Conference Audio: Meeting Speech Criteria Without Overdriving
You are the audio lead for a 300-seat conference. The client’s acceptance criteria state speech level of 75–80 dBA at the back row, no feedback, and intelligible speech in all three zones. During sound check, your meter reads 92 dBA at the front row, 68 dBA at the back row, and back-row listeners report a ‘muddy’ sound. The client says, ‘Just turn it up; people are complaining.’ The system has a digital processor with zone gains, a 31-band graphic EQ, and a limiter set at 85 dBA. The front row is 3 m from the speakers; the back row is 24 m away. The room has a glass rear wall and a low ceiling. An important government speaker starts in 20 minutes.
1. Evaluate the readings against the acceptance criteria and identify the likely causes.
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Measure first, then compare to the acceptance criteria. 92 dBA at the front is above the 75–80 dBA target, while 68 dBA at the back is below it; turning up the master would make the front worse and increase feedback risk. Check that the meter is set to A-weighting and slow response, and that you are measuring at ear height in each zone. The 85 dBA limiter should prevent sustained levels above 85 at its reference point, so a 92 dBA reading suggests either the limiter is not inserted on that output, the measurement is before the limiter, or the meter is not calibrated. ‘Muddy’ at the back with a glass wall and low ceiling points to reverberation and low-mid buildup, not just insufficient gain. The problem is coverage and intelligibility, not raw volume.
2. What corrective actions would you take in the 20 minutes before the speaker arrives?
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Within 20 minutes, prioritize coverage: aim the main speakers down toward the back rows without hitting the glass, reduce front-zone gain, and bring up the back zone only if the processor has separate zone control. Cut 200–400 Hz on the graphic EQ to reduce muddiness, use a high-pass filter on speech mics, and ring out the wireless mic before the speaker arrives. Confirm the limiter is active on the main output and set it so the front row cannot exceed 85 dBA. If delay speakers are available, set delay time for the 24 m distance and use them for the back; if not, accept that the back will be quieter and tell the client. Test with a live talker at the back, not just pink noise.
3. How would you communicate the compromise and get sign-off?
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Show the client the measurements and the criteria, then explain the trade-off: ‘We can make it louder, but the front rows will be over the limit and the room will feed back; the better fix is to re-aim and re-EQ for intelligibility.’ Agree on a final listening check with the government speaker’s representative, record the settings and any residual limitation, and note that the back row may be below the target without delay speakers. Get sign-off on the compromise before the event, and keep the quality record with the measurement positions, times, and settings.