Think back to your teen-age years. You're trying to listen to your new Aerosmith record, but it's hard to hear because your sister is yapping on the phone. The easiest solution? Crank up the stereo volume.
Education institutions use a similar rationale when they install amplification systems in classrooms. In cases where noise from outside the classroom can't be controlled, or where a teacher's voice does not project sufficiently throughout the learning space, schools may opt to use a voice-amplification system.
An instructor is miked for sound, and the increased decibels of the teacher's words being broadcast to students results in a better voice-to-background noise ratio.
But advocates of good classroom acoustics say pumping up the volume is hardly the ideal solution. The teenager turning up the sound on his stereo may be able to hear his music and drown out other noise, but the overall effect is likely to prompt an irritated parent to tell the teen to quit making such a racket. Likewise, the added noise from an amplified voice might make listening uncomfortable for some students.
The position of the Acoustical Society of America (ASA) is that sound amplification should not be used routinely in typical, small mainstream classrooms.
"Sound amplification increases rather than decreases overall sound levels," the ASA says. "Also, unless classroom walls, ceilings and floors are acoustically upgraded to improve their sound insulation, amplified sound may be heard in adjacent classrooms, interfering with learning there."
A 2007 guide produced by the New Zealand Ministry of Education on acoustics in learning spaces lists the pros and cons of systems that amplify a teacher's voice:
Advantages: signal-to-sound ratios are improved at the flick of a switch; the teacher can be heard from anywhere in the room; the teacher's voice is less stressed; and students' on-task behavior and comprehension may be improved.
Disadvantages: the systems are expensive to install; they need regular maintenance; sound levels must be set correctly to be effective; some teachers don't like them and may not use them; the long-term effects on the development of students' listening skills are, as yet, unknown; and they only assist teacher-to-student communication and are not useful in student-to-teacher or student-to-student communication.
Before resorting to amplification, the ASA states, education institutions should design new or renovated classrooms to conform with the acoustics standards developed by the American National Standards Institute. Those standards state that the maximum background noise in an unoccupied classroom should be 35 decibels.
"Background sound levels of 35 decibels or less ensure the 15-decibel signal-to-noise ratio needed for effective learning," the ASA says.
The New Zealand guide agrees that amplification systems should be a last resort.
"Teacher's voice-amplification systems … are not a substitute for good acoustical design and should be used only when all other options have failed," the guide recommends.
In decibels, the recommended maximum background noise level in an unoccupied classroom.
In decibels, the recommended signal-to-noise ratio needed in a classroom to allow for effective learning.
Source: Acoustical Society of America