Posted Dec 12 2023 | By Thomas Böhringer

Inside Bristol Beacon: The Art of Getting the Sound Right

The old hall had much loved sound for certain seats in certain places, but the quality of sound rapidly dropped towards the edges, upper balcony and those seated underneath the acoustic shadow of the very deep balcony.

Its architecturally streamlined ceiling tended to focus the sound on limited locations instead of spreading it across the whole room. Its stage was also far too small to accommodate full size major orchestras and staging touring acts.

The art and science of acoustic design have advanced tremendously since the 1950s reconstruction and the hall lagged behind more recent comparator venues.

In collaboration with acousticians from Sound Space Vision, engineers from Arup and Theatre Consultants Charcoal Blue, Levitt Bernstein carried out a study of the existing building against the geometry of other renowned classical concert halls, to identify the shortfalls of the existing Hall. It transpired that:

  • The balcony overhang compromised the acoustics for unamplified and amplified events, by creating an acoustic shadow for the rear stalls audience.
  • The canopy needed to be replaced for acoustic and technical/safety reasons and it was too short to work over an increased stage.
  • Sound separation between spaces had to be radically improved.
  • The ventilation system was excessively noisy.
  • The room acoustics were not fully adaptable to suit both amplified and non-amplified music.
  • Virtually all the surfaces in the hall required improved acoustical performance, in terms of density, shaping and surface finish.
  • The curved shape of the existing ceiling did not support good room acoustics.
  • The volume of the room was less than ideal for the number of occupants.
  • Performances were impacted by external noise intrusion, including hearing rain on the roof.

This clearly established that a wide range of works would be needed to achieve the acoustic aim. The main changes resulted in:

  • The reconfiguration of one deep balcony into two shallower balconies.
  • The reshaping of the ceiling to remove the sound focussing dome - another significant improvement that has lead to a more even distribution of sound across the auditorium and mitigation of flutter echoes.
  • The re-shape and extent of the over-stage canopy work towards providing a unified stage area, address issues of balance and over-loudness, and improve support for strings when on the extended stage.
  • The installation of flexible auditorium acoustics for high quality amplified sound.
  • The adaptation of the organ console to suit new stage layout.
  • The reduction of the sound transmission between halls during concurrent uses.
  • The reduction of noise intrusion from external noise and building services during classical performances. Low background noise levels are essential for dramatic silence and to provide dynamic range to performance.
  • Providing excellent sound isolation from Lantern Hall music events, foyer activity and education use of the Weston Stage.

Un-amplified orchestral performances require acoustically lively reverberant space, so that the sound can be reflected across the room, whereas amplified rock and pop performances require acoustic damping, so that the sound is full and clear but not deafening.

A range of various shaped solid timber and brick linings contribute to enrichening the sound distribution, by creating a well-balanced mixture of reflecting and diffusing surfaces, improving the room reverberance, and providing scattering and absorbing finishes to improve the acoustic balance between sections.

Variable acoustics in the form of retractable curtains and banners allow the hall to be tuned for different sized acoustic performances and allow switching between orchestra and rock/pop mode in a matter of minutes. Bass absorbers hung above the canopy provide a high degree of bass absorption to control low frequency sound from hung ceiling PA clusters. There is access for lighting and sound equipment which will provide an ambience that can easily and speedily be adapted between performances.

The bold scheme of the triangular curved balcony panels is shaped specifically for acoustical performance to provide sound refraction and is part of the response to Bristol City Council / Bristol Music Trust's brief for distinctive design of the new hall. This motif is reflected also in the over stage canopy.

The success of these acoustic measures is reflected in the varied programme of the Bristol Beacon, which is now a concert hall that is designed to suit all musical genres, and the acoustical compromises inherent in the 1951 design are no longer apparent.