Principles of Speech Intelligibility

1
Principles of Speech Intelligibility

• John Erdreich, PhD
• Ostergaard Acoustical Associates
• West Orange, NJ

2
Predicting Classroom Adequacy for Communication

• Single Measure, Articulation Index
• Developed 70 Years Ago
• Application to Rooms
• Speech Level
• Ambient Noise
• Reverberation

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Examples of Reverberation and Room Noise

• Words in a non-reverberant environment
• Effect of Reverberation
• HVAC Noise
• Classroom Treatments

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Calculating Articulation Index - Signal/Noise

• Speech Level
• Background Noise

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Calculating Articulation Index - Reverberation

• Reverberation Time
• Build up of sound from reflection in the room
• Time for sound to decay by 60 dB

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What is an Acceptable AI in a Classroom?

• Depends on the audience to some extent
• Young children require better S/N

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What is an Acceptable AI in a Classroom?

• Depends on the audience to some extent
• Young children require better S/N
• Generally - S/N Better than 12 dB

8
What is an Acceptable AI in a Classroom?

• Depends on the audience to some extent
• Generally - S/N Better than 12 dB
• Generally - Reverberation Time less than 500 msec