San Lorenzo da Brindisi Church, Italy
The building had undergone a radical transformation from a large open concrete hall into a wooden sanctuary – the largest hemisphere was constructed from wooden ribs. Inside this space sits the congregation to listen to sermons, prayers as well as large choirs (100 or more singers) and organ music.
It is well known that amplified sound in church buildings is a problem. The prolonged reverberation time and hard reflective surfaces confuse the sound waves and make it difficult for the audience to distinguish the spoken words or appreciate the music. These problems were further aggravated in this church by the concave nature of the roof, which focused the sound inappropriately, as well as the wooden structure, which resonated at around 2400Hz, distorting the human voice. The concrete and marble surfaces also reflected the sound waves so that it was impossible to hear anything clearly in the auditorium.
Padre Luca recalled the situation he was facing: “We were very disappointed with the acoustics in the church when the dome was finished. We had designed the space to reflect the religious nature of its use and had envisaged a calm and serene atmosphere where the entire audience could clearly hear and understand the sacraments. We tried two other solutions before Francesco was called in to help and we are delighted that he could resolve the problem so beautifully and in keeping with the devotional ambiance we had created.”
The architect, Paolo Marciani, had met Francesco Pellisari Consulting when he attended the Moltitudini show in Rome the previous year. “The engineers had tried to resolve the acoustic problem using a standard line array speaker system with an electronic delay. This was an expensive system to install and complex to run but unfortunately it did not solve the problem and the speakers looked out of place inside the church. So they replaced this with a multi-source speaker system comprising 24 directional beam speakers suspended from the ceiling. Once again this did not work and they also cluttered the space in the dome. Francesco Pellisari Consulting takes a different approach to resolving acoustic issues so I asked them to visit the dome with me.”
On his first visit Francesco took all the measurements using the latest electronic computer-enhanced recorders but it was his natural ability using a simple whistle and clapping that enabled him to hear and understand the issues. “I needed to reduce the ‘sabine time’. To increase the sound absorption inside the building I had to invent a special translucent cloth. Two layers of this cloth were stretched across the oculus at the apex of the dome so that it acted like a drum. The pews were modified so that they absorbed the same amount of sound whether occupied or not. To dampen the resonance of the wood I used a slat system that reduced the delay from its previous 27 seconds to an acceptable 15 seconds. I have worked on many dome structures in the past and I proposed an omnidirectional sound system as the solution to this particular building. This is completely opposite to the standard approach but I know from experience that it works. It is also simple to use and inexpensive in comparison with alternative systems. I placed the large omnidirectional speaker (Thor) for the organ music above the organist and supplemented this with four smaller omnidirectional speakers (Atun) for the voice. These I could suspend virtually anywhere in the dome due to their omnidirectional nature so I was careful to place them so that they did not distract from the atmosphere. I used a very simple amplifier and equalisation unit and kept the system entirely analogue.”
Speaking to Padre Luca after the opening, he said: “The Church is delighted with the results. The atmosphere inside the dome is exactly as we wanted it to be. The sunlight shines through the central oculus with the shadow of a dove symbolising the Holy Spirit that hovers on the assembly. The design of the speakers also reflects the ecclesiastical nature of the building. The sound is now exquisite and we were pleased when the opera singer, Andre Bocelli, who performed here recently, complimented the sound quality.”