18 Sound 6ND410 – LF Driver

18 Sound 6ND410 – Dedicated 6.5-Inch Neodymium Midrange with 102 dB Sensitivity and 60 mm Depth

The 18 Sound 6ND410 is the highest-output 6.5-inch driver 18 Sound has ever made. At 102 dB sensitivity — 2 dB above the 6NMB420’s 100 dB — with a 44 mm edgewound ISV coil, 11.6 Tm force factor, 8.2 g moving mass, a Qts of 0.24, an EBP of 444 Hz, and a depth of just 60 mm, the 18 Sound 6ND410 is a dedicated midrange transducer designed for the highest-quality horn-loaded and direct-radiating midrange applications in professional audio.

The 102 dB from a 6.5-inch driver puts the 18 Sound 6ND410 in the sensitivity class of dedicated 10-inch midrange drivers. It exceeds the 10M600’s 102 dB while occupying a fraction of the baffle area. It exceeds the 8M400F’s 100.5 dB from a smaller format. No 6.5-inch driver in 18 Sound’s range approaches the 18 Sound 6ND410’s sensitivity — the closest is the 6NMB420 at 100 dB, and the 18 Sound 6ND410 surpasses it by 2 dB while reaching 1000 Hz higher in bandwidth (8000 vs 7000 Hz).

The 60 mm depth is the shallowest of any 6.5-inch neodymium driver in 18 Sound’s range — 13 mm shallower than every other 6.5-inch model (73 mm on the NMB, NTLW, and ND430 series). For horn-loaded midrange applications where the driver mounts in a compact chamber behind the horn, 60 mm of depth means the chamber can be shallower and the cabinet can be more compact. For line array elements where driver depth directly determines element thickness, 60 mm is a transformative advantage.

18 Sound describes the 18 Sound 6ND410 as a state-of-the-art midrange product for high-quality professional use, with extensive research focused on implementing mid-frequency intelligibility. The driver works in horn-loaded, direct-radiating, sealed, and reflex configurations — enclosures as small as 2 litres. 18 Sound now lists the 6NMB900 as the current alternative model.

Design and Construction of the 18 Sound 6ND410

The 18 Sound 6ND410 uses a 44 mm (1.75-inch) edgewound aluminium ISV (Interleaved Sandwich Voice Coil). The ISV architecture places conductor on both inner and outer surfaces of the former for mass-balanced, linear motor behaviour. The edgewound construction packs more conductor into the gap per unit of coil height, maximising force output. The combination of ISV and edgewinding produces the 11.6 Tm force factor from the compact 44 mm format — the highest Bl of any 6.5-inch driver in 18 Sound’s range, matching the 6NTLW2000’s dual-gap motor from a single-gap ISV architecture.

The 11.6 Tm driving 8.2 g of moving mass produces a Bl/Mms ratio of 1.41 Tm/g — the highest of any driver we’ve covered from 18 Sound. The motor has absolute authority over the featherweight cone assembly. The 0.24 Qts and 444 Hz EBP — both 6.5-inch records — are the numerical confirmation of that dominance. At 444 Hz EBP, the 18 Sound 6ND410 is designed exclusively for horn-loaded and vented applications where extreme motor control produces the most defined, fastest, most transparent midrange output.

The curvilinear cone-surround assembly was created using computer-aided vibrational modelling software. This is a specific engineering process where the cone and surround shapes are analysed in simulation to identify and eliminate the bell-mode resonances — the circumferential vibration patterns that generate coloration in the mid-range. 18 Sound’s modelling moved all undesired bell modes out of the usable frequency range (200–8000 Hz), which means the cone operates in pure pistonic mode across the entire operating bandwidth without breakup-induced coloration.

The progressive double roll surround provides controlled compliance through the 2 mm Xmax. The progressive geometry gets stiffer as excursion increases, preventing the abrupt mechanical limiting that standard surrounds can produce at their travel limits. The 2 mm Xmax is the shortest of any 6.5-inch driver in the range — deliberately so. Every parameter trades displacement for sensitivity and midrange transparency. The 18 Sound 6ND410 does not produce bass. It produces the loudest, cleanest, most defined midrange output possible from a 6.5-inch cone.

The external neodymium magnet assembly is encapsulated within the basket for maximum heat transfer from the back plate to the dissipating structure. Three threaded holes in the back plate provide mounting points for an external heatsink — a hardware feature unique to the 18 Sound 6ND410 in the 6.5-inch range. For horn-loaded applications where the driver operates in a sealed chamber at sustained high power, a custom heatsink bolted to the back plate extends the thermal headroom beyond what the standard basket dissipation provides.

The humidity-block cone treatment and corrosion-resistant plate coatings provide outdoor durability against moisture, salt, and oxidation.

The 0.67 mH Le is higher than the NMB’s 0.1 mH and the 6NTLW2000’s 0.22 mH — the single-gap ISV motor produces more inductance than the SDR-equipped and dual-gap alternatives. The ISV coil’s symmetrical winding linearises the inductance across excursion, but the absolute value means passive crossover designs need to account for the inductive rise above 3–4 kHz.

At 1.25 kg, 162 mm overall diameter, 148 mm baffle cutout, and 60 mm depth, the 18 Sound 6ND410 is the shallowest 6.5-inch neodymium in the range. The 9 mm flange thickness and 148 mm cutout match the other 6.5-inch neodymium drivers — the 18 Sound 6ND410 fits the same baffle opening at 13 mm less depth.

Performance and Applications for the 18 Sound 6ND410

The 18 Sound 6ND410 delivers 102 dB sensitivity across a 200 Hz – 8000 Hz bandwidth. The 102 dB is the highest sensitivity of any 6.5-inch driver in 18 Sound’s range — 2 dB above the 6NMB420, 5 dB above the 6NMB900, 9 dB above the 6NTLW2000, and 9.5 dB above the 6ND430. The 8000 Hz upper bandwidth matches the 6NTLW2000 and the 5W430 while delivering 9–13 dB more sensitivity.

In horn-loaded configurations, the 18 Sound 6ND410’s 102 dB sensitivity and 0.24 Qts produce midrange SPL levels that compete with dedicated 8 and 10-inch midrange drivers on larger horns. The horn adds acoustic loading and directivity control, and the 102 dB baseline sensitivity ensures the output within the horn’s coverage pattern is exceptionally high. For compact line array elements where the midrange horn uses a 6.5-inch driver, the 18 Sound 6ND410 delivers more mid-frequency output per element than any alternative in the format.

The 120 Hz Fs and 444 Hz EBP define the most extreme midrange-only alignment in the 6.5-inch range. The driver’s energy is concentrated above 120 Hz — there is essentially no output below the resonance frequency. In a three-way system, the 18 Sound 6ND410 takes over from the woofer at 200–400 Hz and hands off to the compression driver at 3–5 kHz, covering the vocal fundamentals, presence band, and lower brilliance range with 102 dB of sensitivity and the fastest transient response any 6.5-inch 18 Sound driver can produce.

The minimum impedance of 8.2 Ω — above the 8 Ω nominal — confirms the midrange-optimised motor alignment. The impedance curve doesn’t dip below nominal, which means the amplifier sees a benign load at all frequencies. No impedance minimum valley means no unexpected current demand from the amplifier in the operating band.

The four enclosure options provide maximum application flexibility. Horn-loaded produces the highest output with the most directivity control. Direct-radiating produces wide, natural coverage without horn coloration. Sealed enclosures from 2 litres produce tight, controlled response with natural rolloff below the operating band. Reflex enclosures extend the usable range slightly deeper with more output near the resonance frequency.

The 3 threaded back plate holes for external heatsinks are the thermal management feature that horn-loaded applications need. When the driver operates in a sealed chamber behind a horn — surrounded by trapped air with limited ventilation — the voice coil temperature rises faster than in an open-back configuration. An external heatsink bolted to the back plate draws heat from the motor through the plate and dissipates it outside the chamber, maintaining the 180 W AES power rating during sustained high-power operation.

The comparison across the full 6.5-inch neodymium range places the 18 Sound 6ND410 as the dedicated midrange at the top of the sensitivity hierarchy. The 6NMB420 (100 dB) is the high-sensitivity mid-bass. The 6NMB900 (97 dB) is the evolved mid-bass with deeper reach. The 6NTLW2000 (93 dB) is the dual-gap high-power woofer. The 6ND430 (92.5 dB) is the bass-extension woofer. The 18 Sound 6ND410 (102 dB) is the dedicated midrange — the loudest, shallowest, most motor-dominant driver in the 6.5-inch lineup.

Conclusion – 18 Sound 6ND410 Midrange Driver

The 18 Sound 6ND410 is the most extreme 6.5-inch driver in 18 Sound’s range by every motor metric. The 102 dB sensitivity is the highest. The 11.6 Tm Bl is the highest. The 0.24 Qts is the lowest. The 444 Hz EBP is the highest. The 1.41 Tm/g Bl/Mms ratio is the highest. The 60 mm depth is the shallowest. Every specification points in the same direction: maximum midrange output with maximum motor control from the minimum possible format.

The ISV edgewound coil, computer-modelled cone-surround for bell-mode elimination, progressive double roll surround, encapsulated neodymium motor with external heatsink provision, and 2 mm Xmax define a driver that has traded every gram of displacement for sensitivity and transparency. The 18 Sound 6ND410 doesn’t produce bass. It produces the loudest, cleanest, most defined midrange output available from a 6.5-inch professional transducer.

For horn-loaded midrange sections, line array mid-frequency elements, direct-radiating midrange applications, and any system where a 6.5-inch driver needs to deliver 102 dB sensitivity with the shallowest depth and most extreme motor dominance available in the format, the 18 Sound 6ND410 is the 6.5-inch midrange that set the standard. One hundred and two decibels, 60 millimetres deep, 1.25 kilograms — the loudest 6.5-inch 18 Sound has ever made.