Basic Considerations in Classroom Acoustics

Acoustic Factors to Consider

● Distance between talker and listener● Level of signal● Signal-to-noise ratio● Reverberation● Physical Barriers

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

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

Reverberation

● Reflections – early and late

● Early reflections ~80 ms or less

● Late reflections more than 80 ms

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

Classroom Acoustics-Effective Noise-

Classroom Acoustics-Effective Noise-

Reverberation time of room determines equivalent noise level for late reflections

Classroom Acoustics-Effective Noise-

Reverberation time of room determines equivalent noise level for late reflections

Classroom Acoustics-Effective Noise-

Classroom Acoustics-Effective Noise-