18 Sound 8CX650 – Atmos-Ready 8-Inch Ferrite Coaxial with PEN HF Diaphragm and Ultra-Shallow 132 mm Depth
The 18 Sound 8CX650 is the 8-inch expression of 18 Sound’s CX650 Atmos-ready coaxial platform — sharing the same 44 mm EWAL PEN HF compression driver, the same 3P tangerine phase plug, the same copper HF sleeve, and the same Dolby Atmos-ready design as the 10CX650, scaled to an 8-inch format that is shallower, lighter, and more compact than any other coaxial in 18 Sound’s catalogue with this HF technology.
At 132 mm depth, the 18 Sound 8CX650 is the shallowest coaxial 18 Sound makes — 18 mm shallower than the 8CX401F (150 mm), 16 mm shallower than the 10NCX750 (148 mm), and 23 mm shallower than the 10CX650 (155 mm). For ceiling-mounted Atmos channels, shallow-cavity wall installations, and under-balcony fills where the available mounting depth is the defining constraint, the 18 Sound 8CX650 fits behind surfaces that no other 18 Sound coaxial can reach.
The PEN (Polyethylene Naphthalate) HF diaphragm provides the same smooth, natural, fatigue-free treble as the 10CX650 — a high-performance polymer with superior dimensional stability, very high elasticity modulus, and no metallic resonances. Where the smaller 8CX401F uses a polyester diaphragm with a 25 mm HF section crossed over at 3 kHz, the 18 Sound 8CX650 uses the 44 mm PEN section from the 10CX650 crossed over at 1.6 kHz — a significantly more capable HF platform with more output, more power handling, and lower crossover capability.
The 65 mm edgewound CCAW ISV LF coil provides the same ISV linear motor technology in the LF section, with a 12 Tm force factor driving 25.6 g of moving mass through 6 mm of linear excursion. The 90° nominal coverage pattern and Atmos-ready designation confirm the 18 Sound 8CX650 is designed for immersive audio installations and wide-coverage applications where the speaker covers the broadest possible area from each mounting position.
At 5.6 kg with a 210 mm overall diameter, 185 mm baffle cutout, and 30-litre minimum enclosure, the 18 Sound 8CX650 brings PEN HF quality and Atmos-ready design to the 8-inch coaxial format.
Design and Construction of the 18 Sound 8CX650
The 18 Sound 8CX650 integrates a two-way coaxial transducer system into a single 8-inch chassis powered by a ceramic (ferrite) single magnet motor.
The LF section uses a 65 mm (2.5-inch) edgewound CCAW ISV (Interleaved Sandwich Voice Coil) wound on a high-strength fibreglass former. The 65 mm coil is the same diameter as the 10CX650’s LF section — 18 Sound uses the same coil platform for both 8 and 10-inch CX650 models. The ISV places conductor on both surfaces of the former for mass-balanced, linear motor behaviour. The edgewound CCAW construction maximises conductor packing for efficient force output.
The 12 Tm force factor driving 25.6 g of moving mass produces 91 dB LF sensitivity and 1.2% reference efficiency. The 91 dB is the lowest LF sensitivity of any 18 Sound coaxial — a consequence of the 8-inch format’s smaller cone area (227 cm²) and the specific motor sizing for this driver class. For the compact ceiling, wall-mount, and distributed sound applications the 18 Sound 8CX650 targets, absolute LF output is secondary to smooth response, wide coverage, and compact form factor.
The low-profile smooth straight cone provides clean response within the LF operating range and maximum reliability under high mechanical stress. The straight cone profile differs from the curvilinear cones used on the 8CX401F and the larger coaxials — 18 Sound selected the straight profile for its smoother response characteristics and its coupling behaviour with the larger 44 mm HF exit at the cone’s centre.
The 90 Hz – 4700 Hz LF bandwidth confirms the LF section operates from the upper bass through the upper mid-range. The 90 Hz lower frequency limit is higher than the 8CX401F’s 65 Hz — the straight cone and different motor alignment produce less deep bass extension. For Atmos ceiling channels and distributed sound where deep bass content is handled by dedicated subwoofers, the 90 Hz lower limit is entirely appropriate.
The 0.35 Qts and 175 Hz EBP define a versatile alignment suited for both sealed and vented enclosures. The EBP sits on the sealed/vented boundary — builders can choose either topology. 18 Sound recommends enclosures as compact as 30 litres.
The HF section uses the identical 44 mm (1.75-inch) EWAL (Edge-Wound Aluminium) voice coil and PEN (Polyethylene Naphthalate) diaphragm platform found on the 10CX650. The PEN dome provides superior dimensional stability throughout its working life, a very high elasticity modulus for superior transient and intermodulation distortion response, and the flat suspension shape that maintains low stiffness and low mid-band distortion.
The edge-wound aluminium coil is wound on proprietary treated Nomex — the same former material that provides 30% higher tensile elongation at working temperature compared to Kapton, enabling proper energy transfer control in real operating conditions. The Nomex is also suitable for damp and wet environments, adding outdoor durability.
A copper sleeve on the HF pole piece reduces inductance above 10 kHz for improved phase and impedance linearisation. The proprietary 3P hybrid radial tangerine phase plug produces smooth, coherent wavefronts with low distortion and high manufacturing consistency. A specific HF throat design maximises the cone’s profile coupling for the 8-inch format.
The 106 dB HF sensitivity and 70 W AES / 140 W program power handling match the 10CX650’s HF section almost exactly (10CX650 is 106.5 dB). The 1.6 kHz recommended crossover is the same. The 18 Sound 8CX650 carries the full 10CX650 HF capability in the 8-inch format — the HF section is essentially unchanged between the two drivers.
At 5.6 kg, 210 mm overall diameter, 185 mm baffle cutout, and 132 mm depth, the 18 Sound 8CX650 is the shallowest PEN-equipped coaxial in 18 Sound’s range. The 8 mm flange thickness is the thinnest of any 18 Sound coaxial — contributing to the minimal mounting depth.
Performance and Applications for the 18 Sound 8CX650
The 18 Sound 8CX650 delivers 91 dB LF sensitivity from 90 Hz to 4700 Hz and 106 dB HF sensitivity from the 1.6 kHz crossover point upward. The 15 dB sensitivity difference between sections is managed through the crossover network, with the HF section padded to match the LF output level.
The 90° nominal coverage provides wide, symmetrical dispersion from a single driver — the same coverage pattern philosophy as the 10CX650. Both LF and HF sections share the same acoustic axis for point-source coherence. The wide coverage ensures uniform tonal balance across the listening area, which is critical for Atmos ceiling channels where the speaker covers a broad floor area from above.
The Atmos-ready designation confirms the 18 Sound 8CX650 is designed and validated for Dolby Atmos immersive audio installations. Ceiling-mounted overhead channels require wide, uniform coverage from compact, shallow-depth speakers. The 18 Sound 8CX650’s 132 mm depth and 90° coverage meet both requirements from the smallest PEN-equipped format 18 Sound offers.
The 132 mm depth is the 18 Sound 8CX650’s most compelling physical specification for installation applications. Standard ceiling cavities range from 100 mm to 300 mm. At 132 mm, the 18 Sound 8CX650 fits behind ceiling panels where deeper coaxials require modifications or cannot mount at all. For retrofit Atmos installations in existing venues with limited ceiling depth, the 18 Sound 8CX650’s shallow profile is often the difference between possible and impossible.
The PEN HF diaphragm’s smooth, natural treble is particularly valuable in Atmos and distributed sound applications where the speakers operate for extended periods at moderate power. Metallic diaphragm resonances become fatiguing during all-day operation — cinema screenings, retail background music, conference centres. PEN eliminates this entirely, delivering smooth treble that stays comfortable from the first minute to the last hour.
The comparison between the 18 Sound 8CX650 and the 8CX401F defines two fundamentally different 8-inch coaxial philosophies. The 8CX401F delivers higher LF sensitivity (95 vs 91 dB), more LF power (280 vs 200 W AES), deeper bass extension (65 vs 90 Hz), wider LF bandwidth (6100 vs 4700 Hz), and the same 90° dispersion from a 51 mm ISV aluminium coil with a 25 mm polyester HF section. The 18 Sound 8CX650 delivers a larger HF section (44 vs 25 mm), PEN HF diaphragm (vs polyester), lower crossover capability (1.6 vs 3.0 kHz), more HF power (70 vs 25 W AES), higher HF sensitivity (106 vs 105 dB), copper HF sleeve, 3P tangerine phase plug, Atmos-ready design, and shallower depth (132 vs 150 mm).
The 8CX401F is the higher-output LF option for compact PA and multi-way systems. The 18 Sound 8CX650 is the higher-capability HF option for Atmos, installed sound, and applications where the PEN HF section’s smooth treble and 1.6 kHz crossover define the system quality.
The comparison to the 10CX650 is equally relevant. The 10CX650 shares the identical HF section and produces more LF output (94 vs 91 dB, larger Sd). The 18 Sound 8CX650 is lighter (5.6 vs 6.2 kg), shallower (132 vs 155 mm), and smaller (185 vs 230 mm cutout). For installations where the 10-inch format is too large or too deep, the 18 Sound 8CX650 delivers the same PEN HF quality from a more compact package.
Conclusion – 18 Sound 8CX650 Coaxial Driver
The 18 Sound 8CX650 is the most compact Atmos-ready coaxial in 18 Sound’s catalogue. The 132 mm depth is the shallowest of any 18 Sound coaxial. The 44 mm PEN HF section with 3P tangerine phase plug and copper sleeve delivers the same smooth, fatigue-free treble as the larger 10CX650. The 90° nominal coverage provides the wide, symmetrical dispersion that ceiling-mounted and distributed installations demand.
The 91 dB LF sensitivity is the honest trade-off for the 8-inch format — less cone area means less LF output per watt. For Atmos ceiling channels, distributed sound, and compact installed speakers where a dedicated sub handles deep bass and the coaxial handles mid-range through treble, the 91 dB is appropriate. The PEN HF quality, not the LF output, is what defines the 18 Sound 8CX650’s value.
For Atmos ceiling speakers, shallow-cavity wall installations, distributed sound systems, compact monitoring, and any application where the shallowest possible coaxial with PEN HF quality and Atmos-ready design must fit an 8-inch cutout, the 18 Sound 8CX650 is the coaxial that fits where nothing else with this HF capability can. One hundred and thirty-two millimetres deep, PEN polymer smoothness, 90° coverage, Atmos ready — the shallowest PEN coaxial in the catalogue.
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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.
