Time Alignment for PA Systems: Synchronizing Speaker Output

Time alignment synchronizes multiple PA speakers so their sound arrives at listeners simultaneously. Speakers at different distances naturally deliver sound at different times; digital delay compensates for these differences. Proper alignment improves clarity, impact, and coverage consistency.

Principles of Time Alignment

Sound travels at approximately 1,130 feet per second (344 meters per second) at typical temperatures. Distance translates to time: 1 foot ≈ 0.88 ms; 1 meter ≈ 2.9 ms.

Speakers closer to listeners deliver sound earlier than more distant speakers. The time difference equals the distance difference divided by the speed of sound.

Delay on the closer speaker synchronizes arrival times. Both speakers’ sound reaches listeners simultaneously, combining coherently.

Calculating Delay

Measure the distance from each speaker to the alignment position. Calculate the difference between distances.

Multiply the distance difference by the appropriate factor: feet × 0.88 = milliseconds; meters × 2.9 = milliseconds.

Apply this delay to the closer speaker. The result aligns arrivals at the alignment position.

Main-to-Subwoofer Alignment

Mains and subwoofers often occupy different positions—mains flown or elevated, subs on the floor. Distance differences require alignment.

Measure from typical listener position to mains and subs. Calculate delay based on distance difference.

The crossover region is most sensitive to alignment. Frequencies where both mains and subs contribute combine constructively when aligned.

Delay Speaker Alignment

Delay speakers extend coverage to distant areas. They must be delayed so the stage remains the perceived sound source.

Calculate delay based on the distance difference between main speaker and delay speaker to their respective coverage positions.

Add extra delay (5-20 ms) to reinforce stage precedence via the Haas effect. This psychoacoustic phenomenon makes the earlier arrival dominate perception.

Multiple Main Alignment

Left and right mains should arrive simultaneously at the mix position for accurate stereo imaging.

If the mix position is off-center, delay the closer speaker. Calculate based on position offset.

Large arrays may need internal alignment. Elements at different positions within the array should arrive coherently.

Digital Delay Tools

System processors (Lake, BSS, Symetrix) provide precision delay control. These sit between mixer and amplifiers.

Powered speakers with DSP often include individual delay adjustment. Set delay on each speaker to achieve alignment.

Mixer output delays on digital consoles can provide alignment when other tools are unavailable.

Measurement-Based Alignment

Dual-channel FFT analyzers (Smaart, SysTune) measure arrival times precisely. Impulse response shows when sound from each speaker arrives.

Position the measurement microphone at the alignment position. Measure each speaker individually.

Adjust delay until impulse arrivals align. Combined measurement verifies coherent summation.

Listening-Based Alignment

Walk the crossover or coverage boundary while program material plays. Listen for hollow or thin sound indicating misalignment.

Adjust delay in small increments. Listen for the fullest, most impactful sound at the overlap region.

This method works but provides less precision than measurement. Good ears can achieve functional alignment; measurement achieves optimal alignment.

Temperature Effects

Temperature affects sound speed. Higher temperatures increase sound speed; lower temperatures decrease it.

A 20°F (11°C) temperature change affects sound speed by about 2%. For critical applications, recalculate delay as temperature changes significantly.

Typical venues experience smaller temperature variation. Outdoor events with large temperature swings may need adjustment during the day.

Front Fill Alignment

Front fill speakers cover areas too close to the main PA for adequate coverage. These speakers typically mount along the stage front.

The delay required is substantial—front fills are much closer to listeners than mains.

Calculating delay based on the distance difference ensures front row listeners perceive sound from the stage while receiving adequate level from front fills.

Verifying Alignment

Walk the coverage area after alignment. Listen for consistent sound quality throughout.

Measure at multiple positions to verify alignment serves the entire audience, not just the measurement position.

Room reflections complicate verification. Direct sound alignment is correct even if reflections create additional variations.

Practical Considerations

Perfect alignment at one position creates misalignment elsewhere. Choose alignment positions representing the most important listening areas.

Audience presence affects sound speed slightly and changes room acoustics. Final verification with audience present reveals real-world performance.

Simple systems may not benefit noticeably from precise alignment. The improvements are most apparent in larger, more complex systems.