Snow day! It's so quiet...

Snow in the UK is a rare thing, at least where I live in Bristol, where we were subjected to a red weather warning on Thursday night, only the 3rd ever issued in the UK. As I write this article, heavy snow continues to fall outside onto the already 6-inch-thick layer atop my car.

Getting home from work last night was a strange experience, not least because of the unusually light sky, but because it was so quiet!

So why is this? The most obvious reason is simply that there are less people and less traffic. The brave souls that are out in their cars will be driving a lot slower than usual, hence the noise generated from the impact of wheel on tarmac, which increases in amplitude with speed, is lower. In fact, the covering of snow over tarmac significantly changes the soundscape, the sound of tyres of snow is very different to tyres on tarmac.

A fresh layer of snow can provide a high level of sound absorption. In acoustics we refer to products like wall panels, ceiling tiles, mineral wool and fibreglass as porous absorbers. A soft layer of porous snow which is full of small air pockets that interweave and receive sound energy through the air, dissipate some of this energy as heat, acting as an acoustic absorber. The once acoustically reflective road surface is covered with this absorbant, and therefore the noise reflections from traffic are dampened significantly. 

So for those first few hours at least, the world seems a bit quieter.

Unfortunately, as the snow stops falling, temperatures rise and people emerge from their cosy homes, this effect begins to dwindle. The once porous fresh snow starts to compact through foot traffic and vehicles, melted and flattened by the wind and rain, losing some of the porosity that made it so sound absorbent. As this turns to ice and then to water, we may even experience a rise in noise levels. Noise generated through tyres on tarmac can be much louder on a wet road, then a dry one.

But until then, I enjoy the peace outside my house. Thankfully for me as an acoustic consultant, I won’t need to do any treacherous driving to conduct any noise surveys this weekend, as conditions will make it too quiet and unrepresentative of the other 360 odd days of the year!

I hope you enjoyed this short article, and keep an eye out for more articles on the common questions that I get asked by clients in my job as an acoustic consultant.