At GR Technologies we have defined the Gap components and their working relationship. These components are the Mouthpiece Shank, Receiver, and Leadpipe. Measurements: 1. Distance from the end of the receiver to the leadpipe venturi. 2. Engagement of the mouthpiece shank into the leadpipe. 3. Exit diameter of the mouthpiece shank. 4. Leadpipe venturi. 5. Exit wall thickness or the mouthpiece shank. 6. Internal diameter of the receiver.
We use a formula to set gap. A change of .001" on the diameter of the shank will cause a difference of about .020" in the gap distance. You may need to take your horn and have a professional measure it. If you do it at home make sure you do it several times and your numbers repeat. If these numbers are set exact to this formula you will have the optimum or Zero Gap. If the gap is greater it is a positive (+) gap measurement and the result will be a bit more resistance, although, the horn will slot and speak well. If the gap is less it is a minus (-) gap measurement and the result will cause less resistance, as well as, difficulty slotting. Some players like this condition and prefer the gap to the minus side. If your gap is measured correctly and you find it within .030" of the Zero positions you should be fine.
Formula: Exit wall of mouthpiece (#5) multiplied times 5. Example, exit wall of mouthpiece = .025" X 5=. 125" . Next take Venturi (#4) and subtract it from the Receiver ID (#6). You will need to divide this number by “2” to find the” effective wall thickness” of the leadpipe, and finally multiply the” effective wall thickness” by 1.5. Example, Venturi is .345" and Receiver ID is .385. Subtract .345 from .385 and divide it by 2, you get an effective leadpipe wall of .020, multiply it by 1.5 =.030" . Now add the .125 and .030 and you get a Zero Gap of .155. We find this formula to work very well. If you are getting good results there is no need for change. If you make a change measure the gap and calculate the change. It is not expensive to have the Gap adjusted. We recommend you set your gap and leave it alone. Constant change in this area will cause your playing to be insecure.
From The Trumpet Herald Forum: “Even if the shank was standardized, GR has shown that the optimum gap also depends on the exit diameter of the shank, the entrance diameter of the leadpipe and the relative thickness of the two walls.” GR: The optimum gap works when all the parts are made correctly. Therefore, if you have a leadpipe that the front end has a burr, worn and tapered from a shank that was too small, solder build up, or some special cause will throw this right out the window. If I inspect a horn and find and issue between the receiver, venturii, leadpipe front end, something... it won’t work and you need to manipulate to get the sound wave to set up. Rarely will it work; rather the player will become more and more fatigued over weeks, months, and years due to fighting the equipment.
We have a protocol that inspects this area closely. Funny, one guy told me with a GR mpc his gap was off so he was going to try sleeves. Over the phone I had him do a test and something was really wrong so I told him to send me the horn. When I got the horn it was really funky. He said is just returned from the West Coast for a valve alignment so he knew it was perfect. I pushed all 3 valves down and blew in the horn really hard and a shipping wafer came out of the bell. You could play most notes but some would not set up and you felt a vibration.
Before you start messing around get it checked out. I use Charlie Melk and often after a trip to Charlie you are back in business. If the match is so far off or the player had been manipulating for many years the player may need to correct the damage from years of manipulating due to the mis-match. Sleeves cut with the straight section will not seal unless you have a very tight fit or soldier it. The o-ring solves the leak issue but acts as an insulator. Sleeves are an option not a solution. A solution would be match between the horn, mouthpiece, and player (gap is included). Bottom line is that there must be a match between player, horn, and mouthpiece. This match must include the gap. Intelligent play testing will tell if that match exists.
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