Bell Diameter

Discussion in 'Trumpet Discussion' started by, Feb 13, 2008.

  1. Forte User

    Jan 27, 2008
    Brisbane, Australia
    What impact does the bell diameter have on the acoustics of a trumpet? It looks like standard modern bells are 4.5" to 5", but I have seen some antique ones that were supposedly as small as 3.75".
  2. screamingmorris

    screamingmorris Mezzo Forte User

    Apr 4, 2007
    For one thing, it can affect projection, how much your sound does or does not spread out after it leaves the bell of the trumpet.
    A large bell will cause the sound to spread out more,
    while a small bell will cause the sound to spread out less.
    A practical difference is how loud you will sound to different people in the audience.
    With a large bell the sound is spread out so that a large number of people spread out in the audience will hear you at about the same loudness.
    With a small bell the sound is spread out less, so that audience members sitting directly in your line of fire will think you are loud, while audience members sitting off to either side will think you are less loud.

    Also, the size of the bell will affect how loud you are in the absolute sense because there is more metal vibrating with a larger bell.
    The larger the bell the louder you are without additional effort.
    (The bigger the church bell the louder the sound.)

    Also, the bigger bell should have somewhat richer harmonics because of the larger surface area of metal involved.
    Like a bigger piano wire having richer harmonics than a smaller piano wire.

    "Has larger bell, giving it broader tone quality. The greatest trumpet of a great family. Gives you more power with less effort."
    - The Conn Loyalist

    "The two instruments are essentially identical (at least for purposes of this article), except the 36B has a 4 5/8" bell while the 38B has a large 5 1/8" bell. Eventhough the internal bore and taper of the 36B and 38B are the same, the 36B will require more effort to produce the same volume of sound as the 38B since it has a smaller bell."
    - The Conn Loyalist
  3. rowuk

    rowuk Moderator Staff Member

    Jun 18, 2006
    The bell diameter determines the amount of amplification that occurs at a specific frequency. A larger bell amplifies lower notes more. A 5" bell with "standard" exponential flare has maximum amplification at about 880 Hz which is an octave above concert A in the staff. A 4" bell has its maximum amplification at about 1000 Hz, which is an octave above 3rd space C.

    This really does not tell us a lot about what changes with bell size. My experience with piccolo trumpets is that an oversized bell sounds "sweeter" but the upper register is (much) harder to play. With Bb trumpets, the large belled instruments really "bark" in the lower register and have a thicker sound. I have never noticed a difference in the ease of high register though.

    A horns amplification drops with increasing frequency, and that is stretched over about 3 octaves. Above triple C the loudness of the mouthpiece buzz is about the same as what comes out of the bell!

    Practically, a larger bell gives the designer a different set of parameters to balance and the complete trumpet may or may not have other desirable characteristics because of that.

    The spreading of the sound is primarily due to the exit angle of the bell (flare) and not the size. The loudness is due to the overall efficiency of which bell size is one (but not the only factor). The potential is there IF the designer is going for more resonance (which would raise the blow resistance of the horn, which some people may not like......).

    A bigger bell without additional bracing would not be louder to the audience, but the player would hear themselves better. Don't forget, a vibrating bell represents LOST energy as that vibration is too weak to project into the room, but will reach the ear of the player.
    Last edited: Feb 13, 2008

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