Gap issues on Martin Committee...?

Discussion in 'Trumpet Repair and Modification' started by bobmiller1969, Jan 7, 2019.

  1. bobmiller1969

    bobmiller1969 Pianissimo User

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    Hi, Everyone!

    I've pretty much eliminated every possible issue with the "vibration" issues, which I believe are all too common on Committees. No trouble with the bracing, and I had a leak addressed in the 1st slide crook when I had the trigger removed. (There was a screw hole right through it.)

    I was reluctant to send the horn back to my tech, as I wasn't certain what the issue is, nor could he reproduce the issue when he played the horn. I played the horn for about an hour after getting it back from him, and even told him that it was good to go, but after being completely warmed up, the trouble started again. I reached out to Harrelson, and ordered one of their gap solution kits, which didn't solve the problem, but pointed me in the right direction. Reducing the gap actually shortened the length of the standing wave that starts in the entrance to the leadpipe. Actually, it made it more noticeable, but at the same time, it told me that this was indeed the issue.

    So, the question is, do I have him move or replace the receiver for no gap? I switched to a Monette mouthpiece a few months ago, and they do typically have a wider gap in most horns. I don't have any plans of selling the horn, but this option would make the horn pretty much married to Monette mouthpieces, unless I have the receiver moved again. My other option would be Harrelson's VGR, which I feel are a bit clunky looking, and would involve moving the bracing. My tech has already tried to steer me away from this option.

    If this was your horn, what would you do? Any feedback would be greatly appreciated. Thanks!
     
  2. Dennis78

    Dennis78 Fortissimo User

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    Definitely have the receiver moved if that’s the ticket
     
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  3. trumpetsplus

    trumpetsplus Fortissimo User

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    If it plays better for you by reducing the gap, then reduce the gap.

    Two ways to achieve this:
    Open up the morse taper (this can normally be done in minimum time without removing the receiver)
    Move the receiver forward. This involves removing the receiver (always a bit dodgy on an old horn), counterboring the back end of the receiver, then soldering the receiver and brace back on.

    How much gap are we talking about?
     
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  4. bobmiller1969

    bobmiller1969 Pianissimo User

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    Gap with the Monette is .2165. Was .1525 on my old setup, but had the issue before I switched. I actually noticed the same thing on my Selmer after the switch. It had basically no gap at all (.0475) with my old setup, and now is .134. Can't really hear it as much as feel it. It's definitely there. I want to get the gap on both of these horns as close to nothing as possible. I'm sure my measurements aren't perfect, but in the ballpark.

    Interesting that you mention opening the Morse taper. Next on my list would be both of my Conns. There's no ledge between the receiver and leadpipe on either horn, but the mouthpiece doesn't go in nearly as far on either of them. No vibrations or standing waves, but some intonation issues that I never had before might be cleared up by this. Do you think that it would be possible to eliminate the ledge on the Martin and Selmer without screwing things up?

    Thanks for the response! :-)
     
  5. stumac

    stumac Fortissimo User

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    I have made an extended length No1 Morse taper reamer (D bit) to remove the step at the entrance of the leadpipe, this has made improvements in response and I think intonation of the horns I have done, Also I have a reamer with a little faster taper than a normal mouthpiece backbore which I have used to reduce the thickness of the end of the shank to a knife edge.

    Dr Richard Smith has shown that a discontinuity of 0.010" in bore will produce reflections in the wave traveling through a trumpet.

    Regards, Stuart.
     
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  6. bobmiller1969

    bobmiller1969 Pianissimo User

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    I believe that Renold Schilke said something similar. Since he also claimed that he was in fact the "Committee", I believe that's good advice. Thanks!
     
  7. bobmiller1969

    bobmiller1969 Pianissimo User

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    So, just to confirm my theory, since I couldn't close the gap completely with the Harrelson gap/shim kit, I ordered a Schilke 14 mouthpiece, since they typically have a smaller gap on most horns. I was able to close the gap almost completely, but all this did was shorten the length of the standing wave. It confirms what I thought was happening, but I just needed to see it for myself before my tech reams out the step in my receiver/leadpipe. I'm having the same done to my Selmer. I'll let you all know how it turns out. Thanks for the helpful responses!
     
  8. rowuk

    rowuk Moderator Staff Member

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    I hope that your guess is right... My understanding of the gap has nothing to do with the length of any standing wave which in my world is from the acoustic center of the embouchure to the virtual end of the trumpet bell which changes based on frequency.

    In my world, the gap can sometimes change focus a bit but nothing else. My world is based on hundreds of trumpets and many artisans.
     
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  9. bobmiller1969

    bobmiller1969 Pianissimo User

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    I get what you're saying, and definitely understand how gap can effect resistance in a horn. I don't know if I can back up anything I'm about to say with actual science, but if you think of the cup of the mouthpiece as the primary resonance chamber of which you have complete control, and then the air/vibrations hit a wall just as it goes into the horn, creating a 2nd resonant chamber inside the entrance to the lead pipe. It actually sounds like a 2nd note playing along with the first one. I tried quite a few different mouthpieces when I was on my safari, but none of them played any differently, since they were all from the same manufacturer, and likely had the same gap. The Monette, with about twice the gap, actually stretched out the standing wave to the point where it was even noticeable in the upper register. I tried the Schilke, which had very little gap, and the shortness of the standing wave made the horn basically unplayable as the notes were so close together, than it was a very harsh sound.

    I never noticed it at all on my Selmer, until I upgraded to the Prana Resonance, which introduced the exact same thing. Tried the Selmer/Schilke combination. The mouthpiece just bottoms out. No gap at all and it completely went away.

    (Would this be the right time to ask about the possibility of standing waved caused by the small chamber in the water key/tuning slide on my Conns?)

    In any case, both of them were sent out yesterday to have the wall removed. Perhaps my horns are Democrats, which is why they wont work with the wall.

    I'll let you know how it turns out. Thanks!
     
  10. rowuk

    rowuk Moderator Staff Member

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    If we measure the cup, minus the protrusion of out lips, then we may have a "resonance", but certainly not at any audible frequency. My guess (and I have math and physics to back it up) is that we have the "one" resonance based on the acoustic length, The gap is part of the efficiency, as the standing wave is built between the 2 acoustic ends - at the bell side due to a frequency dependent node and at the acoustic center of our embouchure which is modified by the cup, throat, embouchure tension and a little bit of gap. I am pretty convinced that most of what many assume to be effect of gap is more based on a different length of the standing wave due to the mouthpiece going deeper or less deeply into the receiver. Our ears are sensitive to changes in pitch of a couple of cents and if the mouthpiece goes more deeply into the horn, we will relax a bit to adjust for pitch - the sound and tension change.

    I know of NO ONE that adjusted the tuning slide for the difference in gap when changing - because it is easy to lip up and down. This means that their assumptions already have at least one flaw.

    I am not saying that gap makes no difference. There are horns that seem to react more or less. Schilkes were supposedly built for no gap. Every Schilke that I have played has worked better with my Monette mouthpiece which does introduce a gap. I do not believe that the gap was significant in this particular comparison. I think that the geometry of the mouthpiece is far more critical to match.
     
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