The terms quietness and silence are used interchangeably, but are distinct concepts. Let me explain.
Quietness is the reduction of sound
Silence is focused attunement
First, everything is energy. Energy always vibrates at a frequency, and frequency always produces sound, so everything produces sound. Thus, sound can never be eliminated, only reduced. As the range of human hearing is 20-20k hertz, quietness is just the reduction of sound to the limits of our auditory perception.
However, the human soul is a spiritual being (not the body), and is able to access finer frequencies of the soul. The process of access is called silence, i.e. the focused attunement of concentrated energy. Just as noisiness interferes with us hearing someone, so does inner (mind) and outer (environment) noisiness interfere with our perceiving the finer frequencies of the soul.
To achieve the silence of focused attunement, quietness is a tool used to reduce sound, so all energy can be uninterruptedly focused. So, it is possible to be quiet and not silent—reduced sound but noisy mind, silent but not quiet—outward sound but inner focused attunement, and silent and quiet—reduced sound and focused attunement. Naturally, the latter is the best aid for the sharpening of inner perception.
~Ikenna Q. Ezealah