Quirks & Quarks

Why does a snowfall damp sound so well?

Snow has excellent acoustic damping properties because it is so porous.

Snow has excellent acoustic damping properties because it is so porous.

The acoustic properties of snow make this street scene in Vancouver as peaceful as it looks. (Ben Nelms/CBC)

This week's question comes from Christopher Cordray in Winnpeg. He asks:

Why does a fresh snowfall dampen sound?

Corjan Buma, an engineer with Acoustical Consultants Incorporated in Edmonton, and a lab manager at the University of Alberta, explains that fresh fallen snow does an excellent job absorbing sound because it is highly porous. It works in a similar way to the acoustical treatment often seen on the walls of hockey arenas, or on the ceilings of gymnasiums and indoor swimming pools.  
 
 On a microscopic level, acoustic energy is converted to heat energy as it interacts with the structure of the sun absorbing medium, in this case snow. Given the frequency content of road noise, loose packed snow works extremely well to absorb that sound. But as the heat energy is at the microscopic level, it is not enough to actually melt the snow. 

On a scale of zero to one, zero being no sound absorption at all and one being total absorption of the sound energy, a thick blanket of fresh snow will register about zero point nine. This is why with a thick pack of freshly fallen snow will make the sound of a busy nearby road almost completely inaudible.

However as a thick pack of snow that is initially loosely packed settles, and especially as the spring melt progresses and the outer crust hardens, its sound absorbing ability decreases dramatically.

 

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