Experimental results on the overall damping of freely supported uniform beams of circular and rectangular section are reported. These results show that the loss factor is, beyond a certain stage, highly frequency dependent but that this dependency largely disappears when the experiment is carried out in vacuo. The frequency dependency is shown to be due to acoustic radiation from the beam. Theoretical results using an approximate theory for rectangular sections agree well with the observed values. Over a certain frequency (wavelength) region the acoustic damping may be many times the internal damping of the beam for the material tested (mild steel).
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