Martin Audio SX218+
Direct Radiating
2 x 18" Passive Subwoofer
The SX218+ delivers very high output levels and superb transient performance with minimal distortion, making it ideal for the most demanding applications. With an operating range of 38 Hz–100 Hz ± 3 dB, it houses dual 18 in (460 mm) long‑excursion drivers with 4 in (100 mm) voice coils, water‑resistant cones and triple‑roll surrounds. Each driver is rated to handle 1500 watts AES and has a magnet structure and suspension engineered for maximum linear excursion.
Description
The enclosure is constructed from multi‑laminate birch ply and finished with a durable polyurethane coating. Eight reflex ports provide a large frontal area to reduce turbulent air noise, and a perforated steel grille protects the drivers from damage. The internal port geometry promotes laminar airflow.
The SX218+ features an M20 pole‑mount insert for mounting point‑source speakers. Cabinet wheels and a transit cover are available as accessories.
Compared with the SX218, the SX218+ [Shipping Q2 2026] is an all‑new design with enhanced performance and features. It is slightly deeper, so it uses a new transit cover, and it includes new drivers and an improved cabinet. Unlike the SX218, which required two 8 ohm amplifier channels, the SX218+ uses a single 4 ohm amplifier channel.
The SX218+ adds a third NL4 input connector on the front to improve cabling for subwoofers used in cardioid configurations. For outdoor use, you no longer need a WRKIT, but you must seal all three NL4 sockets. Use the correct cable connectors (NLT4FX or NLT4FX‑BAG) for connected sockets and install a Martin Audio weatherproof NL4 sealing plug in any unused socket.
The SX218+ adds a channel crossover on the link output, letting you run two cabinets from independent amplifier channels down a single four core cable. The SX218+ has two LED indicators, one on the front and one on the back, which you can illuminate via Vu‑Net software to identify each enclosure on the circuit. The rear LED is intended for use in cardioid setups.
SX218+ Features
- Dual-driver, direct radiating reflex-loaded subwoofer
- 2 x 18” (460mm) long-excursion drivers, 4” (100mm) voice coils, neodymium motors, waterproof cones
- Very high output capability
- Tour-grade plywood enclosure with M10 mounting points
Resources & Downloads
Data sheets, manuals and resources for the SX218+
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Quick Specs
- TYPE
- Dual driver, direct radiating reflex-loaded subwoofer
- FREQUENCY RESPONSE
- 38Hz – 100Hz ±3dB, -10dB @ 31Hz
- DRIVER
- 2 x 18 in (460 mm) long‑excursion drivers with 4 in (100 mm) aluminium voice coils, neodymium motors with T‑poles and demodulation rings, waterproof cones
- RATED POWER
- 3000W AES, 12000W peak
- RECOMMENDED AMPLIFIER
- iK42 bridged for full output (For details, see SX218+ User Guide)
Technical Specifications
- TYPE
- Dual driver, direct radiating reflex-loaded subwoofer
- FREQUENCY RESPONSE
- 38Hz – 100Hz ±3dB, -10dB @ 31Hz
- DRIVER
- 2 x 18 in (460 mm) long‑excursion drivers with 4 in (100 mm) aluminium voice coils, neodymium motors with T‑poles and demodulation rings, waterproof cones
- RATED POWER
- 3000W AES, 12000W peak
- RECOMMENDED AMPLIFIER
- iK42 bridged for full output (For details, see SX218+ User Guide)
- SENSITIVITY
- 102.5 dB
- MAXIMUM SPL
- 137dB continuous, 143dB peak, 149dB peak with crest factor 4
- NOMINAL IMPEDANCE
- 4 ohms
- DISPERSION (-6dB)
- Omni-directional or cardioid when paired
- ENCLOSURE
- Multi-laminate birch ply
- FINISH
- Textured black or white paint
- PROTECTIVE GRILLE
- Black or white perforated stainless steel
- ENVIRONMENTAL TESTING
- IP rating IP21, MIL-STD-810H, ISO 4892-2 Solar Radiation, ISO 12944-6 Category C3 Corrosion resistance
- LED INDICATORS
- Two LEDs: one front, one rear (rear LED for cardioid subs)
- CONNECTORS
- 3 x NLT4MPXX-BAG (one front, two rear), IP54 weather‑resistant seal with NLT4FX, NLT4FX‑BAG or weatherproof NL4 sealing plug
- PIN CONNECTIONS (INPUT ON FRONT)
- 1+/1-
- PIN CONNECTIONS (INPUT ON REAR)
- 1+/1-
- PIN CONNECTIONS (LINK ON REAR)
- 1+/1- linked to 2+/2-, 2+/2- linked to 1+/1-
- FITTINGS
- Two skids on base, with mating channels on top, M20 thread plate on right side for pole mounting with sub in portrait, 24 x M10 mounting points, 6 on top, 6 on bottom, 4 on left, 4 on right, 4 on back, 4 x bar handles, two on each side, 16 x M8 inserts for optional castors
- DIMENSIONS (INCL SKIDS)
- (W) 1091 mm x (H) 538 mm x (D) 827 mm (955 mm with castors), (W) 43.0 in x (H) 21.2 in x (D) 32.5 in (37.6 in with castors)
- WEIGHT
- 82.3 kg (181 lb), 85.5 kg (189 lb) with castors
- ACCESSORIES
- Pack of four castors WHEELKIT, M10 eye bolt HTKCT06, Weatherproof NL4 sealing plug, Install flying frame SX218GRID, Flying kit SX218FKIT, Transit Cover SX218+TC
The enclosure is constructed from multi‑laminate birch ply and finished with a durable polyurethane coating. Eight reflex ports provide a large frontal area to reduce turbulent air noise, and a perforated steel grille protects the drivers from damage. The internal port geometry promotes laminar airflow.
The SX218+ features an M20 pole‑mount insert for mounting point‑source speakers. Cabinet wheels and a transit cover are available as accessories.
Compared with the SX218, the SX218+ [Shipping Q2 2026] is an all‑new design with enhanced performance and features. It is slightly deeper, so it uses a new transit cover, and it includes new drivers and an improved cabinet. Unlike the SX218, which required two 8 ohm amplifier channels, the SX218+ uses a single 4 ohm amplifier channel.
The SX218+ adds a third NL4 input connector on the front to improve cabling for subwoofers used in cardioid configurations. For outdoor use, you no longer need a WRKIT, but you must seal all three NL4 sockets. Use the correct cable connectors (NLT4FX or NLT4FX‑BAG) for connected sockets and install a Martin Audio weatherproof NL4 sealing plug in any unused socket.
The SX218+ adds a channel crossover on the link output, letting you run two cabinets from independent amplifier channels down a single four core cable. The SX218+ has two LED indicators, one on the front and one on the back, which you can illuminate via Vu‑Net software to identify each enclosure on the circuit. The rear LED is intended for use in cardioid setups.
- Dual-driver, direct radiating reflex-loaded subwoofer
- 2 x 18” (460mm) long-excursion drivers, 4” (100mm) voice coils, neodymium motors, waterproof cones
- Very high output capability
- Tour-grade plywood enclosure with M10 mounting points
| TYPE | Dual driver, direct radiating reflex-loaded subwoofer |
| FREQUENCY RESPONSE | 38Hz – 100Hz ±3dB, -10dB @ 31Hz |
| DRIVER | 2 x 18 in (460 mm) long‑excursion drivers with 4 in (100 mm) aluminium voice coils, neodymium motors with T‑poles and demodulation rings, waterproof cones |
| RATED POWER | 3000W AES, 12000W peak |
| RECOMMENDED AMPLIFIER | iK42 bridged for full output (For details, see SX218+ User Guide) |
| SENSITIVITY | 102.5 dB |
| MAXIMUM SPL | 137dB continuous, 143dB peak, 149dB peak with crest factor 4 |
| NOMINAL IMPEDANCE | 4 ohms |
| DISPERSION (-6dB) | Omni-directional or cardioid when paired |
| ENCLOSURE | Multi-laminate birch ply |
| FINISH | Textured black or white paint |
| PROTECTIVE GRILLE | Black or white perforated stainless steel |
| ENVIRONMENTAL TESTING | IP rating IP21, MIL-STD-810H, ISO 4892-2 Solar Radiation, ISO 12944-6 Category C3 Corrosion resistance |
| LED INDICATORS | Two LEDs: one front, one rear (rear LED for cardioid subs) |
| CONNECTORS | 3 x NLT4MPXX-BAG (one front, two rear), IP54 weather‑resistant seal with NLT4FX, NLT4FX‑BAG or weatherproof NL4 sealing plug |
| PIN CONNECTIONS (INPUT ON FRONT) | 1+/1- |
| PIN CONNECTIONS (INPUT ON REAR) | 1+/1- |
| PIN CONNECTIONS (LINK ON REAR) | 1+/1- linked to 2+/2-, 2+/2- linked to 1+/1- |
| FITTINGS | Two skids on base, with mating channels on top, M20 thread plate on right side for pole mounting with sub in portrait, 24 x M10 mounting points, 6 on top, 6 on bottom, 4 on left, 4 on right, 4 on back, 4 x bar handles, two on each side, 16 x M8 inserts for optional castors |
| DIMENSIONS (INCL SKIDS) | (W) 1091 mm x (H) 538 mm x (D) 827 mm (955 mm with castors), (W) 43.0 in x (H) 21.2 in x (D) 32.5 in (37.6 in with castors) |
| WEIGHT | 82.3 kg (181 lb), 85.5 kg (189 lb) with castors |
| ACCESSORIES | Pack of four castors WHEELKIT, M10 eye bolt HTKCT06, Weatherproof NL4 sealing plug, Install flying frame SX218GRID, Flying kit SX218FKIT, Transit Cover SX218+TC |
About Penguin Media Solutions
Penguin Media Solutions is a professional audio, video, and lighting design, installation, and maintenance company based in Brighton, UK. As an authorised Martin Audio dealer, we provide high-performance AV systems for commercial venues, hospitality, and event spaces across Brighton, London, and South-East England.
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