An observer stands between two speakers, each emitting a constant noise with frequency $f = 800\space Hz$. If the observer moves in any direction, the sound level decreases. Let $D_1$ be the distance in meters from the observer to the first speaker, and $D_2$ be the distance in meters from the observer to the second speaker.
Which of the following relations between those two distances could be correct? Select ALL that apply.
The speed of sound in air is 350 m/s.