To be heard but not seen

Oxford University gave this brief because a Grade I listed building needed refurbishing with a sound system. The Sheldonian Theatre is the second work of Sir Christopher Wren. Because its design resembles that of a Roman theatre, it is called a theatre even though plays are not performed in it. During the last two years re-ordering included cleaning, repairing and painting the ceiling.

All the internal décor has been impressively restored to exactly as it was in 1649 when it was opened.

The project was managed on behalf of the University by David Holt who rightfully insisted that the building needed a high quality sound system which could not be fixed to any original finishes. It should be invisible, and needed to serve ceremonies and lectures in two different orientations.

Meeting the brief
Brian Hillson of B&H sound was given the task of designing a system to meet this specification and chose speakers imported by Sennheiser UK from Italian manufacturer K Array. The main units were just 35 mm wide by 17 mm deep and arranged in a one meter column.

Twelve speakers from the vyper range were chosen and fixed to the rails of portable steps up the organ chamber, as well as door frames and the sides of the buttress on the ground and third floors. Because of the slim dimensions, they were able to be fixed discreetly. So much so that the B&H sound had to photograph them before they were spray painted to match the special colours used in the refurbishment. (They were truly invisible in the photograph taken after the camouflage).

The challenge of the surrounding galleries (Ladies Gallery and the Undergraduate Gallery) were overcome by equally discrete miniature speakers from the Bose Freespace range where the team used thirteen Freespace 3 cube speakers and six Freespace 16 speakers, all in white finish and arranged in a distributed infill design.

The K-Array Sub bass speaker model kks50 were concealed within the same portable staircase, through ported enclosures in the steps, and powered by two ka7 and one ka10 amplifiers.

The Custodian was provided with an Allen and Heath PL6 fader plate to call up the pre-sets to change the orientation of the system from north facing to south facing, programmed on an Allen and Heath idr8.

It was also extremely important that all data cabling (and speaker cabling) be low smoke to meet stringent site conditions.
Appreciative accolade

Oxford University staff were present when the speakers were demonstrated. They were impressed by their directionality and controlled dispersion in the vertical field. When one professor heard the completed system, he asked, ‘by the way, where are the speakers?’ – Probably the best testimonial to the success of the installation!

• For more information on B&H audio please visit www.bhsound.co.uk. They are also exhibiting at Manchester CRE Stand P1.