In order to survive, we constantly assess the quality of our spatiotemporal environment. At every point in time and space, we make use of our multiple senses, which act in concert. Multisensory processing is the norm rather than the exception.
In addition to our sense of sight, we employ our sense of hearing to collect information from our environment in order to gain a greater comprehension of its attributes, such as the extent and gravity of challenges threatening us and the opportunities available to us in our immediate environment.
Over 55% of the world’s population currently lives in urban regions, and by 2050, this number is expected to reach 68%. This necessitates providing people with an optimal and wide range of a valuable resource on which we have evolved to rely for our survival and success: sound.
Beyond decibels
We experience 'sound' when our ears get excited by vibrations in the air around us. The amplitude of the sound wave is perceived as its loudness, and its frequency as its pitch.
Loud sounds above 150 decibels (dB) can burst human eardrums, while sounds above 185 dB can impact the inner organs and even be fatal. Humans cannot perceive low frequencies under 20 hertz (Hz) and high frequencies above 20,000 Hz. However, these frequencies can still affect the ear and have adverse impacts on human health. As low-level negative sound cues can cause the human body to release stress hormones and even cause long-term noise-induced health risks, it is unfortunate that only the amplitude (decibel level) is usually considered in acoustic planning.
Noise can affect human physiology through a direct and indirect pathway (Babisch, 2002). The direct pathway involves outcomes that arise because of high sound pressure levels. The hair cells and sensory receptors of the auditory system become damaged. High-amplitude sounds cause annoyance, disrupt sleep, and also increase the risk of cardiovascular issues. Cognitive and emotional response to a stimulus can also occur through an indirect pathway, resulting in neuroendocrine arousal, which in turn impacts metabolism.
Both the direct and indirect pathways can cause a stress response that activates the autonomic and endocrine systems. With all of the negative impacts of noise, access to periods of silence has become a symbol of a fine life away from the din of the chaotic life of proletarians.
Silence: an irrationally glorified rare commodity
The phenomenon of silence, or quietness, used to be a common good. But with ever-increasing urbanisation, silence has become a rare commodity, and its very scarcity has made it highly valuable. Whether it is noise-cancelling headphones or the quietest cars with the lowest noise, vibration, and harshness (NVH) levels, silence now comes with a price.
The truth is that no place on Earth is silent. What we consider silence, or the deceptive ‘absence’ of sound, is based on our notion of silence, which is moulded by our sensitivity to sounds that are audible to us, and our lived experience. Much like silence, sounds can also inspire us in solitude. And much like sounds, silence can also rouse us from monotony or jolt us into a fight or flight response. Sound and silence are not contraries.
The sound of silence
Physical activity serves as a non-specific signal that triggers the state of alertness necessary to meet cognitive requirements. The body responds to this by increasing precursor cell proliferation during adult neurogenesis. The newly generated immature neurons become available for utilisation for subsequent cognitive stimuli.
In the same way, rich auditory stimuli that are ethologically irrelevant or insignificant to a particular species have been proven in experiments to produce a comparable non-specific effect on adult neurogenesis in mice. Surprisingly, even unexpected or unnatural silence was shown to promote precursor cell proliferation because its unexpectedness or unnaturalness was recognised as a signal to be alert. White noise or ambient, unstructured background auditory stimuli were not seen to have a similar effect because we tend to ignore white noise.
Over millions of years, we have evolved to take advantage of both auditory cues and their absence. When we design our living spaces to achieve silence, the auditory information that we could have exploited to our advantage is missing. Just as sound pollution is a problem that has to be addressed, sensory deprivation is an equally worrying issue. This makes soundscape planning at all scales vital in our built environments and our cities at large.
Sounds make a place
Silence promotes calmness and enhances creativity. However, as extended periods of absence of quality sounds can harm our emotional, cognitive, and physiological health, is the contemporary obsession with silence overrated? Is silence truly golden?
A vibrant neighbourhood is one that brings joy and tranquillity within a radius of a few kilometres. Human-scale streets prioritise people and offer them the luxury of holding a conversation without being interrupted by the cacophony of vehicles. It is not the complete silence of a street that makes it pleasant, but the sounds of buskers and hawkers, children engaged in street play, and exchanges between neighbours. This ensemble of city ‘makers’ shape the city’s form and function. Cities with a productive soundscape are needed since an appropriate soundscape can establish a sense of place and contribute to improved public well-being and health.
Noise exposure is becoming increasingly recognised as a significant environmental predictor of public health. However, for successful acoustic planning, we must consider both amplitude and frequency, the short gaps of relative silence between sounds, as well as the physiological and social significance of sounds and silence for different species.
An ideal acoustic environment achieves a balance between superficial silence and a productive sound mix. Because of variations in vocabulary, shared literature, and training, there is currently a research-practice divide in soundscape studies, particularly in the urban context. This gap must be bridged if we are to incorporate soundscape planning and design into global urban development policies.
(This article is the second in a series on ‘Soundscapes’. Read the first article here.)
(Ann Rochyne Thomas is a bio-climatic spatial planner and founder of the Centre for Climate Resilience - a sustainability and climate change advisory.)
