Sitthichok Puangthongthup. (1999) A study of noise attenuation efficiency in earplugs modified by inserting lead capsules into their stems. Mahidol University,:ม.ป.ท.Sitthichok Puangthongthup. 1999. A study of noise attenuation efficiency in earplugs modified by inserting lead capsules into their stems. ม.ป.ท.:Mahidol University,;Sitthichok Puangthongthup. A study of noise attenuation efficiency in earplugs modified by inserting lead capsules into their stems. ม.ป.ท.:Mahidol University, 1999. Print.