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Thread: Please Define Flare Rate Frequency

  1. #1
    Senior Member 1audiohack's Avatar
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    Please Define Flare Rate Frequency

    With regard to horns, what is flare rate frequency?

    Examples, Steve Schell's "Big Ed" is a 15Hz flare rate, my pals Leviathan's are a 48Hz flare rate, not the LF cutoff, but flare rate in Hz.

    I have scoured this and other sites, just bought the 2008 Handbook for Sound Engineers at the recomendation of a friend, and a week and $104.00 later, have not yet found it.

    Its driving me crazy, the term is used like everyone learned it in grade school, I missed that somehow!

    Thanks all.

  2. #2
    Senior Member Hoerninger's Avatar
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    Cut off frequency <> flare constant, yes.
    The flare constant has the dimension of a reciprocal length.
    http://www.audioheritage.org/vbullet...9&d=1190904530
    ____________
    Peter

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    Quote Originally Posted by 1audiohack View Post
    Its driving me crazy, the term is used like everyone learned it in grade school, I missed that somehow!
    They're just showing off. Only five guys really know what flare rate is, the rest just act like they do.

    BTW - The discussion on it was in 3rd grade on a Friday afternoon close to the end of the second semester. You were probably busy pulling the redhead's ponytail sitting in front of you, shooting spit wads at your buddy across the room, gazing out the window at a spectacular spring day or simply nodding off from shear boredom. It happens...

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    Quote Originally Posted by 4313B View Post
    BTW - The discussion on it was in 3rd grade on a Friday afternoon close to the end of the second semester. You were probably busy pulling the redhead's ponytail sitting in front of you, shooting spit wads at your buddy across the room, gazing out the window at a spectacular spring day or simply nodding off from shear boredom. It happens...

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    Senior Member 1audiohack's Avatar
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    Thank you kindly Peter. Now I need a math reference book!

    OK 4313B, your known around here as a know it all but, how in the HELL do you know about the redhead?!?

  6. #6
    Senior Member timc's Avatar
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    Quote Originally Posted by 1audiohack View Post
    Thank you kindly Peter. Now I need a math reference book!

    how in the HELL do you know about the redhead?!?






    -Tim
    2213 + 2435HPL w/aquaplas + H9800 (Matsj edition)

  7. #7
    Senior Member Ian Mackenzie's Avatar
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    [quote=4313B;228963]

    You were probably busy pulling the redhead's ponytail sitting in front of you, quote]

    As long as it was a female

  8. #8
    Senior Member 1audiohack's Avatar
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    There were no males with ponytails when and where I grew up, hell I was six when I saw my first black person!

  9. #9
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    still going OT

    Flare rate, does that have anything to do with the red-hair bell-bottom pants? 1GHz I'd say...

  10. #10
    Senior Member 1audiohack's Avatar
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    Alright alright already! Everyone knows what I was doing in school and it didn't stop in the third grade.

    Consequently I need a little more help with this subject.

    When I look at what Peter sent me I don't see the key, it looks like all variables to me.

    Peter, or anyone, could you please provide an example?

    Thank you from the back of the class!

  11. #11
    Senior Member Hoerninger's Avatar
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    I don't see the key.

    There is no key, that is why the redhead's ponytail is always more interesting.
    (It is only a compilation I made many years ago which ended up in a drawer.)

    I will go through an example:
    Assuming there is a driver with a throat diameter of 1.5 inches, it should be used with a round exponential horn from 800 Hz up. For frequency response linearity I choose a lower cutoff frequency of 400 Hz. With these data the calculations of the dimensions start.

    The radius at the throat is (about) r0 = 2 cm = 0,02 m. (1 inch = 2,54 cm)
    The flare rate (Formerly I called it flare constant) for 400 Hz is calculated by
    <3> k = 4*Pi*f/c = 14,65 /m ,
    the horn length by
    <11> L = 2/k*ln(2/(k*r0)) = 0,262 m ,
    the mouth area
    <12> AM = 4*Pi/(k*k) = 0,0585 squaremeter ,
    the mouth radius
    <13> rM = 2/k = 0,136 m ,
    For the volume there are calculated
    the throat area
    A0 = Pi * r0*r0 = 0,001257 squaremeter
    and finally the volume
    <15> V(L) = A0/k*(e power (k*L) - 1) = 0,00390 cubicmeter = 3,9 liter.

    Some claim the horn is smoother at the low end when the opening angle is not 45 degrees but 43 degrees. The results are
    horn length
    <9> x(43 degrees) = 2/k*ln(2*tan 43 degrees/(k*r0) = 0,253 m
    mouth area
    <10> A(43 degrees) = 4*Pi/(k*k)*(tan43 degrees)power 2 = 0,0509 squaremeter
    and the volume
    <16> V(43 degrees) = 0,00339 cubicmeter = 3,39 liter.

    These calculations are best done in a spreadsheet. This time I used a pocket calculeter, I hope it is all correct.

    Btw. where is blondie in the second row last week?
    ____________
    Peter

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    Senior Member 1audiohack's Avatar
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    Thank you Peter, you are a great help. This will keep me busy for a while.

    Btw. where is blondie in the second row last week?
    At home with my children of course.

  13. #13
    Senior Member hmolwitz's Avatar
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    Ignoring all of these valuable and pertinant formulae, the Flare Rate that Steve Schell was referring to was the growth in size of the horn, if you have a trapezoid imagine one side with a 15 degree angle, has nothing to do with Hertz or Helmholtz.
    I actually built something approximating his horn and found it fairly successful at producing large quantities of low bass. however my construction methods and materials were fairly insufficient to the task.
    The basic concept behind his device is a rectangular horn that expands at that 15 degree number on one axis, you could construct such an item fairly simply if you incorporate no folds or splits, however it would be fairly cumbersome at around 16 ft long.
    You can use the standard horn calculators to calculate the mouth size for frequency desired.
    I would recommend OSB board in the heaviest thickness you can manage, thoroughly braced.
    I used a pair of Altec 3156 drivers I had laying about, opposed and compression loaded into the throat, each in about a 1.75 cu ft box.
    If I crank it near 150 watts it is fearsome, but it is also a bit buzzy as I used largely random bits of scrap to construct it and was careless in my joinery, and wanted to be able to disassemble and move it.
    It is also missing the last segment for now as I am short of cubic footage.

    pics
    Harry
    Last edited by hmolwitz; 12-03-2008 at 07:48 PM. Reason: Bad links

  14. #14
    Senior Member 1audiohack's Avatar
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    OK I must have missunderstood Steve.

    And the flare rate in degrees for a conical horn is relatively easy to conceptualize, calculate and build.

    What I am working / struggling with is the ability to math model a conical flare, (one dimension at a time, BiRadials later!) so as to correctly create one.

    Conceptually I still don't get how or why flare rate is described in Hz. I never told anyone I was smart!

    I currently have a couple of LF horns and concur that they can't be too rigid! At higher levels the panels contribute significantly, and adversly to the sound. Its amazing what a couple of ratchet straps and bricks for mass will do for testing! Even more that all the anomalies show up in high resolution impeadance measurements, throat leaks, panel resonance, all of it.

    Have fun with yours, thank you for the pic's.

    Barry.

  15. #15
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by 1audiohack View Post
    Conceptually I still don't get how or why flare rate is described in Hz.
    Steve Schell gave an example in this forum:
    http://audioheritage.org/vbulletin/s...15&postcount=3

    Recalculating of " 50" doubling of cross sectional area " gives a cut off frequency of 15 Hz which he states. Steve speaks of 15 Hz exponential flare, which is easy to understand. This means that it is an exponential horn and the flare rate corresponds to 15 Hz.

    But the flare rate itself is expressed in a reciprocal length. The cut off frequency and the flare rate are proportional:
    100 Hz : 3,66 x 1/m = 0,0931 x 1/inch
    200 Hz : 7,33 x 1/m = 0,1861 x 1/inch
    300 Hz : 10,99 x 1/m = 0,2792 x 1/inch

    There seems to be a problem with the conical flare? For the moment I am more interested in Blacky ...
    ____________
    Peter

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