Comparison of modal parameters of loudspeakers in different working conditions

The basic subject of this paper are vibrations of a loudspeakerʹs membrane. Dynamic behaviours of loudspeakers with an opened and closed basket and with a quasi-conical paper diaphragm are presented. An electromechanical driving system of a loudspeaker was not considered. A woofer was either mounted in a closed cabinet or it was freely suspended; a tweeter (with a closed basket) was investigated as freely suspended. Structural behaviour of loudspeakers was evaluated by means of an experimental modal analysis technique. A set of Frequency Response Functions (FRFs) was measured in the experiment and then modal parameters (i.e. modal frequencies, modal damping and mode shapes) were extracted. Structural behaviour of quasi-conical membranes was compared to modes of a frustum of a cone. An influence of a cabinet on the modal parameters of the woofer is discussed. It was found that, for the opened basket woofer mounted in the cabinet, the modal frequencies were changed by the closed enclosure in comparison to the freely suspended woofer. However, changes in the modal frequencies did not reveal any systematic behaviour. The modal damping was smaller when the woofer was mounted in the cabinet. For the loudspeaker with the closed basket, axisymmetric and non-axisymmetric modes were found, showing some discrepancies from the axisymmetric shape of the shell and non-axisymmetric attachment of the voice coil.