Why someone talking may be easily heard.
Be it an open office or say, a restaurant, it is typical that someone elses’ talk – from a nearby table – is overheard.
Especially, in case the ceiling and / or walls are clean flat. The further away these surfaces, the longer the time of echo – the reverb time. Because of the longer travel of sound waves.
To mitigate the echo time, obstacles can be arranged in the main path of a Sound wave. Either absorbing obstacles, and / or path (sound wave) altering obstacles – diffusers.

In the ceiling, where normally there is sufficient space, absorbing plates can be hanged in a vertical position.
Picture of plates, hanged from ceiling :
Sketch of plates hanging from ceiling :

On the walls, where space is more limited depth-wise, diffusing panels is a food option.
Picture of diffusing panel, mounted on to wall.
As these type of solutions is utilized, the overall sound pressure – volume – decreases in the interior space. Therefore, no longer is each table competing to uphold a conversation – no longer difficult for friends at a table to hear eachother.