Fresh snow can make a street seem quieter without making its sources any less noisy. The change lies underfoot. As two people stand in the snow, sound from traffic and voices meets a porous surface that absorbs some of its energy; replace that surface with hard ice, and more sound returns to the air.
Snow is less a blanket than a maze. Between its grains lie interconnected air spaces, through which sound waves force air to move. Friction and heat exchange within those pores convert part of the sound energy into heat, a process known as sound absorption. The effect varies with frequency, snow depth and the size and arrangement of the grains. Fresh, loose snow often absorbs more sound than snow that has been compressed or crusted over. It does not silence everything: a voice can still travel directly from a speaker to a listener, without first touching the ground.
Ice changes the bargain. Its hard, relatively nonporous surface absorbs less airborne sound and can produce stronger sound reflection, allowing waves that strike the ground to reach a listener rather than lose much of their energy there. The result is not a simple increase in every sound: reflected waves can reinforce or cancel direct waves, depending on frequency and geometry. Buildings, wind and temperature layers also shape what reaches the ear. Sound refraction in the atmosphere can bend waves toward or away from the ground, complicating any comparison between the two surfaces. On the same street, silence is not merely the absence of noise; it is also a property of what lies beneath it.
