Sound solutions: Harnessing architecture for better speech environments

Previous studies indicate that clear and strong self-perception of one's voice promotes relaxed voice projection, potentially reducing voice strain in certain environments. Additionally, in multi-talker settings where speech babble can be distracting, innovative design could help create a more comfortable sound experience.

In architecture, the concave right-angle corner, where three surfaces meet, acts as a basic acoustic retroreflector. However, to effectively concentrate sound, numerous visible corners of considerable size are required simultaneously. This poses a challenge: designing surfaces that effectively concentrate speech frequencies, redirecting each talker's voice towards them.

In a groundbreaking first demonstration, researchers at Sydney have transformed a normal office into the world's first intentionally designed acoustically retroreflective room. Associate Professor Densil Cabrera’s office at the University of Sydney’s Wilkinson Building now features 157 explicit concave right-angle corners, many sourced from repurposed Ikea steel box cupboards (Cabrera et al. 2024).  

The room provides five decibels more reflected sound to a talker compared to a standard room. Unlike focusing rooms, such as domes, the retroreflective room uniformly concentrates sound regardless of the talker's position, resulting in surprisingly clear and loud self-perception of one's voice.

While this room represents the first intentional design of a highly acoustically retroreflective space, incidental examples of retroreflection in architecture exist. Some building facades possess unusually retroreflective properties due to numerous deep corners (Cabrera et al. 2020). The researchers have also explored the acoustic potential of Indian stepwells, characterised by multiple visible concave right-angle corners, with on-site measurements conducted in Bundi (Rajasthan) by Dr. Manuj Yadav in 2023.

Further developments also include focusing acoustic retroreflectors by warping the surfaces of retroreflectors to increase the sound concentration on the source.

A simple demonstration of this concept, in collaboration with the School's Lighting Lab, was installed over the Wilkinson Building entrance in late 2023.  Designed by Jonothan Holmes, Associate Professor Emrah Baki Ulas, Associate Professor Densil Cabrera, and Dr Wenye Hu, this installation represents the first publicly accessible realisation of focusing acoustic retroreflectors.

In late 2023, an ARC-funded research project commenced, led by Associate Professor Densil Cabrera, Associate Professor Dagmar Reinhardt, Dr. Shuai Lu, and Dr. Manuj Yadav. This project aims to further explore the use of acoustic retroreflection in architecture to optimise speech environments. Funding will support innovative developments, demonstrations, and human experiments related to retroreflective treatments.  

Other exciting work in this field includes PhD candidate Jonothan Holmes, who is exploring the design of new focusing retroreflector geometries, while Dr. Yoshimi Hasegawa is collaborating on applying focusing acoustic retroreflectors as passive echolocation beacons for individuals with visual impairments.

Leveraging focusing retroreflectors holds significant promise in enhancing everyday acoustic environments for communication, comfort, and wayfinding, and academics at Sydney are leading the way.