How does the sound from an air raid siren travel so far?

Question

I live in portsmouth (UK) and once every 3 months they test the nuclear siren - which is just an old air raid siren, i can hear it clear as day from my house, which is just over 2 miles away, but down at the harbour where the base is it doesn't sound earpoppingly loud, how does it travel so far?

Answer 1

They do not call them Nuclear sirens now, they are used mainly to warn more of flood risks which is a major problem these days.

Sound travels mainly in a horizontal direction as an expanding cone, but some propagate in other directions. The sound cone is interfered with by objects in its path.

This is why most of the sound can be heard where there is little or no buildings within its path. If there are objects, these absorb some of the sound energy and reflect a weaker "signal". Because the sound is sent virtually horizontal, standing underneath, the sound is weaker, but can still be heard.

Answer 2

It's loud.  The sound is directed horizontally, not down toward the base.  It's distinctive, so it's easy to recognize it when it's not loud to the hearer.  Two miles isn't far.  I routinely hear motorcycles more than five miles away.