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Psychoacoustics… Qu’est-ce que c’est?

Are the sounds of the city music to your ears?

The Vienna House team is working to ensure the project’s residents will enjoy the highest possible quality of life. Among other things, that means paying careful attention to what they hear—and what they don’t.

We recently spoke with Maureen Connelly, Director of the BCIT Centre for Architectural Ecology and Faculty, and Paul Marks, partner with BKL Consultants—both renowned experts in the acoustic performance of buildings. Marks and his firm are providing acoustical design services to PUBLIC Architecture + Communication, the company leading the project design.

Why does a building’s acoustic performance matter?

Maureen: Worldwide, excess noise is the second-largest pollution source that creates a burden of disease. We can calculate that burden in terms of actual life expectancy and time performance loss; it relates to stress, sleep disturbance, cardiovascular disease, cognitive delay and development in children, and a reduction in cognitive performance in adults. And on the other side, natural sounds actually have the capacity to heal. There hasn’t been a lot of research on that, but it’s very exciting.

How do we measure acoustic performance?

Maureen: Traditionally, we have used the concept of the decibel, which is a measurement of sound pressure level—but it’s a challenging measure for most people because it’s not well understood. We don’t grow up looking at sound level the way we do with other things. Take temperature: We have a good sense of what our bodies feel like at 15 degrees C versus 25 degrees C. But we don’t have the same connection to sound measurement. My colleagues and I are exploring what the other critical indicators, besides sound pressure level are. There’s a whole handful of ways to quantify sound and noise, in addition to sound pressure level, and we’re looking at other indicators that might help us understand sound quality.

Can you give us an example of what those indicators might be?

Maureen: Well, for example, the field of psychoacoustics allows us to measure “annoyance.” It’s actually a really heavy pile of mathematics and a heavy pile of statistical analysis that seeks to draw a relationship between disruption, annoyance, and sound quality. And to feed those algorithms, we measure a number of indicators such as the spectral gravity of a sound, the temporal sound variance, the frequency spectrums of the sounds. And then from there, we figure out this psychoacoustic annoyance.

That sounds… complicated?

Maureen: Right. It is challenging. And with building acoustics, we want something we can easily measure. We want to tie psychoacoustic annoyance to something we can measure. We’re experimenting a bit with the Articulation Index and the Speech Transmission Index—both are metrics that quantify speech intelligibility. To be honest, we’re not there yet.

Paul, how do you go about your work? I’m guessing you model the acoustic characteristics of a given building by considering size of spaces, materials, and proximity to environmental sounds, and so forth.

Paul: At a high level, yes, that’s pretty much what we do. Vienna House is a challenging site. It’s got a SkyTrain running on its eastern boundary, and even more challenging, it’s an elevated guideway. So we’ve done a frequency-based measurement survey at an elevated height. We measured at a high level because that’s going to reflect the building, which will be six stories.

And what are your measurements telling you so far?

Paul: We look at the whole spectrum—the “content” of the noise. We try to fingerprint the noise a little bit, we try to break it down into its components. Just as road traffic has distinctive components, and children playing in a park have distinctive components, so does the SkyTrain. And that’s where we’d come back into Maureen’s work around how different types of noise create a different response.

Is noise inherently a bad thing? And what does an architect or designer need to take into account?

Maureen: I try not to put negatives and positives on it, but yes we can classify noise as “unwanted sound.” Both Paul and I look at multiple aspects of a building’s acoustic performance. So there’s a big focus on the building envelope. There is the whole issue of  speech privacy between units, and sound isolation from non-desirable sources, such as HVAC noise. And then there is impact noise, which is sound that is carried via the structure of a building, such as foot falls across an upper floor that are audible in the room below. That’s a big one.

Paul: In a multifamily home development such as Vienna House, we’re also facing a number of other pressures, non-acoustic pressures, around sustainable principles. We don’t want to have lots of mechanical equipment located in the building. We’d rather be using things that are sustainable, with respect to low energy, and that also consider how the environment and the temperature is changing in the Lower Mainland. We know that climate change means that we are likely to have an increase in temperature, so we need to introduce cooling, but we don’t want to have to increase our energy consumption. One of those responses is the idea of using a naturally ventilated building, rather than a forced-air system. But that means you open the envelope up. And by doing that, you allow sound in. That sound then becomes noise in someone’s apartment.

Are there any passive cooling strategies that don’t introduce unwanted sound, or noise?

Maureen: There are a couple of fantastic passive systems, like vegetated roofs. We need to look for symbiotic solutions. Right now we have a relatively easy way to quantify energy use, greenhouse gas emissions, and cost. They all fit together, but what is very difficult to quantify is the health outcomes of an unhealthy environment. And because that is so difficult, we have a lack of demanding acoustical criteria. Builders, developers, and designers don’t yet realize that they can resolve many of these acoustical issues simultaneously.

What are the equity implications of unwanted sound? Are you concerned about potential resentment between those who live on the SkyTrain side of the Vienna House project, and those who don’t?

Paul: At Vienna House we are looking at envelopes that are going to a significant mass and thickness. We’re also looking into what is known as a “winter garden” system. The idea is you might have almost a buffer zone between the outer part of the building and the living accommodation—and it would also include some of the passive ventilation systems. And we’re certainly looking at noise-control treatments within those spaces as well. Trying to use more absorbent materials, to absorb some of the sound that may be making it through that envelope. So we are trying to hide this unwanted sound. We want to hit this head on, because yes, there is going to be a difference between the elevation facing the SkyTrain and those facing the other way. I am trying to find an equitable position for all of the households. It’s going to be an important part of that design.

Example of typical “winter garden” passive solution to mitigate exterior noise. (Courtesy BKL Associates.)

Concrete buildings are popular in cities because they are quiet. But of course the material carries a high embodied carbon factor. What different materials lend themselves to better acoustic solutions?

Paul: Mass timber has a lot of potential because it’s easier to build with. And with some of the modular, and prefabricated building systems, they can really help with construction noise, because you’re building some of these offsite and then bringing it to site. We find that with mass timber, that there needs to be some encapsulation to ensure we’re making a sufficient sound blocking process. Concrete does stop a lot of sound, but it has limitations, particularly its ability to transmit low frequency sound. It’s not a fix for everything. Multi-panel systems are probably more effective than relying on a single massive panel or masking the system.

What about the positive, healthy sounds that you want to ensure Vienna House residents will be able to hear?

Maureen: That is where it really comes back down to the early design concepts of bringing in spaces, such as green roofs and living walls. There are positive sounds that occur when people engage with things. For example, contrast the sound of someone watering plants with a hissing mechanical sprinkler system. So it really has to do with people’s activities. And then it has to do with the diversity of plants on the project that will catch the sounds of the wind and the water.

What do you expect Vienna House residents and guests might want to hear?

Maureen: I always try to encourage design teams to literally draw, with some sort of notation, the actual activities that will unfold in a space. And we can then calculate, again with notation, the kinds of sounds those activities will create. You can engage positive sounds in a space, but it has to be purposeful. One of the things our team is finding in our research is that it kind of doesn’t matter if it’s a busker, or a bluejay, or a motorbike, or a moped. People just want to hear something distinct and differentiated, rather than background noise. The sound of the city is dynamic, and many of us are blocking it out with earbuds. We’re at risk of losing all our proprioceptive senses. 

What is the next frontier for acoustics in the built environment, either in research or implementation?

Paul: We are actually beginning to see very interesting projects coming on board. We have one in the downtown core, it’s an office accommodation, and they want to reflect the nature of British Columbia, and in one of the work areas they want to have sort of like a grass theme. So there will be some material hanging down and it’s meant to evoke grass, but it’s also part of the acoustic treatment of the space; it’s an open plan office so they want some sound masking. But the tenants will have a very soft sound of wind rushing through grass.

Maureen: People want something that they can understand, they want something more natural. We’ve got something similar in a care home; there’s a very strong link between dementia and acoustics. They want to use birdsong in the common corridors and walkways. Instead of just having some masking of unwanted sound, why can’t we use birdsong to help make it feel like you’re outside? 

What about the Vienna House project is exciting for you? 

Paul: The design team is really taking acoustics seriously. The mechanicals team is interested and engaged, because they’ve obviously got a challenge in how they’re going to keep the building at the right temperature. As acoustic designers, we might not be center stage, but we’re definitely in the chorus!