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Some brass instrument manufacturers make a feature of the shape of the various slides - some have a semi-circular wrap, other more semi-elliptical. Some have a tight wrap (the two legs of the slide are close together) or an open wrap (legs further apart).

My question is - what effect do the shape and tightness of the tubing wrap have on the sound and instrument playing response?

I'm asking because some manufacturer claims sound like voodoo to me - I'm wondering whether there are good physics reasons for choosing the shape of an instrument, or whether the choice of shape is mostly based on cosmetics and having an instrument that isn't tiring to hold, e.g. the centre of gravity is in a place where the instrument doesn't tip forward or backward when you're playing it.

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  • You're not asking about trombone slides - they're round in section - so is it the tuning slides on trumpets, (also round?) or what?
    – Tim
    Commented Apr 29, 2019 at 12:25
  • Tuning slides are not semi-circular on every trumpet - there's considerable variety of curvature between models and manufacturers. All brass tubes are circular in cross-section - I'm asking about the shape after the straight tube has been bent into a slide.
    – Brian THOMAS
    Commented Apr 29, 2019 at 13:14
  • Likewise, the U at the end of the trombone movable slide is not always semi-circular. It varies between manufacturers.
    – Brian THOMAS
    Commented Apr 29, 2019 at 13:16
  • You can even have different shapes in the same instrument, see french horn in wikipedia. Both parts beneath the mouth piece can be removed for cleaning, as well as the parts at 10 o'clock and 8 o'clock positions.
    – guidot
    Commented May 24, 2019 at 12:19

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Looks like you're asking two things: 1) the equation of the curve for the bent section at the end, 2) the variation in sound, if any, due to spacing between the 'out' and 'in' sections of the slide.
In any case, the answer is that there's next to no effect from the curve selection or the spacing. The most likely effect might come from the choice of location of the stabilizer bar (welded in place perpendicular to the slide tubes), as that could affect harmonic vibration transfer.

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    Yep. Given a constant circular cross section (which is the case here), it doesn't matter what the shape of the curve is acoustically.
    – Scott Wallace
    Commented Apr 30, 2019 at 10:47

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