atom03:Sound
Contents |
what is sound?
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard.
sound reflection and space
Principle of reflection
A reflection wave is yielded when an incidental wave comes to the boundary, and the reflector directs the wave just as light reflector directs light rays. So, in every case, the direction of propagation of the wave is perpendicular to the front, and the reflective wave will be reflected at an equal angle to the incident angle.
Flat surfaces
A flat surface is effective in distributing sound. If the surface is large enough and positioned correctly, a flat surface can project sound toward the listeners. Flat surfaces can also cause problems if placed incorrectly. For example, a flat, reflective rear wall in an auditorium will reflect sound back toward the speaker, this is called "slap-back". Parallel reflective walls can create a reflection between the two surfaces, this is referred to as "flutter echo" or "standing wave". Two flat surfaces coming together to form a peak can act as a megaphone and amplify the reflected sound.
Concave surfaces
Concave surfaces cause reflections to be concentrated rather than dispersed. This causes an abundance of reflection to be heard by the listeners in the focal point, or the point at which all of the reflections are focused. Reflections can also travel along a concave surface bringing delayed reflections around the room.
Convex surfaces
Convex surfaces are the best surfaces for distributing sound. They provide a wide spread of reflected sound.
human perception and reaction to sound
acoustical privacy
sound pressure scenario
sensitivity to db. change
sound vs noise
Sound is a form of energy that is transmitted by pressure variations which the human ear can detect. When one plays a musical instrument, say a guitar, the vibrating chords set air particles into vibration and generate pressure waves in the air. A person nearby may then hear the sound of the guitar when the pressure waves are perceived by the ear. Sound can also travel through other media, such as water or steel.Apart from musical instruments, sound can be produced by many other sources - man's vocal cord, a running engine, a vibrating loudspeaker diaphragm, an operating machine tool, and so on. Noise is a combination of different sounds, that cannot be clarified. Usually the sound of a violin is referred to as music - is something pleasing. Depending on other factors, the sound may be perceived as noise.Noise perception is subjective. Factors such as the magnitude, characteristics, duration, and time of occurrence may affect one's subjective impression of the noise.
sources: environmental protection department - goverment of Hong Kong / Long, Architectural Accoustics. Elsevier Academic Press, London 2006.
