Sound is a sensation or feelingthat we hear. We producesounds by doing something. Themotion of materials or objectscauses vibrations. A soundoriginates in the vibration of anobject, which makes the air oranother substance around theobject vibrate. The vibration ofthe air moves outward in alldirections in the form of a wave In a drum sound is produced when its membrane vibrates
The human voice is produced in thelarynx, which is a part of the throat.There are two small pieces of tissuethat stretch across the larynx with asmall opening between them, thesetissues are our vocal cords. As wespeak, muscles in our larynx tightenthe vocal cords making this smallopening become narrower. When airfrom our lungs passes through thetightened cords a vibration isproduced. This vibration producesvocal sounds. The tighter the vocalcords, the more rapidly the vocalcords vibrate and the higher thesounds that are produced. This iswhat causes the human voices tohave different pitches.6
Animals also produce sounds. Almost allmammals, birds, and frogs have vocalcords or similar structures, which allowthem to produce sounds in a similar wayto humans. However, many other animalsproduce distinctly different sounds. Forexample, bees buzz as they fly because ofthe rapid movement of their wings. Theirwings make the air vibrate producing abuzzing sound. A cricket produces asinging type sound as it scrapes parts ofits front wings together. Some types ofshellfish produce clicks by tapping theirclaws together.7
Musical instruments produce many different sounds in various ways. Thereare three categories of musical instruments, percussion, string, and wind Some instruments need to be struck by an object in order to produce a sound, these are called percussion instruments. For example when the membrane of a drum is hit the membrane vibrates, producing a sound, or when a bar of a xylophone is struck, a sound is produced. Each bar of a xylophone produces a different note when struck.
String instruments, such as aharp or violin, producesounds when one or more oftheir strings areplucked, causing them tovibrate. This vibration causesparts of the body of theinstrument to vibrate, creatingsound waves in the air. Thepitch of a stringed instrumentdepends upon the stringsthickness, its length, thedistance stretched, and thenumber of times it vibrates.
Wind instruments, suchas a flute or trumpetproduce sound when acolumn of air inside theinstrument vibrate. Forexample, with a trumpetit is the vibrating lips ofthe player which makesthe air column vibrate
A sound wave is a transfer of energy as ittravels away from a vibrating source. Soundwaves are formed when a vibrating objectcauses the surrounding medium to vibrate.A medium is a material (solid, liquid or gas)which a wave travels through. As soundwaves move through a medium theparticles vibrate forwards and backwards. Asounds volume, how loud or soft itis, depends on the sound wave. The moreenergy put into making a sound or a soundwave, the louder the volume will be. Thefather a sound wave travels, the more itspreads, this makes it more difficult for us tohear a sound. So the nearer you are to asound the louder it sounds to us. A soundwave enters the ear and is changed intonerve signals, which are interpreted by thebrain.12
Sound is transmitted throughgases, plasma, and liquids aslongitudinal waves, also calledcompression waves. Throughsolids, however, it can betransmitted as both longitudinalwaves and transverse waves.Longitudinal sound waves are longitudinalwaves of alternating pressure wavesdeviations from the equilibriumpressure, causing local regionsof compression andrarefaction, while transversewaves (in solids) are waves ofalternating shear stress at rightangle to the direction ofpropagation. Transverse waves
The behavior of sound propagation is generallyaffected by three things:A relationship between density and pressure. Thisrelationship, affected by temperature, determinesthe speed of sound within the medium.The propagation is also affected by the motion ofthe medium itself. For example, sound movingthrough wind. Independent of the motion of soundthrough the medium, if the medium is moving, thesound is further transported.The viscosity of the medium also affects the motionof sound waves. It determines the rate at whichsound is attenuated. For many media, such as airor water, attenuation due to viscosity is negligible.
Sound waves are often simplified to a description interms of sinusoidal plane waves, which are characterizedby these generic properties:Frequency, or its inverse, the periodWavelengthWave numberAmplitudeSound pressureSound intensitySpeed of soundDirection
The perception of sound inany organism is limited to acertain range of frequencies.For humans, hearing isnormally limited tofrequencies between about20 Hz and 20,000 Hz (20kHz)although these limitsare not definite. The upperlimitGenerally decreases withage Human hearing system
As a signal perceived by one of themajor senses, sound is used by manyspecies for detecting danger,navigation, predation, andcommunication. Earths atmosphere,water, and virtually any physicalphenomenon, such as fire, rain, wind,surf, or earthquake, produces (and ischaracterized by) its unique sounds.Many species, such as frogs, birds,marine and terrestrial mammals, havealso developed special organs toproduce sound. In some species, theseproduce song and speech. Furthermore,humans have developed culture andtechnology (such as music, telephoneand radio) that allows them to generate,record, transmit, and broadcast sound.The scientific study of human soundperception is known aspsychoacoustics.
Sound is a sequence ofwaves of pressure thatpropagates throughcompressible mediasuch as air or water.(Sound can propagatethrough solids as well,but there are additionalmodes of propagation).During propagation,waves can be reflected,refracted, or attenuatedby the medium.
Wavelength: The distance between any point on awave and the equivalent point on the next phase.Literally, the length of the wave.
Amplitude: The strength or power of a wave signal.The "height" of a wave when viewed as a graph.Higher amplitudes are interpreted as a highervolume, hence the name "amplifier" for a device whichincreases amplitude.
Frequency: The number of times the wavelengthoccurs in one second. Measured in kilohertz (Khz), orcycles per second. The faster the sound sourcevibrates, the higher the frequency.Higher frequencies are interpreted as a higher pitch. Forexample, when you sing in a high-pitched voice you areforcing your vocal chords to vibrate quickly.
Sound travels at 330 meters per second or 740 miles per hour.Sound travels the fastest through solids and the slowest throughgases. The faster an object vibrates the higher the frequency, whichcauses the pitch of the sound to be higher. The higher the frequencysounds come from shorter wavelengths. A wavelength is one aspectof a sound wave. A wavelength is the length of one cycle of sound.The period of a sound wave is the time taken for one wavelength topass a certain point before a new wave begins to pass by. Longerwavelengths have a lower pitch. The lowest tones that your ears canhear are about 16 vibrations per second, or 16 Hz. Amplitudespecifies the sounds loudness. A low amplitude will produce a softsound and a higher amplitude will produce a louder sound.14
The speed of a sound wave refersto how fast the disturbance or waveis passed from particle to particle.Since the speed of a wave isdefined as the distance which apoint on a wave travels per unit of S = 330 meter/secondstime, it is often expressed in units S = (330 X 60 X 60 X 3.3)/5280of meters/seconds (m/s). The S= 330M/s X 3.3ft./M X 3600sec/hrspeed of any wave depends upon X 1 mile/5280ft.the properties of the mediumthrough which the wave is traveling.The density of the medium willaffect the speed the wave will travelat. A sound wave will travel faster ina less dense material rather than ina more dense material. Theequation for the speed of sound isspeed = distance/time.
DURATIONThis is probably the qualitythat is simplest to relate to ameasureable quantity: theduration of a sound is thetime interval between itsbeginning and end points.Our hearing system iscapable of detecting anddistinguishing a very shortsound, even if it containsonly a few cycles of airpressure oscillation.
LOUDNESSAnother attribute of soundthat is easily quantified isloudness. It is related tothe amplitude of thepressure oscillation in asound wave. Ourperception extends oversuch a broad range ofamplitudes (with theperceptible limitsdepending on frequency)that we use a logarithmicscale.
Noise pollution is excessive, displeasinghuman, animal or machine-createdenvironmental noise that disrupts theactivity or balance of human or animal life.The word noise comes from the Latinword nauseas, meaning seasickness.The source of most outdoor noiseworldwide is mainly construction andtransportation systems, including motorvehicle noise, aircraft noise and railnoise.Poor urban planning may give riseto noise pollution, since side-by-sideindustrial and residential buildings canresult in noise pollution in the residentialarea.
Noise health effects are both health and behavioral innature. The unwanted sound is called noise. Thisunwanted sound can damage physiological andpsychological health. Noise pollution can cause annoyanceand aggression, hypertension, high stresslevels, tinnitus, hearing loss, sleep disturbances, and otherharmful effects. Furthermore, stress and hypertension arethe leading causes to health problems, whereas tinnituscan lead to forgetfulness, severe depression and at timespanic attacks.Chronic exposure to noise may cause noise-inducedhearing loss. Older males exposed to significantoccupational noise demonstrate significantly reducedhearing sensitivity than their non-exposed peers, thoughdifferences in hearing sensitivity decrease with time andthe two groups are indistinguishable by age 79. Acomparison of Maaban tribesmen, who were insignificantlyexposed to transportation or industrial noise, to a typicalU.S. population showed that chronic exposure tomoderately high levels of environmental noise contributesto hearing loss.
High noise levels cancontribute to cardiovasculareffects and exposure tomoderately high levels duringa single eight hour periodcauses a statistical rise inblood pressure of five to tenpoints and an increase instress and vasoconstrictionleading to the increased bloodpressure noted above as wellas to increased incidence ofcoronary artery disease.Noise pollution is also a causeof annoyance. A 2005 studyby Spanish researchers foundthat in urban areashouseholds are willing to payapproximately four Euros perdecibel per year for noise
Technology to mitigate or remove noise can beapplied as follows:There are a variety of strategies for mitigatingroadway noise including: use of noisebarriers, limitation of vehicle speeds, alterationof roadway surface texture, limitation of heavyvehicles, use of traffic controls that smoothvehicle flow to reduce braking andacceleration, and tire design. An important factorin applying these strategies is a computer modelfor roadway noise, that is capable of addressinglocal topography, meteorology, traffic operations The sound tube designed toand hypothetical mitigation. Costs of building-in reduce roadway noisemitigation can be modest, provided these without distracting from thesolutions are sought in the planning stage of a areas aesthetics.roadway project.