18 Sound 8CX401F – Coaxial Driver

18 Sound 8CX401F – Compact 8-Inch Ferrite Coaxial with ISV Voice Coil, 90° Coverage, and 6100 Hz LF Bandwidth

The 18 Sound 8CX401F is the smallest coaxial transducer in 18 Sound’s range — an 8-inch point-source driver that integrates a full ISV-equipped LF section with a 1-inch polyester HF compression driver into a single coaxially aligned package. With 95 dB LF sensitivity, 105 dB HF sensitivity, 90° conical dispersion, the widest LF bandwidth of any 18 Sound coaxial at 6100 Hz, and an 18 g moving mass that is the lightest of any coaxial LF section by a factor of two, the 18 Sound 8CX401F delivers true coaxial point-source output from an 8-inch format that fits cabinet designs no 10-inch coaxial can reach.

The 6100 Hz LF bandwidth is the specification that sets the 18 Sound 8CX401F apart from every other coaxial in the catalogue. No other 18 Sound coaxial LF section reaches 6100 Hz — the closest is the 12NCX750 at 5000 Hz. The 18 g moving mass and curvilinear cone maintain controlled pistonic output well into the upper mid-range, providing over an octave of overlap with the HF section above the 3.0 kHz crossover. The woofer section handles the entire vocal and presence band before handing off to the compression driver for the treble.

The 18 g Mms is extraordinary — less than half the 10CX650’s 39.5 g, less than a quarter of the 12NCX750’s 48 g, and less than a fifth of the 15NCX910’s 86 g. The featherweight moving mass is the engineering foundation for both the 95 dB sensitivity and the 6100 Hz bandwidth — lighter cones accelerate faster and maintain pistonic motion at higher frequencies.

The LF section shares its complete T/S parameter set with the standalone 8MB400 mid-bass driver — the same 51 mm ISV coil, the same ferrite motor, the same curvilinear cone, the same 9.3 Tm Bl, the same Qts of 0.34. The 18 Sound 8CX401F is essentially an 8MB400 with an integrated 1-inch compression driver at its centre — proven LF performance with coaxial HF integration.

At 4.4 kg with 90° conical dispersion, a dedicated passive crossover available, and suitability for compact reflex enclosures, the 18 Sound 8CX401F brings point-source coherence to the smallest format in 18 Sound’s coaxial catalogue.

Design and Construction of the 18 Sound 8CX401F

The 18 Sound 8CX401F integrates a two-way coaxial transducer system into a single 8-inch chassis powered by a ferrite single magnet motor.

The LF section uses a 51 mm (2-inch) ISV (Interleaved Sandwich Voice Coil) wound with aluminium wire on a high-strength fibreglass former. The ISV architecture places conductor on both inner and outer surfaces of the former — the same mass-balanced, linear-motor technology found on 18 Sound’s flagship coaxials. The aluminium winding sustains the 280 W AES / 400 W program power rating.

The 9.3 Tm force factor driving just 18 g of moving mass produces 95 dB sensitivity. The 18 g Mms is the lightest of any 18 Sound coaxial LF section — the curvilinear paper cone uses a unique wood pulp composition designed for maximum rigidity and stiffness at minimum weight. A polycotton multiroll surround provides increased excursion while controlling breakup modes through the 5.8 mm Xmax.

The 6100 Hz LF bandwidth is a direct consequence of the 18 g moving mass. Lighter cones maintain controlled pistonic motion at higher frequencies because there’s less inertia to overcome — the cone responds faster to the voice coil’s drive signal and stays coherent higher into the frequency range before breaking up. At 6100 Hz, the 18 Sound 8CX401F’s LF section produces useful output in the upper mid-range — a frequency where heavier coaxial LF sections have already rolled off by 1000–2000 Hz.

The 0.34 Qts and 147 Hz EBP define a versatile alignment on the sealed/vented boundary — the same flexible enclosure compatibility found on the 10CX650 and 15NCX750. Builders can design sealed enclosures for tighter transient response or vented enclosures for more bass extension. The 56 Hz Fs and 65 Hz lower frequency limit confirm the LF section reaches into the upper bass.

The humidity-repellent cone treatment provides outdoor durability for touring and festival applications.

The HF section uses a 25 mm (1-inch) edge-wound aluminium voice coil (EWAL) wound on treated Nomex, driving a polyester diaphragm with radial ribs. The 1-inch HF section is the smallest in any 18 Sound coaxial — scaled to match the 8-inch LF section’s output and cabinet format.

The polyester diaphragm is a different material category from the titanium, beryllium, and PEN diaphragms used on the larger coaxials. Polyester provides smooth, natural treble without metallic resonances — similar to PEN in character but at a more accessible price point. The radial ribs moulded into the polyester dome increase stiffness in targeted areas, avoiding uncontrolled vibration modes in the usable frequency range. The ribs provide controlled stiffening where the dome would otherwise break up, extending the useful HF range and improving distortion performance without the cost of exotic materials.

The treated Nomex former provides high-temperature resilience and the moisture resistance that outdoor use demands. The edge-wound aluminium coil maximises conductor packing in the gap for efficient force output from the compact 25 mm format.

Computer-aided FEA was used to maximise the cone profile coupling between the HF exit and the LF cone — the LF cone acts as a waveguide for the HF output, shaping the combined 90° conical dispersion.

The 3.0 kHz recommended crossover is the highest of any 18 Sound coaxial. The smaller 25 mm HF section needs a higher crossover point than the larger 44, 64, or 75 mm HF sections used on the 10, 12, and 15-inch coaxials. At 3 kHz, the HF section takes over in the upper presence band — and the LF section’s 6100 Hz bandwidth provides over an octave of overlap above the crossover for smooth transitions.

At 4.4 kg, 210 mm overall diameter, 186 mm baffle cutout, and 150 mm depth, the 18 Sound 8CX401F fits the same baffle cutout as 18 Sound’s standalone 8-inch mid-bass drivers (8MB400, 8MB500, 8NMB420 all use 186 mm cutout). The 14 mm flange thickness provides a secure mounting interface.

Performance and Applications for the 18 Sound 8CX401F

The 18 Sound 8CX401F delivers 95 dB LF sensitivity from 65 Hz to 6100 Hz and 105 dB HF sensitivity from the 3.0 kHz crossover point upward. The 10 dB sensitivity difference between sections is managed through the crossover network, with the HF section padded to match the LF level.

The 90° conical dispersion provides the widest coverage angle available in 18 Sound’s coaxial range alongside the 10CX650 and the XT120. Both LF and HF sections share the same acoustic axis — no offset, no lobing, no comb-filtering at the crossover frequency. The coaxial point-source coherence is the same regardless of format size — the 18 Sound 8CX401F delivers the same zero-lobing, zero-comb-filtering coherence as the 15-inch flagship coaxials.

The 8-inch format opens applications that no 10-inch or larger coaxial can serve. Ceiling speakers in low-clearance spaces. Ultra-compact stage monitors where the wedge profile must be as thin as possible. Column speaker elements where multiple 8-inch coaxials stack vertically for line-source coverage. Architectural installations where the speaker must be invisible. Compact distributed sound systems where every speaker must fit behind a standard ceiling tile or within a shallow wall cavity.

The 6100 Hz LF bandwidth means the woofer handles the entire vocal range, the presence band, and part of the brilliance range before handing off to the compression driver at 3 kHz. In practical terms, the LF section reproduces the most critical part of the audio spectrum — the frequency range where speech intelligibility, vocal clarity, and musical definition are determined. The HF section handles only the upper treble — cymbals, air, and high-frequency harmonics.

The 280 W AES / 400 W program LF power handling and 25 W AES / 50 W program HF power handling are appropriate for the compact applications the 18 Sound 8CX401F targets. The 280 W LF matches the standalone 8MB400 and 8NMB420 — full professional power handling from the 8-inch ISV platform.

The 0.34 Qts provides sealed/vented flexibility. The 147 Hz EBP sits on the boundary — builders can choose either topology. In a compact sealed enclosure of 5–10 litres, the LF section produces tight, well-controlled mid-bass. In a vented enclosure of 15–25 litres, the bass extends deeper with more output below 80 Hz.

A dedicated passive crossover (model 03708XCR00) is available with 12 dB/oct low-pass and 12 dB/oct high-pass slopes. The factory-designed crossover provides a complete, tested filter solution for builders who want a ready-to-use 8-inch coaxial system — connect the crossover, wire the amplifier, and the point-source system is complete.

The comparison to the 10CX650 defines the two smallest coaxial options. The 10CX650 delivers more LF sensitivity (94 vs 95 dB — actually the 8CX401F matches at 95 dB), more LF power (200 vs 280 W — actually the 8CX401F has MORE), a larger cone for more bass displacement, PEN HF diaphragm, and Atmos-ready design. The 18 Sound 8CX401F delivers a more compact format (210 vs 260 mm overall), lighter weight (4.4 vs 6.2 kg), wider LF bandwidth (6100 vs 4800 Hz), and suitability for the tightest installation spaces where 10 inches won’t fit.

Conclusion – 18 Sound 8CX401F Coaxial Driver

The 18 Sound 8CX401F is the smallest coaxial in 18 Sound’s catalogue — an 8-inch point source that delivers the same coaxial coherence as the flagship 15-inch models from a 210 mm overall diameter and 4.4 kg. The 6100 Hz LF bandwidth is the widest of any 18 Sound coaxial. The 18 g moving mass is the lightest by a factor of two. The 90° conical dispersion matches the widest coverage in the range.

The LF section’s proven ISV technology and T/S parameters shared with the standalone 8MB400 mid-bass confirm this is a professional-grade platform, not a compromise. The polyester HF diaphragm with radial ribs provides smooth, natural treble without metallic resonances. The dedicated passive crossover makes the system builder-ready.

For ceiling speakers, compact stage monitors, column speaker elements, distributed sound systems, architectural installations, and any application where a complete two-way coaxial point source must fit an 8-inch baffle cutout, the 18 Sound 8CX401F is the coaxial that fits where nothing else can. Eight inches, 4.4 kg, 90° conical, ISV linearity, point-source coherence — the smallest coaxial in the catalogue, built on proven technology.