Filling a Large bore trumpet?
Tuesday, October 22, 2019 10:32 AM
Addressing the Testosteronic Myth
How difficult is it to fill a large bore trumpet?
I would like to address the often held belief that it takes a lot more air to fill a large bore trumpet than a medium large bore and will use Bach Stradivarius trumpets as examples. It is helpful to use these instruments because the Conn Selmer parts website has information which is very helpful for this question. Bach and similar design trumpets like Shires and B&S, have a ML bore of 0.459” and a L bore of 0.462”. A difference of 3 thousandths of an inch. The Bach XL bore trumpet has a bore of 0.468”.
This is not about the pros and cons of large bore vs medium large bore, nor is it a description of the differences between the various trumpet models.
The Conn Selmer parts website shows that the lead pipes, pistons, and bells for both ML and L bore Bach trumpets are identical. When we look at our trumpet we see that this only leaves the main tuning slide, valve slides, and lower main slide receiver tube into the third valve as the parts of the instrument that can have different bore sizes.
Lets exclude the valve slides and just concentrate on open notes. Measuring the tubing lengths mentioned above we see that only 15” of the trumpet’s total length of 57” have a larger bore. That is just over one quarter of the trumpet’s total length.
The cross sectional area of a 0.459” ML bore trumpet is 0.1661“2, so the volume of that 15” length is 2.49“3.
The cross sectional area of a 0.462” L bore trumpet is 0.1676“2, so the volume of that 15” length is 2.514“3. The difference in volume of these two 15 inch lengths is 0.024“3 which is the same as the volume of about one eighth of an inch length of ML tube. So if we lengthen our ML trumpet by one eighth of an inch, i.e. pull our main slide out a sixteenth of an inch we have given our ML trumpet the same volume as a L bore.
An XL bore (0.468) bore trumpet has a cross sectional area of 0.172“2 and the volume of the 15” length is 2.58“3. This is 0.090“3 bigger than the ML. Pulling the ML main slide 0.26” (half of 0.523”) will give the ML trumpet the same volume as the XL.
So with all this taken into account there should be no difficulty in filling any large bore trumpet. The difference in volume between all these trumpets is less than half an inch difference in the main slide position!