A truly outstanding project; a tour de force of precision joinery, balancing acoustic performance with the pure rational geometry sought out by the architect.
That was the verdict of the Wood Awards judges and they had no hesitation in awarding Kings Place Concert Hall both the coveted Gold Award and the Commercial and Public Access Award at the ceremony last October. The awards have certainly been gratifying for the teams behind the project: main contractor Sir Robert McAlpine Ltd; architect Dixon Jones Ltd; acoustic engineer Arup Acoustics; and joinery company Swift Horsman Ltd. For them it was acknowledgment of a true labour of love. And timber played a key role in the romance.
The brainchild of Peter Millican of Parabola Land Ltd, Kings Place is a multi-use building comprising seven floors of office space at first floor and above and three floors of public space, including two galleries and refreshment facilities at ground level and below.
The jewel in the Kings crown is the 420-seat public concert hall. This has its feet in the lower basement, but rises three storeys to appear above ground level.
The hall is shielded from the rumblings of nearby Kings Cross station by being a building within a building a box sitting on a series of concrete piers with rubber isolation mounts which provide acoustic separation from the rest of the building and the outside world.
The structure is steel frame, but step inside and its wall-to-wall wood. Timber was always at the forefront of the design, said Dixon Jones associate architect Paul Jolly. As concert halls through the centuries demonstrate, its the material of choice, favoured by musicians and acousticians alike. There is evidence from Arup Acoustics studies that timber areas help with the tonal beauty of chamber recital halls, he said.
When Arup Acoustics came on board, it already had an impressive bank of research into the acoustic performance of existing concert halls worldwide. That included Wigmore Hall, widely regarded as the finest space for chamber music in London, and the decision was made to offer a modern version of the 100-year-old hall.
Key to the acoustics of both venues is the incorporation of sound-diffusing geometry. Kings Place Concert Hall also has the option for a variable acoustic, achieved by drawing a 6m-long absorptive curtain behind columns around the upper half of the hall.
Large, flat walls result in too much reverberation, while traditional details such as niches, pilasters, columns, flutings and mouldings are extremely useful in breaking up the sound and modulating the acoustic, said Jolly. Timber can be moulded into those details fairly easily and weve replicated those types of geometries in a modern style and by using modern construction methods.
That included the use of oak-veneered MDF panels to line the interior. Not only was it a contemporary material but, thanks to its relative density, it also hit the mark for Arup Acoustics.
In a recital hall it is important to get the surface mass [mass per unit area] correct for each surface because this determines how much sound is absorbed or reflected at different frequencies, which determines the frequency balance and quality of the sound, said Arup Acoustics director Rob Harris.
Each element within the hall (stall panels, balcony panels, columns and beams) was given a minimum surface mass requirement typically between 35-50kg/m2. As the resulting joinery elements had to be up to 50mm thick, the use of a solid hardwood was ruled out for financial reasons, as well as the risk of movement. Plywood was considered, but again was discounted as its reduced density, compared with MDF, would have added another 5-10mm onto the panel depth. As MDF is heavier than other boards, the finish or component can be thinner for the same surface mass, said Harris.
Dixon Jones specified European oak for the veneer. We often use it in our buildings because we like the warmth and richness of the colour and because, depending on where the log is cut, it can provide a great deal of variation, said Jolly.
Its here that the true romance of the concert hall lies. Swift Horsman flew us out to their main supplier of European oak, Mehling & Wiesmann in Germany, said Jolly.
Their destination was an FSC-certified beech forest in the Spesshart region of north-west Bavaria, managed by the local community for about 300 years and which Swift Horsmans business development director Matt Roberts describes with affection as magical like Hansel and Gretel.
Interspersed among the beech trees are ancient oaks and they hold such a strong place in the communitys hearts that they are each named.
The 500-year-old Contessa had been felled on the full moon before Christmas 2005, sawn into 5m lengths, boiled at 80ºC for a week in a water bath, and then sliced into 0.7mm-thick veneers with a 5m blade.
Contessa produced an acre of superb quality veneer that was being saved for a suitably worthy project that would use the whole supply. Kings Place Concert Hall was deemed to be that project and the Contessa veneers put back together in log form were shipped to the UK. On arrival at Swift Horsmans workshop the logs were opened out and the companys veneer planner began the painstaking process of bookmatching.
We reserved the wider and more figurative crown veneers for the stand-alone elements, the big columns and beams, added Jolly. Even at 12m you can pick out the figuration in the timber.
However, the panels around the audience at eye-level could have looked a bit busy if wed used this type of veneer here, so quieter, straighter veneers were used. These were from the outer edge of the crowns where the grain appears compressed, producing an appearance of a quarter-cut leaf.
The veneer for the whole of the auditorium was mapped out in this way, taking about six weeks, before the sheets were trimmed and stitched together. Layons were then produced from the veneer map and all the completed joinery elements were treated with a matt lacquer finish to achieve Class 1 surface spread of flame.
When we first fed the range of geometry Arup Acoustics was looking for into our computer model, it produced some quite alarming results, said Paul Jolly. Our initial studies resulted in a visually busy interior which would have been distracting and inappropriate for an intimate recital place. We knew that, acoustically, it would do the job, but from an architectural point of view it wasnt anything like what we wanted to create.
The solution was to reverse the usual tactic of applying mouldings to the flat surface and, instead, to carve into it. Wed created a zone behind the columns to accommodate the acoustic curtain and, as a result, the timber was quite far forward from the walls, so we had plenty of space behind the panelling, said Jolly.
We cut slots and recess boxes into the wall, he continued. Different areas of the hall had to perform differently acoustically. In the ceiling coffers and in the upper half of the hall Arup Acoustics wanted large-scale diffusion to break up the long sound waves, and reflect them down to the audience. The large geometry then splits down into recessed boxes fixed to the back of the panels at balcony level and then at stalls level it splits again into much finer slots to deal with the short sound waves.
In order to achieve the visual regularity demanded by the architects and the variability required by the acousticians, the boxes at balcony level look the same but are in four randomly placed variations: deep recess; shallow recess; angled back; and angled forward. At stalls level, the vertical slots are all the same height, but are at varying spacings and with different widths and depths, with some of them going back about 150mm.
The various recesses were achieved by routing grooves into the MDF panels, inserting solid oak into them, veneering the panels and then routing the same grooves again, effectively lining them in oak.
The panels were designed so the interior construction could be broken down into manageable elements, rather than requiring joiners to work on site. Instead, everything was made in the workshop and fitted together on site like an enormous jigsaw puzzle.
McAlpine made Swift Horsman the lead contractor for the fit-out, but before they could slot the panels and column casings into place, the joiners had to ensure they had a plumb, true and level surface.
Because of the way steel is manufactured and installed on site you cant be too precise and you could have a margin for error of plus or minus 20mm, said Jolly. It was all built within the specified tolerances, but to go from that to an absolutely precise piece of joinery meant that everything had to be corrected and packed out by softwood elements.
Softwood battens also provided the framework for the panels hung on rails rather than nailed or screwed. The joints between the panels are a combination of rebates and biscuit joints and are designed so they are either made into features or are hidden, said Matt Roberts.
After acoustic tests, which the hall passed with flying colours, Kings Place opened in October 2008. Its offices are now home to the Guardian and Observer newspapers and Network Rail and, less prosaically, the London Sinfonietta and the Orchestra of the Age of Enlightenment are orchestras in residence.
Its a great space and it looks as good today as it did when we handed it over, said Roberts. It was such a pleasure to do and its still making people smile.
The Contessa oak was cut into 5m logs before being converted into veneers
Oak-veneered MDF casings were wrapped around the structural steel columns and were also used to form dummy columns and beams as part of the articulation of the surface that was necessary to achieve the desired acoustics