Building Utilities 3: Acoustics and Lighting Systems PDF

BUILDING UTILITIES 3 ACOUSTICS AND LIGHTING SYSTEMS WEEK 2  1.1 DEFINITION ACOUSTICS Acoustics is a science which deals with the ACOUSTICS production, control, transmission, reception and effects of sound in an enclosed space....

BUILDING UTILITIES 3 ACOUSTICS AND LIGHTING SYSTEMS WEEK 2  1.1 DEFINITION ACOUSTICS Acoustics is a science which deals with the ACOUSTICS production, control, transmission, reception and effects of sound in an enclosed space. The science of sound, including the generation, transmission, and effects of sound waves.  1.1 DEFINITION SOUND Sound is the human ear’s response to ACOUSTICS pressure fluctuations in the air caused by vibrating objects; is a vibration at various frequencies in any elastic medium. Generated by a source Requires path of transmission (gaseous, liquid, solid)  1.1 DEFINITION SOUND ACOUSTICS For example, a tap on the wall produces sound because the tap makes a wall vibrate. The vibrating wall produces pressure fluctuations in the air. Sound travels in space by a phenomenon called wave motion. Wave motion in air is like the motion of a ripple produced by dropping a pebble into a water pond.  1.1 DEFINITION BASIC SOUND THEORY Sound is an aural sensation caused by oscillation or vibration in an elastic medium ACOUSTICS such as air, water, building materials, such medium returns to its normal state after sound waves pass through it. Sound travels in any medium except in a vacuum because there is no carrier of sound.  1.1 DEFINITION SOUND GENERATION Any change of stress or pressure producing a ACOUSTICS local change in density or a local displacement from equilibrium in an elastic medium can serve as a source of sound. Other illustrations are provided by struck solids such as a drum, violin, or piano string, flow of air in a jet and underwater explosion. ACOUSTICS 1.1 DEFINITION VIBRATION OF PARTICLE IN AIR A full circuit by displaced particle is called a cycle. The time required for one complete cycle is called the period And the number of complete cycles per second is the frequency of vibration. Frequency is measured in cycles per second, the unit for which is called the hertz (hz).  1.1 DEFINITION SOUND TRANSMISSION Transmission of sound takes place through an elastic medium by means of wave motion. A wave is the motion through the medium of a disturbance as distinguished from the motion of the medium as a whole. For example, when you flick the rim of a glass, the glass will vibrate imperceptibly. These vibrations ACOUSTICS move through the air and strike the ear drum of anyone within hearing range. In fact, these vibrations, or sound waves, can move through any medium: gas, liquid or solid. Sound needs a material medium for their propagation like solid, liquid or gas to travel because the molecules of solid, liquid and gases carry sound waves from one point to another. Sound cannot progress through the vacuum because the vacuum has no molecules which can vibrate and carry the sound waves. ACOUSTICS 1.1 DEFINITION SOUND TRANSMISSION Velocity of sound in still air of normal atmospheric composition at 0°C is 331.45m/s. Another important property of sound transmission is intensity, measured by the average rate of flow of energy in the wave per unit of time and per unit area perpendicular to the direction of propagation. The intensity of all practical sound waves diminishes with distance from the source, a property known as attenuation. ACOUSTICS  1.1 DEFINITION SOUND DETECTION AND EFFECT The detection of sound is made possible by the incidence of transmitted sound energy or an appropriate acoustic transducer. For human beings with so called normal hearing, the most ACOUSTICS important transducer is the ear, a remarkably sensitive organ able to top detect a sound intensity as low as 10˄-16 w/cm². For modern applied acoustics, transducers such as microphone, based on piezoelectric effect, are widely used. Generally speaking, any transducer used as a source of sound is also available as a detector, though the sensitivity varies considerably with the type.  ACOUSTICS 1.1 DEFINITION LONGITUDUNAL AND TRANSVERSE WAVES In wave motion in a material medium, particles of the medium vibrate about their positions of equilibrium. The wave energy is carried forward, but not the medium.  ACOUSTICS 1.1 DEFINITION LONGITUDUNAL WAVES One in which the vibration of the medium is (forward and backward) parallel to the direction of propagation of the wave. TRANSVERSE WAVES One in which the vibration of particles of the medium are perpendicular to the direction of motion of the wave energy. ACOUSTICS 1.1 DEFINITION PURE TONE A pure tone is vibration at a single frequency. For example, A tuning fork, is a fork-shaped acoustic resonator used in many applications to produce a fixed tone. The main reason for using the fork shape is that, unlike many other types of resonators, it produces a very pure tone, with most of the vibrational energy at the fundamental frequency.