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R22-2025 Unit 3 architectural acoustics.pptx
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- 2. Noise Noise is derivedfrom the Latin word “nausea” implying ‘unwanted sound’ or ‘sound that is loud, unpleasant or unexpected’. Any unwanted noise arising in the environment, which has adverse effects on the health of the organism, is noise pollution Inter-related Elements of Noise A noise problem generally consists of three inter-related elements- • the source, • the transmission path and • the receiver.
- 3. Inter-related Elements ofNoise The source can be one or any number of mechanical devices that radiate noise or vibratory energy such as appliances or machines. The transmission path is the way by which noise travels between the source and the receiver. • The path is usually the atmosphere through which the sound is propagated, but can include the structural materials of any building containing the receiver. • Depending on this, noises can be classified as airborne noise or structure borne noise. • Noise can travel from one point to another via any one path or a combination of several paths. The receiver can be a single person/worker or a group of people.
- 4. Types of Noise Dependingon location of source, noise might be of two types: a) Outdoor Noise. Following are some common sources of outdoor noise: i) Traffic noise generated from air traffic, road traffic, rail traffic etc. ii) Noise from zones and buildings within built-up areas, machinery, appliances, construction activity, loudspeakers, people, animals etc. b) Indoor Noise. Following are some common source of indoor noise: i) Household appliances, machinery, footsteps on floor, air conditioner duct etc. ii) Activities performed by occupants, like people, pets etc.
- 5. Types of Noise Basingon transmission path, noise can be classified as a) Airborne Noise Example: Noise from appliances, car horn, telephone ring etc. b) Structure-borne Noise Example: Footsteps, slamming of door, furniture movement, vibrating mechanical equipment's etc.
- 6. Types of Noise Dependingon source of origin and human interventions: 1) Natural 2) Anthropogenic Sources. Natural Sources Although Nature itself is not considered to be a creator of noise pollution, however living organisms such as insects, birds, animals can create excessive noise which causes negative reactions in people and animals in that environment. The chirping of rickets, Cicada and other bugs are examples of insects that can create a lot of noise. Natural calamities such as thundering and lightening of clouds, strong winds and storms can block out all other noise and affect the people mentally and psychologically.
- 7. Types of Noise AnthropogenicSources All the manmade activities which produces noise are termed as Anthropogenic sources of noise pollution. The broad categories of anthropogenic sources are • Transportation (Road traffic, Railways, Aircraft, Vessels), • Industries, • Construction activities, • Commercial places, • Social Events, • Public address system etc.
- 8. Effects of Noiseon Human Behaviour Noise has profound effects on human behavior, influencing everything from communication and productivity to health and emotional well-being. Negative effects of noise on human behavior 1. Physiological stress 2. Cognitive impairment 3. Annoyance and irritability 4. Sleep disturbance 5. Communication interference
- 9. Noise Curves Standard methodologiesfor quantifying noise have been developed. Different rooms, locations, regulations and applications may allow individual acceptable noise ratings. In most cases, the goal is that background noise should not interfere with the purpose of the room, e.g. the noise of an office air-conditioning system should not interfere with telephone calls or conversations. Noise curves are graphical and standardized tools that help assess background noise levels in enclosed spaces by plotting the measured sound pressure levels at different frequencies against a reference curve Common Types of Noise Curves Noise Criterion (NC) curves: Widely used for evaluating noise in offices, residential areas, and other buildings. Noise Rating (NR) curves: Another common system that provides a single number rating based on frequency content. single NR number represents the overall noise level, with higher numbers indicating a louder environment Room Criteria (RC) curves: A system also used for assessing noise levels in rooms.
- 10. NC levels are calculatedby measuring sound pressure across different octave bands and plotting the results on an NC curve chart Noise Rating Curves Room Criteria Curves
- 11. Basic Principles ofNoise Reduction A straightforward approach is to examine the problem in terms of its three basic elements: 1. sound arises from a source, 2. travels over a path, and 3. affects a receiver, or listener. SOURCE-PATH-RECEIVER CONCEPT 1. The source may be one or any number of mechanical devices radiating noise or vibratory energy, such as several appliances or machines in operation at a given time in a home or office. 2. The most obvious transmission path by which noise travels is simply a direct line-of-sight air path between the source and the listener; for example, aircraft flyover noise reaches an observer on the ground by the direct line-of-sight air path. Noise also travels along structural paths. In most cases it travels from one point to another via any one or a combination of several such paths.
- 12. SOURCE-PATH-RECEIVER CONCEPT 3. Thereceiver may be a single person, a classroom of students, or a suburban community near an airport or expressway. Solution of a given noise problem might require alteration or modification of any or all of these three basic elements: (1) modifying the source to reduce its noise output, (2) altering or controlling the transmission path and the environment to reduce the noise level reaching the listener, and (3) providing the receiver personal protective equipment.
- 13. Noise Control atthe Source 1. Select quite equipment: • The preferable features are "slower" and "lower," particularly as they apply to the operation of the equipment • The speed of moving parts, flow velocities, gas or fluid pressure differentials, and power ratings all affect noise output. • For example, large slow-speed fans are substantially quieter than small high-speed fans for a given air flow; low horsepower motors are less noisy than those with high horsepower ratings; likewise low-pressure, low-velocity air ventilation or fluid distribution systems are virtually noiseless compared with their high-pressure high-velocity counterparts. • Low impact load, lower speed in machines and lower pressures in fluid systems, balanced rotating parts, low frictional resistance, isolate vibrating parts, reduce vibrating area etc.
- 14. Noise Control duringtransmission To understand the noise transmission it is important to identify the location of source. Thus, depending on the location of the source we have outdoor and indoor noise. Outdoor Noise • Industrial • Loudspeaker • Construction work • Road Traffic • Trains • Air crafts • Radios and microphones • Machineries and equipment's Outdoor/Environmental noise is the summary of noise pollution from outside, caused by transport, industrial and recreational activities.
- 15. Outdoor Sound Propagation Outdoorsound propagation in architectural acoustics differs significantly from indoor acoustics because sound travels freely and interacts with a dynamic environment rather than being contained by a rigid box.
- 16. Factors influencing SoundPropagation Atmospheric conditions: Wind: Sound traveling with the wind is bent downward towards the ground, increasing audibility. Against the wind, sound is refracted upward, creating a "shadow zone" where it is less audible. Temperature gradients: Normal daytime conditions, where air is warmer near the ground, bend sound waves upward. At night, a temperature inversion (cooler ground, warmer air above) refracts sound downward, which is why distant sounds are often heard more clearly at night. Humidity: Higher humidity and temperature can increase atmospheric absorption, especially at higher frequencies. Topography and terrain: Natural features can act as barriers or reflectors. Valleys may trap and amplify sound, while hills can block it. Ground surfaces also play a role, with soft, porous ground (e.g., thick grass) absorbing more sound energy than hard, reflective surfaces like asphalt or concrete. Obstacles and vegetation: Buildings, walls, and dense vegetation cause reflection, diffraction, and absorption. Dense foliage can effectively reduce noise, while reflective facades can increase reverberation and sound levels in urban spaces. Diffraction: Sound waves bend around obstacles. This is more pronounced for low frequencies, which have longer wavelengths, allowing them to pass over barriers more easily than high frequencies.
- 17. Outdoor Noise Control Outdoornoise control uses sound absorption, sound deflection, and sound masking. Architectural acoustics strategies for outdoor spaces either focus on Enhancing desired sounds and Controlling unwanted noise Building placement and orientation: Arranging buildings to block noise paths from highways or airports can create quieter courtyards and residential areas. Acoustic barriers: Solid barriers placed near a noise source or receiver are effective at blocking sound, especially high frequencies. For maximum effect, a barrier should be high enough to break the line of sight. Facade design: The shape and material of building facades can be optimized. Textured or fragmented surfaces scatter sound instead of reflecting it specularly, while balconies and other protrusions can reduce reflections. Vegetation: Dense, layered vegetation can be a natural sound absorber, contributing to a quieter environment. Absorptive materials: Integrating sound-absorbing materials into outdoor structures can help reduce echoes and reflections.
- 18. Building Placement andOrientation Courtyards can be sources of considerable noise. The buildings shown above have a central courtyard enclosed by parallel walls. The hard-surfaced parallel walls cause flutter echoes which intensify the noise in the courtyard. By angling or staggering the buildings, noise build-up can be reduced.
- 19. Building Placement andOrientation Courtyards directly facing streets can confine vehicular noise between reflective surfaces, causing build-up of sound energy. The preferred orientations, locate courtyards so they will be shielded by facing away from traffic noise. Sound levels at the sides of the buildings can be 3 dB lower than at the front; sound levels at the rear can be 10 dB or lower. Consequently, openings and sensitive areas should be located on sides which will be shielded from noise sources.
- 20. Acoustic Barriers Outdoor barrierscan be used to reduce the environmental noises, especially high – frequency sound energy such as tire “whine” from cars and trucks.
- 21. Noise Barriers They canbe some objection, object which is protecting the propagation or preventing the propagation of sound from the source to the receiver. It does direct reflections, it also scatters the sound, it depends on the surface treatment and the edge finish there are something called edge diffraction's which will happen. Instead of the straight path part of it is get reflected, part of it gets of the barrier because of diffraction and some of it gets diffracted back. So, typically develop a something called shadow zone within which the barrier is effective. Shorter the barrier the shadow zone will be much lesser as the barrier height increases the shadow zone will be more. 1.Place barrier as close as possible to either the source of sound or receiver. 2.The greater the height of the barrier above the direct path from source to receiver, called the acoustical line of sight, the greater the attenuation.
- 22. Façade design –Self Protecting Built Form A self-protecting building has external elements which act as barrier screens by interrupting the acoustical line of sight to nearby noise sources. This feature can protect acoustically weaker elements such as windows and doors. Examples of self-protecting atriums, recessed floors, and podium bases are shown below. Be careful when designing wide podium bases because they can restrict access to upper floors for fire- fighting and rescue operations.
- 23. Façade design –Balconies and Overhangs Balconies and overhangs can be used to isolate buildings from surface transportation noise. Isolation can be improved if the underside of the overhang is treated with sound-absorbing material. Balconies with solid railings should be used in front of windows. Open railings should be closed with weather-treated 112-in-thick plywood, 1/8-in-thick moulded polycarbonate, or glass. Solid balconies and overhangs with sound- absorbing treatment can reduce noise transmitted to interiors by 5 to 10 dB. Openings for ventilation should be in the shadow zone as close to the floor as possible. Barriers near the noise sources also can be effective for low-rise buildings.
- 24. Attenuation from Vegetation Attenuationis a simple term which we use to find out how much the sound pressure levels are cut.
- 25. Speech privacy –Sound Masking and Reinforcement System Attenuation is a simple term which we use to find out how much the sound pressure levels are cut.