Clarinet Ensembles come in various sizes, and first it is useful to review the members of the clarinet family. The most common clarinet is Bb clarinet, and this is generally what we refer to when we talk about the clarinet. It was created in the 18th century and like most woodwind instruments, evolved over time from a simple wooden cylinder with holes which you covered with fingers to the modern clarinet which has a multitude of keys. Unlike the oboe, the inside of the clarinet is a straight cylindrical shape, the same diameter up and down.
The most common types of clarinets are:
Eb Soprano Clarinet
A Clarinet, mostly used in orchestral pieces but is also a solo instrument
Eb Alto Clarinet
Bb Bass Clarinet (looks a little like a saxophone with an upturned bell at the end)
BBb Contrabass Clarinet
Most ensemble sheet music is scored with alternative parts, so for example it may have a Bb clarinet part in the low register to be used instead of an alto clarinet. Clarinet ensembles are sometimes called clarinet choirs. Generally a piece with more than 4 parts will be called an ensemble, anything less than that is described as a duet, trio or quartet.
Duet sheet music is most commonly scored for two Bb clarinets, especially music aimed at beginners.
You can find a selection of music for clarinet ensembles on the website.