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Re: [steam-whistles] Re: bell length

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  • David Wolf
    Peter, What I meant was do you have any information from recording blowing whistles of the same working length with different shaped tops that you did the
    Message 1 of 8 , Jun 10, 2005
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      Peter,

      What I meant was do you have any information from
      recording blowing whistles of the same working length
      with different shaped tops that you did the sound
      analysis on?? Then we could see approximately what
      the differences are. I agree with both you and
      Richard that once you get away from flat tops It would
      be EXTREMELY difficult if not impossible to predict
      the frequencies.

      Dave Wolf

      --- Peter Ommundsen <capewest@...> wrote:

      >
      > ----- Original Message -----
      > From: "David Wolf" <wolfdavidc@...> wrote
      > >>> Peter, Do you have any data on frequency changes
      > from flat tops to domed tops against working length
      > (bell length +cut up)??
      >
      > I agree with Richard, the frequency of a dome-topped
      > whistle seems to be higher than would be predicted
      > if the same dimesnions, ignoring the shape, were
      > applied to a flat top whistle.
      >
      > In my experience a flat top plain whistle usually
      > gives a natural resonant frequency with a wavelength
      > equal to 4 x ( interior length + end correction of
      > 0.3 diameter). For example, if a 6 x 18-inch whistle
      > at room temperature amplifies 169 Hz in an ambient
      > sound field, then:
      >
      > (13553 inches/sec/169 )/4 = 20-inch acoustic length.
      >
      >
      > However, the 1/4 wavelength of the natural resonant
      > frequency of my six-inch diameter domed Lunkenheimer
      > (17.75" internal length) is just about equal to the
      > bell length. Thus there is no easily detectable end
      > correction. This measurement was taken with the bell
      > removed from the center bolt and spider. This would
      > be a tough calculation as the dome is reinforced by
      > four partitions and has a large boss for the center
      > bolt.
      >
      > But precision frequency prediction of conventional
      > whistles under operating conditions is likely a
      > challenge even if the bell dimensions, slot
      > dimension and mouth dimensions are known, for the
      > following reasons:
      >
      > Frequency changes with gas consumption, so the
      > frequency calculation has to be calibrated to
      > pressure. But manifold pressure does not nicely
      > predict gas consumption due to differences in bowl
      > dimensions, gas pathways through valves, and valve
      > stem leakage, all of which may cause pressure drops
      > and which may vary among whistles. I have one
      > whistle with an adjustable bowl - the deeper the
      > bowl, the less the gas consumption, presumably due
      > to a pressure drop in the bowl. Also, if working
      > with air, presumably gas temperature falls with
      > pressure, adding another variable? Ideally our
      > experimental whistles would have a pressure gauge
      > tapped into the bowl?
      >
      >
      >
      >
      >




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    • Peter Ommundsen
      David Wolf wrote ... Perhaps approximately is the key word. As you know, a proper comparison would require that the different bells be
      Message 2 of 8 , Jun 10, 2005
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        "David Wolf" <wolfdavidc@...> wrote
        > What I meant was do you have any information from
        > recording blowing whistles of the same working length
        > with different shaped tops that you did the sound
        > analysis on?? Then we could see approximately what
        > the differences are.

        Perhaps approximately is the key word. As you know, a proper comparison
        would require that the different bells be blown on the same base to
        standardize the bowl configuration, slot size, etc. That is why I thought
        the natural resonance tests of the bells alone would be more meaningful.

        Nevertheless, here are some results from stock 2-inch diameter whistles
        (Lunkenheimer and Powell) blown on their own factory bases at 60 psig.

        Powell (flat-top) internal bell length 2.625 inches, mouth height 1/2 in,
        1107 Hz.

        Lunkenheimer (dome-top) internal bell length 3.75 inches, mouth height 1/2
        in, 854 Hz.

        Keep in mind that 60 psig is an arbitrary sample, and frequency would rise
        with increased pressure.

        My 6-inch Lunk dome-topped chime blows 319-394-531 Hz at about 100 psi
        steam. The full chamber lengths are 13, 10, and 8 inches. The longest
        chamber is the only one that has a 1/3 dome top. The others are flat.
        Relative to the medium chamber, the long chamber is clearly blowing a
        proportionately higher frequency than would be expected from length alone.
        The shortest chamber is of course of squat design and ascends rapidy in
        frequency.
      • Richard J. Weisenberger
        I see the trend you are talking about, but actually the whistle with the longer bell measured higher than expected. I wonder just how much of this was actually
        Message 3 of 8 , Jun 10, 2005
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          I see the trend you are talking about, but actually the whistle with
          the longer bell measured higher than expected. I wonder just how much
          of this was actually due to the domed tops? To be meaningful, we
          really need data on flat topped whistles with nothing unusual inside,
          such as a hidden nut or support near the top, to further increase the
          frequency.

          Your shorter bell whistle measured 1107 Hz. By my calculations, a
          flat top bell of the same dimensions should produce only 1030 Hz, so
          you had a frequency increase of approximately 7.5% higher than
          expected.

          Your longer bell whistle measured 854 Hz. By my calculations, a flat
          top bell of the same dimensions should produce only 757.8 Hz, so you
          had a frequency increase of approximately 12.7% higher than expected.

          This seems to go against what you have been saying in that the
          shorter, squatter whistle did not vary the most, but rather the
          longer, slimmer one. I still believe it has a lot to do with them
          both having those rather unpredictable domed tops that both
          Lunkenheimer and Powell are famous for.



          --- In steam-whistles@yahoogroups.com, "Peter Ommundsen"
          <capewest@s...> wrote:
          >
          > "David Wolf" <wolfdavidc@y...> wrote
          > > What I meant was do you have any information from
          > > recording blowing whistles of the same working length
          > > with different shaped tops that you did the sound
          > > analysis on?? Then we could see approximately what
          > > the differences are.
          >
          > Perhaps approximately is the key word. As you know, a proper
          comparison
          > would require that the different bells be blown on the same base to
          > standardize the bowl configuration, slot size, etc. That is why I
          thought
          > the natural resonance tests of the bells alone would be more
          meaningful.
          >
          > Nevertheless, here are some results from stock 2-inch diameter
          whistles
          > (Lunkenheimer and Powell) blown on their own factory bases at 60
          psig.
          >
          > Powell (flat-top) internal bell length 2.625 inches, mouth height
          1/2 in,
          > 1107 Hz.
          >
          > Lunkenheimer (dome-top) internal bell length 3.75 inches, mouth
          height 1/2
          > in, 854 Hz.
          >
          > Keep in mind that 60 psig is an arbitrary sample, and frequency
          would rise
          > with increased pressure.
          >
          > My 6-inch Lunk dome-topped chime blows 319-394-531 Hz at about 100
          psi
          > steam. The full chamber lengths are 13, 10, and 8 inches. The
          longest
          > chamber is the only one that has a 1/3 dome top. The others are
          flat.
          > Relative to the medium chamber, the long chamber is clearly blowing
          a
          > proportionately higher frequency than would be expected from length
          alone.
          > The shortest chamber is of course of squat design and ascends
          rapidy in
          > frequency.
        • Richard J. Weisenberger
          Sorry. I assummed the shorter Powell was a domed top, but I now see it was a flat top. That expains why it would have been closer in line with my expectations.
          Message 4 of 8 , Jun 10, 2005
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            Sorry. I assummed the shorter Powell was a domed top, but I now see
            it was a flat top. That expains why it would have been closer in line
            with my expectations. You can't really get much from this comparison
            though, since the Lunkenheimer was a domed top and the Powell a flat
            top. It's like the old addage of comparing apples to oranges.

            Again, most of the change can be explained by the Lunkenheimer's
            domed top, but there is something to be said about the 7.5% increase
            in the flat top Powell. I suppose, like you say, it's a matter of the
            extremely large scale. Either way, both of our formulas fail unless
            you take internal bell temperature into consideration.


            --- In steam-whistles@yahoogroups.com, "Richard J. Weisenberger"
            <rjweis00@y...> wrote:
            > I see the trend you are talking about, but actually the whistle
            with
            > the longer bell measured higher than expected. I wonder just how
            much
            > of this was actually due to the domed tops? To be meaningful, we
            > really need data on flat topped whistles with nothing unusual
            inside,
            > such as a hidden nut or support near the top, to further increase
            the
            > frequency.
            >
            > Your shorter bell whistle measured 1107 Hz. By my calculations, a
            > flat top bell of the same dimensions should produce only 1030 Hz,
            so
            > you had a frequency increase of approximately 7.5% higher than
            > expected.
            >
            > Your longer bell whistle measured 854 Hz. By my calculations, a
            flat
            > top bell of the same dimensions should produce only 757.8 Hz, so
            you
            > had a frequency increase of approximately 12.7% higher than
            expected.
            >
            > This seems to go against what you have been saying in that the
            > shorter, squatter whistle did not vary the most, but rather the
            > longer, slimmer one. I still believe it has a lot to do with them
            > both having those rather unpredictable domed tops that both
            > Lunkenheimer and Powell are famous for.
            >
            >
            >
            > --- In steam-whistles@yahoogroups.com, "Peter Ommundsen"
            > <capewest@s...> wrote:
            > >
            > > "David Wolf" <wolfdavidc@y...> wrote
            > > > What I meant was do you have any information from
            > > > recording blowing whistles of the same working length
            > > > with different shaped tops that you did the sound
            > > > analysis on?? Then we could see approximately what
            > > > the differences are.
            > >
            > > Perhaps approximately is the key word. As you know, a proper
            > comparison
            > > would require that the different bells be blown on the same base
            to
            > > standardize the bowl configuration, slot size, etc. That is why I
            > thought
            > > the natural resonance tests of the bells alone would be more
            > meaningful.
            > >
            > > Nevertheless, here are some results from stock 2-inch diameter
            > whistles
            > > (Lunkenheimer and Powell) blown on their own factory bases at 60
            > psig.
            > >
            > > Powell (flat-top) internal bell length 2.625 inches, mouth height
            > 1/2 in,
            > > 1107 Hz.
            > >
            > > Lunkenheimer (dome-top) internal bell length 3.75 inches, mouth
            > height 1/2
            > > in, 854 Hz.
            > >
            > > Keep in mind that 60 psig is an arbitrary sample, and frequency
            > would rise
            > > with increased pressure.
            > >
            > > My 6-inch Lunk dome-topped chime blows 319-394-531 Hz at about
            100
            > psi
            > > steam. The full chamber lengths are 13, 10, and 8 inches. The
            > longest
            > > chamber is the only one that has a 1/3 dome top. The others are
            > flat.
            > > Relative to the medium chamber, the long chamber is clearly
            blowing
            > a
            > > proportionately higher frequency than would be expected from
            length
            > alone.
            > > The shortest chamber is of course of squat design and ascends
            > rapidy in
            > > frequency.
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