Enhanced acoustics

Indonesia may be a predominantly Muslim state, but other religions co-exist peacefully in the democratic archipelago. Reflecting the pre Second World War Dutch colonialism of the region, the northern Borneo city of Pontianak is home to a large Roman Catholic population. At the request of the region's Governor, the city completed the construction of a 2,400 capacity cathedral in time for the 2014 festive season. The design of the 39m high basilica may hark back to the 18th century, but the interior of St Joseph's required a 21st century speech intelligibility solution for its services.

Historically, European cathedrals were acoustically designed to naturally amplify the sermons and choirs of medieval times. Today, sound systems are added to merely assist with the intelligibility without marring the classic cathedral sound worshippers have become accustomed to. St Joseph's cathedral's Priests were of the same persuasion and called upon the services of PT Hesed Kharis Indonesia to provide acoustical works together with a sound reinforcement system that would enhance the natural cathedral sound of the architecture without marring the aesthetics.

'From the outset, the priests realised that there would be a problem with speech intelligibility given the extent of the marbling, stained glass and concrete throughout the building,' explains PT Hesed Kharis Indonesia managing director Dene Dave Laoh. 'Therefore, the initial focus was on taming the reverberation emitting from the basilica and the under balcony areas. The dome is a unique feature but it needed to be tamed acoustically.'

Vincent Lie and the acousticians from Vertical Acoustics would soon have to develop a head for heights, overcoming any vertigo to tame the dome. As such, a scaffold tower was erected to reach the 11.5m surface area height of the dome, some 25m above the main sanctuary floor. 'We created a unique bass trap by covering the dome's surface with 125mm thick cellulose fibre absorption material. The sound enters this material at an indirect angle and becomes trapped,' recalls Mr Laoh.

Shaped as a crucifix, all the seated areas facing the central altar are located on two levels. Here, the acoustics team opted to 42 2m x 2m install absorption panels in the under balcony areas and a further 20 2m x 2.4m panels in the upper balconies. 'The sound remains natural, but the STI index has been lowered significantly to between 1.65s and 2.45s depending on where you are seated,' explains Mr Laoh.

To successfully blend any electro acoustics in harmony with the natural room acoustics was always going to be a delicate process for the PT Hesed Kharis Indonesia team. Congregated in two pews adjacent to the central altar, the choir required gentle amplification and this has been achieved by adding six beyerdynamic MC86 shotgun microphones on permanently fixed pole mounts equidistantly located on each pew.

'They provide a very narrow response pick up avoiding excessive acoustical energy,' furthered Mr Laoh. 'By aiming them correctly and producing a polar pattern, the microphones have succeeded in their aim to avoid feedback, whilst capturing the depth and volume of the choir. Initially we were going to add only two models, but the church wanted more in case they really needed to boost the signal.'

In the corner area of the church adjacent to the choir, Mr Laoh made use of a space that had been earmarked as an elevator by transforming it into an A/V equipment room. 'The location was perfect as the sound engineer operating from this room has a perfect sightline of the altar,' explains Mr Laoh. 'In addition, the cable runs to the speaker points have all been minimised by locating all the amplifier racks in a small dust-free, air conditioned room on the upstairs balcony.'

Twelve loudspeaker brackets have been installed in the lower seated areas. These have been mounted at 6m height and the cabling is run in the above ceiling in conduits some 400mm above to the amplifier racks. A further four speaker points have been added in the tiered balcony seating at a height of 3m with another four added at the front of the altar, dedicated for the front row VIPs.

A total of 20 TW Audio M8 loudspeakers provide gentle reinforcement throughout the seated areas of the church adding to the ambiance of the tamed cathedral acoustics. Each of the German 400W programme-rated M8 speakers operates within a 70Hz-20kHz frequency range and for such an application. As such, no further lower frequency extension was required.

Canare L2T2S11 loudspeaker cable was used to connect the M8 speaker points with the Allen & Heath AR-133 audio rack connecting the GLD80 digital console via Cat-5e cabling. The 20 M8 speakers are powered by five Powersoft M28Q four-channel amplifiers, although a sixth one has been added as a redundant spare offering plenty of headroom in the process but is additionally used for providing the power to a further six monitors in the altar area when required.

Digital signal processing has been applied by adding an Allen & Heath iDR-8 input linked to an iDR-8 output into the control room playing the role of a 16 x 16 matrix mixer. System configuration and pre-sets have been configured via a PC loaded with the proprietary iLive software.

The audio installation is complete with the addition of two Shure Microflex MX412D gooseneck microphones installed into the main central altar and a further two models integrated into two smaller lateral pulpits.

Having won the initial tender in 2012, both Vertical Acoustic and PT Hesed Kharis Indonesia were grateful for being able to work with the dean on the committee who appreciated audio engineering and acoustics. 'We had someone who understood what challenges we were facing and was sympathetic to our course,' confides Mr Laoh. 'This is most unusual as you often spend a lot of time educating or fighting with your client in order to gain approval to conduct works. But at St Joseph's this wasn't the case and everyone pulled together for a common cause. Most Catholic churches are plagued with poor acoustics and reverberation as they aren't blessed with sound separation. So this is an unusual house of worship in that respect.'

The cathedral bells that rung before Christmas in 2014 did not require amplification as a massed crowd heeded their call. Once inside however, they were every bit as awestruck by the sound quality as they were the interior design of this other neo-colonial masterpiece.

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