Expert advice needed: Lengths of tube for change of pitch please...

Discussion in 'Off-Topic Chat' started by TheMusicMan, Nov 19, 2006.

  1. TheMusicMan

    TheMusicMan tMP Founder Staff Member

    Expert advice needed here please. Ok, so here's the lo-down.

    Heather (my 9 yr old daughter) currently has a school project in which she has to make a musical instrument. We have about 6' of 15mm tubing (silver curtain pole) and she has suggested we make a set of small chimes. So... what I am wondering is if I cut the 1st piece say 6" long, how much longer would I need to make the next one (and the next etc) to adjust the pitch so as to end up with 8 chimes that when tapped - sound out an octave...?

    If this is possible... but I would end up with not enough tube, what would the length of the 1st (and subsequent) pieceS of tube need to be so as we could make this using 2 * 3' lengths of metal tubing?

    Thanks all.
     
  2. Jan H

    Jan H Moderator Staff Member

    from a pure mathematical viewpoint, I'd say that to get a 1 tone lower note, the pipe length would have to be multiplied by the 6th-root of 2.

    an octave lower would mean a double pipe length
    there are 12 semi-tones in an octave
    so you would get a semi-tone difference when the length is increased by the 12th-root of 2
    (x = 12th-root opf 2 if x^12 or x to the power of 12 equals 2)

    If I'm not making any sense, just ignore... ;)
     
  3. DaveR

    DaveR Active Member

    In a (very!) vague recollection of a lecture at uni where we looked at Pythagorean commas and such like, I think if you reduce a pipe by a third each time you can generate the harmonic series. It won't be quite in tune by the time you get to the octave (due to the Pythagorean comma) but the other notes should be close.

    Probably not much help to you :(
     
  4. oddbod

    oddbod Member

    That's the most difficult question I've ever read! - I know the ratios for the lengths for a single ended blown tube - but hitting something is a different thing entirely.

    Unlike strings and blown tubes, tubular bells have further complications - wall thickness reaches a point where it's not the fundamental that you hear the loudest, so a really thick or really thin tube doesn't work with the formula of half/double the length for an octave – well it does, but that’s not the part of the harmonic series that you may end up hearing the most.

    If I had to do it, I’d be fairly unscientific –buy extra poles, a really good saw, and have lots of laughs doing it! – surely doing it that way and recording the results (even the wrong ones) would actually be a worthwhile school project rather than just getting the length ratios from a table! – Hope you find a way and that you let us all know what happened…
     
  5. brassneck

    brassneck Active Member

  6. oddbod

    oddbod Member

    Yes - but be careful - they are not chimes you are making - because chimes are solid metal - you're dealing with a hollow pipe with a column of air vibrating through it - and the physics is different! - tubes are even different if they are open both ends or closed at one end!....
     
  7. Spud

    Spud New Member

    Don'nt know if this helps much, but my dad and I once made a set of tubular bells (we got tired of the flimsy designs and transporting problems with the bought ones). The standard was good enough to play at Championship level, so they must have been OK. The tubes were made of brass (can't rememember sizes but my dad may remember) and we capped each tube with a steel core plug (from an engine) which was an exact fit. Now we were dead lucky when it came to tuning them - my grandma has perfect pitch and is an excellent musician, so we took a plumbers pipe cutter (the rotary type, which cut the brass tube perfectly and left a square end) down to grandma's and all the tubing. Within a week or two we had a set of tubular bells. The other comments abouth there not being an exact mathematical forula are very true, there are so many influencing factors, that the only real way we found of determining the tuning is by skilled ear!
     
  8. matthetimp

    matthetimp Member

    Or an electronic tuner!
     
  9. brassneck

    brassneck Active Member

    - now, would you use absolute pitch (electronic tuner's pitch) or would you use the slightlly brighter set pitch of a glockenspiel? :confused:
     
  10. andywooler

    andywooler Supporting Member

    Not sure if this would work but if you had another piece of pipe slightly larger that could go over the original, you could slide it up and down to discover the the right length you need?
    Using the principle of the trombone to discover correct pitch may not work though! ;)
     
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  12. matthetimp

    matthetimp Member

    You can set and electronic tuner to A=436hz right up to A=464hzish. Only the Glockenspiel is set too A=442hz. Orchestral Bells should be set at A=440. Have you seen a set of Percussion Plus Bells? They made me laugh so much................
     
  13. Teflon1961

    Teflon1961 Member

    I had to have the steel posts of my bannister shotblasted recently, prior to painting them.When I got them back from the shotblasters, I hung them up outside ready to paint and was amazed at the volume and tonal quality of the "rings" as they tapped into each other... to this end, I recommend 20mm RHS with a 1.5mm wall ranging in lengths of around 1.5m to 750 mm, the inbetween sizes, well, refer to the table or take Odbodd's advice and document the progression whilst having fun!

    Please let us know how this goes... fascinating!
     

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