Suppose a string bound between two rigid end-points is vibrating and it is a combination of a number of normal modes of vibration, is it possible to isolate a particular mode of vibration in wave by a physical experiment by causing all other modes to die out ?

I think when string is straight we can block nodes of our desired mode but will it cause other modes of vibrations to die and dissipate energy and what about modes which are half in wavelength of our desired mode-They will not die ? I think it is wrong direction of thought and hence posted the questiom


1 Answer 1


yes, the method is as follows.

You equip the clamp that holds one end of the string with a high-impedance force transducer (also called a piezoelectric pickup), pluck the string, and send the output into a device called a spectrum analyzer. This displays signal amplitude on the vertical axis of a screen and frequency on the horizontal axis. All the resonances and overtones show up as spikes on the plot and you can determine their relative strengths and the frequencies at which they are active.

  • $\begingroup$ Thanks , however my question was wrongly framed, I have now modified it. $\endgroup$
    – Kutsit
    Feb 21, 2019 at 18:51
  • $\begingroup$ I needed to isolate the mode on string itself. $\endgroup$
    – Kutsit
    Feb 21, 2019 at 18:52
  • $\begingroup$ yes, you can lightly and briefly touch the vibrating string at its midpoint, this will kill off the fundamental and leave the overtones, which you can then hear. $\endgroup$ Feb 21, 2019 at 19:04
  • $\begingroup$ If the initial shape of the string is a perfect sine, then you should only excite that frequency: IN THEORY. Doing it sounds difficult, unless you got as many pluckers as you could to carefully pull the string at nicely placed points into the shape of a sine (or 1/2 sine wave for the fundamental), and then they all release it simultaneously. $\endgroup$
    – JEB
    Feb 21, 2019 at 19:48
  • $\begingroup$ the overtones are indeed excited by the nonsinusoid nature of the plucking process. $\endgroup$ Feb 22, 2019 at 1:43

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