Cathedral of the Immaculate Conception

Memphis, Tennessee

In response to the needs of the expanding Catholic Diocese of Memphis, Tennessee, Williamson Pounders Architects (WPA) selected Thorburn Associates to assist with the acoustical and audio system design for the restoration of the Cathedral of the Immaculate Conception.

The main challenge for TA was all of the curved surfaces in the altar area. For example, parishioners complained that they could not hear the priest, but could hear a whispered conversation from the other side of the transept (due to the focusing of sound by the curved ceiling and walls). The original design architect used segments of spheres, columns, and circles that created a significant problem with focusing of sound in many different locations within the nave. Sound absorptive material and coffers were introduced into these surfaces to help minimize the focusing of sound.

The reverberation time was adjusted to support a new electronic pipe organ. The longer reverberation time required for the pipe organ and the relocated choir area created a challenge for the design team in selecting acoustical finishes. Both paper and computer modeling of the acoustical environment confirmed this.

The original sound system was loudspeakers located on the columns. Parishioners complained that the old loudspeakers did not work and there were spots where they could not understand what was being said. Our solution was to design a pew back sound system. A pew back loudspeaker system is a hybrid of a distributed audio system. Distributed audio systems use many low powered loudspeakers located close to the listeners versus a central cluster loudspeaker system which has one large loudspeaker system located in a central area, in this case over the altar, to distribute audio throughout the sanctuary. A lighting analogy would be to consider the difference between numerous down lights providing uniform illumination of the floor/seating area versus a single high light output floodlight providing the same illumination from a pole.

The electronic portion of the audio system is automated. The system uses several mixing components, which provide two primary formats. The first format is speech reinforcement, or in this case, the spoken word. The second format is for choir and music. The choir may be accompanied by organ music. Both formats are routed through a main mixer and can be heard throughout the sanctuary.

The spoken word is heard through the pew back distributed loudspeaker system. This provides even coverage throughout the sanctuary. The loudspeaker system is divided into six zones. This allows the church to control each zone as required per worship event. The music audio system is also heard through the pew back loudspeaker system. The loudspeaker system is capable of supporting choir vocals and other music sources, but is supplemented with two larger format column mounted loudspeakers. These loudspeakers are “time aligned” with electronic delay to improve the speech intelligibility of the sound heard naturally from the choir and electronically from the column and pew back loudspeaker systems. The choir and music sources are routed through a local choir mixer, then into the speech audio system.

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