18 Sound 8MB720 – LF Driver

18 Sound 8MB720 – Ultra-High-Sensitivity 8-Inch Ferrite Mid-Bass with 99.5 dB Output and 0.11 mH Inductance

The 18 Sound 8MB720 is the highest-sensitivity 8-inch mid-bass driver 18 Sound has ever made. At 99.5 dB — 3 dB above the neodymium DDR-equipped 8NMB750 and 4.5 dB above the Tetracoil 8NTLW2000 — the 18 Sound 8MB720 produces more mid-band output per watt from a ferrite motor than any neodymium 8-inch woofer in 18 Sound’s range can deliver. The driver achieves this with a 51 mm ISV voice coil, a 13.4 Tm force factor from the ferrite magnetic circuit, an 18 g moving mass, and an inductance of 0.11 mH that is the second-lowest of any LF driver in 18 Sound’s entire catalogue — just 0.01 mH above the 6NMB420/6NMB900’s record.

The 99.5 dB from a ferrite 8-inch is the specification that defies expectations. Ferrite motors are typically associated with lower sensitivity compared to neodymium at equivalent weight — the trade-off for lower material cost. The 18 Sound 8MB720 reverses that assumption entirely. The 13.4 Tm force factor driving 18 g of moving mass produces a Bl/Mms ratio of 0.744 Tm/g — higher than the 8NMB750’s 0.534 Tm/g, higher than the 8NTLW2000’s 0.625 Tm/g, higher than every neodymium 8-inch woofer in the range. The ferrite motor generates more force per gram of cone mass than any neodymium alternative.

The 0.11 mH inductance is equally extraordinary. No SDR, no copper ring, no dual-gap motor — the 18 Sound 8MB720 achieves near-record inductance purely through the ISV coil’s symmetrical winding and the ferrite motor’s magnetic circuit geometry. The impedance curve is virtually flat from DC through the 3500 Hz operating range. Crossover networks see a near-resistive load that requires minimal compensation.

18 Sound designed the 18 Sound 8MB720 for high-performance compact three-way systems. The driver is currently limited distribution U.S. only through Universal Music, 18 Sound’s U.S. official distributor. 18 Sound lists the 8NMB750 as the alternative/current model.

Design and Construction of the 18 Sound 8MB720

The 18 Sound 8MB720 uses a 51 mm (2-inch) ISV (Interleaved Sandwich Voice Coil). The ISV architecture places conductor on both inner and outer surfaces of the former, creating the mass-balanced coil that produces linear motor behaviour and the symmetrical inductance characteristics that achieve 0.11 mH without requiring SDR or copper ring supplementation.

The 0.11 mH Le from an ISV coil without any demodulating ring is the most impressive inductance figure of any ISV-only 8-inch driver. The 8NMB420’s ISV + SDR combination produces 0.35 mH. The 8NMB750’s ISV + DDR dual rings produce 0.29 mH. The 18 Sound 8MB720’s ISV alone produces 0.11 mH — nearly three times lower than the SDR-equipped design and over 2.5 times lower than the DDR-equipped design. The ferrite motor’s magnetic circuit geometry, combined with the ISV coil’s precise winding, creates the inductance-minimising conditions that produce this figure.

The 13.4 Tm force factor from the ferrite motor is exceptional. It matches the 6M44 6.5-inch midrange — the highest Bl of any 18 Sound 6.5-inch driver — from an 8-inch platform. The ferrite circuit produces this force through a larger magnetic structure than neodymium requires, which accounts for the 4.6 kg total weight. The larger ferrite motor concentrates more flux in the gap through sheer magnetic mass.

The 18 g moving mass matches the 8NMB420 exactly — the lightest Mms of any 18 Sound 8-inch mid-bass. The curvilinear cone and the ISV coil together weigh no more than the 8NMB420’s assembly despite the different motor architecture. The Bl/Mms ratio of 0.744 Tm/g is the highest of any 18 Sound 8-inch woofer or mid-bass — the motor has more control per gram of cone mass than any alternative.

The triple roll surround provides controlled compliance through the 2.25 mm Xmax with 3.0 mm Xvar. The short excursion is by design — the 18 Sound 8MB720 operates in the 150–3500 Hz mid-bass and mid-range band where minimal displacement generates high SPL. Every parameter trades excursion for sensitivity, motor control, and the flattest possible impedance curve.

The weather-protected cone treatment and coated plates provide outdoor durability against aggressive environmental conditions.

The 108 Hz Fs and 308 Hz EBP define a mid-bass/midrange alignment — the driver’s energy is concentrated above 108 Hz. In a three-way system, the 18 Sound 8MB720 takes over from the woofer at 150 Hz and hands off to the compression driver at 2–3 kHz, covering the vocal fundamentals and presence band with 99.5 dB of sensitivity.

At 4.6 kg, 225 mm overall diameter, 186 mm baffle cutout, 105 mm depth, and 11 mm flange, the 18 Sound 8MB720 shares the wider 225 mm chassis with the 8NMB750 — the larger ferrite motor and the neodymium DDR motor both require the wider overall diameter. The 186 mm baffle cutout remains standard 18 Sound 8-inch.

Performance and Applications for the 18 Sound 8MB720

The 18 Sound 8MB720 delivers 99.5 dB sensitivity across a 150 Hz – 3500 Hz bandwidth. The 99.5 dB is the highest of any 18 Sound 8-inch mid-bass or woofer — surpassing the neodymium 8NTLW2000 (97.5 dB), the neodymium DDR 8NMB750 (96.5 dB), the neodymium 8NW650 (96 dB), and the neodymium ISV/SDR 8NMB420 (95 dB). A ferrite driver at the top of the sensitivity table above every neodymium alternative.

The 3.1% reference efficiency confirms the 18 Sound 8MB720 converts electrical power to acoustic output more efficiently than any other 18 Sound 8-inch mid-bass. At 99.5 dB, the driver produces roughly twice the acoustic power per watt of the 8NMB420’s 95 dB — needing half the amplifier power to reach the same SPL.

The 150 Hz – 3500 Hz bandwidth is narrower than the 8NMB420’s 5500 Hz and the 8NW650’s 6300 Hz. The 18 Sound 8MB720 is designed for three-way systems where the 8-inch handles a defined mid-bass band — not for two-way systems where the woofer needs to extend as high as possible before handing off. In a three-way architecture, the 3500 Hz upper limit provides adequate overlap with a compression driver crossed over at 2–2.5 kHz.

The 0.11 mH inductance is the specification that crossover designers will appreciate most. The impedance curve is virtually flat from DC through the 3500 Hz operating range — behaving like a pure resistor rather than an inductor. Passive crossover networks need no impedance compensation. Active systems see a load that matches theoretical models with minimal deviation. DSP filters operate at maximum accuracy because the driver’s electrical behaviour is as close to ideal as any 8-inch LF driver achieves.

18 Sound recommends a 10-litre (0.35 ft³) vented enclosure tuned to 120 Hz. The high tuning frequency targets punchy, fast mid-bass in the 120–300 Hz range — the output zone where the 18 Sound 8MB720’s 99.5 dB sensitivity produces the most dramatic advantage over lower-sensitivity alternatives.

The 2.25 mm Xmax limits the driver to mid-bass and mid-range duties. Below 150 Hz, the short excursion runs out of displacement before it runs out of power. A dedicated woofer or sub section handles everything below the 150 Hz high-pass — the 18 Sound 8MB720 handles everything above it with 99.5 dB of output per watt.

The 4.6 kg weight is the ferrite trade-off. The neodymium 8NTLW2000 delivers 97.5 dB at 1.5 kg. The neodymium 8NMB420 delivers 95 dB at 1.7 kg. The 18 Sound 8MB720 delivers 99.5 dB at 4.6 kg — the highest sensitivity at the highest weight. For portable and weight-critical systems, the neodymium options are lighter. For installed sound, horn-loaded applications, and systems where per-unit cost matters more than per-unit weight, the 18 Sound 8MB720 delivers the most mid-band output per watt from a proven ferrite platform.

The limited U.S. distribution through Universal Music positions the 18 Sound 8MB720 as a specialised product — likely developed for specific OEM applications where the combination of ferrite cost, 99.5 dB sensitivity, and 0.11 mH inductance provides a performance profile that no other driver in the catalogue matches.

Conclusion – 18 Sound 8MB720 Mid-Bass Driver

The 18 Sound 8MB720 is the highest-sensitivity 8-inch mid-bass driver 18 Sound has ever made — and it achieves that distinction with a ferrite motor. The 99.5 dB sensitivity exceeds every neodymium 8-inch woofer in the range. The 0.11 mH inductance is the second-lowest of any 18 Sound LF driver. The 13.4 Tm force factor from ferrite matches the best 6.5-inch midrange motors. And the 18 g moving mass matches the lightest 8-inch mid-bass in the catalogue.

The 18 Sound 8MB720 proves that sensitivity records don’t require neodymium. The right combination of ferrite motor geometry, ISV coil winding, moving mass, and cone design produces 99.5 dB and 0.11 mH without SDR, without copper ring, without dual-gap technology. The ISV coil alone, in the right motor, produces near-record inductance and the highest 8-inch mid-bass sensitivity from any magnet material.

For three-way systems, horn-loaded mid-bass applications, and any architecture where an 8-inch mid-bass needs to deliver 99.5 dB sensitivity with the flattest possible impedance from a cost-effective ferrite platform, the 18 Sound 8MB720 is the ferrite 8-inch that outperforms neodymium on output per watt. Ninety-nine point five dB, 0.11 millihenries, ferrite — the highest-sensitivity 8-inch mid-bass in 18 Sound’s history.