Posted by Lew on October 26, 2001 at 08:40:59:
In Reply to: Short Action vs. "Regular" Piston Valves posted by Short Action Cook on October 25, 2001 at 19:37:36:
Valve stroke increases as the bore of an instrument increases, everything else being equal. Therefore, very large bore tubas have a very long travel, which slows down the ability to take passages as fast as on a horn with a shorter stroke. Short stroke horns allowed a larger bore tuba to be made with a faster valve action. Modern metallurgy has allowed the stroke to be decreased by decreasing the spaces between the ports.
I have a 1939 York Band Instrument catalog where they say:
"The action in all basses described is a revalation in rapid, positive, trouble-free response, and as short as possible without tone distortion or loss of power. By removing the piston from any instrument, you will observe that the stroke must be slightly greater than the diameter of the port. The only way to shorten this stroke is to decrease the size or distort the shape of the port. This causes loss of power, hard blowing, and a 'cramped' tone quality...."
This was an obvious response to Conn's short action valves. This is marketing hype, but the truth is that the valve ports on short action valves are flattened rather than round, which changes the air flow through the opening. I assume that the total area of the port is the same as for a round port, but the flattened shape could cause turbulance and therefore resistance. I only took one fluids course in college over 25 years ago, but someone with more of a current and detailed background in fluid mechanics may be able to explain the real impact, if any.
I believe that recording bells were primarily an early 20th century phenomenon. The story I heard was that they were made to allow the tuba sound to be picked up by recording equipment in studios at the time. This reason has become moot. Upright bells were still most often used in orchestral settings.
Interestingly, when Sousa comissioned the first horn that became known as a sousaphone, he asked for a horn with a bell facing upward to allow the sound to wash over the band rather than project forward. He was looking for a replacement for the helicons that were commonly used at that time. This is still the reason why people use upright bells. The sound should encompass the group from all directions rather than be directional. This is more important for the low frequency sounds than the higher pitched instruments. Think of the way a subwoofer works. For this reason the upright bell horn has evolved to be considered a more versatile instrument.
I can't verify the veracity of any of this, but that's my story and I'm sticking to it.
In spite of this, my favorite horn to play is my Conn short action, bell front, 20K sousaphone.