Leadpipe Dimensions

[blap73]

To help understand what makes a horn 'bad' (or good)... inspired from the Bundy post... In that post there was mention of 'free blowing' or not. I posited that the minimum diameter of the leadpipe is probably a significant factor. Reading a bit it actually sounds like both the minimum diameter AND the taper rate affect the 'free blowing'.

To put some facts out here (and I hope others will contribute), since I have the necessary inside gauge and micrometer I've measured 3 horns I have here. I haven't determined a way to measure the taper yet. Maybe someone has these pipes laying on a bench and can measure their lengths.

Horn	Horn Bore	leadpipe minimum	leadpipe / horn bore ratio
Conn 4H 1950	0.485	0.413	0.85
Conn 18H Director (late yellow brass)	0.500	0.412	0.82
King 606	0.500	0.386	0.77
Reynolds Medalist circa 1964 TO-58	0.500	0.407	0.81

I calculated the ratio between the leadpipe bore and the main bore as I'm not sure if the absolute leadpipe bore or the relative bore is more significant. I was quite surprised to see the 606 having the tightest leadpipe bore.

[Doug Elliott]

Just like backbores, you can't really tell anything about the way it plays by one dimension. The overall effect is a combination of many factors - length, venturi, thickness, basic taper, and type of shape beyond a simple taper.

... Says the guy who has experimented extensively with backbores, but not leadpipes. But I have measured some leadpipes.

[Bonearzt]

SO many factors involved in leadpipes above what Doug mentioned!!

You can take two of the same model pipes manufactured in sequence and they will both play slightly differently.

Also, I have been argued with about this thought, but I have never seen a leadpipe with a "venturi" or minimum bore smaller in diameter than the end of the mouthpiece shank!

My unscientific guess is that the leadpipe should be a continuous taper from the end of the shank into the bore of the upper slide tube.
And the rate of taper from the end of the mpce shank to the end of the leadpipe is basically what determines the resistance of said pipe.
Materials, temper, length of pipe, etc also definitely affect the "feel" of the pipe.

[brassmedic]

SO many factors involved in leadpipes above what Doug mentioned!!

You can take two of the same model pipes manufactured in sequence and they will both play slightly differently.

Also, I have been argued with about this thought, but I have never seen a leadpipe with a "venturi" or minimum bore smaller in diameter than the end of the mouthpiece shank!

My unscientific guess is that the leadpipe should be a continuous taper from the end of the shank into the bore of the upper slide tube.
And the rate of taper from the end of the mpce shank to the end of the leadpipe is basically what determines the resistance of said pipe.
Materials, temper, length of pipe, etc also definitely affect the "feel" of the pipe.

I think some leadpipes are designed that way, but definitely not all of them. What you usually have is a sudden expansion of bore where the mouthpiece shank ends, but then another constriction where the leadpipe reaches its narrowest point, i.e. the venturi. The venturi many not be smaller in diameter than the mouthpiece backbore, but it is still a constriction. For trumpets, it's very obvious because you can see a ledge where the leadpipe fits into the receiver, and the distance between where the mouthpiece ends and the ledge begins is called the "gap". It's less obvious for a trombone because the venturi is a smoother curve, without that sudden ledge. but the "gap" still exists. I think this accounts for a lot of what makes different leadpipes feel and sound different from one another. In the process of copying vintage leadpipes, I found that not only does the diameter of the venturi differ from one pipe to another, but also the location of the venturi.