27.09.16

A magnum opus at Salisbury Cathedral

trancept

Installing intelligible networked audio throughout a huge 750-year-old cathedral proved to be real challenge for one integrator, as Paul Milligan found out.

With construction dating back to 1220, Salisbury Cathedral, home to the world’s oldest working clock (from 1386) and a host to one of the four original copies of the Magna Carta, exudes history.

Having recently celebrated the 750th anniversary of its consecration, the Cathedral features imposing early English Gothic architecture and measures nearly 450ft in length and 225ft high.  After reading those facts, if you expected it to be the sort of  venue where installing an intelligible, networked audio system would be extremely difficult, you’d be absolutely right. 

The brave integrator to take on the job was Ed Manwaring from EM Communications.    Having provided some consultancy work at the venue on and off for nearly a decade, he was aware of the issues the cathedral was having with its ageing speakers and network. Manwaring, alongside long-term audio supplier to the cathedral, Harman  distributor Sound  Technology, was tasked with designing and installing a new audio network, with new control system and loudspeakers. 

Alongside updating the old system, the new technology had to be easy to use so the non audio trained cathedral staff could operate it day-to-day and it also had to give the cathedral the ability to run more live events, to generate revenue.  

Salisbury Cathedral

One challenge for Sound Technology and Manwaring to overcome was that the cathedral is split into a number of sections, the north and south  transept, the choir,  the trinity chapel, the crossing and the nave. “You have to treat them as individual spaces.  Each one is treated as an individual room, but delay-wise they are all linked together,” says Manwaring. The spaces are used individually every day, for example
trinity has mass at 0730 every morning, and for evensong the choir area needs audio,  but for big services such as midnight mass at Christmas the whole place is full. “There are prayers every hour the church is open, and that was one of the biggest challenges  of  this project, because you actually only have a 50-minute window in which to install kit,” notes Manwaring.

The whole refurbishment process began with Manwaring and Sound Technology coming
together to provide a series of on-site product tests for the cathedral so they could decide on the best options for them.  Once  those  were whittled down, it was time for the design.  And this is where the difficulty begins. “We ran the design through EASE before we got to site, but it starts to get flaky when you are dealing with 6-second  reverberation,  as  you  have  in  here,” says Manwaring.

“The  problem with multiple speakers coming out at the same time is that you get multiple reflections. With the seating down the sides of the chapel the previous system had a lot of intelligibility issues because of the proximity of the walls.  Changing audio
here from four speakers to one or two speakers per column made a fundamental  difference.”

Battling reverberations in a 70m high building, made of stone and glass was always going to be a huge challenge, but not only has it been overcome, it’s been done with nearly half of the number of loudspeakers of the original install, thanks to  improvements in audio design. “You can now do more with less.  We put 46 speakers
in, and took 70 out, and we now have more coverage,” says Manwaring.

“There are different schools of thought, because the correct approach with delayed
sound is ‘a little and often’, but the right way in a place like this is ‘a little correctly’. The vertical distribution here is a very narrow band, so you don’t have sound going  high up just to come back down again, here it’s fired straight into people’s ears.  Look at the vertical coverage here, the previous speakers were 60 deg, these are 15 deg, so the sound doesn’t get lost in the rafters.”

Another example Manwaring gives highlights what a unique challenge Salisbury  Cathedral was. “We installed a wireless access point on top of a throne dating back  to 1350.   We needed a cherry picker to get on top of  it, but had to be so careful because if I broke it I knew Gorilla Glue wouldn’t suffice. You can’t just walk in here with your boots and hard hat on. We have not drilled one hole as part of our work, we’ve used
all existing holes or built bespoke fittings to the existing bracketry.”  

Other quirks of working in a 750-year old cathedral include no central rack room, instead six racks are dotted around the different sections. The refurb also had to accommodate 38 input channels coming in from different fixed microphone points from the original install years ago. Throughout the cathedral a mix of lecterns mics and radio mics are used.

During the day the system is controlled by staff with the press of just one button (‘Evensong’ etc) on the Harman Motion Control iPad app.  “For the clergy to get the most out of it we had to make the GUI buttons on/off and up/down with some EQ settings,” says Manwaring.  One of the clever touches of the project design is how there has been an EQ assigned to each member of the clergy. On the iPad a drop down box shows each mic input, so regular performers can have their own EQ recorded in the system. 

“If they go up to a pulpit or use a radio mic they can take their settings with them.  We have also set up generic male  and  female  settings  for  the  clergy,”  adds Manwaring.  Adding  personal  EQ  levels  took between 50-60 hours to program. Because it is so simple vergers now train each other in using the system. The day-to-day running is handled by a floor manager, introduced into the cathedral a couple  of  years  ago.  An additional sound engineer comes in just for the Sunday services, and  Manwaring  says  his  help  was  key  to  fine-tuning the system once it was almost complete.

One of  the stated aims of the audio refurbishment programme was to enable the cathedral to host more live events. “Now it’s been EQ’d and delayed properly it’s ready,” says Manwaring. “Last year it hosted a music event and used a seven-box line array hanging in the middle of the crossing. I was by the mixing desk at the font, and there was 70% reflected noise.  

Based on that, we decided on the larger JBL CBTs for a full range, especially for music events, so we get the correct sound pressure and dispersion, without too much reverberation.”

Based on the likelihood of the system being used for live events the cathedral invested in a Soundcraft  Performer3  desk, with Soundcraft Stagebox running Dante.  The backbone of the audio network is three Dante to BLU converters, one  in  the  north  transept,  one  in  the  south transept  and  one  in  the  crossing. All  long distance  audio  distribution  is  done  via  Dante.  

There was a Cat5  point where the original touchscreen control was housed, so Manwaring re-used the cable so the floor manager can plug the desk straight in the PA system if he needs to.

It also has MADI card fitted inside the Stagebox, so if a live broadcast is required it can also be done.The  dramatically enhanced  intelligibility and thoughtful integration  delivers a wholly appropriate solution for the cathedral, while seeing the staff walking  around the cathedral every day controlling the sound via an iPad is testament to the skills of the programming and design. The installation has met all criteria, according to Salisbury Cathedral floor manager, Russell Cruse.  “It has been a great success in terms of speech intelligibility and clarity and I have received positive feedback from the guides, vergers and clergy.”