18 Sound 6M44 – LF Driver

18 Sound 6M44 – High-Power 6.5-Inch Ferrite Midrange with 13.4 Tm Force Factor and SDR Distortion Reduction

The 18 Sound 6M44 is a high-power 6.5-inch ferrite midrange driver that produces the highest force factor of any 6.5-inch driver in 18 Sound’s entire catalogue. At 13.4 Tm — exceeding the neodymium 6ND410’s 11.6 Tm and the dual-gap 6NTLW2000’s 11.6 Tm — the 18 Sound 6M44’s ferrite motor generates more raw electromagnetic force than any neodymium 6.5-inch alternative. Combined with SDR distortion reduction, 200 W AES / 350 W program power handling, 95 dB sensitivity, a 140 Hz – 7000 Hz bandwidth, and suitability for horn and direct-radiating applications in enclosures as compact as 3 litres, the 18 Sound 6M44 delivers ferrite-class power and force factor for builders who need maximum motor authority without the neodymium price premium.

The 13.4 Tm force factor is the specification that defines the 18 Sound 6M44’s motor character. Where the neodymium 6ND410 achieves 11.6 Tm from a compact, lightweight neodymium motor at 1.25 kg, the 18 Sound 6M44 achieves 13.4 Tm from a larger ferrite motor at 3.4 kg. The ferrite motor’s larger magnetic circuit produces 15% more force factor — more electromagnetic grip on the cone, more control over the moving assembly, and more authority in the mid-range band where motor control defines transparency and definition.

The trade-off for that force factor is weight and sensitivity. The 18 Sound 6M44 weighs 3.4 kg — 2.15 kg more than the 6ND410’s 1.25 kg. The 16 g moving mass — double the 6ND410’s 8.2 g — absorbs the motor’s higher force, reducing sensitivity to 95 dB versus the 6ND410’s 102 dB. The ferrite delivers more motor force at higher weight and lower efficiency. The neodymium delivers more sensitivity at lower weight and lower motor force. Different engineering philosophies, different trade-offs, different applications.

18 Sound designed the 18 Sound 6M44 as a high-power, high-output midrange for high-level professional use, with extensive research focused on mid-frequency intelligibility. The driver works in horn-loaded, direct-radiating, sealed, and reflex configurations in enclosures as compact as 3 litres.

Design and Construction of the 18 Sound 6M44

The 18 Sound 6M44 uses a 44 mm (1.75-inch) CCAW aluminium voice coil wound on a fibreglass former. The CCAW winding provides the balance of conductivity and weight that professional midrange applications require. The fibreglass former improves force transmission from the voice coil to the cone — stronger mechanical coupling means less energy is lost in the former and more reaches the cone as acoustic output.

The 13 mm winding depth operating in a 7 mm magnetic gap produces the 2.25 mm Xmax and the 13.4 Tm force factor that define the motor’s character. The 13.4 Tm is the result of the ferrite motor’s larger magnetic circuit — more magnetic material produces more flux density in the gap, generating more force per ampere of coil current. The ferrite motor achieves this at the cost of weight (3.4 kg) but at the benefit of lower material cost and more stable pricing than neodymium.

The SDR (Single Demodulating Ring) reduces inductance and improves transient response and phase control in the mid frequencies. The combination of SDR and CCAW coil produces 0.32 mH Le — lower than the neodymium 6ND410’s 0.67 mH despite the larger ferrite motor. The SDR absorbs the eddy currents that generate inductance variation, keeping the impedance curve flatter through the operating range. For a midrange driver operating to 7000 Hz, the low inductance ensures smooth, predictable response in the upper mid-range and lower treble.

The high-damping pulp cone is one of 18 Sound’s most refined cone designs. The in-house developed cone treatment serves dual purposes: it provides humidity repellency for outdoor durability and it dampens the bell-mode resonance significantly. Bell modes are circumferential vibration patterns in the cone that generate coloration in the mid-range — the frequency band where the human ear is most sensitive. By incorporating bell-mode damping directly into the cone treatment, 18 Sound eliminates these resonances at their source rather than managing them through surround design or crossover filtering alone.

The M-roll surround provides controlled compliance through the 2.25 mm Xmax. The short excursion confirms the 18 Sound 6M44’s midrange-only design intent — every parameter is traded for sensitivity, motor control, and mid-band clarity rather than bass displacement.

The ferrite magnet assembly provides high flux concentration with improved thermal connection and heat dissipation. 18 Sound specifically highlights that the thermal design increases power handling and lowers power compression — the ferrite motor’s larger mass also functions as a thermal reservoir, absorbing heat from the voice coil and dissipating it through the larger surface area that the ferrite structure provides.

The 200 W AES / 350 W continuous program power handling is the highest of any 6.5-inch midrange in 18 Sound’s range — 20 W more AES and 110 W more program than the 6ND410. The larger ferrite motor’s thermal mass and the fibreglass former’s heat resistance sustain this power rating during extended high-power operation.

At 3.4 kg, 162 mm overall diameter, 148 mm baffle cutout, 85 mm depth, and 13 mm flange, the 18 Sound 6M44 is the heaviest and deepest 6.5-inch midrange in the range. The ferrite motor accounts for the additional mass. The 148 mm baffle cutout matches the neodymium 6.5-inch drivers — the 18 Sound 6M44 fits the same baffle opening, just with more depth and weight behind it.

Performance and Applications for the 18 Sound 6M44

The 18 Sound 6M44 delivers 95 dB sensitivity across a 140 Hz – 7000 Hz bandwidth. The 95 dB is 7 dB below the 6ND410’s 102 dB but 2 dB below the 6NMB900’s 97 dB — competitive with the mid-bass drivers despite the 18 Sound 6M44’s midrange-focused alignment. The 16 g Mms is heavier than the neodymium midranges but lighter than typical ferrite 6.5-inch woofers.

The 140 Hz – 7000 Hz bandwidth reaches 60 Hz lower than the 6ND410’s 200 Hz. The lower starting frequency means the 18 Sound 6M44 operates into the upper bass — deep enough to handle the fundamental frequencies of male vocals and the lower mid-range content that the 6ND410 leaves to a woofer section. In a three-way system, the 18 Sound 6M44 can take over from the woofer at 140–200 Hz and hand off to the compression driver at 3–5 kHz.

The 102 Hz Fs and 329 Hz EBP define a motor-dominant alignment suited for horn-loaded and vented applications. The 329 Hz EBP is lower than the 6ND410’s 444 Hz but still firmly in horn-loaded territory — the motor has strong control over the 16 g cone through the 2.25 mm excursion range.

18 Sound recommends a 3-litre enclosure — the most compact of any 6.5-inch midrange option. The 0.29 Qts ensures tight, controlled response in this compact volume. Sealed enclosures at 3 litres produce clean midrange with natural rolloff below the operating band. Reflex designs can extend slightly deeper. Horn-loaded configurations exploit the low Qts and high Bl for maximum output with directivity control.

The 13.4 Tm force factor advantage over the neodymium alternatives is most significant in horn-loaded applications. A higher Bl means more control over the cone at any given excursion — tighter transients, faster acceleration, more defined articulation. On a midrange horn, the 18 Sound 6M44’s 13.4 Tm delivers the most authoritative mid-frequency output of any 6.5-inch driver in the range.

The 0.32 mH Le is lower than the 6ND410’s 0.67 mH — a counterintuitive advantage for the ferrite driver. The SDR’s inductance reduction combined with the CCAW coil’s electrical characteristics produces a flatter impedance curve through the upper operating range. Passive crossover designs benefit from the lower inductance — less impedance compensation is needed. Active systems see a more predictable load.

The comparison to the 6ND410 defines the ferrite vs neodymium midrange decision. The 6ND410 delivers 102 dB sensitivity, 60 mm depth, and 1.25 kg weight — the lightweight, high-sensitivity, shallowest option. The 18 Sound 6M44 delivers 13.4 Tm force factor, 200 W AES / 350 W program power, 140 Hz lower frequency reach, 0.32 mH inductance, and lower cost from the ferrite motor — the highest-force, highest-power, deepest-reaching option at 3.4 kg.

For weight-critical applications — line arrays, portable PA, touring systems where per-driver weight compounds across the rig — the neodymium 6ND410 is the right choice. For installed sound, horn-loaded midrange sections, and applications where motor force, power handling, and cost matter more than minimum weight, the 18 Sound 6M44 delivers the most motor authority available in a 6.5-inch midrange at a fraction of the neodymium price.

Conclusion – 18 Sound 6M44 Midrange Driver

The 18 Sound 6M44 is the highest-force 6.5-inch driver in 18 Sound’s entire range. The 13.4 Tm force factor exceeds every neodymium 6.5-inch alternative by at least 1.8 Tm — the ferrite motor’s larger magnetic circuit generates more electromagnetic force than neodymium achieves in this format. The SDR produces 0.32 mH inductance — lower than the neodymium 6ND410’s 0.67 mH. The 200 W AES / 350 W program power handling is the highest of any 6.5-inch midrange.

The 3.4 kg weight and 85 mm depth are the trade-offs. Ferrite is heavier and deeper than neodymium. For applications where those trade-offs are acceptable — installed sound, horn-loaded midrange, studio monitoring, fixed cabinet designs — the 18 Sound 6M44 delivers more motor force, more power handling, lower inductance, and lower cost than its neodymium counterparts.

For horn-loaded midrange sections, direct-radiating midrange applications, and any system where a 6.5-inch midrange needs the most force factor and highest power handling available in the format from a proven ferrite platform, the 18 Sound 6M44 is the ferrite midrange that outmuscles neodymium on motor force and outdoes it on inductance. Thirteen point four Tesla-metres, 200 watts, 0.32 millihenries — the highest-force 6.5-inch in the catalogue.