A double is an additional instrument you might want to, or need to play. Standard doubles for a saxophonist might include flute, clarinet, piccolo, bass clarinet or any other instrument in the woodwind family. My first double was the clarinet.
When I began high school I found many saxophone players playing clarinet. The majority of them had started on clarinet and later moved to saxophone for jazz band. Today, more kids start on the sax and learn the clarinet as a double. Is the clarinet easy to play? The fingering is very similar to a saxophone's and the clarinet does have a reed just like a sax, but there are many differences also.
The clarinet has a different tube shape, a cylinder that is the same size around, all the way down the key system. The sax has a cone-shaped tube, graduating from small to large at the bell. These are called cylindrical and conical respectively. This small difference makes the fingering a little harder on a clarinet than on a saxophone.
On saxophone, there is an octave key; three fingers closed is a G and press the octave key and a higher G sounds. On clarinet there is a register key; three fingers closed sounds a low C and press the register key with the same fingering and it sounds a high G. The reason it works differently is due to the shape of the inside tube or bore. This little difference requires a few extra keys at the register change and sax players will need to spend some good practice time navigating these keys and getting used to the low register sounding different than expected. Add to the differences an open-hole fingering system and the average sax player will find squeaking a new pass time when starting off.
I learned the clarinet after playing saxophone for a few years. I felt that it came pretty easily and I was playing it in a few different bands that first year. The clarinet is a very different instrument; it is not at all like playing saxophone. But, there are many reasons why you might want to consider playing clarinet.
Many sax charts for jazz band have clarinet or flute parts included for the sax player. You might not see clarinet parts in middle school jazz band music but you can expect it in high school and beyond.
Community and school musicals occur all over the country, and this music often has each woodwind player covering 3 or more instruments in a performance. Another place you find a lot of clarinet is in old school jazz settings, most notably 20's style Dixieland music. Once a player develops ability on a double, you can be sure they will find more musical outlets for it.
As a professional sax player I am required to play and record on my clarinet all the time. I would have had to pass on many of these opportunities had I not played the clarinet proficiently. I would have to say, I am very grateful for that band director who encouraged me to learn clarinet in high school.
There are 4 common sizes of saxophones: soprano, alto, tenor and baritone. If you play 1 size of sax, you can very easily switch to a different saxophone. The clarinet family is very similar to the saxophone family. Once you learn how to play clarinet, you can explore other sizes in the clarinet family as well.
The standard Bb clarinet is the soprano clarinet in the clarinet family. There are many variations and different sizes of clarinets also available. In the west, the Bb soprano clarinet is most common, followed by the bass clarinet, and then maybe alto clarinet, with the A soprano, Eb sopranino and contra bass clarinet found in many larger classical and pit orchestras. Saxophone doubles are usually Bb soprano clarinet with baritone sax often covering bass clarinet.
The real question is when to start a new instrument like the clarinet. For most people, the answer is yesterday. But today is alright too.