18 Sound 15ND840 – Lightweight Aluminium-Coil 15-Inch Neodymium Woofer with Record Low Inductance
The 18 Sound 15ND840 is a high power, high output, extended low frequency neodymium transducer which meets the most stringent requirements in high-quality professional transducers and represents the updated version of the 18 Sound flagship 15ND830, to which it is a direct replacement with improved construction. This mirrors precisely the 12ND830/12ND930 relationship documented earlier in this session — an aluminium-wound coil variant trading some force factor for significantly reduced weight-per-force and, notably here, an exceptionally low inductance figure.
The 18 Sound 15ND840 is available with an aluminium voice coil assembly rather than the copper winding found on the 15ND930/15ND940 pairing. This material substitution produces the same fundamental trade-off documented on the 12ND830: aluminium is lighter than copper per unit of conductor length but has higher electrical resistance, typically producing a somewhat lower force factor for an equivalent coil geometry.
The 0.43 mH Le is the lowest inductance of any conventional (non-Dual-Gap, non-AIC) 15-inch driver documented across this entire session — lower even than the copper-coil 15ND940’s already well-controlled 0.7 mH, and dramatically lower than the 15ND930’s 1.61 mH. The aluminium coil’s different electrical characteristics, combined with the SDR ring, produce this genuinely exceptional result.
Thanks to its versatility, the 18 Sound 15ND840 can be used in two-way compact reflex enclosures, in multiway systems, and in high-loading subwoofers as small as 70 litres, recommended for multiway systems and studio monitoring applications — identical positioning to its sibling ND-series drivers. 18 Sound now lists the 15ND940 as the alternative/current model — cross-referencing the copper-coil flagship rather than a direct aluminium-coil successor.
Design and Construction of the 18 Sound 15ND840
The 75 mm (3-inch) aluminium voice coil assembly, with a 23.5 mm winding depth operating in a 9.0 mm magnetic gap — identical winding geometry to the 15ND940’s copper coil, confirming these two drivers share the same fundamental chassis and motor architecture, differing only in winding material — is wound on a strong fibreglass former to improve force transmission and power handling.
The already low distortion and sound quality are further improved by the Demodulating Ring (SDR) that flattens impedance and phase with a constant power transfer. Combined with the aluminium winding’s different electrical properties, this produces the driver’s remarkably low 0.43 mH inductance.
The 17.9 Tm force factor driving 94 g of moving mass produces 99 dB sensitivity and the 0.37 Qts / 110 Hz EBP alignment — a considerably more flexible enclosure alignment than the copper-coil 15ND930/940’s 0.22–0.28 Qts range, giving builders genuine freedom between sealed and vented enclosure topologies that the copper-coil siblings don’t offer.
The deep-profile curvilinear cone, created from a special high-strength wood pulp, has been designed to achieve the best possible linearity within its frequency range. The cone surround is highly resistant to ageing and fatigue. The in-house developed cone treatment is a humidity repellent and significantly dampens bell-mode resonances — the same dual-function treatment philosophy documented throughout 18 Sound’s premium driver range.
At 4.7 kg, 393 mm overall diameter, 354 mm baffle cutout, 184 mm depth, and 13 mm flange — every physical dimension matches the 15ND940 exactly, confirming the two drivers share the same chassis platform with only the coil winding material differing.
Performance and Applications for the 18 Sound 15ND840
The 18 Sound 15ND840 delivers 99 dB sensitivity across a 38 Hz – 4000 Hz bandwidth — matching the 15ND940’s sensitivity exactly, with a wider upper bandwidth (4000 vs 3500 Hz) but the same 38 Hz lower limit.
18 Sound recommends a 100-litre (3.53 ft³) vented enclosure tuned to 45 Hz — larger than the 15ND940’s 70-litre recommendation, reflecting the different Vas and higher Qts alignment.
The 0.37 Qts and 110 Hz EBP make the 18 Sound 15ND840 considerably more suitable for sealed enclosure designs than its copper-coil siblings — where the 15ND930 and 15ND940’s tight Qts values firmly favour vented topology, this aluminium-coil variant genuinely works well in either sealed or vented configurations, producing a smoother, more extended rolloff in sealed applications.
The 0.43 mH inductance is the specification that distinguishes this driver most sharply from every other conventional 15-inch woofer documented in this session. For passive crossover designers, this near-record-low inductance means minimal impedance compensation is required, and the driver’s electrical behaviour tracks theoretical crossover models more closely than any other conventional (non-AIC) 15-inch driver covered.
The comparison to the 15ND940 shows both drivers sharing the same chassis, sensitivity, and power class, but with meaningfully different Qts alignment (0.37 vs 0.28) and inductance (0.43 vs 0.7 mH) — the aluminium coil variant offers more enclosure flexibility and lower inductance, while the copper coil variant offers a higher force factor equivalent positioning within the flagship range.
Conclusion – 18 Sound 15ND840 Woofer
The 18 Sound 15ND840 is 18 Sound’s aluminium-coil counterpart within the 15-inch ND flagship family — sharing the same chassis, cone, and SDR technology as the 15ND940, but with an aluminium rather than copper winding that produces a more flexible 0.37 Qts and an exceptionally low 0.43 mH inductance, the lowest of any conventional 15-inch driver documented across this entire session.
For applications where enclosure flexibility (sealed or vented) and crossover-simplifying low inductance matter more than the marginally higher force factor the copper-coil 15ND930/940 provide, the 18 Sound 15ND840 delivers a genuinely distinctive specification within 18 Sound’s premium 15-inch neodymium range.
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About 18 Sound
18 Sound products are proudly made in Reggio Emilia, Italy, combining advanced technology with Italian craftsmanship. Known for their high-performance professional audio components, 18 Sound is a trusted name in the global audio industry. Their state-of-the-art manufacturing and strict quality control ensure exceptional reliability and sound clarity. 18 Sound products are designed to meet the demands of speaker builders and audio professionals, 18 Sound offers premium products with outstanding value and performance worldwide.
