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Leadpipe/bell length relationships



 
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mcjweller
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Joined: 02 Jan 2019
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Location: Kitchener Ontario

PostPosted: Thu Mar 28, 2019 11:36 am    Post subject: Leadpipe/bell length relationships Reply with quote

Good day!

I'm working on a purely experimental project to take my old, long-retired trumpet and improve it's play-ability and sound via a series of modifications. The horn, a Bach TR-300 is essentially of no real value, but its monel valves are remarkable and some of the best I've had on any horn (I realize this is not typical, my serial number indicates it was one of the first TR-300's from the mid 1980's, maybe they were better than they are now).

Anyway...

The first issue I wanted to attack was how stuffy this thing was, I found out it's #6 leadpipe had an annulus of over 1/4", I corrected that with rings I manufactured and that made it significantly better.

I then got a Bach #7 leadpipe for a Strad 180 and rigged it on the horn temporarily. That completely changed this beast. Dark sound, I just love it. free blowing, upper register requires far less effort.

It also made the horn flat by about 4Hz according to my tuner.

The strad leadpipe is about 7/8' longer than the TR-300 #6. I could shorten the "7 at the mouthpiece receiver, but I DON'T want to do that! That will end up enlarging the venturi. I could cut it at the tuning slide receiver, but that will change the overall rate-of-taper. I don't want to cut this thing at all.

Since this is an experiment, I can make a custom tuning slide with a different (smoother) radius with offset "tails" that will allow me to mount the leadpipe in the same position as original with the upper slide receiver forward of the lower, the new radius will allow the overall length of the tube from mouthpiece to 3rd valve to be the same as original and therefore in-tune.

Hope folks are still with me...

I noticed that the tail of the bell (a bach #37) is LONG, compared to it's strad big-brother, it has a different radius. It got me thinking...

If I reduce the length of the tail, can I increase the length of the tuning slide? is it an equal ratio of length removed from one to add to another? Are the valve slides tuned to the overall amount of tubing, or to the leadpipe length? Before I start cutting some science would be good here, and I'm not finding much info. I know Harrelson has published a lot of info but I haven't seen anything related to relationships between leadpipe and bell lengths.
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BraeGrimes
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Location: Australia

PostPosted: Thu Mar 28, 2019 6:25 pm    Post subject: Reply with quote

An interesting question...

Something I've though about myself but I don't know the EXACT answer.

Some considerations:

The overall length of a Bb trumpet (no valves) is approximately 46.5" (1180mm or so), a semitones is around 2.75" (2nd valve), tone is 5.5" (1st valve), and 1.5 tones is 8.25" (3rd) valve. These are approximate values and by all means the trumpet won't be perfectly in tune! Someone online has written extensively about this, can't remember who, but the values are confirmed...

It might be worth calculating the velocities through the bends at different pitches, considering you're going THROUGH the valve section.

But, I'd love to hear from people more experienced than myself on the issue!
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mcjweller
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Location: Kitchener Ontario

PostPosted: Thu Mar 28, 2019 6:59 pm    Post subject: Reply with quote

Those figures are consistent with the slide sections on this one. I've been using straight copper wire, applied by tape to the center line of the tubing including curves to form a baseline, so that as I add or remove length I have a measure to relate how those changes impact pitch in Hz.

Before doing anything, I base lined the Hz factors for all valve combinations (including open) from F# below the staff to high C with no valve adjustments. It's interesting to observe how the horn open varies in "tune" up the harmonic series, as do the other valve combinations. The point of this exercise would be to maximize the leadpipe length (equal to a strad) and use gentle tuning slide curves (all adds length) while taking length out of the bell tail, all without changing the Hz factors of all the valve combinations (unless it somehow improves it's ability to be in tune with itself). The assumption is that the valve slides are all a standard length regardless, and the bell, leadpipe and tuning slide are where length variation may exist, the other assumption is regardless the overall length must remain the same.

...and all those assumptions could be wrong so here I am looking for info
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grune
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PostPosted: Thu Mar 28, 2019 7:19 pm    Post subject: Reply with quote

http://la.trompette.free.fr/Smith/Nature/intonation.htm

Good luck with your endeavours! Please keep us posted.
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jimspeedjae
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PostPosted: Fri Mar 29, 2019 12:20 am    Post subject: Reply with quote

Just an idea...
How about getting a replacement lower tuning slide outer to third valve tube (or just the right size brass tube) and shortening that?
It would mean that the leadpipe would be sited a little bit forward, but it's not going to affect taper, or tuning slide.
It's also a fairly quick thing to try and put back if it doesn't work (assuming you don't hack the stock piece)
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JayKosta
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PostPosted: Fri Mar 29, 2019 3:29 am    Post subject: Re: Leadpipe/bell length relationships Reply with quote

mcjweller wrote:
...
It also made the horn flat by about 4Hz according to my tuner.
...

-------------------------------------
At what note (frequency) is that happening. If at 'concert A 440' (trumpet B in staff) that's only a 1.1% difference (about 1/2 inch of total no-valve tubing, per earlier post).

The portion of the leadpipe that accepts the tuning slide is not tapered for the last several inches - right?

I have no idea of whether shortening the untapered section of the leadpipe (and the portion going into the 3rd valve) would affect the sound quality or feel). And the legs of the slide would probably need to be shorter.

Jay
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Don Herman rev2
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PostPosted: Fri Mar 29, 2019 4:43 am    Post subject: Reply with quote

Diameter is a secondary factor in the acoustics so chapping off a little of the bell tail would probably work OK. The bell flare also affects intonation and that includes the tail section. Since it is an experiment, I would take off a little less than you think you need, check it, and nibble in slowly to get the tuning where you want.

The physics follow that of closed tubes/pipes, but with the change in diameter the nodes move a bit and that is not easy to predict unless you know the exact taper and have a math program that can do the flow analysis.

You could also make it a tuning bell trumpet...
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Last edited by Don Herman rev2 on Fri Mar 29, 2019 4:54 am; edited 1 time in total
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mcjweller
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PostPosted: Fri Mar 29, 2019 4:52 am    Post subject: Reply with quote

Hi Jay,

All notes are flattened moving through the 7 valve combinations from low F# up to high C, between 2 and 4Hz. (multiple checks and average because the test apparatus...aka me, is imperfect)

These checks were done with the tuning slide in all the way, meaning the longer strad leadpipe assembly within the rest of the TR300 structure (shorter) makes it impossible to play in tune, the best you can get is below 440 dead on or lower, leaving no room for adjustment required with different mouthpieces, or variations of 440 in different ensembles.

The strad structure has more length between the mouthpiece and the 3rd valve, and less from 1st valve to the end of the bell, the TR300 is an inversion of that. By how much I can't say, as I don't have a strad with a #37 bell here to compare.

I'm considering shortening the tail of the bell to allow an equal length in the leadpipe assembly. But, it would be unfortunate to make that cut in the tail just to discover the relationship is not equal or that the location of the valves/slides within the common-bore tubing is relevant.

grune - excellent link you posted, thank you! That research suggests that the standing wave in the horn is essentially consistent throughout the entire section where the tubing bore is not tapered. This would indicate (at least in theory) that so long as the bell tail is the same bore as the "other side" of the horn, minor reductions in length at the 1st slide end may be balance by addition of length post-taper on the leadpipe side.

jimspeedjae - as it is, the strad leadpipe falls forward of the lower tuning slide outer tube installed in the factory position, so shortening that tube exasperates that difference and it becomes impossible to create a radius of tubing to connect the tube without lengthening the overall tubing between those two points...making it flatter.

At the end of the day, as I'm going for a dark ensemble type sound, I've noted that all other horns I've seen that produce these tones are long on the leadpipe side, shorter on the bell tail side. The paper posted above would support that this is not an accident, allowing the tonal qualities to develop with minimum variations in bore size or intrusions to the bore (such as passing through a valve block). This is what I hope to achieve here, without making the existing tuning of the horn with itself, worse.


Last edited by mcjweller on Fri Mar 29, 2019 5:02 am; edited 1 time in total
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OldSchoolEuph
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PostPosted: Fri Mar 29, 2019 5:01 am    Post subject: Reply with quote

If I were to engage in such an experiment, I think my inclination would be to remove the brace from the tuning slide, remove the legs, and shorten the crook where it is straight for the escutcheon placement, retaining only the radius portion plus maybe 3/32" before re-assembling. Then experiment with brace placement on the sleeves. This would preserve the original radius of the slide and its characteristics.

Shortening the bell is going to alter the position of the flare relative to the valves and also to the player's ear. Together with the bracing landing differently, it could significantly alter the playing experience, so I would be hesitant to try that first.
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grune
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PostPosted: Fri Mar 29, 2019 5:04 am    Post subject: Reply with quote

http://everythingtrumpet.com/schilke/Tunable_Bell_Trumpets.html

I dabbled similarly very long ago. Determined I needed some equipment that was simply unobtainable at the time. Got sidetracked by "life" and solved the need by "quick fix": ie acquiring a new horn.

Keep us posted!
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shofarguy
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PostPosted: Fri Mar 29, 2019 3:10 pm    Post subject: Reply with quote

If you look at various cornet designs, you will see that the valve clusters occur at different points along the length of the instrument. Flip Oakes has posted here, in prior threads, the difference between his American Long Model and his Shepherds Crook Model cornets

Trumpet designs don't vary quite as much, but you can see differences in oddities like the Selmer Balanced model and the Wild Thing/Celebration/Inspiration Bb trumpets.

Rotary trumpets are wound differently, too, as are flugelhorn.
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lipshurt
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PostPosted: Fri Mar 29, 2019 6:49 pm    Post subject: Reply with quote

The tail is not tapered. Cut it off and do t look back. Or cut off the top leg of the tuning slide and let the leadpipe protrude 7/8 farther into the top tube.

The differences between these two choices are due to things like brace placement, and not so much anything to do with tapers. Your mods are not remotely radical
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