1 CONTENTS Lesson 1 Noise Control in Architecture

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CONTENTS • Lesson 1 – Noise Control in Architecture • What is noise? • Sound transmission in architecture • Noise Control through architectural design | Noise Control in Architecture | Lesson 1 – Noise Control in Architecture 2

Lesson 1 Noise Control in Architecture | Lesson 1 - What is Noise? 3

What is Noise? In daily life, noise means unwanted sound. As you have no doubt experienced, unwanted sounds can include distractions, sounds that are loud enough to damage hearing and even sound leakage that could affect privacy. In architecture, one of the many goals of the designer is to create rooms and buildings that maximize sound performance. This means that unwanted sounds should be prevented, and desired sounds should be enhanced. | Noise Control in Architecture | Lesson 1 - What is Noise? 4

What is Noise? Sound Intensity I and Sound Intensity Level L Sound intensity is a scientific concept distinct from the more subjective “loudness”. It is defined as power of sound wave per unit area (Wm-2). For example, sound intensity from ticking of watch is around 1 x 10 -11 Wm-2, but a jet taken off generates 1 x 102 Wm-2. Difference of powers of sound wave between the watch ticking and a jet is 1013 times. This scale is not comprehensive enough to tell the loudness of sound. A logarithmic scale is used to measure sound intensity. It is called sound intensity level. Sound Intensity Level is defended as: L = Sound intensity level (d. B); I = Measured sound intensity (Wm-2); and I 0 = Standard sound intensity (Wm-2), the softest sound intensity that human ear can hear. The standard reference of I 0 is 10 -12 Wm-2. | Noise Control in Architecture | Lesson 1 - What is Noise? 5

What is Noise? Difference Between Noise and Sound Intensity Level Noise is a subjective and relative perception, but sound intensity level is a scientific measure of the power of sound. Even if a sound source has a relatively low sound intensity level, some individuals might find a certain frequency of sound wave annoying because the human ear reacts differently to different frequencies of sound (pitches) and the hearing ability of individuals is subjective. Sound intensity level can only be used as a standard to identify the volume of sound that could cause hearing damage. It does not represent the exact perception of the sound to individuals. | Noise Control in Architecture | Lesson 1 - What is Noise? 6

What is Noise? Sound Transmission in Architecture Sources of Noise The two major sources of noise in architecture are: 1. Airborne noise, or sound waves transmitted from a source to a receiver through the air. 2. Structure-borne noise is caused by vibration from within the building caused by footsteps or machines. The vibration is directly transferred through the building’s structures and materials. A B C A. The sound of a plane’s engine is a kind of exterior airborne sound that may affect communities near airports. B. The MTR’s operating systems are quiet, but the vibration of the train rail generates exterior structure-borne noise. C. In a gymnasium, cheering spectators may cause interior airborne noise to the surrounding rooms, while the athletes’ activities generate interior structure-borne noise. | Noise Control in Architecture | Lesson 1 - Sound transmission in architecture 7

What is Noise? Sound Transmission in Architecture | Noise Control in Architecture | Lesson 1 - Sound transmission in architecture 8

What is Noise? Noise transmission paths Sound waves travel from the source to the receiver via multiple paths. Altering the paths of sound transmission is a common way to control noise in architecture. Flanking transmission of sound Flanking transmission is the propagation of sound wave via building elements. When sound strikes on a surface, part of the sound reflects off the wall surface back into the space, and part An air gap can stop the of it is transmitted through the wall to the space beyond. transmission of sound effectively. [Discussion] How is unwanted sound transmitted in this diagram? | Noise Control in Architecture | Lesson 1 - Sound transmission in architecture 9

Noise Control through Architectural Design Reducing Transmitted Sound Intensity Level When sound wave travels through air or materials, the transmitted sound intensity level is reduced due to sound power loss. Almost every material exhibits sound insulating properties. They only vary in their level of acoustic performance, which is measured in terms of the Sound Transmission Loss or Sound Reduction Index When two partitions or sound barriers are completely separated and isolated from one another, their ability to reduce sound is increased. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 10

Noise Control through Architectural Design Extended Knowledge The Sound Reduction Index of a material as it affects a specific frequency of sound can be found using the following equation: Where, SRI= Sound Reduction Index (d. B) M= The mass per unit area of the material (kgm-2); and f =Frequency of the sound (Hz). The sound insulation performance of any homogenous material depends mainly on its mass. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 11

Noise Control through Architectural Design Possible Perspectives • Sound reduction required from the meeting room = 45 - 35 d. B = 10 d. B • Sound reduction required from the nearby sports courts = 70 – 25 d. B = 45 d. B The wall of the meeting room should have a Sound Reduction Index ranging from 10 d. B to 45 d. B. According to the graph of Sound Reduction Index, three building materials could be suitable for the meeting room: • 50 mm Plastered Breeze Block (a light concrete building block made with cinder aggregate) • 9 mm Glass • 0. 7 mm Sheet Steel After obtaining the data from an acoustic consultant, architects decide what materials should be used for the functions and aesthetics of the space. Other considerations include structural tolerance, environmental concerns and universal design for all users. Sound Reduction Index of common building materials (Source: “Noise Control in Mechanical Services”, 1972) | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 12

Noise Control through Architectural Design [Discussion] The school principal prefers using plywood as the wall surface. He comments that a glass wall is not good for privacy but he wants to introduce natural lighting and ventilation to the new meeting room. What possible solution would you suggest? | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 13

Noise Control through Architectural Design Possible Perspectives A double-leaf plywood wall could be constructed with a row of double-glazed operable clerestory windows for natural lighting and ventilation. Double-partition wall insulation When two sound barriers are completely separated and isolated from one another, sound insulating performance is enhanced. Sound absorption materials like mineral wool can be used to fill the cavity for extra sound insulation against flanking transmission. © NAP Acoustics (Far East) Ltd Double-glazing An operable double-glazed window provides horizontally offset openings that allows natural ventilation while preventing direct propagation of traffic noise. The narrow path between the double window panes dissipates sound energy and lowers noise levels relatively. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 14

Noise Control through Architectural Design Redirecting Sound away from Receivers Artificial noise screen Noise barriers can redirect the paths of noise away from receivers. They can be artificial (for example, a wall) or natural (a forest). One common application for noise barriers is to prevent traffic sounds from penetrating nearby neighborhoods or habitats. Sometimes noise barriers are integrated with the building design. Noise sensitive buildings like residential blocks may be built above a podium or a shopping mall that inhibits the transmission of noise to the apartments. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 15

Noise Control through Architectural Design [Discussion] Can you identify the noise sources and barriers in the images and trace the sound transmission paths? Mark them on the following picture. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 16

Noise Control through Architectural Design Case Study – Kwai Tsing Theatre Isolating structure-borne noise from the building © WAAGNER-BIRO AG Kowloon’s Kwai Tsing Theatre illustrates how architectural design can be used to protect quiet spaces against airborne and structure-borne noises from inside and outside theatre. Its location next to the MTR railway and heavy traffic is particularly challenging given the requirements of theatre’s multifunctional spaces, which sometimes host simultaneous events. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 17

Noise Control through Architectural Design Case Study – Kwai Tsing Theatre Photographs showing how the springs integrate with the structure of Kwai Tsing Theatre; © VIPAC Engineers & Scientists (HK) Ltd Springs placed on the pile caps of the building can absorb exterior structure-borne noise before it is transmitted to the interior. Theatre and music rooms are built inside an isolated shield to reduce flanking transmission of noise. Noise-isolating springs c NAP Acoustics (Far East) Ltd | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 18

Noise Control through Architectural Design Case Study – Kwai Tsing Theatre Improving the Sound Reduction Index of the Structure The ceilings, walls and floors of theatre are isolated from building structure by springs or resilient pads. An air gap around the floating floors and suspended ceilings also improves the Sound Reduction Index of the structure. | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 19

Noise Control through Architectural Design Case Study – Kwai Tsing Theatre The air gap is the most important factor – increasing it (rather than increasing the mass of the floors) would achieve greater reductions in noise as compared to increasing the mass of the structure or the floating floor. © VIPAC Engineers & Scientists (HK) Ltd | Noise Control in Architecture | Lesson 1 – Noise Control through Architectural Design 20

Summary • Noise means unwanted sound. It is subject to human perception. • Sound Intensity Level is a scientific approach providing A logarithmic scale is used to measure sound intensity (Wm-2), and is expressed as: • Noise control in architecture is dealing two sources of noise: airborne and structure-borne. | Noise Control in Architecture | 21

Summary • Two ways to control noise: reducing transmitted Sound Presure Level and reddirecting sound transmission paths to the receivers. • Sound Reduction Index is used for the purpose of choosing the appropriate sound insulating performance for a building. It indicates the degree of sound intensity reduction when a sound wave passes through a material. • Noise barrier redirects noise transmitting paths to the receivers. | Noise Control in Architecture | 22