Acoustics is the science of sound. Classically it has referred to how sound travels as vibrations through media (air, walls etc.) and how it behaves in an enclosed space. It has been a key concern in the design of spaces since the Greco-Roman amphitheatres built around 450 BC, so it’s an old science, and the engineering and mathematical framework we use today hasn’t really changed since the early 1900’s.
These days we consider classical acoustics alongside “psycho-acoustics” – that is how we perceive and react to sound, and what we might infer about its impact on our daily life. Using studies completed in both laboratory and real-world environments we can make predictions relating to annoyance, privacy, cognitive impairment, sleep disturbance, and many other psychological phenomena.
What to consider when designing a building?
We spend our lives indoors; sleeping in houses, working in offices, relaxing in bars and restaurants, sending our children to school etc. so it is important that the design of these spaces considers all aspects of the physiological and psychological needs of its occupants. Noise has a profound and often unnoticed effect on our wellbeing, which has led the World Health Organisation to state that environmental noise is a “threat to public health”. We at Scotch believe that buildings should be built around the people that occupy them and not the other way around, and so acoustics should be a key influence in the design of any building with living occupants.
How loud is too loud?
Acoustics is often seen as a checkbox exercise, and simple questions such as this tend to reinforce a pass/fail mentality that does not exist in the real world. The path we as acoustic experts have to take to answer a question such as this is circuitous, unintuitive, and poorly understood by those outside of the acoustics bubble. It is therefore tempting (and common practice) for us to answer by oversimplifying the situation, or shrouding our methods in secrecy (leading to the pervasive “dark art” moniker).
Personally, I’ve always disliked this approach, and so I think we should seek to cast a light across this dark art.
Perhaps the reason for this lack of common knowledge is that acoustics can be, and often is, very unintuitive. To give you an example, think about throwing a tennis ball against a brick wall. Assuming that the wall and throw are of sufficient strength, you know that the ball will bounce back to you.
However, when a sound wave hits a wall some of it will be reflected back, but also some will pass straight through. Some of the sound will also disappear entirely, the energy being absorbed by the wall structure itself. How much of that first sound wave is reflected, transmitted, or absorbed is dependent not only on the wall itself but also the frequency of the sound wave. Low frequencies are much happier to pass through solid objects than high frequencies, and this is why your neighbour’s sound system just sounds like a rhythmic thudding in your bedroom while you’re trying to get to sleep.
Building acoustics, like all engineering disciplines, is rarely considered important until something goes drastically wrong, at which point we are somehow expected to fix the problem without materially changing the design. Unfortunately, those low frequencies I mentioned before always seem to find a way through lightweight or thin constructions. Easy fixes don’t exist, and products claiming to do so are almost always quackery.
One more reasonable idea we often come across is auralisation, essentially an audio demonstration of how the space will sound once it’s built. This claims to allow the client to actually hear how their space will sound and thus make an informed decision. In reality, however, it tends to cloud the situation even further…
Out of Tune
The problem with demonstrating acoustic phenomena comes from all of the conscious and unconscious biases that exist outside of our control. It is simply not possible to judge how annoying a certain noise will be to, for example an office worker, without actually being that office worker, stressed because you’re behind on a deadline and couldn’t sleep last night because of the rhythmic thudding from your neighbour’s apartment.
Even if you happen to be that person, there’s no way you can guarantee that your reaction will be the same as someone else’s. Maybe you grew up in the countryside and find the incessant blaring of car horns and throbbing motorbike engines incredibly distressing, or maybe you grew up in the city and need those things to feel at ease.
Hopefully I’ve managed to sufficiently forewarn you that the world of acoustics is fraught with confusing physics, personal preferences and questionable opinions. However, I hope I’ve also encouraged you to question and consider the acoustic advice you’re given a little more, and to not just see it as a checkbox exercise.
As a practicing acoustic engineer, my goal is to help guide you through this twisted labyrinth, and with a little luck, perhaps we can illuminate the dark art together.
For further advice or assistance with your building project please contact Jacob Perry, a member of Scotch’s Acoustics Team.
Article written by Jacob Perry, Acoustic Consultant.
T: 020 3544 5400