Field Story
Echo Canyon: When Delay Towers Fight Each Other
A 15,000-seat sports arena installed delay towers at three distances from the stage. Audience members near the second tower heard a distinct echo because the delay was set 28 ms too short. Transfer function coherence dropped to 0.3 in the overlap zone. After measuring propagation delay with the delay finder tool and correcting each tower to within 1 ms, coherence improved to 0.85 and the echo disappeared.
Sports ArenaSTI Measurement per AES-2id
TL;DR
AES-2id system alignment focuses on frequency response and timing, but the ultimate measure of a voice-focused PA system is speech intelligibility. STI measurement per IEC 60268-16 provides the final verdict on whether your AES-2id alignment has achieved adequate speech clarity. SonaVyx STI tool integrates into the alignment workflow as the validation step: after you have tuned the transfer function and set delays, run the STIPA measurement to confirm that intelligibility meets the target. This is especially important for voice alarm systems where STI compliance is a legal requirement in many jurisdictions.
STI as AES-2id Validation
The AES-2id alignment process optimizes system frequency response and timing. STI measurement validates that these optimizations translate into actual speech intelligibility improvements at the listener position.
When to Measure STI
- After completing transfer function alignment and EQ
- After setting all delay lines for multi-zone systems
- Before and after acoustic treatment changes
- As part of final system commissioning documentation
STI Targets for PA Systems
- Voice alarm and emergency: STI above 0.50 minimum, target 0.55+
- Transport hubs (airports, stations): STI above 0.50 per EN 54-16
- Conference and presentation: STI above 0.55 for Good intelligibility
- Houses of worship: STI above 0.50 for natural speech, 0.55+ with PA
Measurement Procedure
Use the STIPA method for PA system evaluation. Play the STIPA test signal through the PA at normal operating level and measure at representative listener positions. Run measurements at the nearest, farthest, and most off-axis positions as minimum coverage.
Interpreting Results After Tuning
If STI is below target after AES-2id alignment, the cause is typically reverberation or noise, not the electronic system response. The transfer function may be flat, but the room degrades the modulation. Consider speaker placement changes or acoustic treatment.
Common Mistakes
- Running STIPA at too high a level, not matching actual operating conditions
- Only measuring at the best position and reporting it as representative
- Not documenting ambient noise conditions during the test
- Attempting to improve STI with EQ when the problem is reverberant energy
SonaVyx Workflow
Complete your system alignment with the SonaVyx transfer function analyzer. Then validate with the STI measurement tool. Measure RT60 with the RT60 calculator if STI is below target. Check SPL coverage with the SPL meter. Run the AI diagnostic for improvement recommendations. Follow the PA tuning workflow for the complete process.
Standard Reference
AES-2id:
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Last updated: March 19, 2026