Free-reed wind instruments have a free reed attached to a tube, and are a unique instrument of Laos, Thailand, China, or Japan. Three examples, a 5-pipe hulusheng from Yunnan, China and two Laotian instruments, a 6-pipe Hmong and a 14-pipe Lao khaen are compared in terms of their construction and acoustic properties. With normal playing pressure the pipes only sound when a hole in the pipe is closed. Then, the pitch is determined by the pipe length. When the holes are open the pipes do not sound. Still with low blowing pressure some pipes sound near the frequency of the free reed. A sudden phase transition from reed to pipe frequency happens at a certain blowing pressure. On the contrary, the bordun pipe cannot be muted and produces two pitches with a one-hole fingering. Using the Impulse Pattern Formulation (IPF), which assumes the instrument to work with traveling pressure impulses through the pipes which are reflected, damped and act back on the reed again, the fundamental behaviour of free-reed instruments is modelled. [Artikelnummer: 2779]