Designed by 18Sound
Double 21"Manifolded Double
Manifolded bandpass subwoofer. Three driver options, one legendary design.
High performance 2×21" manifolded bandpass subwoofer designed by 18Sound. Multiple driver options from cost-effective ceramic to maximum-impact neodymium. Open source plans, precision CNC flatpack.
Specifications
Manifolded Double 21" Bandpass Subwoofer — 18Sound
DSP / Processing
Processing parameters referenced to XTA DP224/DP226/DP448 processors. Gain and limiter values need adjustment for different amplifier gains.
Driver Options
Choose from 3 recommended drivers, or source your own. We can include them in your kit.
18Sound 21NLW9600
Highest efficiency and maximum impact. Augmented-strength neodymium magnet with an outstanding 43.5 BL factor.
- Maximum impact - BL 43.5 Tm
- Neodymium magnet - lightweight
- 1800W AES / 10kW peak
- 5.3" interleaved sandwich voice coil
18Sound 21NLW9000
High power handling and lightweight box. Neodymium magnet equipped with triple silicon spider for reliability.
- High power handling - 1800W AES
- Neodymium magnet - lightweight
- Triple silicon spider (TSS)
- 5.3" interleaved sandwich voice coil
18Sound 21LW1400
Cost effective solution with ceramic magnet. Double demodulating rings for clean output.
- Cost effective - ceramic magnet
- High sensitivity - 99 dB
- Double demodulating rings (DDR)
- 4" interleaved sandwich voice coil
What's Included
Everything in the flatpack kit
CNC-Cut Panels
Precision-cut from 18mm Baltic birch plywood
- Front baffle (driver cutouts pre-routed)
- Rear panel (connector cutout pre-routed)
- Side panels
- Top and bottom panels
- Internal bracing & manifold panels
- Port panels
Hardware Kit
M6 bolts, T-nuts, and all mechanical fixings
- M6 × 35mm bolts
- M6 T-Nuts
- Speakon connector panel
- Recessed handles
- Rubber feet
- Driver mounting hardware
- Gasket tape / EPDM
Damping Material
High density synthetic fibre for interior damping
- Pre-cut damping material
- Placement guide included
Documentation
Assembly guide and DSP settings
- Step-by-step assembly guide
- Wiring diagram
- DSP / processor settings
- Damping placement guide
Build your Double 21"
Flatpack from £899. Optional drivers, stain, mounting hardware, and build service.
Lead time: 2–3 weeks (flatpack) · 3–5 weeks (subject to driver availability) (with drivers)
FAQ
Which driver should I choose?
The 21NLW9600 (Premium) delivers maximum impact with the highest BL factor. The 21NLW9000 (Core) offers the same power handling in a lighter package. The 21LW1400 (Value) is the most cost-effective option with the highest raw sensitivity.
Can I supply my own drivers?
Absolutely. The flatpack kit works with any of the three recommended 18Sound drivers. Order the kit without drivers and source your own.
What tools do I need?
Essential: drill/driver, clamps (min 4), wood glue, rubber mallet, workbench, square, tape measure. Recommended: soldering iron, multimeter, orbital sander for finishing.
Do I need a DSP / processor?
Yes. The manifolded bandpass design requires careful EQ, particularly a -12 dB notch around 105 Hz. We provide baseline DSP settings for XTA-compatible processors.
What about the build and finishing service?
We can assemble and finish the cabinet for you. Select "Build & Finish" when requesting your quote. Lead times are longer but you receive a ready-to-use cabinet.