Chung, D. Y., R. Hardie, and R. P. Gannon. “Letter to the Editor: The Effect of Hair, Glasses, or Cap on the Performance of One Pair of Bilsom Viking Circumaural Hearing Protectors”. Canadian Acoustics, vol. 11, no. 2, Apr. 1983, p. 45, https://jcaa.caa-aca.ca/index.php/jcaa/article/view/504.