Gap - is there more to it?

[Venturi]

We're familiar with the idea that gap matters, and I'm 100% in agreement. I've had a dog horn turned into a blowtorch by nothing more than remounting the mouthpiece with a 1/16 inch difference in gap.

BUT -- how certain is it that the "gap," defined as the distance between the end of the mouthpiece shank and the beginning of the mouthpipe/leadpipe, is exactly what matters?

And why should the gap matter, for the physicists and engineers on TH?

Further to the first question, for example, how do we know that what really matters isn't the distance between the mouthpiece throat and the venturi (narrowest diameter) in the lead pipe? This distance would change, too, as you adjust the position of the mouthpiece receiver relative to the lead pipe.

Or, for another example, how do we know that what really matters isn't the rate of change in diameter between the mouthpiece and the lead pipe? This, too, would typically change as you adjust the receiver's position on the pipe.

Some relevant thoughts by Renold Schilke:
http://www.dallasmusic.org/schilke/Leader%20Pipe.html

Hoping for some good ideas -------

[chuck in ny]

it's a mystery to me as well. whatever point you are measuring from, you just figure to be adjusting harmonics.

[yourbrass]

Practical experience is the teacher. The why isn't always known.
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[razeontherock]

Is the OP aware of GR's formula for "0 gap?"

[richardwy]

[oxleyk]

One of the best explanations. https://stomvi-usa.com/mouthpiece-components/

Kent

[hose]

Here's another theory. The mpc shank is in contact with the receiver only partially.The receiver doesn't grip the entire length of the shank. Different mpc shank tapers result in more or less contact with the receiver. I've been told by a trpt maker/designer that it's preferable to have the receiver grip/contact all of the shank. This may also affect how much gap works best.
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[yourbrass]

[Venturi]

[JohnSnell]

This thread brings up a great question about isolating the gap and, more broadly, the scientific testing of trumpet design. It is a question we have been dealing with for several years here at the shop.

A good experiment will isolate only one variable at a time, like the gap, to determine that variable’s effect (or lack thereof) on the player-mouthpiece-trumpet system.

As noted, you can’t change the gap without changing some other variable. For instance, a change in the gap by altering a mouthpiece shank may also change the distance from the mouthpiece bore to the beginning of the leadpipe, the engagement of the mouthpiece with the receiver, and the overall length of the entire system. To keep these variables constant, other variables like the mouthpiece length, backbore shape, and backbore length would have to change.

The question then remains – does the gap truly matter?

In our opinion, yes.

Here’s why based on what we know to be true:

1. Structural changes in the instrument and mouthpiece (bore size, bends, valves, etc.) result in changes in acoustical impedance of the resonating air column.
   
2. Changes in impedance create reflections and perturbations in the frequency which affect the feel of the instrument to the player.
   
3. The gap between the end of the mouthpiece and the beginning of the leadpipe creates a chamber, or in other words, a bore size change, in a critical spot in the system that will change the acoustical impedance of the resonating air column and therefore, also create a change in feel to the player.
   
4. Through Bob Reeves' experiments, we know that players can feel as small as a .006” change, and possibly smaller, in the size of the gap.

Even though it may not be possible to strictly isolate the gap variable in testing, we know it does something. What is that something? Adjusting the gap allows us to fine tune the acoustical impedance of the entire system to what the individual likes to hear and feel.

The shop has posted few blog articles that dig a little deeper into this topic, including some issues that have been brought up in this thread. I invite you to check them out:

• 3 Inherent Problems with Gap Formulas and Studies
  
• Gap and the Player-Trumpet-Mouthpiece System

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[Venturi]

Yes, it's clear to many of us (myself included, as in the first post here) that "adjusting the gap" can cause a horn to play markedly better or worse.

But we just conveniently refer to all this as "adjusting the gap," and gap isn't the only thing that changes. As noted by a number of people above, when you change the gap you may well change a number of other measurements/attributes at the same time.

Finding out exactly which attribute is truly what's important would be a very valuable accomplishment. With the right knowledge, it could become far easier to optimize a horn than we have conventionally thought.

[stumac]

It has been my observation that of the horns I own the least sensitive to mouthpiece changes are the ones that have a smooth transition ie no step between the receiver and leadpipe tapers, 1941 York custom, 1950s Selmer Balanced, 1950s Besson 10-10, 1970s Benge 3xMLP.

To this end I have made an extended taper reamer to remove the step, I have done this to three horns to date, Getzen Super Delux frankenhorn, Buffet Crampon Balanced and an I and K, C. In each case the horn has become insensitive to mouthpiece change. My test mouthpiece is a Wedge 3CC SST with 5 shanks of various lengths in 1/16" increment.

I am currently using an oddball Bach mouthpiece a 2 1/2 C screw rim on a body marked E,2 1/2 C with a 117 backbore, very thin wall at the exit of the shank. I realize that removing the step will increase the diameter of the venturi, this has opened the blow of the horns I have done, the Buffet-Crampon has been played by several of my friends and all have commented on how easily it plays, and assumed it is a large bore, in fact at 0.442 the second smallest I have.

My next project is to get another leadpipe for my Eclipse so I can A to B change.

Regards, Stuart.

[Craig Swartz]

Back to Schilke's article, in the many conversations I had with him this was also his reasoning behind his horns having "reverse" leadpipes and also the reasoning behind the concept of tuning bells. He was seeking zero interruption from the entrance of the mouthpiece cup through the valve section.

On the opposite side of the coin, I ran into Don Novy (http://www.dmamusic.org/acousticoils/) years ago at the Colorado Music Educators convention selling his "Acousticoils" which actually create an interruption that can be placed at various points around the horn.