I found this equation for predicting the bending natural frequency of a tube but am having trouble working it out. I was hoping that someone might be willing to steer me in the right direction. First the equation and the info provided on the website: w = (B*l)2 * SQRT (E*I/(rho*l4)) w - frequency radian per second E - modulus of elasticity I - area moment of inertia = PI*d3*t/8 for a thin wall round tube d - mean diameter t - wall thickness rho - mass per unit length = Area * mass per unit volume = PI*d*t*density l - length of tube (B*l)2 - Constants based on the boundary conditions. For a wind chime (Free-Free Beam): (B*l)2= 22.373 for the first natural frequency. To get the units correct you must multiply the values inside the square root by gravity (g). g = 386.4 in/sec2 for the units I'm using. for frequency in cycles per second (Hz) f = w/(2*PI) Now, the problem that I'm having is that when following the above format that uses non SI units I end up with a different result than when I swap them out for SI units. So, for example; when using lbmass/in^3 for the density and psi for Young's Modulus (*gravity) along with imperial units for size inputs (inch) the results are different than the results from using kg/m3 and pascals along with metric sizes (meters). When using SI units I'm dropping the *gravity. Here are the values that I am working with: E = 16969415.3 psi (1.17e+11 Pa) density = 0.323 lbmass/in^3 ( 8940 kg/m3) mean dia = .428 in (0.0108712 m) thickness = .048 in (0.0012192 m) length = .3885 in (0.0098679 m) When using the above format I'm getting 2 MHz but when switching to SI units I'm getting 66.7 MHz. So, where am I going wrong here? Any ideas? Any advice would be greatly appreciated.