371
hears not only sounds that have originated from the source but
also sounds that have come from the source but that have been
bounced around the surfaces of the room. A much more complex
situation thus exists that clearly depends on not only the character
of the emanating sound but of the geometrical and physical characteristics of the room itself. The commonly used overall measure
of this characteristic is called the reverberation time (RT; see Section
3.5). Reverberation times, however, are only one of several measures that stem from the fundamental issue that sound reaching a
listener’s ear has both direct paths and indirect (reflected) paths,
including early decay times, loudness measures, initial time delay
gaps, and others.
Analytically modeling the kinds of sound behaviors noted here is
inherently complex. Many types of computer models have been
developed to aid in this process. These simulation models invariably require a 3-D digital model that describes the room geometry
and the placement of various kinds of materials throughout it, as
well as properties of the materials themselves. Source positions and
characteristics must be defined, as must receiver positions. Various
kinds of energy-based or ray-tracing algorithms that draw literally
millions of lines from sources to receivers are then used to predict
resultant sound behaviors. Simulation methods must be benchmarked for accuracy against experimental results. Though simulation models can be quite good for certain applications, various kinds
of physical-scale models are often still used in many applications,
particularly in large spaces with many complex or irregular surfaces
and material distributions. Once the sound behaviors are modeled,
and based on understandings of human hearing and responses as
well as understandings of issues such as “acoustical glare,” design
evaluations are then made. Many other factors play a role in evaluations, including human-based reactions. Is a concert hall “lively”
or not, “warm” or not, or can the term brilliance ultimately be used
to describe the sound heard?
The list of measures noted here that an acoustician has to deal with
could go on and on, and knowing how to design in relation to them
is clearly a task for specialists. Of importance here is that reflection
and absorption properties are clearly fundamental, as are surface
textures, density and hardness, mass, thickness, support conditions,
and the presence or absence of damping mechanisms (implicit
or added devices). It is invariably the play of these many factors
that contributes to whether an acoustical design is good, bad, or
indifferent. What becomes clear is that there is no such thing as
a specific material property (such as absorption) being intrinsiSound and Acoustical Environments
hears not only sounds that have originated from the source but
also sounds that have come from the source but that have been
bounced around the surfaces of the room. A much more complex
situation thus exists that clearly depends on not only the character
of the emanating sound but of the geometrical and physical characteristics of the room itself. The commonly used overall measure
of this characteristic is called the reverberation time (RT; see Section
3.5). Reverberation times, however, are only one of several measures that stem from the fundamental issue that sound reaching a
listener’s ear has both direct paths and indirect (reflected) paths,
including early decay times, loudness measures, initial time delay
gaps, and others.
Analytically modeling the kinds of sound behaviors noted here is
inherently complex. Many types of computer models have been
developed to aid in this process. These simulation models invariably require a 3-D digital model that describes the room geometry
and the placement of various kinds of materials throughout it, as
well as properties of the materials themselves. Source positions and
characteristics must be defined, as must receiver positions. Various
kinds of energy-based or ray-tracing algorithms that draw literally
millions of lines from sources to receivers are then used to predict
resultant sound behaviors. Simulation methods must be benchmarked for accuracy against experimental results. Though simulation models can be quite good for certain applications, various kinds
of physical-scale models are often still used in many applications,
particularly in large spaces with many complex or irregular surfaces
and material distributions. Once the sound behaviors are modeled,
and based on understandings of human hearing and responses as
well as understandings of issues such as “acoustical glare,” design
evaluations are then made. Many other factors play a role in evaluations, including human-based reactions. Is a concert hall “lively”
or not, “warm” or not, or can the term brilliance ultimately be used
to describe the sound heard?
The list of measures noted here that an acoustician has to deal with
could go on and on, and knowing how to design in relation to them
is clearly a task for specialists. Of importance here is that reflection
and absorption properties are clearly fundamental, as are surface
textures, density and hardness, mass, thickness, support conditions,
and the presence or absence of damping mechanisms (implicit
or added devices). It is invariably the play of these many factors
that contributes to whether an acoustical design is good, bad, or
indifferent. What becomes clear is that there is no such thing as
a specific material property (such as absorption) being intrinsiSound and Acoustical Environments