhagen, no.1,

1959.

Sank, J. R.: “Equipment Profile-Nakamichi CM-700 Electret Condenser Microphone System.”

Audio, September 1978.

Shockley, W: “A Unipolar Field-Effect Transistor,” Proc. IRE, vol. 40, November 1952.

Shockley, W: “The Theory of P-N Junctions in Semiconductors and P-N Junction Transistors,”

Proc. JRE, vol. 41, June 1953.

Trent, R. L.: “Design Principles for Transistor Audio Amplifiers,” Trans. IRE PGA, AU-3(5),

September–October 1955.

Walker, P. J.: “A Current Dumping Audio Power Amplifier,” Wireless World, December 1975.

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Microphone Devices and Systems