Air Purifiers – predominantly produce soft wind-like broadband sound, meaning that no frequency range is predominant to any other. These type of sounds are commonly described as ‘flat’. Nevertheless, they often include intermittent water elements too which can become disruptive if louder that the air flow sound. Improving the sound quality of these devices involves minimising their presence within the space, therefore, both water sounds and enhanced tonalities are to be isolated from the outside.