Acoustics is a branch of physics that study the sound, acoustics concerned with the production, control, transmission, reception, and effects of sound. The study of acoustics has been fundamental to manydevelopments in the arts, science, technology, music, biology,etc
Sound• Sound is reflected, transmitted, or absorbed by the materials it encounters.• Soft surfaces, such as textiles, and bat insulation, tend to absorb sound waves, preventing them from further motion.• Hard surfaces, such as ceramic tile, gypsum board, or wood, tend to reflect sound waves, causing „echo‟. Reverberation is the term used to describe sound waves that are reflected off of surfaces.• Dense, massive, materials, such as concrete or brick, tend to transmit sound waves through the material.• High frequency sound waves (think of a high whistle) are not capable of being transmitted through massive, heavy, material.• Low frequency sound waves (bass) are transmitted through massive materials.
The human ear is capable of hearing sounds within a limited range.
Hearing range of some animals• Many animals hear a much wider range of frequencies than human beings do.• For example, dog whistles vibrate at a higher frequency than the human ear can detect, while evidence suggests that dolphins and whales communicate at frequencies beyond human hearing (ultrasound).• Frequency is measured in hertz, or the number of sound waves a vibrating object gives off per second. The more the object vibrates, the higher the frequency and the higher the pitch of the resulting sound.
Decibel levels• 0 The softest sound a person can hear with normal hearing• 10 normal breathing• 20 whispering at 5 feet• 30 soft whisper• 50 rainfall• 60 normal conversation• 110 shouting in ear• 120 thunder
Decibel levels• The human ears response to sound level is roughly logarithmic (based on powers of 10), and the dB scale reflects that fact.•• An increase of 3dB doubles the sound intensity but a 10dB increase is required before a sound is perceived to be twice as loud.• Therefore a small increase in decibels represents a large increase in intensity.• For example - 10dB is 10 times more intense than 1dB, while 20dB is 100 times more intense than 1dB.• The sound intensity multiplies by 10 with every 10dB increase.
Decibel levels• 130dB - Jack Hammer (at 5ft) • 120dB - Rock Concert / Pain threshold • 110dB - Riveter or a Heavy Truck at 50ft • 90dB - Heavy Traffic (at 5ft) • 70dB - Department Store or a Noisy Office • 50dB - Light Traffic • 30dB - Quiet Auditorium • 20dB - Faint Whisper (at 5ft) • 10dB - Soundproof room / anechoic chamber
An anechoic chamber is a space in which there are no echoes or reverberations.The surfaces absorb all sound, and reflect none.
Acoustics: sound• Sound is a mechanical wave and therefore requires a medium in which it can travel.• Acoustics is classically divided into sound and vibration.• Sound refers to waveforms traveling through a fluid medium such as air• Vibration describes energy transmitted through denser materials such as wood, steel, stone, dirt, drywall or anything besides a fluid.• It is not heard as much as felt, due to its extremely low frequency, which is below the range of most human hearing.
The speed of sound versus the speed of light• sound travels at 1130 feet per second at normal room temperature.• light travels at 299,792,458 meters per second, which is roughly 974,325,489 feet per second (974 million feet per second!!)
Radio signals: am & fm• „am‟ means: amplitude modulation: the height of each wave changes• „fm‟ means: frequency modulation: the length of each wave changes• FM signals have a great advantage over AM signals.• Both signals are susceptible to slight changes in amplitude.• With an AM broadcast, these changes result in static. With an FM broadcast, slight changes in amplitude dont matter -- since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude. The result: no static at all.
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Fabric wrapped panels provide good acoustical absorption
Reverberation Time• Reverberation time refers to the amount of time required for the sound field in a space to decay 60dB, or to one millionth of the original power.• In simple terms this refers to the amount of time it takes for sound energy to bounce around a room before being absorbed by the materials and air
Reverberation Time• Reverberation time is important because it can affect how well you understand speech, and it can change the way music sounds.• The effect on speech intelligibility is noticeable in a gymnasium or arena, where you often cant understand someone who is only 10 or 15 feet away from you
Useful Reflections• Reflections are an important part of acoustical design for music performance venues.• For effective musical acoustics, the reflections have to arrive within the correct time window, and from the correct direction.
Useful Reflections• The reflections help to boost the level of acoustic instruments and human voices in the audience area.• They also influence timbre and help define the apparent size or perspective of the instruments.• The critical time interval were talking about is a very brief 0.3 seconds
Useful Reflections• A properly designed acoustical environment provides a good listening experience for the audience by enhancing the performance or presentation.• Even and natural sound coverage, freedom from intruding noise and a sense of presence from the performer or presenter are all-important aspects of "good acoustics.“• Acoustics should be considered very early in the design process and the aesthetic concept developed in accordance with those requirements
Focusing of Sound Occurs with use of parabolic surfaces either behind performers or at rear of auditorium
EchoesHighly reflective flat or parabolic wall shapes Flutter echoes from parallel walls Standing waves between parallel walls
Resonances Parallel wallsRectangular practice rooms Singing in the shower
External noiseBox within a box constructionPractice rooms and concert halls in adjacent areas
Double-valued TRPlayback room with reverberation Concert halls with side areas
Architectural acoustics is the science of controlling sound inbuildings. Embraces all aspects of acoustical design for all types ofarchitectural spaces, in order to optimize environments for many functions,including business, recreation, learning, worship, communication,broadcasting and entertainment. The first application of architectural acoustics was in the design of : •Opera houses •Concert halls •Auditoriums •Radio and television studios •Classrooms, etc.
Aula Magna, in“Universidad Central deVenezuela” it was design by Carlos Raul VillanuevaIn the 80´s this concert hallwas catalogued like one ofthe 5 rooms with betteracoustics of the world.
All the details, materials, forms, elements and the designwere choose for create a good acustical in the space. For this, Villanueva asked help from some Acusticalconsultans: “Bolt, Beranek and Newman Inc”. The selection oftypes of wood, the model of the armchairs and services werecarefully chosen.
Even the fabric of the carpet (casimire) wasselected to contribute with the acusticals properties. The tapestry in Aula Magna has absorptioncapacity, when the room is empty does not distort thesound. The material of the doors, and some elementsubicated in the hall are design to prevent the echo andnoise.
The distinguished element of this famous hall, are their clouds also called flying subjects. This elements were not in the original design, but structure of the hall didn´t For that reason, allow a good acoutic. Villanueva asked help from Alexander Calder who was the designer of this clouds. The clouds moved toadapt to the acousticalrequirement, then were fixed in
Building Acoustics: Room for Music “the most visible and interesting spaces in architectural acoustics”-It is here that the science of acoustics and the arts of architecture and music are blended
Building Acoustics: Room for Music- The acoustician can only work indirectly with the room surfaces that reflect, diffuse, or absorb the primal energy
Building Acoustics: Room for Music*Concert halls are rooms designed specifically formusic in which the musicians and the audienceoccupy the same space.*In good concert halls the number of seats ranges from1700 to 2600, with the best halls averaging around1850.*Above 2600 seats, the chances of success are muchreduced and the preferred capacity is between 1750and 2200.
Building Acoustics: Room for MusicThere is no division between the stage and theaudience in a concert hall.The orchestra is positioned on a raised platform,sometimes with an organ and choir seating behind it.To attain long reverberation times, the ceilings ofconcert halls are high, 15m(50 ft) or more, anddiffusive, with coffered patterns having deep (15cm or 6 in) fissures.Side walls are adorned with columns, caryatids,statuary, and convex shapes that help diffuse thereflected energy.
Building Acoustics: Room for MusicAn opera house is a mix of a legitimate theatre and aconcert hall, which constrains the design more than apure concert hall.In opera, the stage performance rather than the orchestrais the main attractionThe orchestra is seated in a pit below the stage tobalance the level between the singer and the orchestra.The conductor, who must be visible to both the orchestraand the vocalists, stands with his head just at stage level.Open pits, where the orchestra is open to the audiencewith minimal stage overhang, give the best results in largerooms
Building Acoustics: Room for MusicGENERAL DESIGN PARAMETERSThe audience should feel enveloped or surroundedby the soundSound must have adequate loudness that is evenlydistributed throughout the hall.Noise from exterior sources and mechanicalequipment must be controlled so that the quietestinstrumental sound can be heard
Building Acoustics: Room for MusicHeavy plaster is the most commonly encountered walland ceiling materialPlaster may also be applied directly onto groutedconcrete block or concrete When wood is used it should be heavy, at least 1”(25 mm) thick, and be backed with a solid masonryor concrete. Wood can be glued directly to concrete block or concrete walls or applied on furring strips Floors are constructed of concrete or wood on concrete
The nature of soundSound, a manifestation of vibration, travels in wave patterns throughsolids, liquids and gases.The waves, caused by vibration of the molecules, follow sine functions,typified by the amplitude and wavelength (or frequency) Sound waves of equal amplitude with increasing frequency from top to bottom
How sound is measured•Pressure, P, usually Pascals•Frequency, f, usually Hertz P = 1/f•Intensity, I, usually W/m2 I = W/A•Bels, L’, derived from logarithmic ratio L’ = log (Q/Qo)•Decibels, L, derived from bels L = 10*log (Q/Qo) E.g. Implications of the decibel scale: doubling sound level would mean that the sound will increase by 10*log2 = +3dB Ten times the sound level = 10*log10 = +10dB
Reflecting on noise “Noise" derived from "nausea," meaning seasickness Noise is among the most pervasive pollutants today Noise is unavoidable for many machines We experience noise in a number of ways environmental cause and victim generated by others “second-hand” Noise negatively affects human health and well-being The air into which second-hand noise is emitted andon which it travels is a "commons“, a public good
Noise regulationNoise regulation includes statutes or guidelines relating tosound transmission established by national, state orprovincial and municipal levels of government. After awatershed passage of the U.S. Noise Control Act of1972, the program was abandoned at the federal level,under President Ronald Reagan, in 1981 and the issue wasleft to local and state governments. Although the UK andJapan enacted national laws in 1960 and 1967 respectively,these laws were not at all comprehensive or fullyenforceable as to address (a) generally rising ambient noise(b) enforceable numerical source limits on aircraft andmotor vehicles or (c) comprehensive directives to localgovernment.
Local noise regulation Dr. Paul Herman wrote the first comprehensive noise codes in 1975 for Portland, Oregon with funding from the EPA (Environmental Protection Agency) and HUD (Housing and Urban Development). The Portland Noise Code became the basis for most other ordinances for major U.S. and Canadian metropolitan regions. Most city ordinances prohibit sound above a threshold intensity from trespassing over property line at night, typically between 10 p.m. and 6 a.m., and during the day restricts it to a higher sound level; however, enforcement is uneven. Many municipalities do not follow up on complaints. Even where a municipality has an enforcement office, it may only be willing to issue warnings, since taking offenders to court is expensive. The notable exception to this rule is the City of Portland Oregon which has instituted an aggressive protection for its citizens with fines reaching as high at $5000 per infraction, with the ability to cite a responsible noise violator multiple times in a single day. Many conflicts over noise pollution are handled by negotiation between the emitter and the receiver. Escalation procedures vary by country, and may include action in conjunction with local authorities, in particular the police. Noise pollution often persists because only five to ten percent of people affected by noise will lodge a formal complaint. Many people are not aware of their legal right to quiet and do not know how to register a complaint
Power ratio and dBhttp://www.phys.unsw.edu.au/jw/dB.html
Sound and human hearingPeople generally hear soundsbetween the “threshold of hearing”and the “threshold of pain”In terms of pressure,this is 20 μPa – 100 PaThe decibel scale was developed from this factand makes numbers more manageableThe decibel scale generally ranges fromapproximately 0 to 130
Human hearing and Frequency0 16 Hz 20 kHz 5 MHz
Sound and human hearing – Frequency Humans are less sensitive to low frequency sound and more sensitive to high frequency sound. Therefore, sometimes the dB scale is adjusted to take this into account: A-weighting (db(A)): adjusts overall scale so it better matches what the human ear would hear C-weighting (dB(C)): adjusts scale for loud or low frequency sounds B-weighting (dB(B)): adjusts by factors that are “in between” the A-weighted factors and C- weighted factors (rarely used)
The filters used for dBA and dBC The most widely used sound level filter is the A scale, which roughly corresponds to the inverse of the 40 dB (at 1 kHz) equal-loudness curve. The sound level meter is thus less sensitive to very high and very low frequencies. Measurements made on this scale are expressed as dBA. The C scale (in dBC) is practically linear over several octaves and is thus suitable for subjective measurements only for very high sound levels.
Loudness in phonsThe phon is related to dB by the psychophysically measuredfrequency response. Phons = dB at 1 kHz. For other frequencies,the phon scale is determined by loudness experience by humans.
Loudness in sonesThe sone is derived from psychophysical tests wherehumans judge sounds to be twice as loud. This relatesperceived loudness to phons. A sone is 40 phons. A10 dB increase in sound level corresponds to a perceiveddoubling of loudness. So that approximation is used in thedefinition of the phon: 0.5 sone = 30 phon, 1 sone =40 phon, 2 sone = 50 phon, 4 sone = 60 phon, etc.
Other descriptors of soundEquivalent sound level – the level of sound that hasthe same acoustical energy as does a time-varyingsound over a stated time period.Percentile sound level – the sound level exceeded “n”percent of the observation time interval.Day-night average sound level – the equivalent soundlevel for a 24-h period that incorporates a decibelpenalty during night hours.
Major transportation sources ofnoise pollution: rail, road, and air
Rail Noise: A Case StudyThe city of Ames, Iowa, began operation of threeautomated horn warning systems (AHS) in Septemberof 1998. These systems were installed after nearbyresidents repeatedly expressed concerns over thedisturbance created by the loud train horns.The automated horn system provides a similar audiblewarning to motorists and pedestrians by using twostationary horns mounted at the crossing. Each horndirects its sound toward the approaching roadway. Thehorn system is activated using the same track signalcircuitry as the gate arms and bells located at thecrossing.
Roadway Noise• An example of a “line source” of noisepollution (as opposed to a “point source”)• Level of noise is a function of volume,type of vehicle, and speed
Roadway Noise - Solutions• Regulations limit the amount of noisesome vehicles can produce• Some regulations require vehicles to beproperly operated and maintained• Despite regulations, the noise levels areusually only reduced by 5 to 10 dBA
Aesthetic noise barrier:Highway in Melbourne, Australia
Roadway Noise - SolutionsPavement typeCertain asphalts, such as those containingrubber or stone, can be less noisy than otherpavements.However, some studies have shown thereduction in noise is only a few decibels, notenough to be significant.More research is needed before pavementtype can be an effective noise-reducingtechnique
Airport NoiseNoise contours aroundan airport calculatedusing INM (IntegratedNoise Modeling) basedon previous noisemeasurements55 - 60 dB = Light blue60 - 70 dB = Dark blue70 - 75 dB = Red75 - 80 dB = Green80 - 85 dB = Yellow> 85 dB = Pink