Assessment of voice-coil peak displacement Xmax

The voice coil peak displacement Xmax is an important driver parameter for assessing the maximal acoustic output at low frequencies. The method defined in standard AES 2-1984 is based on a harmonic distortion measurement, which does not give a definite and meaningful value of Xmax. After a critical review of this performance -based technique, an amendment of this method is suggested by measuring both harmonic and modulation distortion in the near field sound pressure using a two tone excitation signal. Alternatively, a parameter-based method is developed giving detailed information about the cause of the distortion, limiting and defects. The relationship between performance -based and parameter -based methods is discussed,and both techniques are tested with real drivers.