Gap. This has been a subject that keeps being brought up every couple of weeks on trumpet forums.
To make it very basic, the gap is a resonance chamber. The length of this chamber has entirely to do with the amount that the sound wave must expand as it leaves the mouthpiece shank, then how much it must contract to enter the leadpipe. Think of the gap as having a mathematical "sweet spot".
Simple! Maybe not. There is still a lot of confusion and different theories with this subject.
Martin Committee Gaps. From The Trumpet Herald.
I just had a new Charlie Melk leadpipe on my Committee, and the change is extraordinary. He says that for a GR mouthpiece,the gap should be.220 I play Warburtons, and so I can have always have a dedicated backbore for this horn. I have a feeling that the gap for me should be a little bit smaller.
Charlie Melk does the leadpipes and
receivers. The can adjust the receiver to a specific gap with your mouthpiece.
There are ballpark measurements that a repair genius like Charlie has
documented. I would take his advice. Best advice is when he can fit the receiver
to your mouthpiece or one with the same engagement. If Charlie says the gap
setting for an GR mouthpiece on Charlie’s Brass Works leadpipe and receiver will
play best at .220” then it will be in the ballpark for most mouthpieces with the
same shank diameter. The Kanstul G2 may have a shank diameter that is .003”
smaller than the GR causing the gap to be .06” less.
Remember these old Committee’s are not like the trumpets of today and there is
reason Charlie likes the gap at .220”. Therefore, if you want to use a different
backbore to change the gap on this Committee every .001” off the diameter will
reduce the gap .020”. Charlie uses a special tool to adjust the gap.
“1. If you're replacing the leadpipe there's no need to re-tool your receiver. Have it attached at the right location! (The work's being done anyway)”
It’s not the location but the relationship of the step on the front of the leadpipe and the engagement of the taper. Charlie has a special tool to adjust this before it’s mounted using your mouthpiece if so desired. GR should know as he designed and made the tool Charlie uses.
“It's easy to find the formula on GR's website; not so easy to take all the measurements and make the right adjustment, which would normally be done be re-positioning the receiver.”
You are correct! Without proper training, gauges, and tooling measuring this correctly is near impossible. That’s why Charlie has all the skills, tools, gauges, and years of experience to get it right.
“I have a Schilke trumpet and a Stork mouthpiece , I measured the gap and found it was 1/4 inch . Has anyone else found this with Stork mouthpieces?”
You could have an equipment conflict, but only measurements will give you the full story. The Schilke is designed (or used to be designed by Renold) to use a shank of .382” or so. This would make for a .125” gap give or take .020”. The Stork has a large shank .390 or so, it would need to check on an engagement fixture not by measuring the end with a digital caliper. If you do the GR gap formula with a Stork shank you will find it may require a larger gap due to the thicker exit wall. I have run the calculation for certain Stork Mouthpieces and that .220” was in the ball park for certain set ups. You would need to do the math for your set up. I think the last Stork we set up has an exit wall of .032”; therefore, you need .160” just for the area of rapid expansion plus about another .030” for the area of rapid compression. Total was around .190”. Using the GR gap formula we have calculated correct gaps as low as .060” to over .250”.
Post a reply to this topic on The Trumpet Herald.
Problems Measuring!!
Now, measuring your gap can be tricky, even for those in the business.
Click Here for the forum posts.
As you can see, it can be a challenge, even for those who are accomplished in the business to get accurate measurements. If this is the case, how can the industry make consistent parts? Dr. Dave is correct about the fact that there are no industry standards.
GR once approached major brass instrument manufacturers in an attempt to standardize the trumpet receiver / gap section. He was basically laughed at. Oh well...round and round we go all at the expense of the consumer.
Post a reply to this topic on The Trumpet Herald.