Introduction to Sound

Sound and light both travel as waves.

The properties of these waves differ quite considerably.

Sound waves travel a million times slower than light waves.

They have wavelengths between 1 centimeter and 10 meters, and will easily diffract round corners. Light waves have much smaller wavelengths, and only diffract through very small holes.

This difference is the reason why you can often

hear things that you cannot see.

What Is Sound?

All sounds are vibrations traveling through the air as sound waves. Sound waves are caused by the vibrations of objects and radiate outward from their source in all directions. A vibrating object compresses the surrounding air molecules (squeezing them closer together) and then rarefies them (pulling them farther apart). Although the fluctuations in air pressure travel outward from the object, the air molecules themselves stay in the same average position. As sound travels, it reflects off objects in its path, creating further disturbances in the surrounding air. When these changes in air pressure vibrate your eardrum, nerve signals are sent to your brain and are interpreted as sound.

Fundamentals of a Sound Wave

The simplest kind of sound wave is a sine wave. Pure sine waves rarely exist in the natural world, but they are a useful place to start because all other sounds can be broken down into combinations of sine waves. A sine wave clearly demonstrates the three fundamental characteristics of a sound wave: frequency, amplitude, and phase.

TV Soundsound loudness is commonly measured in decibels (dBs )

Sound dBs

Jet Aircraft Taking Off 140-150

Rock Concert / Gunshots 135-140

Average City Street / Restaurant 70- 75

Quiet Conversation / Phone Dial Tone 60-80

Office Environment 45

Whisper at 3 meters (10 feet) 30

"Silent" TV Studio 20

Two types of VU meters for measuring the loudness

of sound are in wide use

The digital type and the analog type.

Frequency

Frequency relates to the basic pitch of a sound -- how high or low it is

Frequency is measured in Hertz (Hz) or cycles per second (CPS).

The Frequency-Loudness Relationship

The red line on the graph (roughly) shows the frequency response of the human ear to different frequencies.

Because of the reduced sensitivity of the ear to both high and low frequencies, these sounds must be louder to be perceived as being equal to other frequencies.

Major Microphone Designs

There are six common microphone designs:hand held - the type held by on-camera talent or used for on-location interviews

personal mic (lavaliere / clip-on mic) - Whether hung from a cord around the neck (lavaliere) or clipped to clothing, these are all referred to as personal mics.

shotgun - used for on-location production to pick up sounds a moderate distance from the camera

boundary effect microphone - also called PZ or PZM mics These rely primarily on reflected sounds from a hard surface such as a tabletop

contact mics - which pick up sound by being in direct physical contact with the sound source. These mics are generally mounted on musical instruments.

studio microphones - the largest category of microphone. These include a number of application designs that we'll discuss.

Dynamic Microphones

Dynamic Microphones

This type of mic is a good choice for electronic newsgathering (ENG) work, where a wide variety of difficult conditions are regularly encountered (such as this ENG report on a fire).

Condenser/Capacitor Microphones

Condenser microphones (also called capacitor or electret condenser mics) are capable of top-notch audio quality.

Condenser mics aren't as rugged as dynamic mics, and problems can result when they are used in adverse weather conditions.

Summary of Dynamic and Condenser Mic Pros and Cons

Dynamic Mic Advantages Condenser Mic Advantages

Rugged More Sensitive

Lower Cost Better Audio Quality

No Power Required Can Be Extremely Small

Dynamic Mic Disadvantages Condenser Mic Disadvantages

Lower Sensitivity and Power Output Higher self-noise

Larger and Heavier More Fragile

Slower Response Time More Expensive

Not the Best Choice for Maximum Audio Quality

Prone to Weather Problems and RF Interference

Ribbon Mics

Except possibly for an announce booth (shown here), ribbon mics

are seldom used in TV production. Although they can impart a deep, resonant "coloring" to sound, they are fragile and highly sensitive to moving air. This precludes their use outside the studio and on most booms -- which covers most TV produc

Boundary Effect Mics

Contact mics pick up sound by being in direct physical contact with the sound source. These mics are generally mounted on musical instruments, such as the surface of an acoustic bass, the sounding board of a piano, or near the bridge of a violin.

Directional Characteristics

In microphones there are three basic directional categories:

omnidirectional

bi-directional

unidirectional

Unidirectional Mics

There are four subdivisions in this category -- each being a bit more directional:

cardioid

supercardioid

hypercardioid

parabolic

Parabolic Mics

Because of the parabolic shape of the reflector, all sound along a very narrow angle of acceptance will be directed into the microphone in the center.

Handheld Microphones

Handheld mics are often dynamic mics because they are good at handling momentary sound overloads. Although they may be called "handheld," the term is a bit of a misnomer, because this type of mic can be mounted on a microphone stand.

Personal Microphones

Personal mics are either hung from a cord around the neck (a lavaliere or lav mic) or clipped to clothing (a clip-on mic).

This type of mic can be either a condenser or dynamic mic.