C haptEr 9 design Environments and systems
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material. Amplitude is the loudness of the sound and depends on
the amount of compression that takes place. Wavelength is the distance from the crest of one wave to another. Frequency, or pitch, is
the rate at which waves pass a point. Short wavelengths correspond
to high pitches. The velocity of a wave is its wavelength times its
frequency.
The way sound travels from a source to another point depends on
both geometry and the transmission medium. Sound waves emanating from a point source spread out. Amplitudes decrease as the
square of the distance from the source; thus there is inherently a
rapid decrease in sound intensity away from a source. The sound
itself can be carried by different media, and sound can be transmitted from one medium to another, such as from air to a wall and to
the air again. As sound passes through each medium, some sound
intensity is lost due to absorption. Here a portion of the sound
energy is converted into heat, thus reducing the amount of sound
energy that is transmitted.
Absorption levels vary by transmission medium. As sound passes
through various media, changes in velocity occur depending on
the properties of the media. The velocity of the transmitted sound
depends on the density and stiffness properties of the medium.
When a sound wave in one medium or material encounters another
in its path, it is reflected, absorbed, or transmitted. A portion of the
sound is reflected while the remainder passes into encountered
material. Of the portion of sound that enters the media, some
is lost to internal absorption (see the following discussion). The
remainder is transmitted through the material. Dense hard and
solid materials tend to strongly reflect incoming sound waves and
weakly transmit them. Light, highly porous materials normally
have weak reflections and can transmit waves strongly.
The amount of sound that is reflected depends on the hardness and
smoothness of the encountered surface. Controlled directions of
reflections can be achieved with smooth surfaces better than rough
surfaces. The latter causes diffuse microreflections that cause scattering in the primary reflection. When highly porous surfaces
are present, additional absorption can take place because sound
waves can literally bounce back and forth within small cavities on
the surface before finally being diffusely reflected. Another form
of reflection can occur after the sound is transmitted through the
material (with losses due to absorption) and enters the next. When
passing from a dense material, such as wood, to air, this reflection
is small but is still there.
366
material. Amplitude is the loudness of the sound and depends on
the amount of compression that takes place. Wavelength is the distance from the crest of one wave to another. Frequency, or pitch, is
the rate at which waves pass a point. Short wavelengths correspond
to high pitches. The velocity of a wave is its wavelength times its
frequency.
The way sound travels from a source to another point depends on
both geometry and the transmission medium. Sound waves emanating from a point source spread out. Amplitudes decrease as the
square of the distance from the source; thus there is inherently a
rapid decrease in sound intensity away from a source. The sound
itself can be carried by different media, and sound can be transmitted from one medium to another, such as from air to a wall and to
the air again. As sound passes through each medium, some sound
intensity is lost due to absorption. Here a portion of the sound
energy is converted into heat, thus reducing the amount of sound
energy that is transmitted.
Absorption levels vary by transmission medium. As sound passes
through various media, changes in velocity occur depending on
the properties of the media. The velocity of the transmitted sound
depends on the density and stiffness properties of the medium.
When a sound wave in one medium or material encounters another
in its path, it is reflected, absorbed, or transmitted. A portion of the
sound is reflected while the remainder passes into encountered
material. Of the portion of sound that enters the media, some
is lost to internal absorption (see the following discussion). The
remainder is transmitted through the material. Dense hard and
solid materials tend to strongly reflect incoming sound waves and
weakly transmit them. Light, highly porous materials normally
have weak reflections and can transmit waves strongly.
The amount of sound that is reflected depends on the hardness and
smoothness of the encountered surface. Controlled directions of
reflections can be achieved with smooth surfaces better than rough
surfaces. The latter causes diffuse microreflections that cause scattering in the primary reflection. When highly porous surfaces
are present, additional absorption can take place because sound
waves can literally bounce back and forth within small cavities on
the surface before finally being diffusely reflected. Another form
of reflection can occur after the sound is transmitted through the
material (with losses due to absorption) and enters the next. When
passing from a dense material, such as wood, to air, this reflection
is small but is still there.