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Designing for Speech Intelligibility
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Choose the Appropriate Speaker for the Application
Output Capability – Make sure the speaker you choose has adequate power handling and
sensitivity to produce the sound levels required. For good paging, the speaker is typically required
to sustain average speech levels that are at least 10 dB HIGHER than the ambient noise level.
Mid & High Frequency Coverage – Choose a speaker with the appropriate coverage pattern for
your application. For intelligibility, select a speaker that has especially even coverage in the 1 kHz
through 6 kHz range.
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Power the Speaker Adequately – Make sure the speakers are driven with enough amplifier power to
sustain the expected sound levels. It doesn’t help to have speakers with enough output capability if
you don’t provide enough amplifier power to drive them to that capability. Clipping of the power
amplifier adds considerable distortion, degrades intelligibility, and results in unacceptable sound
quality.
Clipping of the power amplifier is especially hard on the high frequency speaker components in a
system and can cause damage or failure.
Setting SPL Target Goals
While the JBL Distributed System Design (DSD) software or acoustic design programs (like CADP2 or
EASE) can predict HOW the system will perform in the room, the system designer must determine
what the GOAL is for each application. The following is intended to help in setting an SPL goal for
the system design.
Here are some GENERAL guidelines to use as starting points in your system designs. The SPL levels
correspond to the “Maximum Average SPL for Music and Speech” figure listed in DSD (which is 4 dB
LESS THAN the computed Maximum Average SPL for Pink Noise).
Factors to consider include the ambient noise, loudspeaker distance from listeners, loudspeaker overlap,
the type of program material, and fidelity expectations of the listener.
Determining SPL ABOVE AMBIENT -- Economy background music installations require an average
music level capability of at least 5 dB above the ambient noise. For good paging intelligibility the
system needs a headroom of 10 dB higher than the ambient noise. Levels of 15 to 20 dB above ambient
yields excellent intelligibility.
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+5 dB for:
Economy background music only
+10 dB for:
Good paging intelligibility and music quality
+15 to +20 dB for:
Maximum intelligibility and highest dynamic range
