18 Sound 15MB650 – High-Output Ferrite 15-Inch Mid-Bass with 101.5 dB Sensitivity and 4800 Hz Bandwidth
The 18 Sound 15MB650 high-output mid-bass has been designed for use as a bass and low-midrange driver in tuned reflex enclosures, in two- or three-way systems. When used in a two-way system, 18 Sound recommends a 1-inch or 2-inch exit compression driver to obtain the best sound quality and directional control. The 18 Sound 15MB650 combines a high sensitivity value (101 dB 1W/1m) with high power handling capabilities.
The 75 mm copper voice coil utilises the same technology fitted to 18 Sound’s top-of-the-range 4-inch voice coil models — the same lineage claim documented on the 15MB700’s aluminium-wound successor, here with copper winding instead. It employs the Interleaved Sandwich Voice Coil (ISV), in which a high-strength fibreglass former carries windings on the outer and inner surfaces to achieve a mass-balanced coil. This results in an extremely linear motor assembly with a reduced tendency for eccentric behaviour when driven hard.
The curvilinear paper cone, in conjunction with the viscose dampened double half-roll suspension, provides excellent transient response and cone damping — a slightly different suspension geometry (double half-roll) than the 15MB700’s multiroll design.
At 8.3 kg — identical weight to the 15MB700 — the 18 Sound 15MB650 delivers 101.5 dB sensitivity, only 1.5 dB below its successor, while offering a genuinely wider 4800 Hz upper bandwidth. 18 Sound now lists the 15MB700 as the alternative/current model.
Design and Construction of the 18 Sound 15MB650
The 75 mm copper voice coil employs the Interleaved Sandwich Voice Coil (ISV), in which a high-strength fibreglass former carries windings on the outer and inner surfaces to achieve a mass-balanced coil. This results in an extremely linear motor assembly with a reduced tendency for eccentric behaviour when driven hard. The low inductance coil gives improvements in transient response.
Excellent heat dissipation has been achieved by incorporating air channels in the basket design, between the basket and top plate. Maximum flux concentration and force factor in the gap are assured by the unique shape and design of the face and back plates, which have been created using 18 Sound’s in-house Magnetic Flux FEA CAD resource.
The 20.0 Tm force factor driving 77 g of moving mass produces 101.5 dB sensitivity and the 0.26 Qts / 148 Hz EBP alignment — the copper winding here produces a higher force factor (20.0 vs 17.6 Tm) than the aluminium-wound 15MB700, at the cost of slightly more moving mass (77 vs 73 g) and correspondingly marginally lower sensitivity.
The special treatment applied to the top and the back plate is far more resistant to the corrosive effects of salts and oxidisation than any other treatment in use — the same strong comparative claim documented on several other premium 18 Sound drivers throughout this session.
At 8.3 kg, 387 mm overall diameter, 353 mm baffle cutout, 167 mm depth, and 19 mm flange — every physical dimension matches the 15MB700 exactly, confirming these two drivers share the same fundamental chassis platform.
Performance and Applications for the 18 Sound 15MB650
The 18 Sound 15MB650 delivers 101.5 dB sensitivity across a 50 Hz – 4800 Hz bandwidth — 500 Hz wider at the top than the 15MB700’s 4300 Hz, giving this predecessor a genuine bandwidth advantage that its successor traded away for the additional 1.5 dB of sensitivity.
The 400 W AES / 600 W continuous program power handling matches the 15MB700 exactly. The 4.0 mm Xmax is notably shorter than the 15MB700’s 5.5 mm — the copper coil’s additional mass reduces the driver’s excursion capability slightly relative to its successor.
For two-way systems, 18 Sound specifically recommends a 1-inch or 2-inch exit compression driver to obtain the best sound quality and directional control — a wider compression driver compatibility range than some other mid-bass drivers documented in this session, reflecting the wide 4800 Hz bandwidth’s compatibility with lower-crossover compression drivers.
The comparison to the 15MB700 gives builders a straightforward choice: the successor delivers 1.5 dB more sensitivity (103 vs 101.5 dB) and more Xmax (5.5 vs 4.0 mm) from a lighter aluminium coil, while the 18 Sound 15MB650 delivers a wider 500 Hz of additional upper bandwidth and a slightly higher force factor from copper winding, at identical weight.
Conclusion – 18 Sound 15MB650 Mid-Bass Driver
The 18 Sound 15MB650 is the predecessor to the 15MB700, sharing the same fundamental 75 mm ISV coil technology and ferrite motor platform, but with copper rather than aluminium winding — trading 1.5 dB of sensitivity for a genuinely wider 4800 Hz bandwidth and marginally higher force factor.
For two- or three-way systems where the wider upper bandwidth matters, or where replacement compatibility with existing 15MB650 installations is required, this driver remains a highly capable, high-sensitivity ferrite mid-bass specification within 18 Sound’s 15-inch 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.
