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	=<span style="color:">what is sound?</span>=		=<span style="color:">what is sound?</span>=
−	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 is a mechanical, longitudinal wave that is an oscillation of pressure (series of compressions and rarefactions) transmitted through a solid, liquid, or gas.
−	=<span style="color:"> sound vs noise</span>=	+	[[atom03: sound glossary|sound terminology]]
−	'''''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.	+	=<span style="color:">sound reflection and space</span>=
−	'''''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.	+
−	=<span style="color:">sound wave terminology</span>=	+	<div style="float: left; width: 310px; margin-right:20px; text-align:left">
−	Sound waves are often described in terms of sinusoidal (smooth repetitive oscillation) two-dimensional waves, and are characterized by the following properties:	+	'''Principle of reflection'''
		+	[[Image:Reflection.jpg|thumb|right |100px|]]
		+	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.
−	'''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.	+	'''Flat surfaces'''
		+	[[Image:Reflection_flat_surface.jpg|thumb|right |100px|]]
		+	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.
−	'''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.	+	</div>
		+	<div style="float: left; width: 310px; margin-right:20px; vertical-align;text-align:left">
		+	'''Concave surfaces'''
		+	[[Image:Reflection_concave_surface.jpg|thumb|right |100px|]]
		+	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.
−	'''Amplitude''' the magnitude of change in the oscillating variable - It translated into the strength of sound waves and determines loudness.	+	'''Convex surfaces'''
		+	[[Image:Reflection_convex_surface.jpg|thumb|right |100px|]]
		+	Convex surfaces are the best surfaces for distributing sound. They provide a wide spread of reflected sound.
−	'''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.
−	=<span style="color:">human perception and reaction to sound</span>=
		+	</div>
−	<gallery perrow="6" caption="8 points">
−	File:Acoustical_privacy.jpg|
−	File:Db_levels.jpg|
−	File:A3sr.png|sound level chart
−	</gallery>	+	<br style="clear: both; height: 0; line-height: 0; font-size: px; /*for IE*/"/>
		+	=<span style="color:">human perception and reaction to sound</span>=
		+	The human hearing system has an average frequency range of about 20 Hz to 20.000 Hz. This frequency range changes as part of te human ageing process, particularly in terms of the upper limit, this limit tends to reduce.
		+	The hearing system of human has  a threshold of hearing and a threshold of pain. These thresholds do mark the boundaries  of the hearing system. The threshold of hearing varies with frequency. The ear is far more sensitive in the middle of its frequency than at it's high and low extrem (see picture of the average threshold of hearing and the threshold of pain).
		+	As we can see from the picture the minimum sound level and the maximum sound level which can be detected are respectively 0 and 130 dB.
		+	The perceived loudness of an acoustic sound depends on the function of both frequency and amplitude.(This is also illustrated in the picture which deals about the equal loudness for the human ear). This picture shows the contours of equal loudness for the human ear. The phon scale is a function of frequency and sound pressure levels.
		+	Apart from frequency and amplitude duration also has an effect on the perception of loudness. When a sound lasts more than 200 ms the perceived level does not change.
−	text / diagrams / annoyance - related to noisiness (absolute /relative)	+	<gallery perrow="6">
		+	File:treshold of hearing and pain.jpg|The average human threshold of hearing and the threshold of pain
		+	File:graph for equal perception of loudness.jpg|Equal loudness for the human ear
		+	File:Acoustical_privacy.jpg|acoustical privacy
		+	File:Db_levels.jpg|sound pressure scenario
		+	File:Human_reaction_to_change_levels.jpg|sensitivity to db. change
		+	</gallery>
−	=<span style="color:"> physical noise characterization</span>=	+	=<span style="color:"> sound vs noise</span>=
−	geometries / ground attenuation / fixed sources....	+	'''''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.
−	=<span style="color:">general sound glossary</span>=	+
−		+
−	'''Absorption''' The tendency of sound waves to be soaked up by soft surfaces.	+
−		+
−	'''Amplifier'''  Increases the amplitude of a signal.	+
−		+
−	'''Attenuate'''  To make weaker.	+
−		+
−	'''Conductor''' element that allows the free transmission of sound.	+
−		+
−	'''dB (Decibel)''' A relative unit of measure between two sound or audio signal levels. A difference 1 dB is considered to be the smallest that can be detected by the human ear.	+
−		+
−	'''Dispersion''' The area throughout which the sound produced is distributed.	+
−		+
−	'''Distortion''' The alteration of the original shape (or other characteristic) of a sound waveform.	+
−		+
−	'''Dynamic Range''' The difference between the softest and loudest extremes within an audio signal.	+
−		+
−	'''Efficiency''' The ratio of a device's energy output to its energy intake.	+
−		+
−	'''Filter''' A device that removes unwanted frequencies or noise from a signal.	+
−		+
−	'''Frequency'''  The number of sound waves that pass a given point in one second. The determiner of pitch.	+
−		+
−	'''Inductance''' A circuit's opposition to a change in current flow.	+
−		+
−	'''Omnidirectional''' Capable of picking-up sound or radiating sound equally from all directions	+
−		+
−	'''Phase''' The relationship of an audio signal or sound wave to a specific time reference.	+
−		+
−	'''Pitch''' The degree of highness or lowness of a tone.	+
−		+
−	'''Sound Level Meter''' A device that measures, in dB, the amplitude of sound waves.	+
−		+
−	'''Sound Reinforcement''' The use of electronic devices to reinforce, alter or increase the level of sound.	+
−		+
−	'''Tone''' Sound that can recognized by its regularity of vibration; The overall quality of sound.	+
−	'''Unidirectional''' Picking up sound primarily from one direction.
−	'''Vibration''' The analogous motion of particles of mass the analogous motion of the particles of a mass of air, whose state of equilibrium has been disturbed, causing the transmission of sound.

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Latest revision as of 11:25, 17 October 2011

Contents 1 what is sound? 2 sound reflection and space 3 human perception and reaction to sound 4 sound vs noise

what is sound?

Sound is a mechanical, longitudinal wave that is an oscillation of pressure (series of compressions and rarefactions) transmitted through a solid, liquid, or gas.

sound terminology

sound reflection and space

human perception and reaction to sound

The human hearing system has an average frequency range of about 20 Hz to 20.000 Hz. This frequency range changes as part of te human ageing process, particularly in terms of the upper limit, this limit tends to reduce. The hearing system of human has a threshold of hearing and a threshold of pain. These thresholds do mark the boundaries of the hearing system. The threshold of hearing varies with frequency. The ear is far more sensitive in the middle of its frequency than at it's high and low extrem (see picture of the average threshold of hearing and the threshold of pain). As we can see from the picture the minimum sound level and the maximum sound level which can be detected are respectively 0 and 130 dB. The perceived loudness of an acoustic sound depends on the function of both frequency and amplitude.(This is also illustrated in the picture which deals about the equal loudness for the human ear). This picture shows the contours of equal loudness for the human ear. The phon scale is a function of frequency and sound pressure levels. Apart from frequency and amplitude duration also has an effect on the perception of loudness. When a sound lasts more than 200 ms the perceived level does not change.

• 

  The average human threshold of hearing and the threshold of pain

• 

  Equal loudness for the human ear

• 

  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.