Older MW tubas

[Roger Lewis]

are bigger in diameter so that the bends in the tubing inside the valve ports could be smoother and occur over a longer distance, rather than abrupt, somewhat tighter bends. This will increase the air flow and decrease some resistance in the instrument.

Roger

[iiipopes]

are bigger in diameter so that the bends in the tubing inside the valve ports could be smoother and occur over a longer distance, rather than abrupt, somewhat tighter bends. This will increase the air flow and decrease some resistance in the instrument.

Roger

Especially if the bend happens upon a compression node for a particular note.

[iiipopes]

Math and physics. For example, the wavelength for a BBb is about 18 feet long, which is why the horn is that long. Octaves are even fractions, so you don't want a kink 1/2, 1/4 1/8 etc of the way from the mouthpiece to the rim of the bell, or at approximately 9 ft, 4 1/2 ft, 2 1/4 ft, etc. Fifths and their octaves are multiples of 1/3. So for F you don't want a kink 1/3 1/6 1/12 etc of the way from the mouthpiece to the bell, or 6ft 3ft 1 1/2 ft and so forth. The rest of the intervals can be calculated by how many half steps away from BBb, multiply or divide, depending on which way you went, by 2^x/12, with x being the number of half steps, and taking that fraction times the length of the horn with that valve down. For example, to find the nodes for A's, multiply the 18 feet by 2^1/12, as A is one half-step below Bb. This is approximately 18 X 1.0594631, or about 19 feet, give or take. So, including measuring the path through the second valve loop, you would want to avoid kinks at @ 9 1/2 ft 4 3/4 ft etc. If a kink or loop is inevitable, then enlarge the radius as much as possible and even the diameter of the knuckle, as Schilke did with his trumpets, to avoid the node causing back pressure and resonating out the actual tubing, which is one cause of "stuffiness."