1. BASIC THEORY OF SOUNDSound is a vibration in an elastic medium such as air, water, buildingmaterials and earth. Sound energy progresses in atmospheric pressureand travel a great distance. Sound is the physicalphenomenon thatencourages the sense of hearing. It is generated by vibrated bodies in theform of waves of compression and rarefaction in the air. A full circuit by adisplaced particle is called a cycles. The time required for one completecycle is called period and the number of complete cycles per second is thefrequency of vibration. Wavelength of Sound: It is the distance a sound wave traveling during onecycle of vibration or wavelength is the distance between adjacent regions whereidentical conditions of particle displacement occur.

2. To fine the wavelength of sound in air at a specific frequency by the followingequation;=Where = wavelength in FeetF = frequency in Hz1130 = speed of sound feet per secondVelocity of Sound: The speed at which the sound travels is called as velocity ofsound. Velocity of sound primarily depends on the elasticity and density of themedium. In air, at normal temperature and atmospheric pressure the velocity ofsound is approximately 1130 feet per second. Sound may travel at 16,000 ft/s alongsteel pipes and duct walls. Speed of sound in concrete is about 12,000 ft/s. Some ofthe important points in sound velocity as follows;These sound waves can travel from source of origin by air in different directions and these sound waves set the ear drum to vibrate then the vibrating ear drum translates by the brain in to sound sensation of hearing. 3. In humans, hearing takes place whenever vibrations of frequencies from 15 hertzto about 20,000 hertz reach the inner ear. The hertz (Hz) is a unit of frequencyequaling one vibration or cycle per second. Sound has the following characters When the sound waves are periodic, regular and long continued, they producepleasing effect of sound and this sound is also called audible sound. When the sound waves are non-periodic, irregular and very short duration, itproduces displeasing effect of sound and this sound is also called audible noise. Sound waves are longitudinal waves and they can move backward and forwardalong a line in the direction of in which sound is traveling. The velocity of sound depends upon nature and temperature of medium throughwhich it travels. The velocity of sound can be measured by meter per second.See the velocity of sound through different medium given bellow. 4. Name of the medium Velocity of sound at 200C in m/sAtmospheric air343Hydrogen 1305Nitrogen 338Pure water 1450Brick4300Concrete 4000Granite6400Glass5000-6000Aluminum 5100Iron 4700-5100Copper 3900Brass3500Silver 2600Cork 450-530Rubber 40-150 5. Propagation of Sound: When sound is generated in a place, it can move orspread in all direction by air is called as propagation of sound. Sound canpropagate for origin to in all directions like a person blowing up a balloonwith his moth. See some of the sound propagation principles given bellow; The propagation of sound energy through a media via sound waves i.e. compressionand rarefaction of sound waves. The propagation of sound depends up on the frequency of sound source and thecapacity of listener ear drum. The propagation of sound depends up on the weather conditions like air temperature,presence of moisture, air velocity etc. The propagation of sound depends up on the topographical features like ground cover,hills and obstacles between the source and receivers, type of space like open orclosed. 6. Diffraction of Sound: The bending of sound waves due to obstacles calledas diffraction of sound. Sound diffraction causes decreasing of frequency,loudness, pitch ate. Example if you brought a concert ticket without lookingseating arrangement chart. When you enter inside the concert hall your seatwill be behind a huge pillar. After starting the film you cannot hear a clearvoice due to the obstacle in between you and the music source and becauseof this the sound wave can bent around the pillar before reaching you.Hearing Sensitivity: The ability of understanding or listening of sound is called assensitivity of hearing. The hearing of sound depends up on person eardrum, intensity ofsound, type of sound tone, distance between the source and the listener, climaticconditions. A healthy young person is capable of hearing sound form about 20Hz to20,000 Hz. The extent of hearing sensitivity for an individual depends on many factors likeage, sex, ethnicity (character of person), previous exposure to high noise level etc. 7. Physical Character of Sound: The physical characters sound as follows; Frequency Loudness or intensity Quality or timbre.Frequency or Pitch: It is the number of cycle or pressure vibrations produced by abody in unit of time. The greater the number of cycles or vibrations, the higher will bethe pitch. The grater the frequency higher the pitch and the lesser the frequency thelower the pitch. Frequency of sound is the measure of the quality of sound. Frequencyof sound can be measured in cycles per second or hertz (Hz). A healthy young personis capable for hearing sound energy from about 20 to 20000 Hz. 8. Loudness or Intensity: It is the flow of wave energy crossing per unittime through unit area. Sound intensities are measured in decibels (dB).For example, the intensity at the threshold of hearing is 0 dB, theintensity of whispering is typically about 10 dB. Sound intensities arearranged on a logarithmic scale due to a wide range of variations of theintensity of sound. Intensity of sound can be calculated by the followingequation; I=WhereI = sound intensity (w/m2 W = sound power (Watt) d = distance form sound source (m) 9. Quality or timber: It is the quality of musical note. It is one of the importantcharacters of the sound that allows the ear to differentiate between tones producedby different instruments when the sound waves are identical in aptitude andfrequency. Example if a person played a violin, second person played piano andthird person a tuning fork, all at the same volume, the tones are identical infrequency and amplitude, but different in quality. From these three sources, thesimplest tone is produced by the tuning fork; the soundBecause of the acoustical properties of the ear and the resonance properties of theears vibrating membrane, however, it is doubtful that a pure tone reaches the innerhearing mechanism in an unmodified form. The principal component of the noteproduced by the piano or violin also has a frequency of 440 Hz, but these notesalso contain components with frequencies that are exact multiples of 440, calledovertones, at 880, 1320, and 1760 Hz, for example. The exact intensity of theseother components, which are called harmonics, determines the quality, or timbre, ofthe note. 10. Amplitude or Volume: Amplitude is the characteristic of sound waves thathumans perceive as volume. The amplitude corresponds to the distance that airmolecules move back and forth as a sound wave passes through them. As theamount of motion in the molecules is increased, they strike the ear drum withprogressively greater force. This causes the ear to perceive a louder sound. Thiscomparison of samples at low, medium, and high amplitudes demonstrates thechange in sound caused by altering amplitude. These three waves have the samefrequency, and so should sound the same except for a perceptible volumedifference.Measurement of sound: Generally sound can measure in terms of pressure levelor decibel (dB) and it is used as convent unit to measure the magnitude of sound.By measuring the sound, we can achieve following objects;Sound measurement can helps us to improving of building acoustics and loud speakers and thusimprove our enjoyment of music both in concert hall and home;Sound measurement can indicates when sound may causes hearing damage and it helps in takingcorrective measures to be avoiding damage; 11. It permits evaluation of the hearing sensitivity of individuals; It permits the improvement of quality of our daily lives.