C haptEr 9 design Environments and systems
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the work habits of many) or simply to mask uncontrollable
sounds.
If objectives are to reduce or eliminate unwanted noise within a
space from a source outside the space, attention is normally directed
to reducing source levels or using barriers and isolation techniques.
Many wall systems in buildings are commonly designed to prevent
sound from being transmitted from one space to another, and the
enclosures around products containing noise-generating devices are
similarly designed to reduce sound transmission. Passive control
approaches are common. As previously noted, dense materials and
high mass assemblies tend to strongly reflect incoming sound waves
and weakly transmit them, whereas light materials and assemblies
normally have weak reflections and can transmit waves strongly.
The more the sound is reflected from the source area and the more
that is absorbed in the wall or enclosure materials, the less will be
transmitted to the space where noise control is sound. Hence thin,
hard surfaces can be helpful because they aid reflection. Reductions
in sound transmission can also be obtained via the use of highly
absorptive materials in wall or product enclosure assemblies or
via introducing deliberate separations between materials (a form
of isolation strategy discussed shortly). The obviousness of the
approach, however, stands in distinction to the problematic nature
of its application. In building environments, for example, there are
obviously many reasons that barriers cannot be monolithic continuums—consider the need for doorways, windows, ventilation
ducts, and so on.
Many common assemblies use varying combinations of mass, reflective, absorptive, and separation strategies simultaneously. The strategy chosen often depends on the frequency and amplitude of the
sound source. In walls of buildings, troublesome low-frequency
sounds (such as those associated with music) are really only effectively mitigated by high-mass systems and separation strategies;
little absorption takes place. High-frequency sounds associated with
many products are more easily mitigated using absorptive materials.
Many sound-deadening product enclosures are remarkably sophisticated and consist of multiple layers—for example, thin foils with
multiple layers of butyl damping materials are commonly used for
sound dampening in refrigerators, ventilators, and other devices.
Structure-borne sounds result when vibrations from machines or
equipment are induced in supporting structural elements. The source
need not be in the considered space. In buildings, vibrations can
result from passing trains or cars or from remote heating, ventilating,
368
the work habits of many) or simply to mask uncontrollable
sounds.
If objectives are to reduce or eliminate unwanted noise within a
space from a source outside the space, attention is normally directed
to reducing source levels or using barriers and isolation techniques.
Many wall systems in buildings are commonly designed to prevent
sound from being transmitted from one space to another, and the
enclosures around products containing noise-generating devices are
similarly designed to reduce sound transmission. Passive control
approaches are common. As previously noted, dense materials and
high mass assemblies tend to strongly reflect incoming sound waves
and weakly transmit them, whereas light materials and assemblies
normally have weak reflections and can transmit waves strongly.
The more the sound is reflected from the source area and the more
that is absorbed in the wall or enclosure materials, the less will be
transmitted to the space where noise control is sound. Hence thin,
hard surfaces can be helpful because they aid reflection. Reductions
in sound transmission can also be obtained via the use of highly
absorptive materials in wall or product enclosure assemblies or
via introducing deliberate separations between materials (a form
of isolation strategy discussed shortly). The obviousness of the
approach, however, stands in distinction to the problematic nature
of its application. In building environments, for example, there are
obviously many reasons that barriers cannot be monolithic continuums—consider the need for doorways, windows, ventilation
ducts, and so on.
Many common assemblies use varying combinations of mass, reflective, absorptive, and separation strategies simultaneously. The strategy chosen often depends on the frequency and amplitude of the
sound source. In walls of buildings, troublesome low-frequency
sounds (such as those associated with music) are really only effectively mitigated by high-mass systems and separation strategies;
little absorption takes place. High-frequency sounds associated with
many products are more easily mitigated using absorptive materials.
Many sound-deadening product enclosures are remarkably sophisticated and consist of multiple layers—for example, thin foils with
multiple layers of butyl damping materials are commonly used for
sound dampening in refrigerators, ventilators, and other devices.
Structure-borne sounds result when vibrations from machines or
equipment are induced in supporting structural elements. The source
need not be in the considered space. In buildings, vibrations can
result from passing trains or cars or from remote heating, ventilating,