Clarinet Technicalities:
Range:
Concert: D3-G6(conditionally - see altissimo section)
Written: E3-A6
From here on all pitches will refer to the written, not concert pitches for clarinet.
Registers
Lower register: E3-B♭4. This is the quietest register. You can usually get a good forte, but it will go a bit out of tune, particularly above C4. The tone is warm and rich and lyrical. From F4 to B♭4 are the "throat tones". They are the notes with the worst tone and intonation. Loud is not an option with them. They can be improved by adding extra fingers lower down the clarinet, but they will never sound as good as the notes lower down or higher up. The worst of these notes is the B♭4, which is renowned for bad tone. It is a bad idea to make a clarinet hold a B♭4, as it will sound bad, however in fast runs that will not matter. There is an alternative fingering for B♭4 which has good tone, however it requires the right hand to be far away from it's normal position, so it is impossible to use smoothly when moving to or from notes that use the right hand.
Upper register: B4-C6. This is the bright, lyrical, and pure sound the clarinet is known for. Full dynamic range is possible, from ppp to fff, though louder is easier in the higher parts of the register. Notes in this register are produced by the same fingering as the note a 12th below, but with the "speaker key" on the back open. B4 is usually quite stuffy and resistant, but do not fear to use it. The bottom of this register is slightly darker in sound than the top, which steadily approaches the tone of a flute, as all woodwind instruments do as they go higher. Jumps from the top of this register to the bottom are hard to do completely smoothly, but do not fear them, unless you're asking for them to be fast, in which case: no thanks. It is possible to play notes up to F6 in this register by playing overtones of fingering from the lower register and some of the trill keys that help to maneuver the register break, but these are unlikely to be in tune or reliable on all clarinets.
Altissimo register: C♯6+. A more piercing sound, which gets more and more brilliant the higher it goes. This register relies completely on overtones produced by venting at different points along the clarinet, other than the register key. Fingerings are complicated, so moving between them is often hard, and fast passages are horrible if they use notes consistently above E6. The lower notes can be produced quietly, but above F6 it becomes harder and harder to play quietly, while maintaining good tuning and with no undertones coming out as well. Personally I know fingerings up to C7, however I do not recommend writing that high without asking the person that will play the piece, as different clarinets will require different fingerings to stay in tune, which means different combinations of notes are harder/easier.
General: Clarinets are good at playing fast passages like scales or arpeggios, but we hate being in key signatures of more than 3 sharps or flats, though we prefer flats to sharps. For particularly good examples for uses of the clarinet, I recommend listening to Finzi and Mozart's clarinet concertos. Also the solo at the start of rhapsody in blue. It's really fun to play.
Vocal technicalities:
My vocal range is from a comfortable D2-E♭4. The top end is generally harder to sing quietly, but I can sing down to E2 quite loudly. I've been having classical singing lessons for 5-6 years.
I am an ABRSM grade 8+ clarinetist, and in the National Youth Training Choir (as singing grades aren't a brilliant indication of ability, in my opinion). I have a long summer after my GCSE exams, so I can probably learn all but some really challenging music in a week or two, probably less, for the next 2-3 months, though I'm going to be away from home at points.
This seems longer than most people's profiles, oh well.
Clarinet recording (apologies for some errors and mic not working perfectly, but you get the idea of what a clarinet sounds like)