Steerable speakers prove the solution to intelligibility issues

The Church of St Mary and St Joseph, Poplar (pictured), is a Grade Two-listed building designed by celebrated architect Adrian Gilbert Scott as part of a project associated with the Festival of Britain. It was constructed between 1951 and 1954 and is a powerfully imposing structure.

Historians report that the building was regarded as old fashioned when it was built, but that it is now appreciated architecturally for its workmanship, materials and design. It is widely considered to be Adrian Gilbert Scott’s finest church.

Both parishioners and clergy at the church had been aware for many years of a lack of good speech intelligibility and ‘gain’ before feedback, and were hoping it could be improved; so they asked Peter Kenny of Torpedo Factory Group to investigate.

Peter’s main concern was, of course, with sound reinforcement and the acoustics of the interior, which is formed of a vast open space, cruciform in plan, with the central congregation seating being formed in a square. North and south transepts accommodate further seating, with chancel and narthex on the west and east respectively.

The investigation

Peter takes up the story: “On attending the church we met Fr Keith Stoakes, the parish priest. The existing sound system was demonstrated using radio and wired microphones and it was agreed that the sound was largely unintelligible, achieving an intelligibility measurement using the NTI Acoustilyzer of worse than 0.4, and suffering from a particularly ‘boomy’ characteristic. It was also judged to be on the threshold of feedback even with a low level of reinforcement.

“The speech transmission index is a recognised standard of test and measurement which sets out to ensure that an electro-acoustic system achieves adequate levels of intelligibility, and enables us to avoid dependence upon subjective opinion.

“Speech intelligibility (Sti) measurement techniques use synthesised test signals that do not sound like speech but which have common characteristics to real speech signals. The resulting sounds are then received to a meter through a calibrated microphone. Sti ratings range from 0-1, with 0.5 being fair and 1 being a level of almost unachievable excellence. In other venues the worst I have measured was 0.35 and the best was 0.83.”

The old sound system at the church comprised several small column type loudspeakers distributed around the walls and pointed in toward the congregation at the centre of the open space.

Peter explained the problem: “Experience of similar buildings where the volume of space is disproportionately high when compared to the amount of acoustic absorption – and in the case of St Mary and St Joseph there was none at all except the clothing of the congregation – guides us to conclude that such an arrangement of loudspeakers is incapable of delivering intelligible speech. We therefore recommended that a demonstration test of a steerable array type loudspeaker, such as we have used to achieve successful solutions in churches such as St Mary le Bow in Cheapside, St Bartholomew in St Albans and also St John’s Parish Church, Pinner, should be carried out to confirm the potential for improvement using current, leading-edge technology.”

The demonstration and proposal

A Fulgor Focus loudspeaker was borrowed and set up with the objective of confirming to how much of the congregation it could provide intelligible speech. It was left in place for a weekend so that it could be tested during a number of services. Prior to one of the services, Peter was able to take an intelligibility measurement reading of  greater than 0.6 while covering more than half of the congregation: an impressive result.

The Fulgor Focus loudspeaker was proposed because it is possibly the only true powered steerable array that can receive power and audio signal through a single two core cable while control signals are communicated directly with the loudspeaker’s digital circuit – reducing the number of installed cables from three to one: a twin-core speaker cable. In a listed building installation such as the church of St Mary and St Joseph that alone would save thousands of pounds.

The Fulgor Focus loudspeaker is manufactured in Italy, where it was designed specifically for the Catholic Church, who have many historic monuments to care for. Steerable beam technology is often the best technical solution to improve speech intelligibility in such environments, but installation cost and disruption due to wiring requirements had always been prohibitive. The Fulgor speaker technology overcomes that with its two-core connection, yet still outperforms its more expensive rivals.

The result

Happily, the demonstration test proved to be entirely successful, with parishioners and clergy commenting very positively; specifically, on how it was possible to hear the difference from being within the defined pattern of the loudspeaker or outside it. That proved the need for two loudspeakers, to take account of the considerable width of the seating area into the transepts.

Peter concluded: “In addition to confirming speech intelligibility now better than 0.6 – an excellent achievement in such a difficult space – it is pleasing to report that not only is speech now delivered intelligibly, but also with a notably natural quality that is not always possible where processing associated with beam steering is necessary.”

Univox Audio is the UK distributor for the full product range of Fulgor systems, including the Activo Focus speakers used in this installation. For more information on this and their other specialist sound products, including induction loops, FM and IR assistive listening systems, visit their website or give them a call: they will be happy to advise and put you in touch with a trusted installer.

• For further information visit www.tfg.com and www.univoxaudio.co.uk