Studies have been done to measure noise in decibels for activities occurring in representative classrooms in Dallas and Chicago areas.
Noise in a carpeted class for hearing impaired children in a mainstream environment with 15 students and 2 teachers is about 59dB HL.
A normal teacher speaks at about 65 dB HL.
This gives us a signal to noise ratio of +6dB which is not adequate for hearing impaired students.