The acoustics of air source heat pumps - part 1: Why noise matters

In 2021 Max Fordham Senior Acoustic Engineer, Pedro Novo, was invited to take part in an unusual study – to measure the acoustic intimacy of the drained Gala Pool at a Grade-II listed Edwardian swimming baths in Birmingham.
The pool has been closed since 2003 and Moseley Road Baths, a site of importance to the local community, has been closed since 2023 while undergoing renovations – a project we are also involved with as MEP and sustainability consultants.
Opera director Rosalind Parker and theatre designer Leanne Vandenbussche were commissioned to compose an opera for the disused space. They were struck by the pool's impressive aesthetic and its visual and aural qualities. Recognising the potential of the highly reverberant nature of the space for an opera, they realised the need to consider the behaviour of the sound, assembling a team of specialists to help with the study.
For Pedro, the aim of the project was to try and make objective the subjective, to translate the acoustic quality of Moseley Road Baths into data. Now Pedro and Rosalind have co-authored a chapter on the study in a new book, The Routledge Companion to the Sound of Space, which was officially launched at an event at University College London last week.
Rosalind has years of experience working with communities on arts and music events. The idea of the Moseley Road Baths project was to explore the space from a new angle, looking at the potential for an arts-based project.
Pedro said: “In that process of exploring the space, they realised that the acoustics of Moseley Road Baths was somehow special – it was highly reverberant because it has all hard surfaces and had a quality to it that they felt inspired to try and measure.
“Rosalind had done performances in churches and cathedrals, spaces that are even more reverberant, and her default approach was to fight the reverberation, and so the thinking was what about if we understand better the acoustic properties of the space and make it work, rather than fighting it. I’d known Rosalind for a while and she was aware of the specialist acoustic services we can provide at Max Fordham, so she invited me to take part.”
Gala Pool showing the location of the ambisonic microphone, and loudspeaker measurement locations (1–4) (Model Created by Emma-Kate Mathews).
Model Created by Emma-Kate Mathews
Having visited Max Fordham previously, Rosalind was aware of the specialist facilities we have for making a 3D acoustic measurement of a space. The book's editor, UCL Lecturer in Architecture, Emma-Kate Matthews, has also used Max Fordham's Sound Space for simulations, which she mentions in her chapter, Spatiosonic dialogues: Exploring architecture's role in music composition and performance.
Pedro visited the baths during a performance to start work on the measurements, not knowing what the result would be.
He said: “While I was working more on the technical aspects and Rosalind on the artistic side, we both agreed that even when there was a singer on the opposite side of the space, the singer felt very close to us. There was a sense of proximity in this highly reverberant space which was very interesting. This made me think about the acoustics literature on concert halls and in particular on ‘acoustic intimacy’.”
Acoustic intimacy in concert halls refers to the listener's perception of being physically close to the performers, fostering a sense of connection and involvement with the music. It has been proposed in various research publications that this quality is influenced by the timing of strong early sound reflections, i.e., the first sound waves that arrive at a listener after reflecting off nearby surfaces, such as walls, ceilings, or floors.
“We were excited to see that they were actually present. That’s the key finding of this project: the correlation between the subjective impression of the space – that it sounds intimate with a sense of proximity between the audience and performer, and objective acoustic measurements, which reveal the presence of early sound reflections within a time window as proposed in the literature.”
Upper Graph: Early impulse response, W component. Lower graph: Direction of incidence of three sets of strong reflections identified on the upper graph (CATT acoustic software). Note: The horizontal axis represents time (ms) and the vertical axis represents sound pressure level (SPL). Zones of higher SPL have been circled in green.
The Routledge Companion to the Sound of Space explores a range of conceptual and practical relationships between sound and space across various disciplines, providing insights from technical, creative, cultural, political, philosophical, psychological, and physiological perspectives.
The content spans a wide range of spatial typologies, from large reverberant buildings to modest and intimate ones, from external public squares to domestic interiors, and from naturally formed environments to highly engineered spaces. These compiled insights and observations explore the vast diversity of ways in which sonic and spatial realms interact.