The soundscape of an ancient Chinese bridge

Chinese interlocked timber-arched covered (CITAC) bridges serve an important function in Chinese culture. In daily life, nearby residents pray to statutes housed under the bridges, and during larger holidays, they gather to sing and chant during rituals.

Due to their architectural and cultural importance, Zhang et al. set out to investigate CITAC bridges’ acoustic characteristics. Studying four CITAC bridges, the researchers discovered that dimensions, enclosure structure systems, and occupancy all influenced the bridge’s sound fields.

The mid-frequency reverberation times (RTs) of the bridges — the time taken for a sound to drop 60db from its initial value — ranged from 0.37 to 0.50 seconds. Small Western churches, for comparison, have mid-frequency RTs of 0.81 to 1.72 seconds.

Since the bridges aren’t enclosed on all sides, the volume under the bridge is considerably smaller than indoor theaters. The exposed structural elements under the bridge also influence the volume.

“Their rough wooden surfaces contribute to multiple internal sound reflections within the roof space, which increase sound absorption,” author Dongxu Zhang said. “As a result, the interior surfaces of traditional pitched roofs can be considered to have relatively high sound absorption, contributing to the shorter reverberation times observed.”

Apart from the cross-sectional aspect ratio of the bridge, however, the researchers found the sound characteristics follow the same properties as other long spaces.

In the future, they will study users’ sound perception to brainstorm solutions that preserve the cultural heritage and soundscape of the bridges while also improving their sound quality.

“This study enhances our understanding of the sound field characteristics of CITAC bridges through more comprehensive research, providing a valuable acoustic reference for their preservation,” said author Jian Kang.

Source: “Sound field characteristics and influencing factors of traditional Chinese interlocked timber-arched covered bridges,” by Dongxu Zhang, Guanyu Ren, Fei Cheng, Dong Xiao, Mei Zhang, and Jian Kang, The Journal of the Acoustical Society of America (2025). The article can be accessed at https://doi.org/10.1121/10.0038959 .