Posted by Rick Denney on October 22, 2003 at 11:46:02:
In Reply to: Re: Tuba MP Throat Size vs. Bass Trombone posted by Doug Elliott on October 21, 2003 at 19:42:29:
Sez Doug--The throat needs to be in proportion to the depth of the cup or the intonation suffers and the resistance feels wrong.
Absolutely. This has been clearly shown in the acoustics literature, by both Benade and by Fletcher and Rossing. The larger throat provides wider slots for adjusting pitch, but it must be matched by a larger cup volume to retain the same impedance, and therefore the same influence on pitch.
The reason tuba players can tolerate such large throats is because they have a different concept of air flow. While trombone players are seeking a highly focused sound with some brilliance, tuba players want a round tone with relatively little brilliance. Trombone players talk about blowing faster air while tuba players talk about great gobs of slow, warm air. Too much resistance in the mouthpiece can brighten up the sound too much, depending on its shape, I suppose.
Jacobs experimented and discovered that at the same absolute pitch, top brass performers move the same quantity of air flow no matter which instrument they are playing. If a trombone on a low Bb is playing the same absolute pitch as a tuba on a high Bb, and if the flow is the same, then to maintain the same flow the pressure must be higher and the orifice smaller, by my observation. The velocity of the air will by necessity be faster. A smaller throat helps with this, it seems to me, as does the smaller rim.
Rick "exploring the differences between trombone and tuba lately" Denney