Hopkins Architects’ second school music building was a tall order, literally: to achieve the volume necessary for a natural acoustic space, the only way to go was up
Recently awarded an RIBA National Award, the music building at King’s College School Wimbledon is the second school music facility designed by Hopkins Architects.
This one is a cracker inside and out. Designed with a nod to the arts & crafts buildings found within its West Wimbledon Conservation Area location, it has a distinctive, steeply pitched roof over the main auditorium. Externally, this is covered in hand-made, clay roof tiles in a triangulated pattern that expresses the structure. Inside, the glulam roof is exposed, with the geometry of the structure further emphasised at the rear of the hall. Here, the triangular infill panels are subdivided into further triangles by detailing configured to provide the optimum acoustic conditions for the music activities that take place within the space.
Another acoustic consideration was the sound of the mechanical ventilation system
Commissioned to design a new music building at the edge of the campus, Hopkins came up with three linked volumes. The largest is the main performance space, which seats up to 200 and can accommodate a 70-piece orchestra. A second volume contains music classrooms and a rehearsal space while a third houses offices and cellular practice rooms.
The triple height volume of the auditorium was driven by the sound requirements for the natural acoustic space. According to project consultant Adrian James Acoustics, unamplified music requires long reverberation times of around 1.3-1.5 seconds when the hall is occupied. This can be achieved with a combination of a large volume and strong reflections off the side walls.
‘The challenge was getting the volume we needed for the acoustics in a way that fits properly on the site – that’s why it’s such a tall space,’ says Hopkins associate director Tony White.
Hopkins achieved this with a combination of a steel framed lower structure topped by a triangular glulam ‘lid’ that forms the roof structure. The glulam structure is supplemented with unintrusive tension rod supports. White says that as well as controlling the loads, visually these add ‘a bit of sparkle’. This timber structure – which has an eighth of the embodied energy of a steel-structured roof – sits on an exposed steel ring beam. With the help of an acoustic model of the hall, the acoustics were then tuned to the desired degree of diffusion and reflection, with the use of American white oak for the surface of the glulam and the matching oak infill panels with CNC-cut slots as required.
‘Because we had a timber lid that could partly reflect, partly diffuse or partly absorb, we had the toolbox in place to provide what the acoustician needed,’ says White.
The bulk of the oak veneered infills – those on the flat roof and the sloping roof soffits – have smooth surfaces to give the necessary reflection required for natural sound. These are sealed airtight to the glulam beams to prevent an air path for sound to enter the void behind the panels. The rear wall is quite another matter, and is instead designed to diffuse the sound. Here, Hopkins worked with joiner Decor Systems to create panels with four triangular sets of rounded horizontal slots in different depths as acoustically required. This was achieved with a build-up of four, 25mm layers of MDF with the facing layer veneered in American white oak. The acoustician specified shallower wells of 25-30mm in the centre of the panels with deeper wells of 75-90mm towards the corners of the triangular panel. The lower row incorporates an elliptical aperture for a concealed downlighter.
These acoustics of these rear panels is calculated to take account of the absorption properties of both the brick walls at the lower level of the auditorium, and the fixed, upholstered seating from Race.
Another acoustic consideration was the sound of the mechanical ventilation system, which needed to operate with low air velocities and low turbulence to achieve the low background noise level required by Building Bulletin 93 performance standards for the acoustics of school buildings. This ventilation method is assisted by the use of header-sized extraction openings in the brick stage wall.
The design theme of the auditorium was carried through into the walls and ceiling of the large classroom/rehearsal space on the first floor. This is covered in similar triangular and square ceiling and wall panels. Here, the smaller volume and type of use required a different acoustic treatment to achieve mid-frequency reverberation times of between 0.6 and 0.8 seconds, suitable for recording use and big band rehearsals.
The central flat roof is clad entirely in absorbent panels, while acoustically absorbent triangular panels are alternated with acoustically reflective panels over the sloping soffit. As in the main hall, the reflective panels are solid and non-perforated. The absorbent oak-veneered MDF panels, however, have a void of 75mm filled with mineral wool or melamine foam with acoustically transparent and flame retardant fabric within the rounded slots.
This treatment gives an even acoustic throughout the space. This is important since unlike the main auditorium, the performer could be located in any part of the room. While both the main performance hall and the rehearsal room meet their acoustic requirements, the spaces also deliver in terms of look and feel.
As well as its distinctive proportions, the 11.65m high space provides a pleasingly calm and uncluttered environment, with the brick and timber giving a visually warm atmosphere and the oak infills subtly animating the expansive roof area. The lighting rig was designed to be bolted into the steel ring beam while the organ is tucked into its own purpose-designed niche. Unusually for an auditorium, the space is naturally lit by full height windows to the sides of the performance space, angled to avoid distracting the performers.
White feels the design, with its use of brick and timber, delivers both the acoustics and the ambience that the client required.
‘There’s the sense of permanence and durability that institutions like this school value,’ he says.
Client King’s College School Wimbledon
Architect Hopkins Architects
Structural engineer Cundall
Environmental / M&E engineer Chapman BDSP
Acoustic/AV engineer Adrian James Acoustics
Selected suppliers Decor Systems (acoustic timber panels); HESS Timber (glue laminated timber framing); Michelmersh Brick Holdings (brickwork); Input Joinery and Gildacroft (joinery); Junckers (timber flooring); Race Furniture (auditorium seating); Lamilux (rooflights).