Protecting Acoustic Heritage

Acoustician, Gavin Stevenson, analyses the importance of acoustics in realising major heritage refurbishment projects.

The built environment is responsible for around 40% of global carbon emissions. Across the industry in response the use of renewable sources to supply operational energy and generally improve the energy efficiency of buildings is now routine. To mitigate this further, there is a current drive to refurbish existing buildings, hence the adage ‘the most sustainable building is the one that already exists’. This is reflected in our portfolio of acoustics projects, a third of which are now refurbishments – a ratio which is increasing year on year.

Not all buildings are fit for renovation. Site dimensions, structural limitations, and state of repair can restrict the ability to reuse old buildings. Our aim is to ensure that acoustic suitability is not one of those reasons.

Oldham Town Hall, a dilapidated Grade II listed building, was converted into a multi-screen cinema complex in 2016, acting as a catalyst to rejuvenate a struggling town centre. For the scheme to be commercially viable, the operator required modern cinema acoustic standards, which necessitated a non-standard approach to cinema design. The primary issue was structural loading constraints, requiring the use of lightweight timber assemblies rather than the typical concrete approach. This had a significant impact on the wider design, influencing the spacing, structural grids, isolation assemblies, and even dead/live load deflection allowances. Whilst lightweight ‘box-in-box’ arrangements were used for the majority of screens, we were also able to retain one of the most historically significant rooms, the original courtroom, which was converted into a cinema. This was achieved through extensive site investigations and benchmark acoustic testing at the very start of the project to determine viability.

University of Roehampton Library

Benchmark testing is particularly crucial for historic projects, where potential enhancements may be limited due to heritage constraints yet the space must be acoustically fit-for-purpose. Acoustic performance is controlled by the weakest element; for example a thick masonry wall could be compromised by a hidden fireplace or poor head detail which would require invasive investigative works to identify. Acoustic testing enables these weaknesses to be detected and understood without the need for invasive or destructive surveys. Our work on the Palace of Westminster Restoration and Renewal Programme included extensive acoustic benchmark testing, undertaking hundreds of individual tests and gaining thousands of data points, resulting in a comprehensive understanding of the Grade I UNESCO World Heritage Site. Another benefit of benchmark testing is that is gives very accurate results compared to computer modelling, which, in turn, reduces the risk of under (or over) design – this means that all design recommendations are necessary and appropriate.

Sometimes our role is to ensure that the acoustic performance is not changed due to renovation, as was the case at Aberdeen Music Hall. This Grade A listed building is one of Scotland’s oldest and most historic concert halls. The main hall has a capacity of 1,300 and is used for a wide variety of events ranging from conferences to classical music concerts. It is particularly well regarded for its wonderful acoustics. Our primary goal during the renovation works was to retain the hall’s excellent acoustic quality, which, in addition to detailed benchmark testing, required the detailed assessment of all new materials and finishes to confirm they provided the same acoustic properties as the originals, many of which were of significant age.

Aberdeen Music Hall, UK

Regardless of end goal, early consideration of acoustic requirements is key: whether improving the acoustic standard, not compromising the existing performance, or – dare I say it – agreeing a reduced standard but one which is still fit-for-purpose. While this is the case for most projects, it is particularly important for refurbishment and heritage schemes, where fewer design options are available and so a greater level of coordination with the wider design is required.