The Sopranino Saxophone is one of the smallest members, the second smallest to be entirely accurate, of the Saxophone family. It's only a little bigger than the Soprillo.
This little horn is tuned in the key of E-flat, along with the Alto and Baritone. The difference in size means that a low A on the Sopranino Sax would sound the same as a high A on the Alto Sax.
Little saxophones like this one are generally not curved, unlike other members of the saxophone family, due to their being so small in size. Saxophones were generally designed with a curve or two in them because they would be simply too long without the curves. Can you imagine a full length Baritone or Bass saxophone without the curves, stretched out along the room. That would make the Bass Sax nearly 100 inches long. Kind of awkward, I'm sure. The bent soprano is an exception here, where it's curves are only used to enhance its looks.
The rare and tiny sopranino is capable of producing a sweet and beautiful little sound, all dependent on who is playing it of course... Built as delicately as it is played, the sopranino can sometimes sound thin and shrill in the sound they make, but are welcomed in cheerful, fast and up-beat musical pieces. Due to the distinctive shape and size of the sopranino, players will often find themselves provided with quite a task to fit their fingers onto the tiny keys.
The size of the mouthpiece makes for a serious amount of lip strength and control needed in order to produce the beautiful sound that one would expect from this instrument.
These characteristics make it 'an instrument to progress too', after having mastered the basics on maybe an Alto or Tenor.
It may appear surprising that the sopranino has survived the market as a member of the saxophone family, but the sopranino, however, is becoming increasingly chosen for contemporary music.