The Elements of Architecture by Scott Drake

Author:Scott Drake
Language: eng
Format: epub
ISBN: 9781317973270
Publisher: Taylor and Francis

The dimensions of sound

Sound is caused by vibration of the air, which is transferred by the eardrum to the nerves of the inner ear. The experience of sound depends on a number of factors, especially the frequency of vibration, the energy level and the duration. The frequency, measured in hertz (Hz), is experienced as pitch, or whether a sound is high or low. The energy level, measured in decibels (dB), determines the apparent loudness of the sound. The duration, measured in seconds, determines how long a sound lasts for and, in particular, how it interacts with other sounds that follow it. Because the human ear is able to detect multiple vibrations, any particular sound is usually made up of several different frequencies that are heard together as a single sound, or even a number of different sounds that are heard together at the same time. This enables the harmonious quality of musical instruments or voices, as multiple frequencies reinforce one another to give depth or complexity to sound.

But as well as these three dimensions, sound can be identified as occurring in a particular position or direction relative to the listener. That position may also change in time, indicating a relative movement between the listener and the source, which is also experienced as a change in loudness as the sound source comes closer or moves further away. In extreme cases, that motion can give rise to the Doppler effect, where the speed of the source compresses the sound waves, making the frequency appear higher as the source moves towards the listener and lower as it moves away. The direction of sound is complicated by the acoustics of space. A direct line of sight and sound makes it possible to identify the source as the loudest and first heard version of any sound, but subsequent reflections will distribute a sound throughout a space. This can be beneficial for music, but can be problematic for disruptive or unwanted sound.

The final quality that affects the experience of sound is what might be described as its information content. Through language and intonation, sound enables communication between people. But, sound also identifies its source, as we recognize the sound of a bird, a lion or a train. This can be vital for safety, as it enables people to be aware of, and hopefully to avoid, things that threaten them. Or it may lead to annoyance, as we sense the presence of unwanted guests: a barking dog, a mosquito, a lawnmower, or even just music that is suited to different tastes.

The various dimensions of sound – pitch, loudness, duration, location and information content – are all affected by the environment in which they occur. Once produced at a source, sound waves move out in each direction until they decay due to friction, or until they are reflected from or absorbed by objects around them. In general, sound is reflected by hard surfaces and absorbed by soft surfaces. By the time sounds reach the listener, they have usually been affected in some way by the surfaces around them.

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