Architectural Acoustics: Principles and Applications, Study Guides, Projects, Research of Building Materials and Systems

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BUILDING UTILITIES 3

Lecture 2 - ROOM ACOUSTICS

INTRODUCTION

The architect deals always with the human senses when designing a building’s environment. The acoustical environment in and around the buildings is influenced by factors associated with the building planning-design- construction process ƒ Selection of site ƒ Location of the buildings on the site ƒ Arrangement of spaces within the building ƒ Materials and construction elements that shape the finished spaces

BRANCHES OF ACOUSTICS

ENGINEERING ACOUSTICS

ƒ Engineering Acoustics deals with the development of devices to generate (e.g., loudspeakers), record (e.g., microphones) and analyze (e.g., frequency analyzers) sound of all kinds. ƒ The field of sound production, recording and reproduction, with all its attendant electronics and measuring instruments, is an important part of engineering acoustics.

MUSICAL ACOUSTICS

ƒ Musical acoustics considers the workings of traditional, experimental and electronic musical instruments. ƒ The interaction of musicians, instruments, listeners and performance spaces means that many branches of acoustics influence work in this field.

BIOACOUSTICS

ƒ Bioacoustics studies all aspects of acoustic behaviour in animals and biological media in general. ƒ This field includes such topics as sound production by animals, biosonar, sound reception by animals, effects of noise on animals and medical diagnostics using acoustics, especially ultrasonics.

ARCHITECTURAL ACOUSTICS

ƒ Architectural Acoustics is concerned with sound in buildings. One aspect of this field is the control of sound within rooms to maximize the acceptability of music or intelligibility of speech. ƒ This branch of architectural acoustics deals with sound in lecture or concert halls, meeting rooms and classrooms. − Sound production, by one or more live players, vocalists or lecturers, whether assisted by loudspeakers or not, is greatly affected by the character of the room in which it takes place. − The correct choice and placement of sound-absorbing and sound- reflecting materials in a room and the level of noise in it are critical to obtaining an acceptable space. − Properly placed reflectors can direct the sound to where it will do most good. Properly placed sound-absorbing materials will prevent reflections that might cause unpleasant echoes or cause sounds to interfere and cancel each other out.

ARCHITECTURAL ACOUSTICS

• The design of spaces, structures, and mechanical/electrical systems to meet the hearing needs
• Deals with sound in the built environment
• The function is to simply follow this logic: to enhance desired sounds and to attenuate noises. - It becomes the designer’s job to qualitatively balance the interaction between acoustic properties of spaces when establishing design intent and criteria - Proper acoustic design responses early in the design process for all acoustical situations are thus, critically important to avoid costly repairs and alterations

MAJOR BRANCHES OF ARCHITECTURAL

ACOUSTICS

ƒ Room acoustics − involves the design of the interior of buildings to project properly diffused sound at appropriate levels and with appropriate aesthetic qualities for music and adequate intelligibility for speech. ƒ Noise control or noise management − involves the reduction and control of noise between a potentially disturbing sound source and a listener. ƒ Sound isolation − involves site consideration, location of activities within the building, construction of barriers, background sound levels in coordination with room acoustics ƒ Sound reinforcement and enhancement systems − use electronic equipment to improve the quality of sounds heard in rooms.

DIFFICULTIES IN ACHIEVING GOOD

ACOUSTICS

• For cost-cutting measures, the weight of various materials has been reduced
• Population density vis-à-vis spaces has increased steadily, thus raising the amount of noise generated
• Design of many office areas today is open, with only cubicles separating workers
• Mechanical and electrical systems intended to provide comfort to building occupants also generate noise
• There is no unified theory of acoustical comfort to guide design efforts, unlike that of thermal comfort

THREE ACOUSTICAL TOOLS

SOUND PRESSURE

• Sound pressure or amplitude is the objective measurement of the degree of change (positive or negative) in atmospheric pressure (the compression and rarefaction of air molecules) caused by sound waves.
• Sound pressure is caused by the acoustic power output of a sound source but is influenced by the nature of the environment between the source and the receiver; sound pressure is an environment-source property
• Sound pressure must be referenced to a particular location in a space, as pressure will often vary from location to location in a room.
• Sounds with greater amplitude will produce greater changes in atmospheric pressure from high pressure to low pressure.
• A woodwind player may increase the amplitude of their sound by providing greater force in the air column i.e. blowing harder.
• Amplitude is measured in the amount of force applied over an area. The most common unit of measurement of force applied to an area for acoustic study is the Newtons per square meter (N/m 2 ).
• One Newton is the amount of force it takes to accelerate a 1-kilogram object by one meter per second (m/s)

SOUND POWER

• Sound power is an independent property of a sound source that quantifies the source’s acoustical output
• It is constant for any given source operating under defined conditions and is not influenced by the nature of the surroundings into which a source is placed
• If we picture a sound wave as an expanding sphere of energy, power is the total amount of kinetic energy contained on the sphere’s surface; power is a measurement of amplitude over time. - The unit of measurement for power is the watt , named after James Watt. 1 watt = 1 Newton of work per second