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basic info about sound for architecture

basic info about sound for architecture

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Part 1 Part 1 Presentation Transcript

  • Unit -2Introduction and theory of soundAcoustics – definitions, terms related to acoustics.Theory of sound : generation, propagation, transmission, reception ofsound, sound waves, frequency, intensity, wavelength, sound pressure,measurement of sound, scales- decibel scale ,• Characteristics of speech• Music and hearing• Distribution of energy in speech• Music frequencies• Intelligibility of speech, high fidelity reproduction of music• Human ear characteristics- making of sound• Binomial hearing g• Behavior of sound in enclosed spaces. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • INTRODUCTIONAND THEORY OF SOUND STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• What is Acoustics ? – Acoustics is defined as the science that deals with the production, production control, control transmission, reception, and effects of sound. – The physical principles of this science are utilized in architecture to attain distinct hearing conditions in enclosed spaces. p STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • • The study of acoustics helps to – To appreciate and analyse the problems involved in the propagation of sound in these enclosures. – To suggest ways and means of producing optimum conditions of hearing – To obtain both subjective and objective assessments j of the results achieved. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• What is resonance ?• resounding or reechoing• i increasing the intensity of sounds by sympathetic i th i t it f d b th ti vibration – Eg) Put two tuning forks of equal frequencies side by side, but not touching. Strike one tuning fork so that g g you can hear its tone, and then suddenly silence it. You can still hear a faint tone. This is because the second tuning fork g has started vibrating sympathetically. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• What is Reverberation? – It is the persistence of sound in a particular space after the original sound is removed. – A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air. – This is most noticeable when the sound source stops but the reflections continue, decreasing in amplitude, until they can no longer be heard. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• What is Reverberation time? – Standard reverberation time has been defined as the time for the sound to die away a a to a le el 60 decibels belo level below its original level. The reverberation time can be modeled to permit an approximate calculation. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• The reverberant sound in an auditorium dies away y with time as the sound energy is absorbed by multiple interactions with the surfaces of the room. In a more reflective room, it will take longer for the g sound to die away and the room is said to be live.• In a very absorbent room, the sound will die away room quickly and the room will be described as acoustically dead. But the time for reverberation to completely die away will depend upon how loud the sound was to begin with, and will also depend upon the acuity of the hearing of the observer STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • • What is echo? DEFINITIONS – In audio signal processing and acoustics acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. • Typical examples are the echo produced by the bottom of a well by a well, building, or by the walls of an enclosed room. A true echo is a single reflection g of the sound source. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • SOUND1. A sound is a vibration in an elastic medium, which may be y a solid, liquid, or gas, which can be registered by the ear.2. It can be pleasant or unpleasant, loud or soft, high or low. Sound is made b l S di d by vibrations, something moving back and forth. Stretch a rubber band tightly between your fingers, and pluck it. You can see it quiver and hear the sound it makes. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • CHARACTERISTICS OF SOUND WAVESSounds are generally audible tothe human ear if their frequency(number of vibrations per second)lies b tli between 20 and 20,000 d 20 000vibrations per second, but therange varies considerably with theindividual.The range of audible sound is also differentiated into 3main categories. Subsonic or low frequency sound isdefined in the range of 20Hz to about 500Hz.Midrange frequencies inhabit the realm of 500Hz to g q6KHz (6000Hz)With high frequency sound defined in the remaining6KHz to 20KHz 20KHz. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Those with frequencies above the audiblerange are called ultrasonic.A sound wave is usually representedgraphically by a wavy, horizontal line; theupper part of the wave (the crest) indicates a f h (h ) i dicondensation and the lower part (thetrough) indicates a rarefaction. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • GENERATION OF SOUND WAVES GENERATION OF SOUND WAVES Sound waves are generated by any vibrating body. For example, when a violin string vibrates upon b i i li i ib being bowed or plucked, its movement in one direction pushes the molecules of the air before it crowding them it, together in its path.When it moves back again past its original position and on to theother side, it leaves behind it a nearly empty space, i.e., a space withrelatively few molecules in it In the meantime however the molecules it. meantime, however,which were at first crowded together have transmitted some of theirenergy of motion to other molecules still farther on and are returningto fill again the space originally occupied and now left empty by the g p g y p py yretreating violin string. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • •In other words, the vibratory motion set up bythe i li t ith violin string causes alternately i a given lt t l in ispace a crowding together of the molecules ofair (a condensation) and a thinning out of themolecules (a rarefaction). STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • •Taken together a condensation and ararefaction make up a sound wave; such awave is called longitudinal, orcompressional, because the vibratorycompressionalmotion is forward and backward along thedirection that the wave is following.•Because such a wave travels by disturbingthe particles of a material medium, soundwaves cannot travel through a vacuum. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • THE PROPAGATION OF SOUND1. Sound is propagated in air, much like blowing up a large balloon, balloon which expands equally in all directions. For sound to be generated and heard it must g have a source, a medium through which to pass and a receiver.2.2 Propagation means "movement movement through“ Sound will propagate through air and water. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • All media have three properties which affect thebehavior of sound propagation: A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the i f i i medium. The motion of the medium itself, e.g., wind. Independent of the motion of sound through the medium, medium if the medium is moving, the sound is moving further transported. The viscosity of the medium. This determines Th i i f h di Thi d i the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • TRANSMISSION OF SOUNDTRANSMISSION OF SOUNDThere are three requirements forsound to "occur" in an environment: (1) A vibrating source to initiatesound,sound (2) A medium to transmit soundvibrations throughout theenvironment and (3) A receiver to hear or record soundvibrations.Sound is initiated in an environmentby a vibrating source. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Water is a more efficient transmitter of sound compared toair as sound travels faster and further in water.The movement of the gas or liquid medium is identical tosurface waves found on any large body of water water.The wavelengths of speech are of the size of ordinaryobjects, unlike light, whose wavelengths are extremely small.Because of this, sound does not ordinarily cast "acousticshadowsshadows" but, because its wavelengths are so large, can betransmitted around ordinary objects STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  •  For example, if a light is shining on a person, and abook is placed directly between them, the person will themno longer be able to see the light (a shadow is cast bythe book on the eyes of the observer).However, if one person is speaking to another, thenpplacing a book between them will hardly affect the g ysounds heard at all; the sound waves are able to goaround the book to the observers ears.On the other hand, placing a high wall between ahighway and houses can greatly decrease the sounds ofthe traffic noises if the dimensions of the wall (height h ffi i h di i f h ll (h i hand length) are large compared with the wavelength ofthe traffic sounds.  STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • RECEPTION OF SOUND – HEARING MECHANISMS - HUMAN EAR CHARACTERISTICS- MAKING OF SOUND Th ear consists of three basic The i t f th b i parts The outer ear serves to collect and channel sound to the middle ear. The middle ear serves to transform the energy of a sound wave into the internal vibrations of the bone structure of the middle ear and ultimately transform these vibrations into a compression wave in the inner ear. The inner ear serves to transform the energy of a compression wave within the inner ear fluid into nerve impulses that can be transmitted to the brain. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Sound waves enter your outer ear andtravel through your ear canal to themiddle ear.The ear canal channels the waves toyyour eardrum, a thin, sensitive membranestretched tightly over the entrance to yourmiddle ear. The waves cause your eardrumto vibrate. It passes these vibrations on to thehammer, one of three tiny bones in your  Inside the cochlea,ear. The hammer vibrating causes the there are hundreds ofanvil,anvil the small bone touching the special cells attached tohammer, to vibrate. nerve fibers, which canThe anvil passes these vibrations to the transmit information tostirrup,stirrup another small bone which touches the brain. The brain processesthe anvil. From the stirrup, the vibrations the information from thepass into the inner ear. ear and lets usThe stirrup touches a liquid filled sack p q distinguish betweenand the vibrations travel into the cochlea, different types ofwhich is shaped like a shell. sounds. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Monaural and Binaural hearing • Monaural‐ Hearing with one ear• Binaural‐Hearing with both the ears.In open air as well as in enclosures, the hearing is direct andbinaural (i.e.with both the ears). This helps to localize sound andobtain a correct idea of the sound perspective.Binaural hearing could be easily compared to binocular vision. Justas an observer gets an impression of direction and distance or depthwith two eyes, similarly his two ears enable him to appreciate thedirection of sound and to a certain extent, the distance of sound aswell.It is quite easy to imagine how the two ears enable him to see thedirection of sound which is primarily due to the difference in theintensity of the two sounds reaching the two ears It is the depth or ears.the perspective of sound. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • It may be observed that the reflected sound varies much weakenedin intensity as the recede from the speaker Consequently the ratio of speaker.direct to the reflected sound varies considerably.It is for this reason that as we go farther from the speaker the directsound is weakened while the reflected or reverberant soundbecomes more and more noticeable. It is this factor which permitsbinaural hearing to appreciate distance or depth. It is not difficult to appreciate how monaural hearing causes loss ofdirection. It is common experience to observe that the two earsenable the person consciously to suppress sounds coming from onedirection and to concentrate on desired sound from a given direction.Single ear is unable to do this and consequently the noises and thereverberation present in the room or apparently increased. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Behavior of sound in enclosed places Behavior of sound in enclosed places STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Behavior of sound in enclosed places  Behavior of sound in enclosed places1. Sound is absorbed in the  5. Sound is emitted by the  y air also appreciable to  resonance of the wall in  reflected sound. both directions.2. Sound in reflected at the 2 S di fl t d t th 6. Sound is inter‐reflected  6 S di i t fl t d wall surface. between bounding surface 3. Sound is absorbed from  setting at reverberation. the wall surface or its  7. Resonance of the enclosed  surface finished. volume of air by direct cross 4. Sound is conducted by the 4 S di d db h reflection.  reflection wall to other part of the  surface. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • CHARACTERISTICS OF SPEECH• Any audible sound has three important characteristics 1. Frequency(Pitch) 2. 2 Loudness 3. Tonal quality STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• What is Frequency? q y• The number of cycles per unit of time is called the frequency. For convenience, frequency is most often measured in cycles per second ( ) or th i t h d (cps) the interchangeable H t (H ) (60 cps = 60 H ) bl Hertz (Hz) Hz), named after the 19th physicist. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Characteristics of speech Frequency(Pitch) It is independent of intensity of loudness of sound. Pitch is a psychological phenomenon determined by frequency of a sound wave whereas frequency is a physical quantity and can be measured . Sound is called a pure tone when it consists a single frequency and when two or more frequencies are present it is called a complex tone. Pure tone complex tone STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Characteristics of speech  Characteristics of speechLoudness:– Loudness is a physiological effect of sensation produced  through the ear and depends on the intensity of sound  or amount of energy present in sound waves while  or amount of energy present in sound waves while entering it. – In oat , Loudness falls down as distance increases “Loudness is inversely proportional the the square of the distance from source “(Not applicable for semi closed enclosures) STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Tonal quality or timbreTimbre is a general term for the distinguishablecharacteristics of a tone. Timbre is mainly determinedby the harmonic content of a sound. timbre is what makes a particular musical sounddifferent from another, even when they have thesame pitch and loudness. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• What is wavelength? g• The wavelength of sound is the distance between analogous p points of two successive waves. λ = c / fwhereλ = wavelength (m)c = speed of sound (m/s)f = frequency  STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • • Sound Intensity. – The sound intensity in a specified direction is the  DEFINITIONS amount of sound energy flowing through a unit  area normal to that direction. The sound intensity  is normally measured in watt per square metre is normally measured in watt per square metre (W/m2). – The scale for measuring intensity is the decibel  scale. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • DEFINITIONS• Sound pressure p Sound pressure or acoustic pressure is  the local pressure deviation from the ambient  (average, or equilibrium) atmospheric pressure  (average or equilibrium) atmospheric pressure caused by a sound wave.  Sound pressure can be measured using  Sound pressure can be measured using a microphone in air and a hydrophone in water.  The SI unit for sound pressure p is the Pascal. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • HIGH FIDELITY REPRODUCTION OF MUSICHigh fidelity—or hi‐fi—reproduction is a term used by home stereo listeners and h db h li d home audio enthusiasts (audiophiles) to refer to high‐quality reproduction of sound [ or i li d i f d images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment.  d db i i di iIdeally, high‐fidelity equipment has minimal Id ll hi h fid li i h i i lamounts of noise and distortion and an accurate f t frequency response. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • Frequency RangesFrequency Ranges STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • THRESHOLD OF AUDIBILITYThe threshold of audibility at any specified frequency isthe minimum value of sound pressure of a pure tone ofthat frequency which is just audible The term is used forcomplex waves such as speech and music . It ismeasures in dynes per sq cm ( dynes – cgs‐force) cm.THRESHOLD OF FEELINGSound pressure that can cause discomfort and pain. It issituated around 120 dB above the threshold of hearing. It ismeasures in dynes per sq cm and also in watts per sq cm. STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA
  • PHONA unit of apparent loudness equal in number to the loudness,intensity in decibels of a 1,000‐hertz tone perceived tobe as loud as the sound being measured.EFFECT OF REVEBRATION ON HEARINGThe hang over effect of one syllable on the next g ydistorts the speech by blending the end of the firstwith the beginning of the second so as to mask thesecond syllable completely. Th d ll bl l t l The reverberation b ticharacteristics may give an effect of frequencydistortion because of reverberation time beingdifferent for various frequencies. The effect of both willdepend upon position of the observer . STUDY OF SOUND ‐ ACOUSTICS                                      HANDLED BY G.YOGAPRIYA