This document discusses key acoustic factors to consider for effective communication in classrooms. It outlines that the distance between speakers and listeners, signal-to-noise ratio, reverberation, and physical barriers all impact sound transmission. Early reflections contribute positively to the effective speech signal while late reflections and background noise contribute to the effective noise level. The proportion of speech signal that exceeds the effective noise level allows an estimate of speech perception regardless of individual characteristics. Reverberation time determines the equivalent noise level from late reflections.

1. Basic Considerations in
Classroom Acoustics

2. Acoustic Factors to Consider
● Distance between talker and listener
● Level of signal
● Signal-to-noise ratio
● Reverberation
● Physical Barriers

3. Effective Signal and Effective Noise
● 4 primary considerations for relating speech perception to
room acoustics
– Effective signal is both incident speech signal and its
early reflections
– Effective noise is both background noise and late
reflections of speech signal
– Dynamic range of speech ~30 dB in any given
frequency band
– Proportion of speech signal exceeding effective noise
allows for estimate of speech perception independent
of patient characteristics

4. Effective Signal and Effective Noise
● 4 primary considerations for relating speech perception to
room acoustics
– Effective signal is both incident speech signal and its
early reflections
– Effective noise is both background noise and late
reflections of speech signal
– Dynamic range of speech ~30 dB in any given
frequency band
– Proportion of speech signal exceeding effective noise
allows for estimate of speech perception independent
of patient characteristics

5. Reverberation
● Reflections –
early and late
● Early reflections ~80 ms or
less
● Late reflections more than
80 ms

6. Reverberation and Distance
● Early reflections contribute to effective signal
● Early reflections important for speech perception because
they are constant in level throughout room.
● Direct signal follows inverse distance law – sound
pressure is inversely proportional to the distance from the
sound source
p ∝ 1/r
● Sound pressure decreases by 6.02 dB for every doubling
of distance from the sound source

12. Classroom Acoustics
-Effective Noise-

13. Classroom Acoustics
-Effective Noise-
Reverberation time
of room determines
equivalent noise
level for late
reflections

14. Classroom Acoustics
-Effective Noise-
Reverberation time
of room determines
equivalent noise
level for late
reflections

15. Classroom Acoustics
-Effective Noise-

16. Classroom Acoustics
-Effective Noise-