A circular domed building on the banks of the tidal River Lagan (with mud flats exposed twice a day), floating on a bed of Belfast 'sleech' and with a nearby elevated railway and hovering helicopters may not at first sight appear the most desirable place for a new arts and conference centre. However, a major new public building such as this does not come along every day of the week, and so Sandy Brown Associates (SBA) had no hesitation in expressing interest in the project in 1989 and commencing discussion with Robinson and McIlwaine, a local firm of architects, leading up to a commission from Belfast City Council later that year. We joined the architects and theatre consultants (Carr and Angier) who had worked since 1978 to bring the project to life and were able during the next year to develop the general design to a point at which, the decision to go ahead having been taken, a full design team could be appointed. From that point to tenders took only one year. This completed a triad of SBA projects in the Celtic fringe with St. David's Hall in Cardiff, the Royal Concert Hall in Glasgow and now the Waterfront Hall in Belfast.
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The hall at night.
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Since that time the situation has improved all the time. The circular domed building comprised foyers, bars and other accommodation wrapped around an auditorium whose shape could be adjusted to our requirements. The River Lagan acquired a downstream weir which maintains a lagoon alongside the hall and, while the marina moorings shown in early artist's sketches never materialised, the environment became that of a 'waterfront hall'. The Belfast 'sleech' was a soft estuarine silty clay which demanded piling but had no more adverse effect than that; and the exclusion of train and helicopter noise and vibration is the normal day-to-day task of the acoustic consultant.
Measurements on a test pile, constructed down to the bedrock, indicated that although train passages were detectable the resulting noise levels in an auditorium would be acceptable. In view of the tight financial restraints the decision was taken not to vibration-isolate the building.
The brief for the project was to provide a prestigious civic building incorporating a concert hall and conference facility to seat 2250 and a minor hall with a capacity of 500. The usage spectrum had to be very wide, ranging from symphonic orchestral to theatrical performances, pop concerts, boxing and snooker matches, exhibitions and major conferences. This required a main auditorium with a world class acoustic, yet with the flexibility which would make it the most versatile in Europe incorporating different floor configurations including an orchestral pit, an arena format and a possible proscenium arch. Most of the requirements have been satisfied but, given the financial constraints, some compromises have been necessary.
The architects were impressed by the aesthetic and acoustic
of St. David's Hall so it is no surprise that the design
is reminiscent of that hall. Given the recent accolade awarded to this
Hall by Beranek
whose book 'Concert and opera Halls – How do they sound' placed it
among the top 11 halls in the world which were included
in this survey, this can be seen to have been a perceptive decision!
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A view from the stage.
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At 2250, the seating capacity of the Waterfront Hall is greater than the 2000 of St. David's Hall, necessitating an increased volume. Because St. David's Hall did not quite reach the design RT, the decision was taken to increase the volume even more than the enhanced audience numbers would require. Much of this enhanced volume would be placed above the stage to house the provision of flying facilities for stage use; the remainder was accommodated above the rest of the seating using a partially acoustically transparent ceiling to keep the visual ceiling at the optimum height.
The overall shape of an elongated hexagon was retained with the audience seated in small blocks arranged to give good sight lines. The blocks are much less varied in height in the Waterfront Hall compared to St. David's Hall but it is probable even so that the upstands between each seating block contribute to the lateral reflections for listeners.
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A view from the stage.
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The visual ceiling is of timber on steel frames. Those parts which are acoustically transparent are 100mm slats at 200mm centres giving a 50% open area but enhanced by openings between each set of frames. Those parts which are to reflect sound to the seating areas are of 12mm plywood. The preliminary acoustical design of this ceiling positioned specific reflecting areas to supply each of the seating blocks but, of course, looked extremely bitty! The final solution which is seen in the completed auditorium was an architectural solution based on our general ideas and will be seen to give a unified appearance to this element and to mirror the external shape of the building. Additional dished reflectors over the stage area are adjustable in height and designed to allow members of an orchestra to hear one another for balance and ensemble.
Ventilation is by a displacement system, air being introduced beneath each of the seats and rising by natural convection to extract ducts at ceiling level. The required degree of cooling is reduced by the technique and, given the large number of inlets, the air flow can be at an extremely low velocity. Measurements were made at the manufacturer's test facility in Finland. This type of ventilation system requires the structure to accommodate plenums below the seating tiers and for the seating wagons at stalls level also to be coupled to the ventilation system and to distribute the air. The system noise control has been extremely successful with design noise levels of NR20 being usefully bettered to NR15 with no additional modifications.
Model studies were carried out by Mike Barron at Bath University at completion of the design which came about the time that the project was going out for tender. The results of these tests suggested that there were improvements necessary to achieve really excellent acoustics. The fitting of model tests into a design programme is always a tricky problem; the design has to be well enough advanced for the model to be realistic but the programme has to be flexible enough to accommodate changes which may be required by the study. I am pleased to say that, while not happy at the prospect, the architects undertook the necessary modifications which required seating tiers to be moved closer to the centre line, splaying of the side walls at rear of stalls and the redesign of the ceiling mentioned above together with a raising of the sections of ceiling above the rear tiers. On re-testing there was a significant improvement in the results which showed that the degree of diffusion had increased, echoes had been eliminated and listening conditions in the rear tiers had been substantially improved.
Sufficient roof weight to exclude external noise was defined at an early stage as a total weight per unit area and the structural engineers were allowed to allocate this weight between the two skins as they wished. Deep three-dimensional beams in a cruciform configuration were needed to span over the auditorium and to reach to the outer edge of the drum; this design allowed one quadrant to accommodate the fly grid without restricting access over the grid. Grouted concrete planks formed the lower surface while the outer roof was to be a dome, designed initially of pre-case planks but finally built as an in-situ slab in lightweight concrete, with an external decorative finish of boarding and copper sheet over a ventilated air-space. Thermal movement of all the steel meant that the beams rested on sliding bearings and acoustic sealing of those points around the perimeter of the drum which penetrated the sound insulating skin proved to be a major challenge requiring large areas of plasterboard and the application of some ingenuity and care.
An additional performance space in the foyer necessitates good sound insulation between the foyers and the auditorium. Double doors with effective compression seals and acoustically treated lobbies were therefore incorporated in the design.
The Minor Hall (now known as The Studio) is a very simple but adaptable space intended for a wide range of performances. While music rehearsals and chamber groups may feature occasionally in the schedule, it is probable that drama and other speech related activities will be more common. Thus, while the space can be kept reasonably live with bleacher seating retracted, it will be much more dead when occupied by an audience of five hundred. In addition retractable panels surrounding the space at floor level can be rotated to show reflecting or absorbing faces and fabric drapes at high level can be manually extended to introduce a moderate amount of absorption.
Plant space is concentrated in two major (sensitive) areas; immediately above the minor hall and at upper level surrounding the auditorium. The minor hall, and particularly the plant space above, is constructed as a steel framed building with the upper (plant) areas having the steel frame isolated by resilient bearings. Additionally, to give added air-borne sound insulation, a jack-up floor was built over the concrete slab forming the ceiling of the Hall. Individual items of plant are, of course, seated on anti-vibration bearings on the major steel members. All pipe and ductwork is resiliently hung.
The block walls separating the main building plant rooms from the auditorium are double skin dense concrete blocks having no wall ties and with the outer skin tied to the adjacent columns with resilient wall ties. All walls are plastered on the auditorium side. The auditorium is well isolated from external noise, partly by the surrounding accommodation, but also protected from building noises by double skin walls and ceiling.
The wide range of activities in addition to concerts will benefit from deader acoustic conditions in the auditorium and to provide this a limited area of acoustic absorbing curtains at high level behind the two lighting bridges can be drawn out. These are in fact motor operated and form part of the smoke containment system in the event of a fire. In that case, they are supplemented by additional curtains hanging below the lighting bridges which prevent smoke spreading to the rear of the auditorium. The main technical provision to overcome the live acoustic is, however, a highly directional speech reinforcement system which, while normally retracted above the ceiling line, can be lowered to its design level from which point it directs sound to each of the seating areas with a minimised spill into the reverberant field. A second high-powered but non-directional sound system for pop use has also now been installed.
In order to open up the stalls area for promenade concerts and similar arena events the greater part (some 600 m2 ) of the stalls seating is mounted on wagons which can be removed from the auditorium on air castors to create a large open space. The entire stalls floor so exposed can be adjusted in height by screw jacks in addition to the front stage section which can be dropped to form a pit. A suspended, retractable proscenium of plywood and fabric is being constructed for theatrical performances. There is a platform provided for the later addition of an organ.
Acoustic measurements have been carried out and confirm that the reverberation time has been well maintained at some 2 seconds in the occupied auditorium; this value increases towards the low frequencies to give a warm sound quality. Much analysis remains to be done and it is intended that fuller information will be available at the Institute's conference on concert hall acoustics to be held in Belfast.
During the limited orchestral experience so far, the auditorium has received rave reviews. The liveness of the acoustic and sense of surround sound have been commented on while a remarkable degree of intimacy is achieved in the rear tiers.
The acoustic consultants to the project were Sandy Brown Associates (Alex Burd FIOA, Laurence Haslam MIOA and Stephen Stringer MIOA). Sandy Brown Associates are members of the Association of Noise Consultants.
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