Sunship Audio

Setting the right crossover point between a midrange horn and a subwoofer

Blending a horn-loaded midrange with a subwoofer is rarely as simple as turning two knobs until the bass sounds loud. The crossover frequency is where the compression-driven midrange hands off acoustic energy to the cone-driven low end, and any misalignment at that junction becomes immediately audible as a dip, a peak, or a smeared image. In practice, the goal is a seamless acoustic transition, where the listener cannot localise the subwoofer as a separate source.

Australian listening rooms tend to be more varied than the average European or American space. A freestanding Queenslander in Brisbane with high ceilings, a fibro cottage in coastal Gosford, or a converted warehouse apartment in Fitzroy each present different modal behaviour. Combined with the country's love of open-plan living, polished concrete floors, and large glass sliders opening to outdoor decks, the room itself is often the biggest variable in the crossover decision.

Understanding the acoustic handoff

A midrange horn typically delivers usable output from roughly 200 Hz up to its compression driver's upper limit, often 8 kHz or beyond. The subwoofer, whether sealed, ported, or horn-loaded in its own right, takes responsibility for everything below that band. The crossover frequency sits in the overlap region where both drivers are capable of producing sound, and the designer must decide how much of that region to share and how steeply each driver rolls off.

The horn's high sensitivity usually means the midrange can keep going lower in frequency than a typical dome or cone unit before distortion rises. This is one of the genuine advantages of horn loading: the transition can be set lower than with a conventional driver, which moves the handoff away from the ear's most sensitive region of 1–4 kHz. In a properly designed system, the result is lower distortion in the critical vocal band and a more natural midrange presentation.

Measuring the driver and the room

Before setting any crossover, the actual response of each driver must be measured in the room where it will live. Free-field specifications rarely survive contact with real walls, especially in Australian homes where brick veneer, timber framing, and glass create a complex mix of reflective and absorbent surfaces. A calibrated measurement microphone, a USB interface, and software such as REW or ARTA can reveal baffle step losses, boundary-induced peaks, and the actual -3 dB point of the subwoofer in-room.

Once the raw measurements are in hand, the crossover point is chosen based on where the subwoofer's response is still clean and where the horn begins to lose efficiency. Many Sunship-style systems work well with a transition in the 150–300 Hz region when the subwoofer is a high-excursion cone design, or as low as 80–120 Hz when a second horn is used for the bass. The lower the crossover, the less the subwoofer's directivity becomes an issue, but the more stress it places on the horn.

Slope selection and phase behaviour

The slope of the high-pass and low-pass filters determines how much overlap exists between the two drivers. Common choices are first-order (6 dB/octave), second-order (12 dB/octave), and fourth-order (24 dB/octave) electrical or acoustic slopes. Each has consequences for phase response, power handling, and the way the drivers sum at the crossover frequency.

Slope Crossover depth at f_c Phase shift at f_c Typical use in horn systems
1st order (6 dB) -3 dB 90° Minimalist, requires careful time alignment
2nd order (12 dB) -3 dB (Linkwitz-Riley) 180° Standard for many two-way designs
4th order (24 dB) -6 dB 360° Steep isolation, common in pro audio
4th order Linkwitz-Riley -6 dB 360° (flat sum) Popular for horn + sub integration

In horn-based systems, fourth-order slopes are often favoured because the horn's rising sensitivity with frequency helps offset the attenuation above the crossover point. A Linkwitz-Riley alignment at 24 dB/octave provides a flat summed response on axis, but only if the drivers are physically time-aligned so their acoustic centres arrive at the listener simultaneously.

Tuning by ear and instrument in Australian spaces

After the math says one thing, the room often says another. In a Perth apartment with double-brick construction, low-frequency ringing can mask the precision of a 200 Hz crossover, pushing the practical handoff closer to 250 Hz. In a heritage Adelaide terrace with timber floors and plaster walls, the same setting might sound lean and need reinforcement from the subwoofer. Acoustic treatment, subwoofer placement, and toe-in of the horns all interact with the chosen crossover point.

Listening tests with familiar material remain essential. Slow, deliberate sweeps around the chosen frequency, followed by full-range music, help identify any chestiness in male vocals (crossover too high) or loss of midbass warmth (crossover too low). For Australian listeners who frequently attend events like the Melbourne International HiFi Show, comparing the in-room result to a known reference system can be revealing. Many owners eventually settle on a slightly higher crossover than the textbook recommends, accepting a small amount of overlap in exchange for fuller midbass.

Long-term stability and common pitfalls

Crossover settings that sound correct on day one can drift as drivers break in, as room furnishings change, or as amplifier gain is altered. Re-measuring every few months and keeping a written log of settings, room changes, and listening impressions helps track these shifts. Environmental factors unique to Australia, such as high summer humidity in Darwin, salt-laden air on the NSW South Coast, and the dust load during a Canberra westerly, can also affect crossover components and driver surrounds over time.

A more detailed treatment of time alignment, passive network design, and bi-radial horn behaviour is available on the Sunship FAQ page, which also covers common integration questions raised by owners of custom systems. For a contrasting perspective that compares passive and active crossover philosophies, this detailed crossover guide approaches the same subject from a slightly different angle.

Practical recommendations for a clean acoustic handoff