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ISVR6136 Fundamentals of Acoustics

Module Overview

This module provides an introduction to the basic elements of acoustics for the purpose of meeting the fundamental needs of practising engineers. This module provides the knowledge and tools to understand and predict the behaviour of complex acoustical systems, including the behaviour of sound propagation in free field and simple bounded environments, and the characteristics of source radiation. It provides the fundamental knowledge required in order to study a range of other modules on more specialist aspects of acoustics.

Aims and Objectives

Module Aims

• To introduce students to the physical principles that underpin the behaviour of sound in free field and bounded environments, and the behaviour and characteristics of simple acoustic sources. • To introduce students to the formal acoustical basis for the study of acoustic wave motion in fluids. • To develop a competence in the theoretical analysis of simple acoustical systems • To allow the student to gain laboratory experience in analysing and interpreting the acoustic measurements in complex scenarios. To present their results formally, together with a critical assessment of the experimental methods and the limitations of their data.

Learning Outcomes

Knowledge and Understanding

Having successfully completed this module, you will be able to demonstrate knowledge and understanding of:

  • The propagation of longitudinal acoustic disturbances in the form of plane waves and waves in a free environment.
  • The derivation of the wave equation and Helmholtz Equation from linearised conservation equations.
  • The behaviour of sound in enclosures including analytical descriptions of sound propagation at both low and high frequencies
  • The limitations and characteristics of acoustic sources.
  • Methods of estimating source sound power from measurements of sound pressure level and sound intensity under different conditions.
  • The use of a sound level meter and the use of standard bandwidths and frequency weightings.
Disciplinary Specific Learning Outcomes

Having successfully completed this module you will be able to:

  • Read, understand and interpret the literature relating to basic topics in acoustics.
  • Model simple acoustical problems involving sources of sound in simple geometries.
  • Undertake acoustic measurements and provide critical analysis and conclusions.
  • Manipulate complex numbers in the solution of problems associated with wave motion.
  • Produce a formal technical report.

Syllabus

1. Introduction to Acoustics: Acoustic pressure. rms and mean square pressures. Definition and use of the decibel, and the reasons for its use. Addition of quantities (coherent and incoherent) in decibels. Third-octave bands. Human hearing. A-weighting. Sound level meters. Other acoustic metrics. 2. Introduction to the propagation of acoustic disturbances: Longitudinal wave motion, introduction to plane acoustic waves. Speed of sound, frequency, wavelength, wavenumber, particle velocity, characteristic acoustic impedance. Thermodynamics of acoustic compressions. Linear relationships between basic acoustic quantities. Variation of speed of sound with temperature and pressure. 3. One-dimensional acoustic wave motion: Conservation equations in one dimension; linearisation of governing equations; derivation of onedimensional wave equation. Solutions to the one-dimensional wave equation. Complex exponential representation of wave motion. Helmholtz equation. Linearity and the superposition principle. Specific acoustic impedance. Acoustic energy density and intensity. Standing waves. Application to impedance tube measurements. Concepts of nonlinear propagation. 4. Waves in three dimensions: Conservation equations in three dimensions; derivation of the three-dimensional wave equation. Solutions to the three dimensional wave equation. Spherical waves. Impedance of spherical waves. Sound radiation from a pulsating sphere. The point monopole source. Sound intensity due to a spherical wave. Sound power output of a pulsating sphere and its radiation efficiency. Sound Intensity measurement. 5. Sound in enclosures: Solution to the three-dimensional wave equation in a room with rigid walled boundaries. Room modes and their natural frequencies. Modal statistics; modal density, modal overlap and the Schroeder frequency. The concept of a diffuse field. Average absorption coefficient and the energy balance equation, reverberation time. 6. Sound radiation: The Rayleigh integral for the solution of sound radiation problems. Radiation from a plane vibrating piston. On axis radiation in near and far fields of a circular piston. Directivity and interference. Radiation impedance. 7. Multipole sources: The point monopole source. The point dipole source; vector dipole strength. Quadrupoles. Green Function. Kirchoff-Helmholtz Integral. 8. Sound reflection, transmission, refraction and attenuation: Reflection and transmission at a fluid-fluid interface. The transmission and reflection coefficients. Normal and oblique incidence. Refraction in the atmosphere and underwater: Snell’s law. Sound attenuation. 9. Laboratory sessions: Use of sound level meters. Sound power measurement

Learning and Teaching

Teaching and learning methods

This is a one-semester course, three lectures per week with two laboratory sessions. Lecture notes and tutorial sheets are provided and one-to-one assistance and verbal feedback is facilitated through six tutorial classes with short tests in some. Past exam papers are supplied to aid personal study, feedback and revision. Blackboard is used to allow the lectures and additional material to be disseminated (including solutions to past exam papers). The students have to write-up two laboratory reports. Students are encouraged to read supporting texts and a booklist is provided.

TypeHours
Practical classes and workshops6
Revision30
Lecture30
Completion of assessment task18
Tutorial6
Wider reading or practice60
Total study time150

Resources & Reading list

Fahy F.J. and Walker J.G. (1998). Fundamentals of Noise and Vibration. 

Blackstock D.T.. Fundamentals of Physical Acoustics. 

Kinsler L.E., Frey A.R., Coppens A.B., and Sanders J.V. (2000). Fundamentals of Acoustics. 

Pierce A.D. Acoustics (1989). An Introduction to its Physical Principles and Applications. 

Laboratory space and equipment required. The practical sessions will be held in teaching laboratory 13/4061 using existing experimental designs.

Assessment

Summative

MethodPercentage contribution
Exam  (120 minutes) 75%
Laboratory Report 10%
Laboratory Report 10%
Test 2.5%
Test 2.5%

Referral

MethodPercentage contribution
Exam  (120 minutes) 100%

Repeat Information

Repeat type: Internal & External

Linked modules

Pre-requisite module/s - MATH1054 Mathematics for Engineering and the Environment or equivalent course

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