London landmark St. Paul’s Cathedral has installed an RG Jones Ampetronic induction loop system.
Despite a perimeter loop being installed around the cathedral’s dome many years ago, a comprehensive Ampetronic system has been installed to cover the entire floor area, plus the crypt and adjacent Chapel of St Faith, more generally known as the Chapel of the Order of the British Empire (OBE).
The OBE chapel is used for weddings and baptisms, while the crypt is used for a variety of events, as well as being host to the tombs of Lord Nelson, the Duke of Wellington and Wren himself.
“One of the key challenges was the fact that the crypt is, as you would expect, directly beneath the cathedral’s nave,” said Jon Berry of Wimbledon-based RG Jones Sound Engineering.
“We discussed the issues of vertical spill and how the system could best be controlled - the answer was a loop system divided into five zones, each zone covering a different area of the cathedral floor.”
One of the key features of the design is that Berry and his team used the issue of vertical spill to their advantage.
“When all the cathedral floor needs to be covered, all five zones are switched in,” he said. “However, the loops that cover the nave and chancel are dual-purpose, also covering the crypt and the OBE chapel. If an event is taking place in either of those areas, the inputs to the loop are switched via DSP, so users receive audio from the microphones in those areas, not from the main body of the cathedral.”
All five loop systems are switchable, with an SP5 phase shifter, which aligns the middle section so that it works correctly with each of the other sections. Each of the systems feature Ampetronic ILD1000G loop amps with the nave, as the biggest area, using four. The chancel uses three, with the remaining areas one each.
Inputs are from microphones that are an extension of the cathedral’s PA system and use a BSS SoundWeb system designed and installed by RG Jones. All of the mics feed into that system, which does all the required automated mixing. From there, the expansion DSP unit in the induction loop amp rack provides the feeds to the various loops and activates the switching.
“Because we obviously couldn’t disturb the fabric of the building, there were limited routes where we could run loop cables,” added Berry. “This meant that there were inevitably some peculiarities with the way the cable had to be run. But Tom Lane from Ampetronic came down, looked at the measurements and advised us on where we needed to optimise the loop amplifiers.
“The result is that there has been no compromise on the quality or strength of the loop signal anywhere in the cathedral. It is all working very well, it’s straightforward to control and the cathedral staff are very happy with it.”