PROJECT ECHO
“For designers, architects, engineers, and innovators the answer to the question “what would nature do...?” is a revelation. There’s not one new idea, but millions of ideas [from the natural world] evolved in context, tested over eons, and proven to be safe for this generation and the next... Biomimicry is about learning from and then emulating natural forms, processes, and ecosystems to create more sustainable [and innovative] designs.”
- Janine Benyus, author of ‘Biomimicry: Innovation Inspired by Nature’
INTRODUCTION
Christine Lintott Architects (CLA) undertook a project to design built infrastructure solutions for the organization Power To Be, at their new program site on the southern tip of Prospect Lake in Saanich, BC, Canada - a location most recently utilized as a golf course and prior to that was inhabited by homesteaders and the indigenous Coast Salish people.
As a nonprofit organization that empowers people, particularly youth and those with disabilities, Power To Be operates inclusive adventures rooted in nature, encouraging participants to explore their limitless abilities (powertobe.ca). As such programming makes use of significant outdoor time and space, which introduces some additional environmental and sensorial factors for the CLA design team to take into account.
As the result of an ecological performance assessment (EPA) by Christine Lintott of the project site, a disturbed site, in comparison with a nearby intact reference site, she identified that traffic noise (and parking lot noise) generated at the west end of the property from Prospect Lake Road was a noticeable issue likely to negatively impact Power To Be program experiences. According to Christine’s EPA that utilized the ESii Tool by Ecometrix:
... the project site, a disturbed site, contains some trees, but is characterized by an open understory and open grassland with relatively tall vegetation, with similar elevation as the surrounding map units. The site’s current functional performance in attenuating sound from anthropogenic sources as it travels across the site to a potential recipient from the western side is only moderate at 47%. The intact reference site is characterized by a tall tree dominant strata and a dense understory, while also sharing similar elevation with surrounding map units, yielding a higher functional performance of attenuating sound at 81%.
The EPA would tend to indicate that the denser forest of the reference site, particularly that of the denser understory and no open grassland being present, could be making a significant contribution to sound attenuation.
During the EPA Christine also observed a reduction in biophony - the sounds produced by organisms at the project site versus the reference site. She hypothesizes that animal behavior and spatial distribution are being affected by the anthropogenic sound (noise), leading to a decrease in overall health of the ecosystem at the project site.
CLA asked Biomimicry Lab Ltd to undertake a biomimetic innovation process to identify nature-inspired ideas for managing sound at the project site, which will include attenuating (weakening the performance of) human-generated noise, to optimize the acoustics for outdoor (and ideally even indoor) spaces on the site, not just supporting human experiences, but those of all life forms at the location - in essence creating conditions conducive to life.
INNOVATION PROCESS
PHYSICS OF SOUND
When we refer to ‘sound’ we are referring to the pressure waves (also known as acoustic waves) specifically that humans are able to register within their audible range. Outside of this range however pressure waves still occur. Those below 20Hz we label as infrasound (very low frequency) while those above 20KHz we label as ultrasound (very high frequency). Some animals have audible ranges that extend into one or the other of these realms.
The transmission of pressure waves can be altered within mediums themselves if they are not homogenous (a consistent density throughout) or where a boundary occurs with another medium of a differing density. When an obstacle, something of different density, occurs or is placed in the trajectory of a sound wave, it is subject to fragmentation. After the incidence of the sound wave into an obstacle, the incident sound is divided, mainly, into reflected sound (including in a scattered or diffused way), absorbed sound (which will partially transfer into heat energy) and transmitted sound.
WHERE CAN WE INTERVENE IN THE SYSTEM: SOURCE, PATH AND RECEIVER
SOME OF THE WAYS BIOMIMETIC SYSTEMS CAN APPLY
SET OF NATURE'S TECHNOLOGIES AS STRATEGIES AND DESIGN PRINCIPLES
When a pressure wave encounters another medium with the surface normal to the propagation direction of the wave, a portion of that wave is reflected at the interface and some is transmitted into the new medium. A portion of the transmitted energy is
absorbed and the rest is transmitted through the material.
The larger the difference in the characteristic impedance between the two media, the more energy is reflected. [For example, if we consider the differing densities of air (a gas) versus a structure made of silica (a solid)], the density of dry air at standard
conditions is 1.34 kg/m3... while for fused silica [it] is 2210 kg/m3. [In this case due to impedance differences] 99.99 percent of the energy is reflected from the silica surface; [while] only 0.01 percent is transmitted.
Lower density materials, [such as porous solids] will reflect less energy, as will materials with lower sound speeds. Since a solid has much higher density than a gas, the efficiency of sound transmission into a solid material from air is unlikely to be high unless the speed of sound in the solid can be decreased dramatically.
A high number of internal reflections [within the interconnected pore network] can transfer energy to the [surrounding] solid structure through frictional losses and efficiently absorb sound. [We will explain viscous and thermal dampening separately]. This scattering is essential to the performance of acoustic absorbers fashioned from materials such as glass fibers, polymers, and metal foams. In order to achieve a large number of interactions, the pressure wave must penetrate deeply enough into the material so as to not immediately be reflected back into the surrounding air. As the pore size decreases, less energy is transferred into the solid structure and more is reflected from the surface, making the material less useful as an acoustic absorber - see figure 1 below.
If the material pores are too coarse, the pressure wave will pass through it with minimal interaction with the structure. If the porosity is too fine, the majority of
the energy will reflect back into the environment from a region in the immediate vicinity of the surface, never entering deeply enough to undergo the multiple interactions with the structure to absorb a substantial fraction of the energy.
