Room Reverberation Design

St John's College, Cambridge

Some acoustic problems come dressed in oak beams and stained glass. That was the challenge at St John’s College, Cambridge, where we were asked to tackle reverberation in the historic dining hall as part of a wider refurbishment.

Our survey found reverberation times of around 1.8 seconds — noticeably livelier than ideal for a working dining hall. But this was no ordinary retrofit. Any intervention had to be minimal, discreet, and acceptable to both the College Fellows and Heritage England.

To find the right solution without disturbing a single moulding, we turned to sophisticated 3D acoustic modelling. Using specialist room-acoustics software, we built a digital model of the hall calibrated against our on-site measurements, then used it to test a range of treatments and quantities before a single panel went up. The result: around 100 m² of specialist acoustic absorption, using either sound-absorbing plaster or slim perforated timber panelling, bringing reverberation down to a comfortable 1.0–1.5 seconds — with virtually no visual change to the space.

It’s a project that sits comfortably alongside our work in similarly cherished halls at Trinity College Oxford, Eton and Regent Street Cinema: heritage spaces where good acoustics and good conservation must work hand in hand.

Watersprings Christian Centre

Cass Allen was instructed to assess the design of a proposed Gospel Hall on behalf of the Watersprings Christian Centre. This presented a unique challenge as the Gospel Hall; operates over long periods in which nearby residents would typically be at home relaxing (i.e. Sunday afternoon), has associated activities that would involve singing and amplified music, would have no strict guidance or criteria to assess against, and as part of the proposal would be operated out of a converted office building.

To address these challenges our assessment involved the comparison of the existing noise environment over a “worst-case” period against the calculated breakout and parking noise from the proposed hall. This assessment was based on measurements taken during surveys of the site and typical service, and modelling of the external wall.

Based on this and our application of guidance given in the Noise Planning Policy Guide (NPPG) we were able to provide evidence that, provided windows were kept closed during the service, it would be unlikely that noise from the hall result in any change in behaviour of local residents and hence would not be expected to require any costly mitigation.

The United Synagogue – Bushey Cemetery

Client: United Synagogue
Architects: Waugh Thistleton

Cass Allen was instructed to acoustically design the four prayer halls at the new synagogue site in Bushey.

The project was particularly challenging due to the highly acoustically reflective internal finishes required in the construction of the halls and limited scope for acoustical solutions.

In order to control excessive reverberation within the halls, Cass Allen designed a bespoke system integrated into the proposed finishes themselves that provided an invisible, yet effective, solution.

New Crematorium – Milton Keynes

Client: Milton Keynes Council
Architects: Architecture MK
Main Contractors: Kier Marriott

Our brief was to ensure that the acoustics of this new £6.2m crematorium would be at least as good as the existing crematorium, which was regarded as having excellent acoustics. We surveyed the existing crematorium to develop design criteria for the new building, based on the existing but upgraded where feasible and economically viable.

The primary design feature linking the various spaces throughout the new facility was a cycloid barrel-vaulted concrete roof. This posed some complicated acoustic questions with respect to speech intelligibility inside the chapel. The situation was further complicated by the requirement for state of the art audio visual facilities inside the chapel so that services could be filmed and webcast live around the world. To address these issues a sophisticated 3D acoustic model was developed. This enabled us to specify the type, quantity and location of acoustic treatments required.

New Library and Medical Centre – Clapham, London

Client: United House
Architects: Studio Egret West and DLA Architects
Mechanical Consultants: Scott Wilson

To carry out the detailed acoustic design of the scheme to achieve the Employers Requirements and Planning Conditions. The main library area doubles as a performance space for music and theatre and so detailed 3D modelling was carried out to determine the optimum compromise between the conflicting requirements. The Health Centre was designed to HTM 08-01 acoustic criteria, to ensure suitable speech privacy and acoustic insulation throughout the facility.

Cellar Multimedia Centre at Stowe House

Client: Stowe Preservation Trust

Cass Allen Associates was commissioned to give acoustic design advice for an exhibition on behalf of the Stowe Preservation Trust.

This multimedia exhibition is being created in the cellar of Stowe House which is a Grade I listed country house, also home of Stowe School. The exhibition will tell the history of the family and estate using three audio-visual `Talking Portraits’ which will run simultaneously.

The existing cellar had highly acoustically reflective room surfaces and had high reverberation levels. By generating a 3D noise model, Cass Allen designed the speaker placement and required acoustic absorption into the cellar in order to reduce the reverberation levels and achieve optimum listening conditions for visitors of the exhibition.