A method of testing an elongate wooden element includes injecting an input acoustic signal into the element, detecting a return acoustic signal at a surface of the element, and determining a spectral profile for the return signal. In at least a predetermined range in the spectral profile, each resonance peak is detected whose amplitude exceeds a first predetermined value, and from the resonance peaks so detected the number of higher peaks is determined whose amplitude exceeds 3 dB. For each of said higher peaks a quality factor Q is calculated, a mean quality value Qm is determined, and Qm is then compared with a predetermined value to provide an indication of the presence or absence of external decay of the element. A ratio R of the number of higher peaks to the number of resonance peaks detected, and the statistical spread S of the average Q for the spectral profile, are calculated and compared with a predetermined boundary function Fn(R,S) to determine acceptability or unacceptability of the pole.