ISVR3064 Noise Control Engineering
Noise control engineering is concerned with the application of basic acoustics and vibration theory to reduce noise in practical situations. The noise control engineer needs to know how to set targets, how to characterise and quantify noise sources, and how to reduce noise either at source or, more commonly, in the transmission path. Suitable formulae are provided and explained for each of these steps. The main assessment consists of a design calculation study which makes use of these formulae to solve a practical problem. The report is written in a form suitable for a client.
Aims and Objectives
• Introduce students to the requirements, principles and methods of noise and vibration control; • Provide basic knowledge and understanding of noise and vibration control necessary for professional practice as a noise control engineer; • Encourage the application of this knowledge to practical problems.
Disciplinary Specific Learning Outcomes
Having successfully completed this module you will be able to:
- use common units of noise measurement, characterise noise sources, be familiar with standard methods for the measurement of sound power
- use appropriate formulae for sound propagation, radiation from vibrating sources, transmission through partitions, absorption by porous materials, vibration isolation and damping, attenuation by silencers
- select appropriate noise control techniques for the solution of practical noise problems and evaluate their performance
- apply the noise control techniques considered in an integrated way to a practical design case
Noise control requirements: Motivation for noise control, EC directives on machinery noise and outdoor equipment, specification of noise control targets. Units of noise measurement: Overview of decibels for sound pressure, intensity and power levels; combining sound pressures (incoherent and coherent); basic frequency analysis including one-third octave bands; A-weighting and other measures of sound. Characterization of noise sources: Physical nature of noise sources, idealizations; acoustical efficiency; frequency spectrum; parametric dependencies including operational speed; directivity; estimation of source sound power (including engines, fans etc). Summary of sound power measurement methods. Sound propagation outdoors and indoors: Point source and line source; geometric spreading; ground effects; meteorological effects; noise barriers; sound in rooms, reverberant field. Principles of passive noise control: Effect of multiple sources and multiple paths; noise path models; control at source; airborne transmission; structure-borne transmission. Sound radiation from vibrating structures (engineering approach) Definition of radiation ratio; radiation from monopole and dipole sources; radiation from bending waves in plates; corner modes, edge modes, coincidence; means of reducing radiation ratio. Transmission of airborne sound through partitions Transmission loss of a single partition, mathematical derivation for normal incidence; coincidence and the transmission loss for particular angles of incidence and for a diffuse field (qualitative); double partitions (qualitative); measurement methods for sound reduction index; machinery enclosures using Sabine formula. Sound absorbent materials and applications: Surface impedance and its relation to absorption coefficient; qualitative treatment of dissipation mechanisms; practical forms of sound absorber; measurement techniques for absorption. Vibration control: Force and velocity excitation, blocked force and free velocity; vibration isolation - low and high frequency models; damping treatments; effects of damping; structural modification; vibration absorbers and neutralisers. Silencer design: Acoustic impedance; insertion loss; reactive silencers: side branches, expansion chambers; flow-generated noise; lined ducts, splitter attenuators; pressure drop; break-out noise.
Learning and Teaching
Teaching and learning methods
This is a one-semester course, normally three lectures per week. Detailed lecture notes are provided and one-to-one assistance and verbal feedback is facilitated through tutorial classes relating to the assignment. Various practical demonstrations are included within the lectures. Blackboard is used to allow the lectures and additional material to be disseminated. Students are encouraged to read supporting texts and a booklist is provided.
|Wider reading or practice||40|
|Completion of assessment task||60|
|Total study time||150|
Resources & Reading list
D.A. Bies and C.H. Hansen (1996). Engineering Noise Control.
F.J.Fahy and J.G. Walker (1998). Fundamentals of Noise and Vibration.
F.J. Fahy (2001). Foundations of Engineering Acoustics.
Key Texts available in Hartley and EJ Richards Libraries..
Repeat type: Internal & External