A nebulisation device (I) capable of generating a mist (BR) of droplets of a liquid from a liquid (L), said device comprising: - a tank for receiving said liquid, - a piezoelectric element able to emit acoustic waves into said liquid (L), - a nebulisation chamber comprising: means for admitting air into this chamber means for generating said mist of droplets (J) at least one channel for diffusing mist out of said device , having a downstream diffusion orifice - a box which is substantially closed, said tank and said nebulisation chamber being arranged in this box, said device further comprising the following two features i) and ii): i) the section (d21) of each diffusion orifice is comprised between 2 and 50 millimetres, preferably between 3 and 15 millimetres, more preferably between 4 and 10 millimetres, in particular close to 6 millimetres; ii) the height (H23) of the droplet diffusion conduit, connecting the admission means and the diffusion channel(s) , is comprised between 2 and 100 millimetres, preferably between 4 and 20 millimetres, more preferably between 8 and 12 millimetres, in particular close to 12 millimetres, this device being characterised in that the bottom of the nebulisation chamber is situated at an altitude lower than that of the bottom of the tank for receiving said liquid, thus allowing the flow of the liquid from the tank to the nebulisation chamber , and in that the tank occupies a major part of the total surface of the box . - a tank for receiving said liquid, - a piezoelectric element able to emit acoustic waves into said liquid (L), - a nebulisation chamber comprising: means for admitting air into this chamber means for generating said mist of droplets (J) at least one channel for diffusing mist out of said device , having a downstream diffusion orifice means for admitting air into this chamber means for generating said mist of droplets (J) at least one channel for diffusing mist out of said device , having a downstream diffusion orifice - a box which is substantially closed, said tank and said nebulisation chamber being arranged in this box, said device further comprising the following two features i) and ii): i) the section (d21) of each diffusion orifice is comprised between 2 and 50 millimetres, preferably between 3 and 15 millimetres, more preferably between 4 and 10 millimetres, in particular close to 6 millimetres; ii) the height (H23) of the droplet diffusion conduit, connecting the admission means and the diffusion channel(s) , is comprised between 2 and 100 millimetres, preferably between 4 and 20 millimetres, more preferably between 8 and 12 millimetres, in particular close to 12 millimetres, i) the section (d21) of each diffusion orifice is comprised between 2 and 50 millimetres, preferably between 3 and 15 millimetres, more preferably between 4 and 10 millimetres, in particular close to 6 millimetres; ii) the height (H23) of the droplet diffusion conduit, connecting the admission means and the diffusion channel(s) , is comprised between 2 and 100 millimetres, preferably between 4 and 20 millimetres, more preferably between 8 and 12 millimetres, in particular close to 12 millimetres, this device being characterised in that the bottom of the nebulisation chamber is situated at an altitude lower than that of the bottom of the tank for receiving said liquid, thus allowing the flow of the liquid from the tank to the nebulisation chamber , and in that the tank occupies a major part of the total surface of the box . <EOS>