Research project to reduce the sound level in the pit

London South Bank University and the Royal Opera House Covent Garden Foundation signed a joint agreement to fund a 3-year studentship signed on 17th December 2017. The aim of this project was to reduce the sound level in the orchestra pit. Mr Eric Ballestero was contracted to undertake the necessary research as part of his PhD programme.

A previously commissioned feasibility study to reduce the sound level in the pit had shown that traditional noise control approaches were both impractical and extremely expensive whilst having a minimal effect, 2 dBA. As such a new novel approach had to be found capable of delivering the ambition of the project.

New cutting-edge wave-based mathematical modelling, a collaboration with Edinburgh University, was used to demonstrate that the solution to the problem was to rapidly redistribute the music. This would allow the sound to leave the pit as soon as possible thus mitigating high pressure hotspots. An additional benefit of this solution would be that more of the music would reach the audience. An existing solution was found, a broadband quadratic residue diffuser. However, there was no space in the pit to retrofit such a solution due to the depth of the diffusers. The depth being necessary to accommodate the wide range of musical notes that need to be diffused.

To solve the diffuser depth issue an entirely new type of material was created, a metamaterial. The world’s first acoustic metamaterial was designed using an optimised mathematical structure to create an ultra-thin diffuser. The ultra-thin diffuser was then prototyped using 3-D printing technology to create a 30cm by 30 cm panel. Acoustic tests were undertaken, a collaboration with Le Mans University, to verify the performance characteristics of the ultra-thin diffuser. This verification confirmed that strategically positioned ultra-thin metadiffusers would redistribute a wide range of musical notes in the orchestra pit.

The final step in the programme of research was to calculate how much and where to position the panels. The Edinburgh University model was used to calculate that 20m2 of the 2 cm deep panels are required to rebalance the acoustic and mitigate against the hotspots. The panels would need to be installed on all the pit walls and beneath the overhang.