What makes an echo audible if there isn any snow?
What we need is some way to amplify the sound. If we could get more of it, we’d be able to hear it, even on a noisy summer day. What happens is that the sound from the wall that doesn’t bounce directly back to your ear has to be given a chance to get there anyway, by bouncing again! What you need is several walls or other flat smooth surfaces, that will bounce more of the sound towards your ear. Let’s look at a situation where there are several such walls: The sound that bounces directly back is now accompanied by more of your voice … that bounced off other walls back to you (1) … and more sound that came from the original wall by way of a bounce off a second wall (2). If these other walls are situated just right, a lot more of the sound will arrive back at your ear … enough to hear the echo even on a normal summer day. The walls inside a big building work especially well (big, because the sound has to travel about 75 metres, remember?) but the building must be mostly empty so th
