Airflow Inside Your Valves.
The scope of horn design is huge. There are endless variables and combinations that create different effects. This fact is one reason horn making is so challenging and enjoyable. There is always something else to learn, some other nuance to add. Unfortunately it also makes things difficult to understand unless you devote an extended amount of time to slogging through it. Since very few actually have or make that time, a series of “shortcuts” have arisen to explain how the horn works. These are the things that “everyone knows”, but they are rarely more than slightly right. One such shortcut is the concept of “smoothing” out the air flow.
At the time I was building this CAD model, I was waffling between a 20 and 22mm change valve. So I left it off to do the analysis.
Creating a cutout of the valve ports and the internal wind ways to analyze.
If you are a player who believes in and advocates for a smooth airflow as a driving philosophy, I recommend that you exclusively play on a trompe de chasse. Otherwise, it’s rather silly to get all bent out of shape over a few sharp bends in a horn given what happens inside your valves. In the wire frame below, the dark section shows the inside of the valve. If you look closely, you can see that the windway is far from round. Worse, it does not line up with the ports so there is a substantial lip when the air enters and exits the rotor.
From this model you can see the wind ways do not line up with the ports, there is a substantial lip that “should cause all kinds of turbulence and other nonsense”.
On the surface, it would seem that the design of the Meinlschmidt valve section is remarkably flawed. However, if you believe, as I do, that cubic volume plays a large role in how a compression wave forms, it’s interesting to note that the clearance around the sides of the ports makes the total volume of the air column equal to a straight tube of the same length. The valve design is critical to preserving the volume inside the valves in spite of all the sharp bends, lips, ledges, lumps, and other anti air smoothing characteristics.
The air column (blue) has an internal volume of .7400 cubic inches.
A theoretical straight tube of the same length (blue) has a volume of .7407. I’d say .0007 is close enough to call identical.
Next time the question of smooth airflow comes up over dinner, as is often the case, remember that valves are the great catastrophe of modern horn building and go buy a great natural horn.
A 3D rendering of the air flowing through the valves.