Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Helmholtz resonator equation. How do I do this? Please help.

  1. Oct 8, 2013 #1
    Helmholtz resonator equation. How do I do this?? Please help.

    helmholtz.JPG

    L = 0
    Vo = 473.17 (I think its cubed though I calculated it from 16 ounces, so I should be cubed right??)
    A = What im solving for
    F = 480 hz
    V= speed of sound which is 340.19 at sea level

    If Vo needs to be cubed then A should be squared, but I dont know if Im supposed to do that

    Ive put all this down on paper and im not sure how to run this equation to solve especially when it comes to the square root of a fraction, especially if the fraction is cubed and squared.

    How do I do this??? Been searching the internet for 2 days now trying to figure this out.
     
  2. jcsd
  3. Oct 8, 2013 #2

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    What do you mean by cubed or squared??
    You have a formula.
    Solve it for A.

    L cannot be 0, do you understand why?
     
  4. Oct 8, 2013 #3
    Yes because then the it would be multiplied by Vo and would end in zero. By zero I me L is non existant in the equation, there is no neck to the helmholtz resonator. So L needs to be left out.

    By cubed and squared I mean that it asked for Volume, the volume is 473.17 cubic centimeters. So it should be cubed right?? Really stupid question but I just want to make sure thats the case
     
  5. Oct 8, 2013 #4

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    I'm sorry.
    What you write is completely incomprehensible.
    It doesn't seem that you even know what the number 0 is, nor what an equation is, either.
     
  6. Oct 8, 2013 #5
    uh its very comprehensible.
     
  7. Oct 8, 2013 #6

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    No, it is not
    1. You can't put 0 in the denominator of an expression.
    2. Volume cubed?? The volume stands there without any cubing done at all.
    3. Why should you square A? You are to solve for it.
     
  8. Oct 8, 2013 #7
    L is now .028448 centimeters. I guess you have to account for the thickness of the metal.

    It what sense does the volume sit there without any cubing? Its 473.17 cubic centimeters. So, wouldnt you put in the equation as 473.17^3?

    The result of A should be equal to centimeters squared correct? Thats just one other thing im unsure of. Is that I took the volume and converted it from ounces to cubic centimeters, so how should I input it in to the equation?
     
  9. Oct 8, 2013 #8

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    "Its 473.17 cubic centimeters. So, wouldnt you put in the equation as 473.17^3?2
    Why?
    You have 473.17 cubic centimeters, not 473.17^3 cubic centimeters.

    A cubic centimeter is a unit for volume counting.
     
  10. Oct 8, 2013 #9
    Ok I understand then, that is what I was unsure of.

    Let me try again to see if I can run this equation
     
  11. Oct 8, 2013 #10

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Run an equation?
    Shouldn't you solve it for A??
     
  12. Oct 8, 2013 #11
    2wqvdxe.jpg

    Thats where I got to, now what? and is it correct?
     
  13. Oct 8, 2013 #12
    thats what I meant by run it?
     
  14. Oct 8, 2013 #13

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Here's how you may do it:
    1. NEVER insert numbers until your last step, solve it algebraically!
    2. We have:
    [tex]f_{H}=\frac{v}{2\pi}\sqrt{\frac{A}{V_{0}L}}[/tex]
    We multiply with 2pi/v, gaining:
    [tex]\sqrt{\frac{A}{V_{0}L}}=\frac{2\pi{f}_{H}}{v}[/tex]
    We square both sides,
    [tex]\frac{A}{V_{0}L}=\frac{4\pi^{2}{f}^{2}_{H}}{v^{2}}[/tex]
    We multiply with V_{0}L, and gain:
    [tex]A=V_{0}L\frac{4\pi^{2}{f}^{2}_{H}}{v^{2}}[/tex]
    3. NOW, insert numbers to calculate A!
     
  15. Oct 8, 2013 #14

    DrClaude

    User Avatar

    Staff: Mentor

    If I may add: with units, otherwise you are in for a bad surprise.
     
  16. Oct 8, 2013 #15
    Thank you!
     
  17. Oct 8, 2013 #16
    Har har har. Sorry im not a pro with math.
     
  18. Oct 8, 2013 #17

    DrClaude

    User Avatar

    Staff: Mentor

    If you just plug in the numbers, as you did in post #11, you will get the wrong answer because your units won't match.
     
  19. Oct 18, 2013 #18
    Ok I did 240 hertz instead, so an octave lower, and got 1033.4 that looks a bit better.
     
  20. Oct 18, 2013 #19
    So basically if what I have come up with is 9cm will give 120herts and 4.5 will give 60hertz.
     
  21. Oct 19, 2013 #20
    Just to be sure, the speed of sound need to be converted to the same units that I am using for the resonator correct? In this case, centimeters
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Helmholtz resonator equation. How do I do this? Please help.
Loading...