Qin, H., A. Nakashima, D. Li, and M. Hodgson. “Experimental Studies on the Multi-Channel Active Control of Complex Sources in the Free-Field”. Canadian Acoustics, vol. 31, no. 3, Sept. 2003, pp. 86-87, https://jcaa.caa-aca.ca/index.php/jcaa/article/view/1563.