Re: Re: Re: Re: Re: Smaller mouthpiece for bigger horn


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Posted by Rick Denney on December 12, 2003 at 12:25:18:

In Reply to: Re: Re: Re: Re: Smaller mouthpiece for bigger horn posted by Doug Elliott on December 12, 2003 at 01:55:20:

In studying the literature where all this has been measured and calculated, here's how it seems to work:

Mouthpieces have a broad, single-humped, frequency response curve (i.e., impedance curve). Tubas have a curve with a series of resonance peaks, or spikes, over a range of harmonics. A player's embouchure also has an impedance curve based on its stiffness and flexibility. The three of these combine to create a note with a recognizable pitch and tone.

If you look at the combined frequency response of the tuba and the mouthpiece together, the single, broad hump of the mouthpiece raises the resonance peaks of the tuba in that hump and diminishes the peaks outside that hump. This is what gives the instrument its characteristic sound. If the hump has a different shape, it will emphasize some resonance peaks of the tuba and de-emphasize others. This will change the tone. But if the hump is centered higher, then it has some of the same effects of the player lipping a tone, and it will change the pitch characteristics.

Increasing the cup volume lowers the impedance curve, as well as adjusting its shape. Increaseing the backbore lowers the impedance curve as well, and also adjusts its shape, but in different ways. Changing the shape of the cup but not the volume seems to adjust the shape of the impedance curve but not its center location, so its effect on intonation should be much smaller. Enlarging the backbore also broadens the impedance curve, which has the effect of broadening the pitch slots on each note. Same tubas with intonation problems can be corrected by giving a good player a mouthpiece that makes it easier for him to adjust the pitch with his lips.

If I found a mouthpiece that had good intonation, but I wanted a bigger sound, I might go with a bigger cup that has a smaller backbore. When you and I experimented with mouthpieces for my York Master, we started with a big T cup which made that instrument sound good, and then went to larger and larger backbores until the intonation became too hard to control. Had I been able to make a big sound on a smaller cup (which I can't because of general embouchure weakness--which you identified during our session, reinforcing what I was already hearing from my teacher), I might have been able to go to that 7 backbore, instead of having to stop at the 6. All these factors have their effects, and intonation is just one effect of many, of course.

Lots of people want instruments that are as "open" as possible, but I find I can't make notes on them. They likely have the strength in their embouchures to keep that broad impedance curve of a big mouthpiece on an open tuba under control and focused. I only wish I had that strong an embouchure. I have found that my Holton has much more resistance than the 2165 I tried a while back, even though the latter is supposedly modeled on the former (it may be because my Holton is a BBb). But that is in keeping with the experience of a few top pros, who have reportedly transformed their 2165's with smaller leadpipes.

Rick "who thinks 'bad design' is a little too simplistic a diagnosis" Denney


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