An alternative view of loudspeaker nonlinearities using the Hilbert-huang transform

This paper presents a new approach to nonlinear loudspeaker characterization using the Hilbert-Huang transform (HHT). Based upon the empirical mode decomposition (EMD) and the Hilbert transform, the HHT decomposes nonlinear signals into adaptive bases which reveal nonlinear effects in greater and more reliable detail than current approaches. Conventional signal decomposition techniques such as Fourier and Wavelet techniques analyse nonlinear distortion using linear transform theory. This restricts the nonlinear distortion to harmonic distortion. This work shows that real nonlinear loudspeaker distortion is more complex. HHT offers an alternate view through the cumulative effects of harmonics and intra-wave amplitude-and-frequency modulation. The work calls into question the interpretation of nonlinear distortion through harmonics and points towards a link between physical sources of nonlinearity and amplitude-and-frequency modulation. The work furthermore questions the suitability of traditional signal analysis approaches while giving weight to the use HHT analysis in future work.