Posted by Rick Denney on May 16, 2003 at 14:00:31:
In Reply to: Re: Re: Tuba Bells posted by Frank on May 16, 2003 at 11:55:09:
Different horn shapes color sound differently, to be sure. But I'm beginning to think that what happens outside the tuba is more important to how its sound is perceived than what happens inside it. And the shape of the bell stack has a huge effect on how the sound is radiated into the room.
The curve of the bell changes the point at which a sound reflection occurs for each frequency. This would widen the slots on the instrument. At some point of curvature, however, more bell has no effect on the internal resonance of the tuba, though it will effect how the sound radiates from the tuba. Dr. Young has suggested in the past that the bell outside of about 40 degrees from axial no longer affects the frequency response and intonation of the instrument.
From the standpoint of horn shape, those horns with more of an exponential shape seem to project sound more strongly on a central path, and those with a more rounded shape seem to project sound along a wider array of paths. Dr. Young suggests that this effect varies by frequency, more widely dispersing low frequencies while higher frequencies are more on the central path. That can be measured by testing sound at different orientations to the bell outdoors where there is no environmental resonance. That said, I think one of the traits of the big tuba bells is a happy confusion of pitches in a live room that result from multi-path errors. Stated more simply, if the sound is radiating along all those paths, then the sound reaching the listener is coming from more directions.
Some of those paths are longer than others, and some get there sooner. For example, the sound that goes from the tuba to the listener via the right wall of the hall might travel 400 feet, while the sound getting their by the direct path might only got 275 feet. Thus, the reflected sound will get there about 110 milliseconds later than the sound along the direct path. This is called a phase shift, and it is greater than the time required to transmit a wave of any tuba sounds. Therefore, some of those frequencies in the sound will be amplified and some canceled out. Every path will have a subtly different effect on the overall sound. Thus, the sound at the listener is greatly affected by all that reflection in the hall. The more paths there are from the tuba to the listener and the larger the space, the more the sound will be blurred by all those phase shifts. This blurring will peel off many of those upper harmonics.
I'm approaching a grand unified theory here, so hang with me.
The big tubas with the wide bells create a wide dispersion of sound paths, and that wide dispersion helps carry the sound to the far corners of the hall. It also cleans off some of the upper harmonics that might make the sound edgy up close. (How many times have you heard that a good sound does better out front than up close?) Large bells with large bell throats seem to be the ones that do this the most. Speculation: Bell stacks that are narrow with large flares do it some, but not as much. Bell stacks with large-throated bells but narrow flares come in third, and narrow bell stacks with small flares do it least. Short bells still contain the mixing up of path errors that happens in the bottom bow (as it does in all tubing bends), and tall bells do so less. Thus, short bells with large throats and wide flares seem to build the most multipath error into the sound, when played in a live hall.
I think my construct will explain forward bells, too. A forward bell to some extent negates the effect of the room, but emphasizing the central path to the listener to a much greater extent compared to all those reflected paths. Thus, the sound is colored less by the multipath effects of the room, and some of the blattiness of big horns doesn't get filtered out as it would with an upright bell. The curve of the forward bell helps here. Also, there is the suggestion by Dr. Young that low frequencies radiate more outward and high frequences more along the central path.
Outdoors, there is no multipath effect, because only the central path reaches the listner unless there is a shell. It's the opposite of a live hall. Thus, the forward bell helps to get some sound to the listener, and ambient outdoor noises often mask the higher frequencies. But a tall bell with that exponential shape might do even better, because it can project that sound with more laser-like intensity. So, for pure loudness, a convertible tuba pointed right at the listener might be louder than a sousaphone, but it won't have the same built-in multipath effect of all that curved tubing and wide bell flare, and won't have the same richness of sound. The sousaphone will also spray the sound more widely, which was a priority before marchers learned how to walk sideways to keep their horns pointed at the judg...er...audience.
So, there it is. Why all things are the way they are.
I wonder if any of it is true?
As to horns of different concepts working and playing well with others, that is a matter of conjecture. I just played a concert with Bob Pallansch, who was using a Sear CC rotary tuba with a rather small bell flare. I think we blended just fine. Our sounds as different players (him being far better than me) had a much bigger effect than our different instruments. But I'm one that believes that mixed horns do not good blend ruin: the Tubameisters blended just fine with a 4/4 rotary CC, a 3/4 piston F (my Yamaha), a 3+1 compensating euphonium, and a rotary kaiser-baryton.
Rick "who thinks what happens outside the tuba--at both ends of the tube--is as important as what happens inside it" Denney