The Mouthpiece “gap”
 
Disclaimer: The trumpet related information on this site might be just my opinion, It could be wrong, and in some cases you may find others that strongly disagree with something. What I am trying to do with this website is help people work on their own horns, and maybe learn some of my experience as an experimenter. In no way am I trying to keep any repair techs from making money, or anything like that. I will say, that often times, people in the trumpet business tend to try to make things more mysterious than they really are. Take everything with a grain of salt. Nobody knows everything. If you would like to add your insight, drop me an email, and I’ll include your thoughts.



One of the best trumpet websites on the internet is the GR mouthpiece site. There are articles about all kinds of things including a great short article about the mouthpiece “Gap”, which has a formula for computing an optimum gap given certain mouthpiece and receiver dimensions. (by the way, GR makes superb mouthpieces which are well worth the money)


The mouthpiece “gap” is the space between the end of the mouthpiece and the end of the leadpipe when the the mouthpiece is inserted in the receiver. If the mouthpiece goes to far in, and comes too close to the leadpipe, the horn may play worse than it should (maybe a LOT worse). If the gap is too big, it’s usually not as bad, but still not optimal. Back in the 70’s, Clifford Blackburn wrote an article for the ITG newsletter that basically said that the gap should be a 8th of an inch or so.


The main issue with this situation is the sharp edges at the end of the mouthpiece, and then  the sharp edge at the beginning of the leadpipe. Basically, if the wall of the end of the mouthpiece is thicker, that mouthpiece would play better if the space between the end of the mouthpiece and the leadpipe was a little longer. The same is true about the thickness of the end of the leadpipe. If that edge is thicker, then the best gap should be relatively a little longer. GR has come up with a formula that takes the thickness of the exit wall of the mouthpiece, and the thickness of the entrance wall of the leadpipe, and computes an optimal gap length. If you know the thicknesses the formula is easy to run. Simply multiply the exit wall thickness of the mouthpiece by 5, and multiply the entrance wall thickness of the leadpipe by 1.5. Then add those two numbers together.


The GR formula as I run it, almost always gives a best gap of about .160 on an inch. An 8th inch is .125. It’s pretty hard to do all the measurements in the GR formula without taking the receiver off, but I did it a few times with some very different setups, and it always came out to between .157, and .170. GR says that if you are within .025 you are ok. That would make a gap of an 8th inch at the very small end of the acceptable range. The effective wall at the beginning of the leadpipe is usually .020 on a Bach, or bach copy, or yamaha, or most modern horns. You cant get that measurement without taking off the receiver sometimes. On a Connstellation the leadpipe wall is a whopping .034 or so. That makes for a best gap that is pretty big, and might be a problem.


I think that the GR formula which basically tells you to have a gap of around .160 to be very workable. It’s pretty consistent with modern horns because they are made so much alike. It is amazing how if the gap is too small, the horn can really play bad. Clifford Blackburn said that if it’s too small the high range will be stuffy but the low range ok. I think that is not really correct. If the gap is too small, the whole horn is weird in lots of ways like bad soft response, weird slotting, notes that are hard to hit accurately every time, and squirly articulations in all registers that sneak up on you at just the wrong time.


It’s pretty rare to have a gap that is too big because as the receiver wears, the mouthpiece sinks in farther and farther. I actually have never seen an overly big gap except on Benge and Olds receivers, and those actually work pretty good. Curry mouthpieces seem to have larger gaps than Bachs or GRs, but not so much as to make a gap of more that .190 which would be out of the GR acceptable range.


The best way to check the gap is with a dial or digital calipers that has a depth gauge. That is the little stick that slides out the end as you open the calipers. Poke the stick into the receiver until it hits the end of the leadpipe, and then slide the body of the calipers until it hits the end of the receiver. This will tell you how far the leadpipe is from the end of the receiver. On a Bach it’s usually 1.065, or at least I have four right here that are all exactly 1.065.


Then put your mouthpiece in question into the receiver and take the sharp little nib on the calipers and make a scratch in mouthpiece right where the end on the receiver is. Take the mouthpiece out and measure from the scratch to the end of the shank, and you know how far the mouthpiece goes in. Usually about 1.215, which would give you a gap of .150. Perfect-ish.


You can do it down and dirty and get almost as good information with just a wooden pencil. Stick the eraser end into the receiver until the metal barrel hits the leadpipe end. Hold it there while you make a fingernail mark against the receiver. The hold the pencil next to your mouthpiece with the end of the metal at the black ring that forms after a few days on the mouthpiece. It should be about a 5/32 to 3/16 inches. look at a ruler to see about how big 5/32 is, and you can tell right away if the gap is to big or small.


There are lots of articles that say if you are suspicious that the gap is too small to try putting a strip of paper along the shank to keep it from going all the way in, and then play it. If it plays better, then you want to look into it at least. I think that scotch tape works way better than paper, but neither one tells you whole truth. That is because with paper, or tape between the mouthpiece and receiver, the horn does not really play the same. It will maybe play a little better with the paper there, but not NEARLY as good as actually changing the gap, and having a real metal to metal connection between mouthpiece and receiver. This experiment does point in in the right direction though.



So how do you change the gap? Other than getting a new mouthpiece? First you have to determine if the receiver is the problem or the mouthpiece is the problem. Don’t change the mouthpiece if the problem is the receiver. Don’t change the receiver if the mouthpiece is the problem. See if your mouthpiece has a normal gap in a brand new yamaha or bach, or conn vintage one, or nearly any new horn that is made to compete with Bach. If the gap is too small or big consistently with a few horns, it’s the mouthpiece that is at fault.

or get a few unworn mouthpieces and see if they all have the same gap problem with your receiver.


If the gap is too small (most common problem) and the receiver is at fault, here is what you can do:


  1. 1)   Pull the receiver off of the leadpipe a little bit by heating it and then re-soldering it. I say that this is suspicious because it makes a very weirdly shaped gap which because the leadpipe is not actually butting up to the end of the receiver. I have seen repair techs do this for people and it just did not seem to work as well.

  2. 2) replace the receiver and hope that is correct after you solder it on. You won’t know until it’s on there. Sometimes it is REALY REALLY hard to get the receiver off from a leadpipe. It can bend pretty easy because it will be hot!

  3. 3) get a whole new leadpipe assembly with the receiver already on, and maybe check the gap, just to be sure before buying it and/or soldering it on. If the receiver was the problem, a new one should fix it.



If the gap is too small, and the mouthpiece is at fault, you have a few choices. You can either get a new mouthpiece made which may involve having yours copied, and waiting for a long time for that to be done, or you can get adventurous and alter the mouthpiece. Dont do that unless you know you can get a new one that you like as well. Some makers are so consistent that you can just get a new one. Your situation is likely going to be a worn out shank that is now too small, and that is letting the mouthpiece go in too far. It may be hard to find a perfect replacement.


  1. 1)Bevel the inside edge of the end of the mouthpiece shank. Thinning the wall by about .005 (a small amount) will allow the mouthpiece to work with a gap that is .025 smaller, according to GR’s gap formula, and that may do the trick. Joe Scheply in new york did this for a LOT of people. Other mouthpiece guys have known this for years and years. Leonard Merretta told me they did it back in the 30’s. He did it with a woodworking countersink bit! (too steep of an angle actually I think) It really does work. Some people freak out about changing the mouthpiece in any way. Don’t change the mouthpiece if the receiver is the problem.

  2. 2)cut the end of the mouthpiece off a little bit, which really takes a lathe to do a good job. Take some material out of the inner edge of the end of the shank to keep the wall thickness the same as it was before. Use calipers. If you shave the end off, the mouthpiece might only work in that particular horn, That is, of course if the receiver was too big. If the mouthpiece shank was too small, the mouthpiece should work fine in other horns after being shaved down on the end, and the wall thinned back out to original thickness. I would say that the problem less likely to be the mouthpiece than it is to be the receiver.


If the gap is too big, and the receiver is too tight, wrap some 400 grit emory paper around and old mouthpiece, and ream it out bit by bit. I takes a surprisingly long time, so you wont over-do it.

If the mouthpiece is too big, spin it in the lathe and use some 600 grit, and just barely go through the silver plating.


Or you could get the reeves sleeves put on your mouthpiece.