Sacks, M. P., R. Behboudi, and J. C. Swallow. “Tuned Mass Dampers for Soldier Field Stadium Grandstand Vibration”. Canadian Acoustics, vol. 33, no. 3, Sept. 2005, pp. 42-43, https://jcaa.caa-aca.ca/index.php/jcaa/article/view/1736.