Posted by Kenneth Sloan on October 10, 2003 at 11:20:06:
In Reply to: Re: Need some info on F tuba posted by Mary Ann on October 08, 2003 at 09:41:39:
"it is the same tube length as a French horn. It plays lower because the mouthpiece and tubing are a lot bigger."
Same length - check.
plays lower - only if the player want to.
because the mouthpiece...bigger - check.
because the ...tubing...bigger - BZZT!
In my opinion, the mouthpiece is the big factor. The main tubing of an F tuba (or a Horn) produces a relatively flat spectrum, with sharp peaks at each "partial". The mouthpiece can be thought of as an amplifier with a more-or-less bell-shaped envelope. This envelope provides significant "amplification" over a 2-3 octave range. the important parameter here is where that 2-3 octave range is centered. Small mouthpiece = higher pitch.
So, in this simplified model, the F tuba and the F Horn are very similar, until you fit them with a mouthpiece. Then, the F tuba "wants" to play an octave or so lower (with an F tuba mouthpiece) than does the F Horn (with a Horn mouthpiece). The F Horn mouthpiece "discourages" the use of the lower partials and "encourages" use of the very high partials.
I don't think that the diameter of the tubing has a significant effect on the *pitch* - but it does affect the tone quality.