Sunship Audio

Horn mouth aspect ratio and loudspeaker dispersion

A horn mouth is more than a finished opening around a compression driver. Its dimensions, flare and edge treatment determine how sound leaves the horn near the high-frequency crossover. Good geometry can preserve detail without making the loudspeaker narrowly focused or excessively diffuse.

The influence of horn mouth aspect ratio on vertical and horizontal dispersion is easiest to grasp as a proportion rather than a stand-alone specification. Using width to height, a wider mouth offers more space across the horizontal axis, while a taller mouth offers more vertically. Absolute size and crossover frequency still govern the finished behaviour.

These patterns affect the room differently. Vertical coverage changes energy directed towards floors and ceilings, influencing reflections and perceived warmth. Horizontal coverage shapes stereo imaging, dialogue focus and the apparent width of a performance, making listening position as important as musical preference.

Sunship Audio builds custom horn-loaded systems around TAD-Pioneer compression drivers and woofers, combining bi-radial wooden horns, time-aligned passive crossovers and heavily braced birch plywood cabinets. Its Berlin listening and demonstration room allows direct comparison of configurations. Across Australia’s specialist hi-fi market, from Sydney and Melbourne to Brisbane, Adelaide and Perth, that evaluation is valuable when international freight, customs clearance and local room conditions complicate a purchase.

Reading the mouth proportions

At a fixed crossover frequency, mouth dimensions must be judged against wavelength. A small mouth relative to wavelength radiates broadly; as its edges become an effective aperture, radiation becomes more directional along each axis. The effect changes with frequency.

Proportion also interacts with mouth area, flare rate and edge diffraction. Enlarging both dimensions can lower the practical horn crossover, but demands a larger cabinet. A coherent flare matters more than a dramatic outline, because irregular paths can spoil the apparent directivity advantage.

For a bi-radial horn, separate low- and high-frequency paths can use different expansion rates before meeting at the driver. Their junction must create a coherent wavefront, since a step or mismatch near the mouth can disturb the pattern. The shape should therefore be developed from the driver exit, crossover and intended radiation angles.

Balancing vertical and horizontal coverage

A square mouth provides a balanced starting point because neither axis has a clear size advantage. A width-to-height proportion around 1.4:1 tends to favour broad horizontal coverage, while an inverse proportion favours vertical reach. These are tendencies, not fixed laws: flare continuity, diffraction and the compression driver’s own pattern can alter the measurements.

Vertical behaviour is often consequential at home. A controlled vertical lobe can reduce floor and ceiling reflections, making dialogue and centrally placed sounds easier to locate. The same restriction can feel dry from a low sofa or too concentrated for listeners spread across a rear row.

Horizontal off-axis response determines whether a stereo pair remains coherent away from the sweet spot. An overly narrow pattern can pull attention towards a centre speaker, while excessive width can weaken the sense of a bounded soundstage. Proper specification drawings should show horizontal and vertical response at several off-axis angles, rather than an on-axis curve alone.

Integrating crossover, cabinet and room

The crossover must be settled before the mouth is drawn. Its slope, phase alignment, sensitivity match and the distance between horn and woofer establish where useful horn directivity begins. Sunship’s guide to bi-radial crossover design explains how the passive network and horn paths are coordinated. A well-proportioned mouth cannot compensate for poor driver integration.

Cabinet geometry then shapes what the horn radiates. A mouth placed close to a cabinet edge can diffract around it and introduce uneven off-axis lobes. Deep, heavily braced birch plywood keeps panels from moving, but stiffness alone does not solve alignment; horn position, baffle profile and crossover timing need to be modelled as one system.

Australian conditions add practical checks without changing the acoustics. Coastal homes in Sydney, Melbourne and Perth can alternate humid summers with air-conditioned, dry interiors, while inland climates can be much drier. Stable joinery, sealed horn joints and finishes suited to Australian conditions protect the cabinet and its repeatable performance.

Selecting for Australian installations

The best proportion follows the listening brief. A near-square horn is a sensible baseline for most two-channel systems, with a slightly wide format helping coverage in open-plan living areas. A taller format can suit a dedicated room where broad vertical reach is wanted, but should not be selected merely for appearance.

Room height and seating position should be measured before fixing the horn axis. Australian homes often combine high ceilings with open-plan family rooms, yet compact apartments in Brisbane or Melbourne can place listeners near reflective walls. These spaces reward controlled vertical output and careful aiming more than an unrestricted lobe.

Commercial details need equal attention. A custom loudspeaker may travel from Berlin to an Australian dealer or client, with documentation, GST, insurance and freight time affecting availability. Clear specifications, robust packing and planned commissioning reduce the uncertainty created by a long lead time.

Comparing practical configurations

Ratio decisions become clearer when practical effects are separated from marketing shorthand. A useful brief records the room, listening positions, desired coverage and acceptable levels of floor or ceiling interaction before choosing a mouth.

Design priorities for Australian installations

Pattern priorities

Build and commissioning priorities

These priorities connect the acoustic brief to the build and the route to the client. They also give an Australian dealer meaningful points to verify during auditioning and commissioning.

The principal proportion and scale trade-offs are evident in practical configurations:

Configuration Vertical dispersion Horizontal dispersion Useful application Main caution
Wide, shallow, about 2:1 width to height Narrower Broader Wide stereo coverage Less consistent vertical reach across seating
Near square, about 1:1 Balanced Balanced General two-channel and multipurpose rooms Boundary and crossover checks remain necessary
Tall, narrow, about 1:2 width to height Broader Narrower Vertical reach with focused stage imagery Reduced horizontal coverage
Larger square, about 1:1 Balanced Balanced Lower horn crossover and higher output Greater cabinet volume and shipping weight

Sunship Audio resolves these choices through its custom design process and Berlin demonstration facility, integrating directivity with the horn, crossover and cabinet. The intended room behaviour can therefore be defined before a system reaches its Australian listening space.