atom03:Sound
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'''Doppler effect''' is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. | '''Doppler effect''' is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession. | ||
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'''''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. | '''''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. | ||
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Revision as of 08:00, 17 October 2011
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 wave terminology
Sound waves are often described in terms of sinusoidal (smooth repetitive oscillation) two-dimensional waves, and are characterized by the following properties:
Frequency the number of occurrences of a repeating event per unit time. The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example, if a newborn baby's heart beats at a frequency of 120 times a minute, its period (the interval between beats) is half a second.
Wavelength the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase.
Amplitude the magnitude of change in the oscillating variable - It translated into the strength of sound waves and determines loudness.
Sound pressure level The sound pressure level is used to describe the amplitude of the sound wave. However the sound intensity is also a way to describe the amplitude of a sound wave. The difference between the two is the following; the sound intensity level (SIL) is the power density from a sound source at the measurement point and the sound pressure level (SPL) is the sum of the sound pressure waves at the measurement point. The SIL and the SPL are equivalent if there is only one pressure wave from the sound source. When extra pressure waves due to reflection occur the SIL and SPL differ. It's confusing that both the SIL and SPL are able to describe sound amplitudes, however a general reference to sound level implies that the SPL is being use. The pressure component corresponds most closely to what we hear.
Sound intensity level The sound intensity represents the watt (energy) per unit area from a sound source. This formula describes the sound intensity level: 10log10(Iactual/Iref)
Speed of sound distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). This is 1,236 kilometres per hour (768 mph), or about one kilometer in three seconds or approximately one mile in five seconds.
Direction Information contained in the relative position of one point with respect to another point without the distance information
Diffraction uses the edges of a barrier as a secondary sound source that sends waves in a new direction.
Doppler effect is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.
sound reflection and space
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.
