Posted by Rob P-M on October 26, 2001 at 08:43:10:
In Reply to: Short Action vs. "Regular" Piston Valves posted by Short Action Cook on October 25, 2001 at 19:37:36:
The length of the stroke on a valve instrument is in large measure determined by the bore of the instrument at the valves, since the size of the holes (ports) in the piston and the distance that must be maintained between the holes dictates how far the piston must move between the open position in which the airstream passes directly through the piston and the down position in which the airstream is diverted through the piston's branch tubing.
The only way to shorten the stroke on a piston valve is to make the holes smaller. The Conn patented short action valve did so by making the piston ports oval in shape, flattening them so that they were about 1/3 smaller on the stroke dimension. The valves were also slightly fatter overall. Conn used this on both baritones/euphoniums and basses (2XJ series recording basses/uprights and 2XK series sousaphones). The short action valves on the basses also had the valves stems offset for ease of playing.
The argument of those who don't like short action valves is that by changing the shape of the tubing and the ports, and hence the airstream, you change the sound. The Conn 2XJ series is considered by many to have some squirrely intonation right below the bass cleff staff. My own experience has been mixed with 2XJ horns, some seem to be a bit hard to play in tune, others very easy to play in tune. But, in fairness, I started playing a 20K sousaphone pretty early on, so I may simply have gotten used to lipping the notes.
Those who like short action valves note that they are much faster. It's much easier to play fast passages with lots of sixteenth notes on short action valves than on regular valves. I like them.
It's hard to tell if the short action valves would really always be acoustically worse, as only Conn has built them -- at first because of patent protection and subsequently because they are apparently very difficult and expensive to make compared to regular valves. They are now only available on the 20K.
Recording bells are another matter. They were a Conn innovation in the late 19th century (Wonderphone) and became very popular in the early days of acoustic recording, as a nondirectional upright bell didn't record well. The argument seems to be that you get a more directional sound with a recording bell and a more fundamental sound with an upright bell. Almost all tuba players prefer upright bells, and over the years directors have moved from recording bells back to upright bells. There was an article in The Instrumentalist on this many years ago that's in the big bound collection of articles from the 50's to 70's.