Electroacoustics

Learning Outcomes

Disciplinary Specific Learning Outcomes

Having successfully completed this module you will be able to:

• Judge loudspeaker and microphone performance in terms of frequency response, directivity, and distortion.
• Model the behaviour of electroacoustic transducers using lumped element representations, analogous circuits, and two-port networks.
• Describe the principles of operation of condenser, ceramic, electret and dynamic microphones as well as different microphone calibration methods.
• Explain the principles of operation of moving coil loudspeakers and assess the effect of enclosures on loudspeaker performance and the use of crossovers in loudspeaker systems.
• Create computational models of electroacoustic transducers using finite- and boundary-element simulation software and critically compare the results to simplified analytical models.

Learning Outcomes

Having successfully completed this module you will be able to:

• C1/M1 As part of the individual assignment, the students must demonstrate the application of a comprehensive number of mathematical techniques and engineering principles to solve complex problems in the design of electroacoustic transducers. C2/M2 As part of the individual assignment, the students must formulate and analyse the physical behaviour of electroacoustic transducers using first principles of mathematics, physics, and engineering (e.g. by deriving two-port models or electroacoustic analogies). The students must also demonstrate an awareness of the limitations and uncertainties of these models. C3/M3 As part of the individual assignment, the students must select and apply appropriate computational (e.g. FEM/BEM simulations) and analytical (e.g. lumped elements) techniques to model electroacoustic transducers. In the assignment, the students must also discuss any limitations of their approaches. C4/M4 As part of the individual assignment, design decisions and approaches to find solutions to the design of their electroacoustic transducer designs must be justified using relevant technical literature. C6/M6 As part of the individual assignment, students must apply an integrated approach in the design process, taking into account the complex interactions between acoustical, mechanical, and electronical elements in electroacoustic transducers. C12/M12 As part of the loudspeaker laboratory session, students must use practical skills, such as setting up electronical measurements to measure the impedance of loudspeaker drivers, to investigate the behavior of a real electroacoustic transducer. C13/M13 As part of the individual assignment, the students must select appropriate materials in their transducer designs (e.g. for the coils, permanent magnets, diaphragms) and discuss the limitations of their choices, for example in terms of weight and cost of the transducers.

General Theory (4 lectures):

Description of electrical, mechanical and electroacoustic systems as two-port networks. Coupling. Analogies. Acoustic networks. Reciprocity. Microphone and loudspeaker arrays.

Loudspeakers (10 lectures):

Equivalent models for moving coil loudspeakers, and relationship to practical loudspeakers. Loudspeaker performance in terms of frequency response, directivity, and distortion, and their measurement. The influence of an infinite baffle, closed box and tuned cabinets. Crossover networks. The horn equation, simple solutions and application, loudspeaker specifications. Power output and mutual coupling. Diaphragm dynamics.

Microphones (8 lectures):

Pressure and pressure gradient principles. Diffraction. Diaphragm dynamics and transduction mechanisms, hence complete frequency responses for various microphone types. Methods of calibration. Directivity of first order microphones. Diffuse field response. Highly directional microphones. Microphone specifications. Hydrophones.

Microphone and loudspeaker arrays (2 lectures):

Line microphone. Linear arrays. Delay and Sum Beamforming. Higher Order Ambisonics.

Computer labs (1 lab/week):

Implementation of analytical/theoretical models. Analysis of equivalent electroacoustic circuits. COMSOL simulation of loudspeakers and microphones. Crossover filter programming.

Electroacoustics Laboratory:

Estimation of the Thiele Small parameters of a loudspeaker driver.

This is a one-semester course comprising two 45 minute lectures and one 45 minute computer lab per week. Lectures include a combination of presentation, the discussion of the properties of examples of practical loudspeakers and microphones handed round in class. In a separate lab session, electrical measurements of a loudspeaker driver will be performed to estimate the Thiele-Small parameters of the driver and predict its frequency response. This prediction will be compared to acoustic measurements performed in the world-class anechoic chamber at the Institute of Sound & Vibration Research. 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.

Formative

This is how we’ll give you feedback as you are learning. It is not a formal test or exam.

Lab Report

• Assessment Type: Formative
• Feedback:
• Final Assessment: No
• Group Work: No

Summative

This is how we’ll formally assess what you have learned in this module.

Referral

This is how we’ll assess you if you don’t meet the criteria to pass this module.

Repeat

An internal repeat is where you take all of your modules again, including any you passed. An external repeat is where you only re-take the modules you failed.