silencing and separation in a cold - air , essential - oil , diffuser apparatus and method pass flow through a channel having comparatively high aspect ratios of length to thickness and width to thickness . curved , tapered , non - parallel , and quasi random surfaces reduce probability and power of resonant frequencies . offsetting flow through a channel is followed by impingement against an obstructing surface , redirection elsewhere within a drift chamber , and exiting through a smaller , and differently oriented exit port . silencing is improved by changes of cross - sectional area creating high - pass and low pass acoustic filters , changes of direction , and absorption of acoustic energy in fluid - droplet - laden air .