Flanagan Lawrence and Idibri on making University of St Andrews’ hall of ‘tuneable’ acoustics

The £12.5 million Laidlaw Music Centre is not only the University of St Andrews’ first building dedicated to music, the centre’s McPherson recital hall is also the world’s first to have both a reverberation chamber hidden above its ceiling and a fully adjustable, moving floor. Flanagan Lawrence partner Jason Flanagan and acoustic consultant Nicholas Edwards of Idibri talk through the thinking behind the hall’s ‘tuneable’ acoustics.

How were you appointed for the project?

JF: In 2016 we won an invited design competition for a music centre at the south end of the 16th century St Mary’s Quadrangle. The focal point of the new public space is a century-old arboretum, so we had to fit the building in among the trees, in a Conservation Area alongside three listed university buildings. The university’s director of music, Michael Downes, had toured conservatoires and knew of our auditorium at the Royal Welsh College of Music and Drama, so he asked us to submit a design for the Laidlaw.

What did the brief call for?

JF: A dedicated music building, with the recital hall complemented by three large sectional rehearsal spaces, 10 individual practice rooms, recording studio and amplified music suite. They wanted a world-class rehearsal space big enough to handle symphony orchestras, chamber music and vocal recitals but that local community choirs could also use. It needed to be inherently flexible, both spatially and acoustically.

It also had to fit into its surroundings. We put the 18m-high, steel-framed McPherson Hall adjacent to the tallest building on the site and wrapped everything else around it, with the foyer in the middle. This means it steps up in scale, with cornices locking into adjacent listed structures. The entrance colonnade allowed us to respect the root base of the mature trees on the site, so the first floor could step out. The whole building is clad in Darney sandstone.

The chamber is externally clad in stone and twice the size the client had anticipated, at significant extra cost. How did you convince them?

NE: It wasn’t easy but having a track record for major international concert halls helped us. I designed the Symphony Hall, Birmingham and the Morton H Meyerson Symphony Centre in Dallas and for some, these are the best concert halls either side of the Atlantic. And both of them have reverberation chambers. The brief required a room that was good for a solo, symphonic and choral work – which needs a range of reverberation. But they also wanted the intimacy of a modest-sized room.

Technically, the most difficult thing was having to do a virtual reality simulation of the space with and without the chamber. We connected the VR software with headphones rigged to a mic you could sing into, and it would create the exact sound you’d hear in the space.

What is so special about the McPherson Recital Hall?

JF: Its more about what you don’t see than what you do. The reverberation chamber, hidden above the hall’s 9m open ceiling line, almost doubles the volume of the hall. It works to generate the long reverberation times necessary for orchestral and choral works. 

You can go from very live to dry acoustics, which is when you fully drop acoustic banners around the walls. The latter cuts reverberation from about four seconds to one. It creates a wonderfully rich range of very clear sound – the hall is effectively an instrument in itself.

And how is the acoustic performance achieved?

JF: The aim was to achieve a solid, monolithic, reflective surface. In the McPherson Hall, wall build-up was 75mm Darney stone 50mm cavity, 200mm mineral wool insulation and 215mm dense block, then plaster. To this we then screwed the oak panels that line up to the main body of the space to the open ceiling soffit. There are no gaps past the blockwork – the build up is solid.

Internally, the reverberation chamber is a very simple blockwork space with plaster lining; again, it’s all hard, smooth surfaces. A huge manually-drawn curtain that’s hung off its walls can be pulled around to soak up bass frequencies and to stop the sound bouncing round the space.

Half of the ceiling is open to the chamber above. Timber beams run across, and above them is the walkway servicing zone for the chamber. The underside of these walkways is lined with black-painted acoustic plasterboard. Voids between these zones amount to 50% open area, but as they are coloured black, some people don’t realise that there are voids there at all. 

How is the design informed by the HVAC strategy?

JF: Heating is by occupancy, not volume. Conditioned air is all low velocity feed trickling in from the perimeter via low level gaps below the oak panels from the 1m-deep floor void plenum. Low velocity means that both feed and high-level extract are silent. 

Given the reverberation chamber’s extra cost, did you look at other options?

JF: We believed it was the only way we could achieve the different performance flexibility that the client wanted. It could have been 12m high room with adjustable ceiling reflectors but that wouldn’t have achieved the requisite level of reverberance – especially for organ or choral work. Site constraints prevented us making the physical space on plan any bigger and reverberance is a factor of volume. Nicholas auralised this aspect for the client via virtual acoustic modelling to show how the sound would be under various conditions.

And why a simple ‘shoe box’ hall?

NE: There is always debate over the need for acoustic diffusion, with some experts breaking up wall surfaces to do it; but I don’t agree with that. Precedents like Vienna’s excellent Musikvereinssaal – a classic ‘shoe box’ – have flat walls, and we merely repeated that concept here. 

The classic error in music space design is to rake seating but this means that sound that should be reflected off the back walls is instead absorbed by the audience. That doesn’t happen in ‘shoe box’ design. When you perform here, the sound hits the back wall and reflects. And because we want surfaces to reflect sound perfectly, the walls are completely flat, apart from the side columns.

It’s an 18m-high room in effect. Why didn’t you make the room itself that big?

JF: Because the chamber itself is basic in terms of finish – it’s just plaster lined; so all the high spec detailing need only occur below the ceiling line. Practically, you need a reflective surface for performers at about 9m. It’s only 18.7 by 14m in plan, so 18m would have felt too tall. What’s nice is that the hall  feels intimate and warm, with plenty of natural light. 

NE: Had the main ceiling been any higher, we would have needed a balcony all the way round and a soffit to throw the sound back into the room. But we stuck with the simple box form, because what you get from the reflection off the 9m ceiling is clarity. Sound that passes into the reverberation chamber persists there momentarily before bouncing back down through the ceiling slots, which gives the sound its reverberance. The sound is analogous with a good wine. There is the initial ‘clarity’ followed by richness and complexity, and the simple rectangle form is what gives the room magical acoustical properties.
What was the story behind the moving floor arrangement?

JF: The ideal starting point for a recital room is flat floor with the performers on a low rostrum. The moving floor came out of a conversation where we were considering having an element of the rostrum moving and we thought ‘but wouldn’t it be amazing if the whole floor was moveable? Nick worked out the mechanics of ninety 2x1m timber-clad boxes on metal trays raised and lowered on a scissor mechanism.

NE: I didn’t think the moving floor would happen. I did a client presentation where we imagined it like the Giant’s Causeway and we must have convinced them. But even if they had decided not to fund it, the under-floor air plenum was always in the contract and any future moveable floor could sink into it.
JF: In most conditions, the room is set up with the seats dropping into the void, meaning the stage is at the same level as the foyer and 600mm higher than the front seats; so in the main, the sound is reflected off the back wall.

The floor of the timber boxes is so hard and reflective that the void below has no effect at all on the hall’s acoustic qualities, creating only subtle changes in the overall volume. The nosing on the edge of each box consists of an ingenious magnetic steel flat that flips to reveal a contrast strip, to meet guidance. 
The mechanism has 40 pre-set modes. Costing about £1 million, this required separate fundraising and was only instructed towards the end of the contract. All but the ones near the side walls move up and down. It’s mesmerising to see – like watching a 3D kinetic sculpture.