Abel, S. M., and D. L. Spencer. “Active Noise Cancellation Vs. Passive Sound Attenuation: Help or Hindrance?”. Canadian Acoustics 23, no. 3 (September 1, 1995): 23-24. Accessed May 18, 2021. https://jcaa.caa-aca.ca/index.php/jcaa/article/view/925.