Posted by Klaus on January 24, 2003 at 20:07:16:
In Reply to: Re: Re: Piston F tubas posted by Mike Sherline on January 24, 2003 at 18:56:28:
That means, that when the air passes any of the slides, then it will enter the slide through a male branch of the tubing that is a fixed part of the tuba body. And it will leave the slide through a male branch of the slide.
The purpose of this is to avoid the airstream having to encounter a reversed step-bore as seen in normal slides.
With some of my many very diverse brasses I have experienced, that reverse step-bores can cause turbulence. They are experienced as an undue resistance and heard as a bit of "dust" on the sound. In reality this is a bunch of non-harmonic high frequency overtones.
My remedy has been to undercut/chamfer the end of the male slides. Either with a scraper or with one of my reamers.
You can see the difference in the reversed main tuning slides of King and Benge trombones as opposed to the standard ones from Bach.
You can see the reversed tuning slides of the Apollo, if you zoom in on the .pdf file linked to below.
As usually you will have to join an open, free, and non-posting Yahoo group of mine to access that .pdf file. The file is large, but that is what makes it possible to zoom in on details.
Klaus