Factors Affecting Acoustic Responses of Apples

Sound pitch levels of fourteen apples were evaluated by human auditory sensing and compared with instrumental measurements of acoustic response of the fruits. Results indicated that the sound pitch level had a direct correlation with the first and the second resonant frequencies of the fruit. A linear model based on amplitudes of the power spectrum at selected frequencies could determine the sound levels of the fruit with a coefficient of multiple determination (R2) of 0.96. The acoustic impulse generating method, test location on the fruit, and fruit holding method did not affect the resonant frequencies of the fruit, but affected the amplitudes of vibrations at the second and higher resonant frequencies.