Speech intelligibility, a crucial aspect of voice alarm systems, is influenced by several factors:
- Loudspeaker coverage: Consistent sound coverage throughout the area ensures everyone can hear the message clearly.
- Overall frequency response: A balanced frequency response ensures all speech frequencies are reproduced accurately, enhancing clarity.
- Proportion of reflected sounds: Excessive reverberation can muddy the sound and reduce intelligibility. Proper acoustic treatment and loudspeaker placement can mitigate this.
- Reverberation time (RT60): A shorter reverberation time generally improves intelligibility, especially in larger spaces.
- Background noise level: High background noise can mask the message, making it difficult to understand.
- Loudspeaker type: Choosing appropriate loudspeakers for the environment and application is essential for optimal intelligibility.
- Acoustic considerations: The room's size, shape, and materials can significantly impact sound reflections and intelligibility.
Speech intelligibility can be measured objectively using the Speech Transmission Index (STI) scale, with a value above 0.5 considered acceptable for voice alarm systems. The Common Intelligibility Scale (CIS) is another measure, with values above 0.7 deemed satisfactory.
