Riverside Church is an interdenominational Christian church known for its activism on social issues and for its landmark worship space, a 2,500-seat sanctuary that opened in 1930. The neo-Gothic church was modeled after a 13th century French Gothic cathedral, with limestone interiors, high vaulted ceilings, and a spectacular bell tower. It also integrated such modern touches as steel structure and “Akoustolith” Guastavino tiles in the ceiling vaults. The sanctuary’s interior volume of 1 million cubic feet is larger than most concert halls.

Akoustolith tile was a common ceiling finish in neo-Gothic churches of the early 20th century. It is a rigid porous tile that, from a distance, resembles stone, but up close looks like a man-made block of sponge or coral. At nearly 2” thick, it efficiently absorbs mid and high frequency sound, reducing reverberation at frequencies critical to speech intelligibility. In its day it was a brilliant engineering solution for achieving the visual grandeur of Gothic cathedrals while restricting reverberation to a level that would allow preaching to be understood without amplification.

Churches with Akoustolith ceilings have a “dry” sound that does not match their appearance, and they are often disappointing spaces for choral singing and pipe organ. With the improvement in audio systems over the last hundred years, there is no longer a need to sacrifice musical acoustics to achieve speech clarity. Consequently, many congregations have chosen to seal their Akoustolith tile to increase reverberation. A more reflective ceiling typically provides greater support for congregational singing and improved projection for pipe organ and choir. Since Riverside Church is home to a massive historical organ, there was a strong desire to increase the sanctuary’s reverberation.

Early efforts at sealing Akoustolith were hit-or-miss. For Riverside Church, Kirkegaard devised an approach that was successful on the first pass, increasing the mid frequency by 30%. Kirkegaard also explored replacement of the pew cushions, developing a cushion design that would be more reflective at high frequencies, further increasing reverberation and providing more support for congregational singing.

Photos: © Riverside Church NY