TromboneChat

I understand that silde positions on every partial are not equal, and those are also different between brand to brand or even model to model (also maybe horn to horn of the same model). A Yamaha 647 of my school has a noticeable flatness in the middle F partial, while it is very slight on 882UII and my 830 bass.

But I recently encountered a horn, a Yamaha 354S, that is in tune in 1st position, and out of tune by more than 1/2 to 1 inch starting from position 3 onwards, while other horns in the herd (there are 2 more of the same model) have no problem with that.

This disrupts teaching somewhat, because the student playing it has not yet had much ear training, so he normally relies on visual guidance of the bell. Also the method book teaches the slide position using pictures.

At first I thought it is because of the student, but I also had the same problem. Next I compared the bell position to my bass because I think the bell may be longer by design, but there is no noticeable difference. The fact that other horns have no such problem also tells me it should not be because of the design. Granted, the horn is pretty beaten up, but with no large dent or ding in the crucial area (like slide or tuning slide). The bell is also mostly intact except for massive silver tarnish.

So, what fault in the horn could cause this type of quirk? Also, for the sake of information, when designing a new horn, what element could shift slide position, affect intonation, and should be handle with care?

The horn: design, construction, and damage. Can’t be helped other than a good tech to repair the horn.

The other three places where intonation is established and affected are the lips, the hand, and—most importantly—the mind/ears. When they aren’t coordinated, or the horn’s design, construction, and damage don’t allow them to coordinate, poor intonation results.

If there isn’t much actual damage to the horn, then perhaps the construction is poor. Sometimes horns that are built with parts that don’t quite fit together, manufacturers then have to “make” the parts fit by bending or “reshaping” them so they fit. Sometimes, there’s a blob of solder in just the wrong place. If you or the school can afford it, have a tech take it apart and put it back to together again.

If it's one horn out of three in the same model, the only thing I can think of is that the bell section or slide is not the correct length.

Might be a big piece of gunk hanging out in an inopportune place.

Invest $10 US in a Borescope that plugs into your cellphone or laptop computer. Inspect the interior of the bore from the comfort of your home. That will answer your concerns as to whether there is something impeding the flow of air through the instrument. Cheap ---- and FUN !!

All slide positions get gradually farther apart as the slide gets longer. But, there are surprisingly lots of factors that affect intonation, and the good trombone manufacturers spend a whole lot of time and effort getting that stuff under control. But, as a basic guideline, any distortion in the shape of the air chamber has the potential to affect intonation.

Along the lines of gunk hanging out, maybe it just needs a good cleaning with warm, soapy water and a cleaning snake. Could be some old hotdog chunks hanging out in the slide crook!
I had a private student who was playing on a Bach Aristocrat when she first started taking lessons, and she was having issues with the partials in 3rd and 4th positions not lining up. (I know most horns require a slight adjustment, but this one required at least an inch) At first I thought it was her, but then I tried it and had the same problem. I brought an old Conn Director for her to try, and she was amazed how much easier it was to play, and the major tuning issues went away. The Bach was a relatively new instrument, so I just assumed it was something with the design. (made in China and imported by Bach. In comparison, the Bundy is a much better and more durable horn, IMO.)

Too broad of a question. Many, many variables.
Would suggest swapping out parts with one of the known "good" horns to see if you can isolate the problem to say, tuning slide, bell section, inner slide, outer slide, etc. and post your findings. There are some super knowledgeable members on this forum who could probably point you in the right direction if they had a little more information.

Clean the leadpipe from dirt. Where the mouthpiece ends is a place where a lot of dirt is collected.

I have played a King 2b where the dirt at that place in the leadpipe was hard as concrete. I had to use a knife to remove everything. The horn was really bad, the sound was unfocused and the intonation was all over the place.

After cleaning it turned out to be a perfect instrument.

/Tom