So here’s the goal: An instrument with eight holes (for left thumb and fingers 1–3, right fingers 1–4), preferably sounding the following notes:
or, if that isn’t feasible, a probably easier fallback:
The first of these is the pitches produced by the finger tone holes (and one of the R4 levers) on a contra-alto clarinet. The second shifts the semitones from L1/L2 to LT/L1 and R1/R2 to L3/R1, where they’d be easier to obtain, and changes R4/End to a semitone to keep the End note in the scale. But I think the “standard clarinet” option is worth a try.
I’ll work from bottom to top, because adding a tone hole above an existing one hardly changes the note produced at the latter, while adding a hole below an existing one makes it flatter. Start with smaller holes and enlarge them if needed. Probably best to start with a “lower joint” made of elbows but just let a straight pipe stand in for the “upper joint” at first. Once that’s in good shape perhaps glue the “lower joint” together, unless it seems feasible to leave it dry-fit, then build and tune the upper joint.
First things first, though, which is: given the mouthpiece effect noted before, I need to decide what mouthpiece I’m going to use. Tone holes set up for one mouthpiece will be wrong for another. I have several B♭ soprano clarinet mouthpieces, as well as one each for E♭, alto, and bass clarinets… and a baritone sax mouthpiece I picked up cheap back in 2005, just in case I had a use for it. Theoretically you don’t want a big mismatch between the diameters of the mouthpiece and the instrument, and even the E♭ mouthpiece is wider than the tubing I’m using. But that little soprano reed really struggles and it’s hard to force enough air through the small mouthpieces for such low notes. The alto works better. The bari sax mouthpiece has an inner diameter similar to the alto and also works okay; I think I like the alto’s sound a little better, though. But what I’m happiest with is the bass clarinet mouthpiece. I took a 1/2″ CPVC coupler, put about 3 wraps of electrical tape around it, stuck it on a tube, and pushed it up into the mouthpiece. That way the air column really “sees” rather little of the mouthpiece’s volume and diameter; that can’t hurt. It looks crazy but it blows easily and sounds good. Part of that might be the reed. On the other mouthpieces I have old cane reeds, long neglected and not exactly in peak condition. On the bass I have a Legére plastic reed, which you can sit on top of for a year and it’ll still work just as well the moment you try to use it again. I know from experience. (It had slipped down under a cushion.) I thought I had a Legére soprano reed, too, but I haven’t found it. I should check the sofa. But anyway, I think the cane vs. plastic aspect is not the main factor here.
Bass clarinet mouthpiece it is, then.