"Smoothing" Air Flow is Not a Thing.
A lot of makers and retailers extoll big round looping geometries as “smoothing out the air column” thus making the horn less resistant and more open. It’s one of those things that “everybody knows” without much actual evidence to back it up. It’s hard to say how this idea got so much traction, but I have a few theories.
Theory 1: An unsophisticated design analysis of the piston CF Schmidt.
A lot of folks with whom I’ve discussed this open air flow concept point to the piston in the CF Schmidt wrap. They say the piston smooths the air through the valve and gives that horn its open quality. They conveniently ignore the extreme switchback going into the piston, but it is true that the piston wind way is much rounder than a rotor. Also true is that generally, the Schmidt branch tubing is laid out with larger radius tuning slide crooks and more incremental bends. While all of this could point one to conclude that the CF Schmidt has a smooth air flow and thus low resistance, there is a more compelling explanation. The CF Schmidt horn has the longest continuous solder joint between the bell tail and first branch of any horn ever made, as well as an extremely long joint between the lead pipe and bell tail, and significant parallel joints between sections of branch tubing. Having tested these joints extensively, I am convinced that these jointing techniques are more influential in the playing quality of the horn than the loopy bends. Perhaps this is why modern attempts to duplicate the magic in those early piston horns have thus far failed; no maker has as of yet been willing to go through the trouble of duplicating those jointing techniques.
Theory 2: Poor execution of “sharp” bends on older horns.
While studying older horns, it’s apparent that the bending execution was more about getting a tube from point A to point B, rather than keeping tubes round or worrying about their lattice integrity. Many times, the half tone bows and sharper angles on older horns are incredibly out of round. This is likely a reflection of how difficult these bends are to do, especially out of a industrial setting. It take a great bit of skill to pull these off in a small shop, one reason why so many other makers today buy these from the industrial complex. It is also possible that older horns simply don’t play as well as more sophisticated modern horns and the blame is misplaced on the sharpness of bends rather than other more likely reasons.
Theory 3: Incorrect reliance on fluid dynamic theory.
Fluid dynamics would say that in fact, Jacob Medlin is a idiot and smoothing out the air flow is incredibly important. It would suggest that even a little bit of extra smoothness can remove turbulence inside the tube. And since air is technically a fluid, things must work exactly the same inside the horn. People who view the horn through this lens imagine air molecules zipping along the insides of tube, barreling around corners and getting tossed about by even the tiniest constriction. That model is not how sound is created in the horn. The standing wave inside the horn is a compression wave. It doesn’t actually move that far or that fast and the pressure inside the horn is quite low. Using fluid dynamics to explain why horns need smoother air paths with less kinks and sharp bends just doesn’t hold water (pun intended).
Theory 4: “The pink elephant.”
If you hand someone a horn and tell them that you smoothed the air flow, gush about how open it is and then ask them how much they love the open qualities, they will likely feel the horn as open. Do this enough times, and people expect that anything that is done to smooth the airflow makes a horn more open. Eventually “everyone knows” that a smoother, more open wrapped horn with no sharp bends is more open. Is there any actual evidence? At that point it doesn’t matter.
Frankly, I find big loopy horns to have a rather goofy, silly look to them. Horns need to have some geometrical bite to them, an aesthetic that conveys precision and sleekness. I sometimes wonder if the smooth airflow theory got started as an excuse for makers to stop attempting the more angular and difficult bends and get players to accept larger wraps that are easier to make.
I’d make a special exception for my friend Doug Hall who, along with George McCracken, has made some horns with big loopy bends that are DEFINITELY NOT easier to make. I believe that he may have actually sat down and thought of ways to make big loopy bends even harder. While I applaud his effort I’m still not convinced that it’s better acoustically. Sorry Doug :)
If it were true that smoothing out air flow really was so important, dents that deform the tube would have to be taken much more seriously, and technically deficient makers would never be able to get away with out of round or lumpy branch tubes. In reality, as with much of horn making, the truth is much more complex and nuanced. I don’t blame folks for believing shortcuts like this with little evidence, there are days that I want to throw my hands up and do an easier job like professional coloring book colorer. Challenging conventional wisdom, especially in regards to smoothing air flow, will hopefully expand our understanding of horn acoustics and help us craft even better horns.