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The effects of dynamics on the pitch of reed instruments

Discussion in 'General Acoustics Discussion' started by jbtsax, Aug 21, 2012.

  1. jbtsax

    jbtsax Distinguished Member Distinguished Member

    Most players know that reed instruments when played at their softest levels have the tendency to go sharp. Conversely when played at their loudest levels they have a tendency to go flat. To investigate and discuss why this phenomenon happens is the purpose of this thread.

    Band directors have long had to deal with intonation issues in younger groups when they play outside of their comfort zone which is mf. Compounding the problem is the fact that the tendency of the flutes and brass instruments is the exact opposite of the reeds.

    There you have it. Why does my sax and clarinet want to go sharp during a diminuendo and flat during a crescendo?
  2. Got some groovy areodynamic issues goin on here :cool: cooool
    Bagpipe double reeds also *tend* to flatten with increased pressure; but there is no dynamic change (crescendo) because they are made to operate in the 'crow' stage. They simply shut down under decreased pressure.
    (The Uilleann pipe and some continental pipe chanter reeds overblow into an upper octave with increased pressure, but they are exceptionally designed to do so)
    Bagpipe single reeds (chanter or drone) are designed to remain stable within a certain window of pressure /velocity; no matter how big or little this 'window' is, they retain pitch stability despite fluxuations in airflow. But once that window is exceeded, they shut down, or in some cases 'doubletone' (hitting a highly undesirable upper partial):emoji_astonished:

    Im no physicist, & math is NOT my strong suit, but I think there are some key issues here that apply to all reed (& probably fipple) instruments:

    In a air column,Velocity & pressure are positively corelated. (increase airflow increases pressure in an air column) Greater pressure PSI on the vibratory surface of the reed means less vibe per second, becasue the reed has to work against a harder 'load' to keep vibration constant, and brings the pitch down.
    For piano& diminuendo, one must lessen the aperture for airflow, usually by tightening the embrochure. (pipes do it by decreasing the staple opening btw, which sets off all manner of intonation issues :???:), smaller aperture means less surface area available for vibration, hence a rise in pitch.
    thats my theory anyway :)
  3. tictactux

    tictactux Distinguished Member Distinguished Member

    I too would say that it is the inherent embouchure change that equals "lipping up" or "lipping down". Plus, the louder one wants to play, the more air must be pushed through the mouthpiece/reed gap, which results in a higher vibration amplitude which in turn (due to reed stiffness) employs a longer part of the reed. A longer part means more mass that is to be kept in motion, which would result in a lower pitch.

    So much my intuitive explanation.

    I am no aerodynamics/acoustic expert; I make my money as a consultant, making intuitive guesses and easily understandable explanations. :)
  4. pete thomas

    pete thomas Distinguished Member Distinguished Member

    I have solved this problem.

    Just play sharp, it's better than playing out of tune.
  5. Steve

    Steve Clarinet CE/Moderator Staff Member CE/Moderator

  6. jbtsax

    jbtsax Distinguished Member Distinguished Member

    I always though the "Brits" kept a "stiff upper lip"---not a lower one as well. :emoji_relaxed:
  7. Steve

    Steve Clarinet CE/Moderator Staff Member CE/Moderator

    I've learned that if you tune a piano exponentially sharp on the low notes and exponentially flat on the high notes with a proportionate curvature of intonation through the entire keyboard, then it all sounds the same anyways. :)
  8. pete

    pete Brassica Oleracea Staff Member Administrator

    Well, then you get into the discussion of tempered/stretched tuning, where you tune notes a bit flat or a bit sharp or the instrument doesn't sound "right."
  9. pete

    pete Brassica Oleracea Staff Member Administrator

    Personally, I have a tendency to always go a little flat the softer I play. Admittedly, I have not studied acoustics, nor have I taken a survey of players to determine if what you mention, JBT, is the prevalent theory. I'm sure someone has done some research on this, though.

    IMO, in a vacuum, I'd say that why I personally go a tad flat has to do with my embochure more than anything else. Again, remember that on sax I generally played those fat Sigurd Rascher mouthpieces, too.
  10. Wow. Pipes blow a lot of this theory out of the water. (Ive heard all the puns before, let em rip. )
    Im not trying to derail your thread jbtsax, but as ive described above, our inst reacts diferently regarding several key points.

    "If" being the operative word :) We;ve become condtitioned to piano's inherent, consistent out-of-tune-ness..

    Although, kind of hard to chalk louder=flatter completely up to embrochure, when it happens to bagpipes also. Theres something going on over & above the control zone of the player.
    Last edited: Aug 22, 2012
  11. kymarto

    kymarto Content Expert/Moderator Staff Member CE/Moderator

    One important thing to consider is that if one relaxes the embouchure to play louder, that will increase the effective volume of the mpc which will make the notes flatter, and increasingly so the higher the note--all other things being equal.
  12. From what I remember, a few people noticed that with some period clarinets they play, it doesn't work this way. The pitch got sharper when they played louder. The instrument works the same, but the difference seemed to come from the mouthpiece. If I were you I would email Tony Pay and ask if he can send you links to his posts on the subject.
  13. jbtsax

    jbtsax Distinguished Member Distinguished Member

    That is a good point. Isn't it also true that at louder levels the reed is traveling farther away from the mouthpiece each "beating" cycle? That would also affect the mouthpiece volume. I am curious as to whether there may be other factors determining the pitch as well.

    It would be great if we could get Antoine LeFebre to participate in some of the acoustic discussions on this forum. I got the impression that his experience at the "other place" was not entirely positive. I think this would be a great question to ask Joe Wolfe as well. I have revisited the UNSW site and couldn't find any discussion of this particular topic.
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