Time Alignment

Add delay to the nearer box so both waves land together: ragged smear becomes one clean +6 dB hit.

What it is

Adding tiny electronic delays so sound from every driver and speaker hits the listener at the same instant.

Key facts

• Speed of sound in air = 343 m/s at 20 degrees C (rises ~0.6 m/s per +1 degree C)
• Sound travels ~1 metre in 2.9 ms; rule of thumb = ~3 ms per metre
• Delay needed (ms) = distance gap (m) divided by 0.343, i.e. ~2.92 ms x metres
• Two identical signals in phase add = +6 dB (double pressure, 4x power); fully out of phase (180 deg) = cancel
• Half power = -3 dB, the standard crossover/coverage edge point
• Comb-filter notches sit at f = 343 / (2 x path-difference m) and odd multiples
• Wavelength (m) = 343 / frequency: 100 Hz = 3.43 m, 1 kHz = 0.343 m, 10 kHz = 34 mm
• Haas (precedence) effect: delays up to ~30-40 ms heard as ONE sound, localised to the FIRST arrival
• Delay tower = distance from mains (m) x 2.92 ms PLUS 5-15 ms Haas offset
• 1 sample at 48 kHz = 20.8 us; pro DSP delay resolution ~10-20 us; polarity flip is NOT the same as delay

How it works

1. Measure or calculate the distance from each source to the listening position.
2. Find the gap: subtract the near source distance from the far one.
3. Convert gap to time: multiply metres by 2.92 to get milliseconds of delay.
4. Add that delay to the CLOSER source so it waits for the far one.
5. Verify with a dual-FFT tool (Smaart, Open Sound Meter) on the impulse response.
6. Slide delay until the two impulse peaks stack and the crossover phase traces overlap.

Real examples

• Sub 1 m closer than the top: add ~2.9 ms delay to the sub (or the top, whichever leads).
• Delay tower 34 m behind mains: 34 x 2.92 = ~99 ms, plus ~10 ms Haas = ~109 ms total.
• Front-fill on stage lip vs main hang 4 m back: delay the front-fill by ~11.7 ms.
• Centre cluster vs left/right hangs offset 2 m: align with ~5.8 ms on the nearer box.

How it helps in live sound

• Align sub-to-top FIRST at the crossover (e.g. 80-100 Hz) using measured phase, not guesswork.
• Use a measurement mic at mix position + dual-FFT; stack the impulse peaks, then overlay phase.
• Set delay-tower time = distance x 2.92 ms, then ADD 5-15 ms so mains still localise the source (Haas).
• Account for temperature drift: a 10 degree C swing across a show shifts long-throw timing audibly.
• Try a polarity flip on the sub before reaching for delay; sometimes 180 deg aligns the crossover better.