@article{harwood1972loudspeaker, title = {Loudspeaker Distortion with Low-Frequency Signals}, author = {Harwood, H. D.}, journal = {J. Audio Eng. Soc}, volume = {20}, number = {9}, pages = {718--728}, year = {1972}, url = {https://www.aes.org/e-lib/browse.cfm?elib=2032} }