Re: Re: Re: Yet another change to The Tuba Sound


[ Follow Ups ] [ Post Followup ] [ TubeNet BBS ] [ FAQ ]

Posted by Rick Denney on July 17, 2001 at 14:25:32:

In Reply to: Re: Re: Yet another change to The Tuba Sound posted by Carl on July 11, 2001 at 23:22:14:

I've studied the papers used as the basis for the development of the BIAS and BIOS systems that Carl has presented to us. There is some good stuff in these papers, if you are not afraid of the math.

Several points emerged in my mind while I read them:

1. The papers confirm what I had seen in the BIAS promotional materials, that the optimization software looked at intonation only, though the measurement system also looks at response (i.e. the peakiness of the acoustic impedence curve). This is still a highly useful tool for a manufacturer, because it could be used to correct the fault of an otherwise worthy instrument, by constraining the geometry as much as possible. In this case, one would start with a heauristic optimum--that is--resulting from trial and error, and then fix specific problems. I'm sure that the more progressive companies are doing this already.

2. The papers do not consider widely conical profiles. The more conical the profile, the more errors in their two-dimensional reduction model. The American BAT is likely to be more error-prone than the German rotary tuba with a much longer cylindrical section.

3. They reference some experiments with finite-element anlysis, which is a numerical method that looks at the instrument in three dimensions. They don't use it because it is computationally impractical. But even finite-element analysis looks only at first-order frequency-domain issues, which is the problem John Swenson mentioned. It represents the frequency domain as a static transformation of periodic vibration, when many aspects of a horns performance are dynamic in that domain, such as when attacking note, slurring, and controlling pitches. They DID talk about the acoustics underlying some of these parameters in useful ways, but not to the point where they could include them in their optmizer.

4. The make reference to some attempts to quantify the trial-and-error process directly, by use of genetic algorithms. Their attempt to use this approach in the computer was not too successful, as they rightly point out, and probably as a result of a poor model. The optimization algorithm they use has a lot of art built into it, and they are completely honest about that, too.

5. They warn of increasing errors as a result of the bell flare. One of the primary characteristics of different tubas is the difference in bell shapes. They attempt a heuristic correction for other factors, too, such as the annealed state of the brass.

6. Their approach, working from scratch, produced something that looked like a trumpet. Sort of. They described it as resembling a historical trumpet, wondering if perhaps those old makers knew something we didn't. We should make one and find out! Shouldn't be too hard with a trumpet.

7. They mention but do not characterize the effect of the overtone series and bell shape on the propagation of sound in the listening environment, which is just a fancy way of saying "projection." Yup, it's a mess, as I've been saying all along, but it's one of the most important factors in tuba performance.

8. I came away knowing much more than when I started. I am perhaps slightly more favorable about the prospects of success, because I see that in Germany, they have been devoting far more resources to this issue than I imagined. Remember, my pessimism was not based on impossibility, but on the unwillingness of our small industry to devote the needed resources.

9. I was thinking a lot about Fred Young as I read these papers. He has told us of computer programs that will correct intonation deficiencies in taper designs for a long time. Here it is.

10. ITEA and the tuba academy in this country should point some of their more scientifically minded researchers in these directions rather than writing yet another dissertation on 19th-century convoluted serpent performance in Outer Slobovia.

11. Carl should be thanked for braving the debate of sticks in the mud like me to bring us this information. But we still should recognize that the science that has been conducted is still in its infancy.

I will probably put a link to these papers from my web page.

Rick "still looking for a concrete example" Denney


Follow Ups: