Sunship Audio

Time Alignment Between a Horn and Woofer with a Delay Unit

A horn-loaded loudspeaker can deliver remarkable clarity, dynamic impact and efficiency, yet its woofer and compression driver rarely radiate from the same acoustic position. The horn throat, diaphragm, crossover network and cabinet depth all affect when sound reaches the listener. A delay unit can correct this arrival-time difference, allowing the two drive units to behave as a more coherent source.

The adjustment is especially valuable around the crossover region, where the woofer and horn overlap. Correct timing can improve vocal focus, bass definition and image stability, while incorrect timing may produce a hollow midrange, a vague centre image or uneven response that changes as the listener moves. For builders and owners of high-efficiency systems, alignment is a practical part of voicing the loudspeaker rather than a minor technical refinement.

Why acoustic timing matters

A woofer mounted low in a cabinet often has an acoustic centre several centimetres behind the compression driver’s diaphragm. A deep wooden horn can place the horn driver even further forward. Although both units receive their electrical signal simultaneously, their wavefronts may reach the listening position at different moments.

At a typical crossover frequency of 800 Hz to 1.2 kHz, a small time error is significant. One millisecond corresponds to roughly 34 centimetres of sound travel in air, and the resulting phase shift can cause addition at some frequencies and cancellation at others. The audible result is frequently a dip through the vocal range, reduced punch or a blurred transition between bass and midrange.

What a delay unit changes

A digital delay usually holds the earlier-arriving driver’s signal for a carefully selected period. If the horn is acoustically forward of the woofer, the horn channel commonly receives the delay. The aim is to make the acoustic wavefronts coincide at the chosen listening position, not to make the front panels or voice coils appear physically level.

The required value depends on cabinet geometry, horn profile, driver construction, crossover slope and measurement distance. A delay of 0.2 to 1.5 milliseconds may be enough in many systems, but no universal setting can be assumed. Digital processors often display milliseconds, samples or centimetres, so the owner must confirm the unit’s conversion and whether its delay is applied before or after other processing.

Delay, polarity and phase are connected

Time alignment is closely linked to polarity and crossover phase. Reversing the polarity of one driver can sometimes create a deep null that helps identify the correct delay region. With a suitable crossover, the cancellation becomes strongest when the acoustic centres are aligned. Restoring normal polarity should then produce the strongest and smoothest summed response.

This test is useful, but it should not be treated as a complete setup method. A delay unit may introduce filters, latency or phase rotation of its own. Steep digital filters can alter the acoustic relationship even when the displayed delay looks correct. A passive crossover, particularly a carefully designed time-aligned network, may already account for driver behaviour, so adding external processing without measurement can undo the intended balance.

Measure the acoustic centres

The most dependable approach uses a calibrated measurement microphone, measurement software and a repeatable microphone position. A nearfield measurement can help identify each driver’s impulse arrival, while a far enough measurement reveals how the horn and woofer integrate in the listening region. The crossover band deserves particular attention because alignment outside that range may not produce the best summation where it matters.

Room reflections complicate measurements in homes across Sydney, Melbourne and Adelaide, especially in rooms with timber floors, glass and low ceilings. Gated measurements can reduce the effect of early reflections, while multiple listening-position checks reveal whether the alignment is robust. After adjusting delay, inspect the impulse response, frequency response, phase trace and polar behaviour rather than relying on a single graph.

Integrating delay with a horn-loaded cabinet

A high-sensitivity horn system can expose small setup errors because its direct sound is so immediate. Gain matching is therefore as important as timing. Compression drivers may require substantial attenuation relative to the woofer, and the delay processor must preserve adequate signal-to-noise performance without clipping the input or output stages.

Sunship Audio’s custom horn loudspeakers illustrate why system-level integration matters: the horn, compression driver, woofer, cabinet and crossover are selected as a related set. In a comparable custom build, a delay unit should be considered alongside the passive network and cabinet geometry, not added as an isolated accessory. A technically perfect delay cannot compensate for an unsuitable crossover frequency, excessive horn resonance or a woofer that operates poorly above its intended range.

Practical realities for Australian rooms

Australian listening rooms vary widely, from compact apartments in inner Melbourne to open-plan houses in Brisbane and detached suburban rooms around Perth. In a smaller room, the main seat may be close to the loudspeakers, making the correct delay slightly different from the value measured at three metres. Near-wall placement can also reinforce the woofer while leaving the horn’s direct field comparatively exposed.

Long distances between Australian cities make specialist loudspeaker shipping expensive, and large birch plywood cabinets need careful freight planning. Owners buying an imported electronic processor should check 230–240 V compatibility, local warranty support and the applicable RCM requirements for electrical equipment. GST, delivery charges and customs handling can materially change the final cost of a delay unit purchased from overseas.

Daily listening habits also influence the result. A system used for low-level evening listening in an Adelaide terrace may need a different tonal balance from one used at concert levels in a rural Queensland room. Keep the measurement microphone and listening seat stable during setup, and avoid tuning solely for a temporary furniture arrangement. Loudspeaker toe-in, ceiling height and the distance to the rear wall can all affect the perceived success of alignment.

Setup recommendations for reliable integration

Start with conservative settings and record every change. A delay adjustment should be judged through measurements and familiar recordings, with the crossover region given priority over an impressive but isolated bass reading.

Checking the result over time

A well-aligned system should produce a stable centre image, articulate bass transients and an even vocal region. Snare attacks should appear connected to the body of the recording, while double bass and kick drum should retain pitch rather than sounding detached from the horn. If the presentation changes dramatically with small head movements, revisit the measurement position, toe-in and vertical alignment.

Cabinets can shift slightly after transport, spikes can settle into flooring, and a new listening room may require a different delay value. Keep the original measurements, processor file and final notes so the setup can be restored. In a custom high-efficiency loudspeaker, time alignment is a repeatable engineering adjustment that supports the design’s clarity, scale and control rather than a substitute for sound quality elsewhere in the system.