Microphones in Audio Technology

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Questions and Answers

What is the primary function of a microphone?

To record sound waves

To convert acoustical energy to electrical energy (correct)

To transmit sound signals over long distances

To amplify sound signals

What is the first stage of the conversion process in a microphone?

The air pressure sets the diaphragm into mechanical vibration (correct)

The sound wave is transmitted over long distances

The diaphragm vibrates mechanically

The diaphragm generates an electric voltage

What is the purpose of the small vent hole in the casing of a pressure-operated microphone?

To improve the microphone's frequency response

To equalize the internal and external pressures (correct)

To amplify the sound signal

To increase the microphone's sensitivity

What is the force on the diaphragm in a pressure-operated microphone?

Equal to the product of sound pressure and the area of the diaphragm Signup and view all the answers

What happens to the diaphragm in a pressure-operated microphone when audio frequency swings occur?

It moves outwards and inwards Signup and view all the answers

What is the characteristic of a microphone's response at low frequencies?

It is the same for all angles of incidence Signup and view all the answers

What are the two stages of conversion in a microphone?

Diaphragm vibration and electrical energy conversion Signup and view all the answers

What type of operation is used in microphones where the rear surface of the diaphragm is enclosed?

Pressure operation Signup and view all the answers

At higher frequencies, why do pressure operated microphones become more narrowly directional?

Because the microphone dimensions are equal to or greater than the wavelength Signup and view all the answers

What is the resulting force on the diaphragm in a pressure-gradient microphone?

The instantaneous difference in pressure between front and back Signup and view all the answers

What is the typical frequency range of human hearing?

20-20000 Hz Signup and view all the answers

What is the main problem with microphone frequency response?

The microphone itself begins to act as a physical obstacle to sound waves for shorter wavelength (higher frequency) sounds Signup and view all the answers

What is directivity in a microphone?

The ability to respond equally to sounds arriving from all directions and to discriminate against sounds from particular directions Signup and view all the answers

What is the purpose of high sensitivity in a microphone?

To increase the signal-to-noise ratio Signup and view all the answers

What is self-noise in a microphone?

The noise generated by the microphone itself Signup and view all the answers

What is plotted on a circular or polar graph paper to illustrate directivity?

The output signal level for a fixed sound pressure level at all angles in a particular plane Signup and view all the answers

Study Notes

Microphones

Microphones act as the first link in the chain of equipment used to transmit sounds over long distances, as in broadcasting and telephony.
They are also used for short-distance communication in public address, sound reinforcement, and intercom applications.

Basic Parts of a Microphone

Microphones are transducers that convert acoustical energy to electrical energy.
The basic function of a microphone is to convert acoustical energy to electrical energy.

Basic Operation

All microphones convert acoustical energy to electrical energy through mechanical vibrations in response to sound waves on a thin lightweight diaphragm.
The conversion happens in two stages:
- Varying air pressure sets the diaphragm into mechanical vibration.
- Diaphragm vibrations generate an electric voltage.

Pressure Operation

In pressure-operated microphones, the rear surface of the diaphragm is enclosed, and the actuating force is simply the instantaneous air pressure at the front.
A small vent hole in the casing equalizes the long-term external and internal pressures.
The force on the diaphragm is equal to the product of sound pressure (per unit area) and the area of the diaphragm, and is essentially independent of frequency.

Pressure Gradient

Designed with both faces of the diaphragm open to the air.
The resulting force on the diaphragm is then not simply due to the pressure on the front but to the instantaneous difference in pressure between front and back.
A pressure-gradient microphone has a figure-of-eight directivity pattern.

Microphone Characteristics

Microphones come in all shapes and sizes.
When choosing a microphone for any particular application, some or all of the following features need to be considered:
- Frequency response
- Directivity and sensitivity
- Self-noise and distortions

Frequency Response

The microphone should respond equally to sounds over the whole frequency range of interest (20-20000 Hz, the nominal limits of human hearing).
Unfortunately, this criterion is seldom met, the most common fault being irregular and falling response at oblique angles for frequencies above about 5 kHz.

Directivity

A microphone's directivity is its ability either to respond equally to sounds arriving from all directions or to discriminate against sounds from particular directions.
Directivity is most easily illustrated by plotting on circular or polar graph paper the output signal level for a fixed sound pressure level at all angles in a particular plane.

Sensitivity

Sensitivity is the conversion efficiency of a microphone.
The output voltage produced by a given incident sound pressure level should be as high as possible.
This boosts the signals in relation to noise and interference along the signal path.