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In typical acoustical design situations where sound quality is to
be enhanced, a commonly expressed and straightforward desirable objective is to be able to dramatically increase (or otherwise
control) the sound reflection and absorption properties of various
walls or enclosures by directly using selected materials and without
using complex assemblies of multiple materials. Doing so, however,
is proving difficult. A primary reason is that the wavelengths associated with sound are quite long (see Sections 4.8 and 7.6) with
respect to nanoscaled imensions. With light, for example, many
interesting and useful interaction effects take place on surfaces
because the short wavelengths of light are quite close in size to the
dimensions of many nanostructures, including the variation of the
wavelength of emitted light as a function of particle size in quantum
dot applications, the surface plasmon effect, or the transparency
of many types of nanocoatings. By contrast, the long wavelengths
of sound do not directly correspond to dimensions of nanosized
surface structures, and are invariably much longer. This mismatch
between the wavelength of sound and nanostructure dimensions
inherently poses challenges in effectively utilizing nanomaterials
in attempting to improve a material’s sound absorptive qualities.
Common sound absorption wall and ceiling panels in buildings,
for example, have surfaces with relatively large surface pores or
roughness that trap sound waves and cause them to dissipate by
internal bouncing within the pores. Making surface pores nanosized will not enhance this energy dissipation since the wavelengths of the sound are so long that they would not interact
with the tiny pore sizes. The pores would be invisible (so to
speak) with respect to the way they affect sound impinging on
the surface.
A further inhibiting factor is that quantities such as sound velocity, sound-wave impedance, and sound radiation factors for a
material depend on the direct physical properties of a bulk material (density, ρ, and the modulus of elasticity, E; see Section 4.8)
and are not easily changeable in many common bulk materials by
simply adding nanomaterials. For example, when nanocomposites
are made by adding a nanomaterial as a second phase, the quantities of nanomaterials used are typically quite small, which have
relatively little effect on the overall density. This situation is particularly problematic for applications in passive building acoustics with its needs for large material volumes. Hence a more direct
approach is to use nanomaterials with useful sound properties that
can be made directly in bulk form (see the discussion on aerogels
that follows).
Sound and Acoustical Environments
In typical acoustical design situations where sound quality is to
be enhanced, a commonly expressed and straightforward desirable objective is to be able to dramatically increase (or otherwise
control) the sound reflection and absorption properties of various
walls or enclosures by directly using selected materials and without
using complex assemblies of multiple materials. Doing so, however,
is proving difficult. A primary reason is that the wavelengths associated with sound are quite long (see Sections 4.8 and 7.6) with
respect to nanoscaled imensions. With light, for example, many
interesting and useful interaction effects take place on surfaces
because the short wavelengths of light are quite close in size to the
dimensions of many nanostructures, including the variation of the
wavelength of emitted light as a function of particle size in quantum
dot applications, the surface plasmon effect, or the transparency
of many types of nanocoatings. By contrast, the long wavelengths
of sound do not directly correspond to dimensions of nanosized
surface structures, and are invariably much longer. This mismatch
between the wavelength of sound and nanostructure dimensions
inherently poses challenges in effectively utilizing nanomaterials
in attempting to improve a material’s sound absorptive qualities.
Common sound absorption wall and ceiling panels in buildings,
for example, have surfaces with relatively large surface pores or
roughness that trap sound waves and cause them to dissipate by
internal bouncing within the pores. Making surface pores nanosized will not enhance this energy dissipation since the wavelengths of the sound are so long that they would not interact
with the tiny pore sizes. The pores would be invisible (so to
speak) with respect to the way they affect sound impinging on
the surface.
A further inhibiting factor is that quantities such as sound velocity, sound-wave impedance, and sound radiation factors for a
material depend on the direct physical properties of a bulk material (density, ρ, and the modulus of elasticity, E; see Section 4.8)
and are not easily changeable in many common bulk materials by
simply adding nanomaterials. For example, when nanocomposites
are made by adding a nanomaterial as a second phase, the quantities of nanomaterials used are typically quite small, which have
relatively little effect on the overall density. This situation is particularly problematic for applications in passive building acoustics with its needs for large material volumes. Hence a more direct
approach is to use nanomaterials with useful sound properties that
can be made directly in bulk form (see the discussion on aerogels
that follows).
Sound and Acoustical Environments