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.