Classroom Acoustics and ANSI Standard S12.60:
Every day, thousands of students across the country are unable to understand 25 to 30 percent of what’s said in their classroom. Excessive noise and reverberation in a classroom interferes with a student’s ability to clearly hear their teacher.

Before reviewing the new standard, it’s important to be familiar with the attributes of sound found in the classroom that affect a student’s ability to hear and learn.

Direct Sound
The sound of a teacher’s voice traveling directly from the teacher to the student is direct sound. It is always beneficial in terms of speech intelligibility because it is not affected by anything in the room, making it clear and distinct.

Reflected Sound
Reflected sound takes longer to reach the listener than direct sound because its path to the listener is longer. Reflected sound can be good or bad depending on the time delay.

Reverberation Time
The overall effect of reflected sound is called reverberation, and the time required for reflected sound to become inaudible is called reverberation time. Short reverberation times are good for speech intelligibility. 

Background Noise
Any sound that is generated outside the building, such as playground activity, traffic and planes can be considered background noise. It generally intrudes in the classroom by way of the windows. Within the building, an HVAC system and corridor noise can contribute to background noise.