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Sound
is the sensation perceived by the human ear resulting from rapid fluctuations in the air pressure. These fluctuations are usually created by some vibrating object which sets up longitudinal wave motion in the air
Sound level
(or energy, strength, amplitude, loudness)
Frequency
(or pitch, tone, wavelength)
Propagation
(or path, elapsed time)
Frequency
When sound includes abundant high‐pitched or treble energy, it is said to be heavy on high‐frequency content, and when sound includes abundant low pitched or bass energy, it contains ample low‐frequency content.
Sound Propagation
Direct sound decays at the same rate inside as outside, shedding six decibels per doubling of distance because the same sound energy is spread over four times the area every time the distance is doubled.
Amplitude
is determined by the magnitude of the pressure fluctuation. But the range of pressures to which our ears can respond exceeds a ratio of one to a million and the response is not linear.
Decibel
to measure differences or to measure sound (or other) amplitudes. In both cases, the choice of a logarithmic scale overcomes the problem of large numbers.
pure tone
eis vibration produced at a single frequency.
hertz (Hz)
If a surface is vibrating, the frequency of vibration is the number of cycles per second, though this is now expressed in ?
Directivity
is a measure of the directional characteristic of a sound source.
ISAAC NEWTON
on his theory of light (Guillen, 1995), published in 1675 the law of elasticity that now bears his name, in the form of a Latin anagram
CEIIINOSSSTTUV
which decoded is "Ut tensio, sic vis" (Lindsay, 1966). It established the direct relationship between stress and strain that is the basis for the formulas of linear acoustics.
Plane Wave
When corresponding wavefronts of a sound wave propagate parallel to each other then the sound wave is known as a plane sound wave e.g. the sound wave produced by a piston oscillating in a long cylinder.
diverging sound wave
is one where the sound energy is spread over a greater and greater area as the wave propagates away from the sound source.
spherical sound wave
is produced by a sound source which radiates sound energy equally in all directions e.g. a monopole source.
Progressive Wave
When there is a transfer of energy in the direction of propagation of the sound wave the wave is designated as __________________________?
standing wave
is produced by the constructive interference of two or more sound waves which gives rise to a pattern of pressure maxima and minima which is stable with time
frequency (F)
The number of cycles per second is called the
Hertz
The unit of frequency is the ?
1 Hertz
_____________ = 1 cycle/sec
period (T)
The time taken for the oscillation to repeat itself is known as the ?
Sound waves
are longitudinal waves (i.e involve oscillations parallel to the direction of the wave travel) that propagates through a medium (e.g. air, water, iron)
Speed of Sound
The speed of any mechanical wave depends on the both the inertial property of the medium (stokes kinetic energy) and the elastic property (store potential energy).
free-field conditions
Sound Waves from a point source outdoors with no obstructions called ____________________ are virtually spherical and expand outward from the source as shown below
intensity
from a point source outdoors at a distance d away is the sound power of the source divided by the total spherical area And^ of the sound wave at the distance of interest.
sabins
The total absorption in a room, the "room constant," measured in a unit called ?
noise reduction coefficient NRC
is the arithmetic average, rounded off to the nearest multiple of 0.05, of the sound absorption coefficients a's at 250, 500, 1000, and 2000 Hz for a specific material and mounting condition.
Reverberation Time
Defined as the persistence of sound.
steeply sloped seating
When _________________ is used, the sound level outdoors falls off primarily with distance. An overhead sound-reflecting panel or ceiling can provide reflected sound to reinforce the direct sound.
hard, sound-reflecting enclosure
outdoors near the sound source can greatly improve listening conditions by reflecting sound energy toward the audience and by shielding the audience from noise sources located behind the enclosure.
Sight lines
are normally drawn to converge at a point on stage called the arrival point of sight APS. Audiences should be able to hear and to see clearly and comfortably to fully perceive the intended effects of performances.
ray diagram
is an acoustical analogy to the specular reflection of light where the angle of incidence ∠i of an impinging sound wave equals the angle of reflection ∠r, with angles measured from the perpendicular to the surface.
Reflection
is the return of a sound wave from a surface. (x > 4 λ)
Diffusion
is the scattering or random redistribution of a sound wave from a surface. It occurs when the surface depths of hardsurfaced materials are comparable to the wavelengths of the sound. (x = λ)
Diffraction
is the bending or "flowing" of a sound wave around an object or through an opening. (x < λ)
Concave Reflector
can focus sound, causing hot spots and echoes in the audience seating area.
Flat Reflector
can effectively distribute reflected sound.
Convex Reflector
can be most effective as sound-distributing forms. The reflected sound energy from convex surfaces diverges, enhancing diffusion, which is highly desirable for music listening.
Echoes
The distinct repetition of the original sound and is sufficiently loud to be clearly heard above the general reverberation and background noise in a space.
Rear Wall Echo Control Treatment
A flat, sound-reflecting rear wall can produce echoes or unwanted, long delayed reflections in medium to large auditoriums.
Flutter Echo
Repetitive interreflection of sound energy between opposing parallel or concave sound-reflecting surfaces.
Pitched-Rood Flutter Echo
The echo phenomenon which occur in rooms with non-parallel walls.
Audible resonance
is the emphasis of sound energy at particular frequencies. It can occur in small rooms entirely finished with sound-reflecting materials when the dimensional ratios are whole numbers (e.g., cube).
Reflection
from a finite surface depends on the relationship between the size of the reflector and the wavelength of sound.
diffraction
A textured surface will provide some scattering of sound, but the degree of texturing must be high for efficient scattering. The general principle is that the deeper the scattering treatment, the lower the frequency down to which the surface will scatter sound.
absorption
removes acoustic energy. there are three possible mechanisms: porous absorption, panel absorption and helmholtz resonance. porous absorption, as already mentioned, occurs with any porous material.
Daylighting
is an excellent light source for almost all interior spaces. It is best for offices, schools, and workspaces requiring a lot of light and for public spaces such as malls, airports, and institutions.
Windows, skylights, and other forms of fenestration
are used to bring daylight into the interiors of buildings.
Daylight
is highly desirable as a light source because people respond positively to it.
Daylighting
is the complete process of designing buildings to utilize natural light to its fullest.
Top lighting
behaves as direct electric lighting does by radiating light downward.
Side lighting
employs vertical fenestration (usually windows) to introduce natural light.
Windows
have the advantage of providing both daylight to the interior and a view out.
Clerestory windows
are strictly a narrow strip of windows high up on the wall.
Rooflights
are a glazed opening in the roof of a building.
Atria
have become an increasingly popular feature of buildings. ____________ are often used to light central circulation or social area by daylight admitted through a glass roof or wall.
Remote distribution
all collect daylight and sunlight in some way and transmit in through a shaft or pipe by reflection to a distribution point in the space.
Borrowed light
is a term used to describe the lighting of an enclosed internal space through a window that connects to an adjacent daylit space
visual problems
are glare and veiling reflections. Glare is caused by a direct view of either the sun or the bright sky.
thermal problems
Daylight admitted to a building represents a heat load. In winter this may be useful but in summer it can represent an additional cooling load.
privacy problem
Extensively glazed buildings can present _____________, particularly on the ground floor. Concerns about privacy can lead to blinds being closed at all times with a consequent lack of daylight and view out.
flame of fire
first artificial light source was the ?
Incandescent gas light
was accompanied practically simultaneously by the development of electric arc and incandescent lamps, which were joined at the end of the 19th century by discharge lamps.
"phlogistos"
Until the birth of modern chemistry, the belief laid down by the ancient Greeks was taken to be true: during the burning process, a substance called _______________ was released
combustion
It was only through Lavoisier's experiments that it became clear that _________________ was a form of chemical action and that the flame was dependent on the presence of air.
Francois Argand
constructed a lamp that was to be named after him, the Argand lamp.
Mirrors
are known to have been used by ancient Greeks and Romans and the theory behind their application set down in writing.
optical lenses
At the turn of the first millennium, there were a number of theoretical works in Arabia and China concerning the effect of ?
the first telescopes
were designed by Dutch lens grinders.
microscopes and projector equipment
n the 17th century these instruments were then perfected by Galileo, Kepler and Newton; ______________________ were then constructed.
Huygens
saw light as a phenomenon comprising waves.
photometrics
With the development of _______________ - the theory of how to measure light - and illuminances - through Boguer and Lambert in the 18th century, the most essential scientific principles for workable lighting engineering were established.
Augustin Jean Fresnel
developed a composite system of stepped lens and prismatic rings which could be made large enough to concentrate the light from lighthouses; this construction was also first installed in Cordouan.
Incandescence
When an object is heated to a high temperature, the atoms within the material become excited by the many interactions between them and energy is radiated in a continuous spectrum.
electric discharge
is an electric current that flows through a gas.
Electroluminescence S
some materials will convert electricity into light directly
Luminescence
The process involves a material absorbing radiation and then re-emitting light.
Radioluminescence
This occurs in a similar manner to luminescence, but the primary source of the activation energy is particles or gamma rays emitted by a decaying nucleus of a radioactive atom.
cathodoluminescence
he energy driving the phosphor is an electron that has been accelerated away from a cathode. This process is the means by which light is generated in a cathode ray tube.
Chemiluminescence
Some chemical reactions can produce light directly, not via the heat the reaction creates. The process is used by some living organisms to generate light; the best-known example being the glow worm.
Thermoluminescence
This is exhibited by some materials when they are heated. The materials give out much more light than would be expected due to black body radiation. The best-known practical use of the method of light production is the mantle used in some types of gas lamps.
Skylight
is the light from the sun which is scattered in the atmosphere. The distribution and amount of light received at ground level is dependent on atmospheric conditions.
incandescent lamp
is operated by heating a filament in the lamp to a high temperature, so that it emits light. The hotter the filament, the whiter the light.