Extending the Low Frequency Acoustic Centre Concept to Directional Loudspeakers

This is a recording of an Acoustics Lunchtime Research Seminar given by Dr Jonathan Hargreaves on 7th February 2024.

ABSTRACT:
The Acoustic Centre of a loudspeaker is defined as being the point from which spherical waves appear to radiate. This is useful to know when performing phase, level, or time alignment, for example. For a single driver in a sealed box, it is typically on-axis a few centimetres in front of the diaphragm. Standard methods involve measuring level and/or phase at two or more points, and then fitting a monopole model to it. This works satisfactorily if the loudspeaker is omnidirectional, but it is not appropriate for ones that are not – modern cardioid subwoofers for example. This paper therefore explores an alternative definition based on a spherical harmonic representation of its directivity. This is still valid for omnidirectional sources but supports directional ones too. Its properties are investigated through simulation and used to optimise cardioid radiation from a loudspeaker.

BIOGRAPHY:
Jonathan Hargreaves MIOA was awarded an MEng in Engineering & Computing Science from the University of Oxford in 2000 and a PhD in Acoustic Engineering from the University of Salford in 2007, where he remains as a Lecturer in Acoustic and Audio Engineering. He is best known for his research on novel computational acoustic algorithms – notably Boundary Integral Methods – but he also has strong research interests in loudspeaker design and characterisation, material characterisation, and microphone arrays. He is a member of the IOA Research Coordination Committee and the UK Acoustics Network Special Interest Group for Computational Acoustics. Jonathan has had the pleasure of being involved in a wide variety of public engagement activities, including several TV appearances, and is passionate about performing, engineering and enjoying live music. He was awarded the UK Institute of Acoustics’ Tyndall Medal, for outstanding contribution to acoustics research and education, in September 2016.