The chalumeau is a medieval instrument generally considered to be the ancestor of the clarinet. It was the first of a class of instruments known as the single reeds (in contrast with the oboe/bassoon family, which are double reeds). The instrument had a range of about 1.5 octaves.
In the late 1690s or early 1700s (the exact date is uncertain), German instrument-maker J.C. Denner created the clarinet by moving the register key (which you can’t see in this picture – it’s on the back) further up. The register key allows a woodwind to easily play beyond a one-octave range. On the chalumeau, the key was diametrically opposed (directly opposite) the single key seen on the front – meaning if you played a note and added the register key, you would hear the same note one octave higher. This is called overblowing at the octave. The clarinet’s acoustics are unique in that it overblows at the 12th (one octave + one fifth), a phenomenon allowed by Denner’s innovation.
The chalumeau stuck around for a while because it sounded better in the low range than the clarinet did – the early clarinet sounded clear in the upper octaves but weak in the low notes. However, as further improvements were made to the clarinet, the chalumeau gradually fell out of use, disappearing for good after the mid-1700s.
Canadian Clarinet 