Delay Speakers in Live Sound: Extending Coverage

Delay speakers extend PA coverage to distant audience areas that main speakers cannot reach effectively. Properly configured delay systems maintain consistent sound quality and level throughout large venues while preserving the perception that sound originates from the stage.

When Delay Speakers Are Needed

Sound level decreases with distance—roughly 6 dB each time distance doubles. Distant audience positions may not receive adequate level from main speakers alone.

Coverage angle limitations of main speakers may leave rear or side areas with insufficient direct sound. Delay speakers fill these gaps.

Long throw distances in large venues or outdoor settings challenge even powerful main systems. Delay speakers bring reinforcement closer to distant listeners.

The Haas Effect

The Haas effect (precedence effect) determines perceived sound source localization. The first-arriving sound establishes the perceived direction, even if later-arriving sound is somewhat louder.

Properly delayed speakers arrive after main PA sound, reinforcing level without pulling localization toward the delay position.

This allows delay speakers to add substantial level while listeners perceive sound coming from the stage rather than the delay location.

Calculating Delay Time

Delay time equals the distance difference between paths divided by sound speed. Sound travels approximately 1.13 feet per millisecond (343 m/s).

If mains are 100 feet from the delay coverage area and delays are 50 feet, the 50-foot difference requires about 44 ms delay.

Adding 10-20 ms additional delay beyond alignment reinforces the Haas effect, ensuring main speakers establish localization even if delay speakers are slightly louder.

Speaker Placement

Delay speakers position within or near the areas they cover, significantly closer to listeners than main speakers. Common locations include mid-venue, back of room, or under-balcony positions.

Elevation improves coverage while keeping speakers out of sightlines. Ceiling mounts, high stands, or balcony rail positions work well.

Symmetrical left-right placement maintains stereo imaging if the main system runs stereo. Single centered delays work for mono systems or speech reinforcement.

Level Setting

Delay speaker level should supplement mains without obviously increasing perceived volume. The combination should sound seamless.

Setting delays approximately 6-10 dB below main level at the coverage boundary typically provides adequate support while maintaining localization.

Walking the transition zone while adjusting level reveals the optimal setting—enough support for consistent coverage, not so much that delays become audible sources.

Coverage Transition Zones

The area where main and delay coverage overlap requires careful attention. Level and timing should transition smoothly.

Excessive overlap can cause comb filtering where both sources contribute equally. Careful level balancing minimizes this.

Slightly underlapping coverage—where delays add level rather than create equal-strength interference—often sounds cleaner than perfect overlap.

Digital Delay Implementation

System processors like Lake, BSS, and dbx DriveRack provide precise delay control. Delays can be set to the millisecond or fraction thereof.

Powered speakers with DSP, such as QSC K Series or JBL PRX800, include individual delay adjustment. Each speaker’s delay can be set independently.

Digital mixer outputs can provide delay when dedicated processors are unavailable, though system processors offer more flexibility.

Multiple Delay Rings

Large venues may need multiple delay rings—near, mid, and far positions each receiving appropriately delayed signal.

Each ring requires its own delay calculation based on its distance from mains. Delays increase with distance.

Level typically decreases for further rings as their contribution supplements earlier speakers rather than replacing main coverage.

Under-Balcony Fills

Balconies shadow the area beneath them from main speaker coverage. Under-balcony delay speakers address this.

These speakers mount beneath the balcony, aimed at the shadowed seating, delayed to align with main arrival.

Under-balcony delays may require slightly different mix content—more high frequencies to compensate for the absorptive balcony underside.

Temperature Considerations

Sound speed varies with temperature—faster in warm air, slower in cold. Outdoor events may need delay adjustments as temperature changes.

A 20°F temperature change affects delay by several milliseconds at longer distances. This can shift localization perceptibly.

Critical installations may benefit from delay adjustment during the event or delay systems that compensate automatically for temperature.

Measurement-Based Alignment

Measurement systems like Smaart or SysTune provide precise delay alignment. Impulse response measurement reveals exact arrival times.

Measuring at the intended coverage position ensures delays align where listeners sit, not just where convenient to measure.

Combined measurement (mains plus delays) verifies coherent summation without destructive interference.

Practical Setup Process

Position delay speakers based on coverage requirements. Calculate initial delay times from distance measurements.

Set delay times in the processor or speaker DSP. Set delay levels conservatively—too low is easier to fix than too loud.

Walk the venue during soundcheck, adjusting level and timing for seamless coverage. The best delay systems are inaudible as separate sources.