Introduction

Because it is difficult to "picture" a sound wave it is helpful to show most of the characteristics of a sound wave in a graphical diagram showing the pattern of changing air pressure. These diagrams are called waveform diagrams.

The diagrams on this page show the waveform of a sine wave.

Sine wave

When a source expands and contracts absolutely consistently (unfound in nature) it is said to be moving in simple harmonic motion. The wave it produces is known as a sine wave.

The diagrams on this page show a sine wave. We could have used any other wave but a sine wave is nice and simple and makes it easier to show how waveform diagrams work.

A single isolated sine wave can only be created by an electronic sound source (an oscillator) which creates electrical pressure soundwave according to the strict mathematical principals of electronics design.

Waveform diagram (of a sine wave)

Amplitude

The "amount" of compression and rarefaction of the air is the amplitude of the soundwave, the volume or loudness which the ear perceives. As long as the air pressure is changing (rising and falling), sound will be heard.

Cycles

When a source has expanded and contracted once it is said to have cycled. This is a single vibration.

Wavelength

The physical distance between two adjacent points on a sound wave (from any point on one cycle to the same point on the following cycle) is known as the wavelength and is denoted by the Greek letter lambda. Because a sound source can vibrate at many different speeds this wavelength is variable.

The wavelength of sound at 20 cycles per second (deep bass) is approximately 17 metres. The wavelength of sound at 20,000 cycles per seconds (high treble) is 1.7 cm. Wavelength is critical to understanding of how sound behaves when it encounters a physical obstruction. (See transmission, reflection and absorption later).

Frequency

The speed at which the source vibrates is known as the frequency of the soundwave and is expressed in hertz (Hz) or cycles per second (cps). 1000 hertz = 1 kilohertz (kHz).