Sunship Audio

Machined Crossover Inductors on Custom Bobbins for Reliable Performance

Every crossover network lives or dies by the consistency of its individual parts. In horn-loaded loudspeakers that use TAD-Pioneer compression drivers and high-efficiency woofers, even a small variation in inductance can shift the crossover point, alter phase behaviour around the target frequency, and colour the midrange that the wooden horns are so carefully voiced to reproduce. Sunship Audio treats this as an engineering problem rather than a boutique preference, and that is why every inductor in a Sunship crossover is machine wound onto a custom bobbin before it is fitted into the time-aligned passive network inside the birch plywood cabinet.

The approach runs against a long tradition in the high-end audio world, where hand-wound inductors on off-the-shelf plastic bobbins are sometimes presented as a sign of artisanal quality. In practice, hand-wound coils vary in wire tension, layer spacing, and turn count from unit to unit, and the audible result is a network that behaves slightly differently in every loudspeaker that leaves the workshop. For a manufacturer building integrated systems that need to perform identically from pair to pair, that variability is unacceptable.

Australian listeners approach this discussion from a particular angle. The country has a thriving two-channel community spread across Sydney, Melbourne, Brisbane, Adelaide, and Perth, with smaller but passionate scenes in Hobart and Darwin. Hi-fi events in Melbourne and Sydney routinely pull together listeners who want to audition horn-loaded systems, and many of those visitors end up asking detailed questions about crossover construction. Local retailers and importers are also bound by Australian electrical safety standards, which means components and finished goods must satisfy AS/NZS requirements and carry the RCM mark before they can be sold to the public.

The sections below look at the practical reasons behind machine-wound inductors on custom bobbins: what the inductors actually do in a horn-loaded network, why hand-wound coils fall short, what a custom bobbin contributes, how core and wire choices affect stability, and how the approach shows up in real listening rooms.

What Inductors Actually Do in a Horn-Loaded Network

In a passive crossover, inductors handle the low-pass side of the split, blocking higher frequencies from reaching the woofer while passing the band the woofer is asked to reproduce. In a time-aligned Sunship system, the inductor sits next to the capacitor and resistor networks that shape the signal feeding the TAD-Pioneer compression driver, and the inductor's electrical behaviour influences how cleanly the two drivers hand over at the crossover frequency.

Because the cabinet geometry, horn flare, and driver placement are all engineered as a single acoustic system, the crossover has to behave predictably. An inductor whose measured value drifts by even a small percentage can push the handover point up or down the band, which in turn changes the on-axis frequency response and the way the horn loads the room. That is why the inductor is treated as a precision component, not a generic part pulled from a parts catalogue.

Why Hand-Wound Coils Fall Short

Hand winding has a romantic appeal, but it introduces several sources of variability. Tension on the spool varies as the coil grows and the wielder's hand tires. Layer transitions happen at slightly different points on each coil, which changes the parasitic capacitance between layers. Turn counts can be off by a fraction, and the resulting inductance value lands somewhere inside the tolerance band rather than at the target figure.

For a single coil in a single loudspeaker, these variations may be small enough to ignore. For a manufacturer producing matched pairs that need to behave the same way in the customer's listening room, the cumulative effect is significant. Two pairs of loudspeakers built with hand-wound inductors can sound subtly different from each other in the same room, and that is precisely the problem Sunship set out to eliminate. Engineers familiar with overseas engineering notes have published comparable observations about layer spacing and inductance drift in commercial coils.

Custom Bobbins and Machine Winding

A custom bobbin does more than hold the wire. It defines the inner diameter, the winding width, the terminal layout, and the mounting interface that lets the finished inductor bolt cleanly onto the crossover board inside the heavily braced birch plywood cabinet. Off-the-shelf bobbins force compromises on all of these points, and they often arrive in production batches that vary slightly in dimension themselves.

Machine winding on a custom bobbin removes the operator from the critical path. Wire tension is set and held by the machine, turn counts are exact, and layer transitions land in the same place on every coil that comes off the line. The resulting inductors measure within a tight tolerance window and behave identically once installed. Visitors to the Sunship workshop in Berlin can see the bobbins and the winding machines in the build gallery alongside the finished loudspeakers.

Core Material, Wire Selection, and Inductance Stability

The choice of core material and wire gauge interacts directly with the geometry of the bobbin. Sunship generally favours air-core inductors in the signal path of its horn systems, because iron-core coils introduce saturation effects and hysteresis losses that colour the sound. Air cores also avoid the mechanical hum that magnetostrictive cores can develop at high drive levels, which matters when a high-efficiency woofer is asked to deliver concert-level dynamics.

Wire selection follows the same logic of predictability. Round copper wire in a defined gauge, wound in a controlled pattern, gives an inductance value that holds steady over time and across temperature. The custom bobbin keeps the geometry stable, and the machine keeps the wire placement stable, so the inductance stays where it was designed to be.

Practical considerations that guide the build:

Listening Results and System Integration

The point of this engineering is not visible on a single measurement. It is audible across a pair of loudspeakers that behave the same way in any room they are asked to fill. Australian listeners who have installed Sunship loudspeakers report consistent imaging and the same scale of presentation whether they are auditioning in a small room in Adelaide or a larger open-plan space in Perth. The piece at a conversation with a Sunship Audio owner: real-world impressions covers this in detail, including comments from listeners who have compared the systems with other horn-loaded loudspeakers in their own homes.

For Australian customers who travel to Berlin to audition the demonstration room, or for those who listen at hi-fi events in Melbourne and Sydney, the consistency shows up as something more fundamental: the loudspeakers sound the same as the reference units in the workshop. That match between the design intent and the delivered cabinet is the practical outcome of machining crossover inductors on custom bobbins.

What experienced listeners tend to notice: