Here in Scotland, winter transforms the landscape - echoing icy lakes and crisp flowing rivers that cut through the silence of the snow. But I am sure you realise I am inferring that it's not just the scenery that changes during the winter, the way that we experience sound is also entirely and distinctly transformed.
Before we get into this, I want to prove that you are almost definitely able to hear cold. Let's listen to the familiar sound of running water. I am going to pour the same amount of water from two identical cups into another pair of two identical cups. Can you figure out which is hot and which is cold?
Yes, the first in cold. In fact, we are so good at hearing cold 90.8% of us will get it right. But what are you actually hearing?
It seems that this is actually quite a contentious subject, there are a few disagreements on physics Reddit thread on this. So I will give you the most straightforward answer, but if you would like to know a bit more, I'll link the thread in the description. You will see lots of different theories are put forward. I always think the best way to really understand what is going on is to turn sound into a visual. I found a blog by Intelligent Sound Engineering who analysed the frequencies of pouring hot water and pouring cooled water by putting the sounds through a Spectrogram.
Hot Water
Cold Water
Contrary to instinct, it seems that both hot and cold pours produce the same frequencies (or pitches), but different frequencies are boosted at different parts of the pour depending on the temperature. So the colder water actually had stronger higher frequencies at the start and end of the pour whereas when hot, frequencies are boosted in the middle of the pour.
The first theory I found is in line with a famous YouTube video by Steve Mould. When water cools, the molecules move around less quickly, making the water more viscous, dense and stickier. This process is more apparent in liquids like honey, where it is thick when cold and runnier when hot. With water it is a much more subtle difference, one that we can’t see with the eye but can apparently hear. The cold water's viscosity means that the water forms bigger droplets which in turn boost the frequencies at the start and end of the pour. Another theory by Roby Selfridge is that the steam from the hot water could have an acoustic filtering effect. However, it isn't just boiling water that changes the sounds. I have a theory that we can also tell the temperature of water anywhere, even in a stream.
So, whether you are listening to a boiling cup of tea or if my theory is right, a winter stream, it seems that humans have a superpower for hearing temperature. But, it's not just water we can hear.
On February the 3rd 1947 Snag, Yukon, recorded Canada's coldest day ever reaching -62.8C. It is said, that people could hear the hiss of their breath as the moisture turned to ice crystals, the bangs as the expanding ice cracked on the White River and voices from the airport more than 6km away! What was happening, surely this can't be possible.
We are told in school, that the speed of sound is 343 meters per second or 767 mphl. But this is not entirely true. This figure assumes that the listener is at a room temperature of 21°C (70°F). In reality, temperature directly affects the speed of sound—the speed of sound increases as the temperature increases. On cold days sound travels slower. But this doesn't explain why you can hear so acutely, surely the sound would die out before it gets to you?
Earlier we talked about how water gets more viscous when it gets cold, well the same thing happens for air, it gets thicker. The cold air forms a dense mass that sinks down to ground level. The thinner faster moving and warm air sits above this layer — a weather phenomenon called temperature inversion. Our coldest record day was no exception with temperature on the high ground in Snag recorded at -23.4 C - still cold but not quite -62.8C.
Now here is the fascinating part. Sound waves tend to bend away from less dense warm air toward the thicker, colder air. This means sound waves coming from a person bend back towards the ground when it reaches the less dense air. When it reaches the ground it bounces back up and so on. If the ground is frozen, it works even better. Just like smooth, hard surfaces like glass reflect light, the smoother and harder a surface, the better it reflects sound. This means the sound waves are essentially focused along the cold air level, meaning less of the sound wave is lost and this allows them to travel further. This is compounded because the cold layer of air is so dense, it doesn't move very much, meaning there is no competing noise from the wind. The sound will be crisp and clear.
But something different happens when it snows, and our winter soundscape is entirely made over with silence. Some of the quiet after a snowstorm makes sense, people tend to stay home, there are not as many cars on the road, and wildlife hunkers down in a warm spot. But there is science to this silence as well. Snowflakes are six-sided crystals, beautiful and full of open spaces. These spaces in the structure of the snowflakes absorb the sound waves, and the snowfall coats the surfaces of anything that reflects sound, creating that relaxing silencing effect. But this effect is short-lived. As the snow melts and refreezes the snowflakes change shape reducing the spaces and reducing the noise-cancelling effects. And when it turns to ice, the clarity of sound is restored, reflected and amplified again.
I found researching this fascinating as it got me thinking about how much time most of us spend relating to our visual world and ignoring the information we take in through our other senses. It seems that when we step outside and take a moment to listen you never know what you might find - you might even find a superpower!
In the northern hemisphere winter transforms our soundscape, to a place where we can find both silence and clarity.
IF YOU HAVE ANY QUESTIONS PLEASE GET IN TOUCH OR BOOK A LESSON HERE.
Resources
What does cold sound like?: https://www.npr.org/2014/07/05/328842704/what-does-cold-sound-like?t=1609788944286
https://blog.weatherops.com/sound-travels-further-in-cold-weather-heres-why
