18 Sound 12″ Koax
Compact 12″ coaxial top from 18 Sound with the 12NCX750, the manufacturer’s passive crossover and polar plots – Application Note.
Primary source checked; some values are missing from the source or still open.
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Specifications
Link to section “Specifications”Every value with its provenance. If a value is missing from the source, it reads “not available”.
- Drivers
- 1 × 18 Sound 12NCX750 Manufacturer
- Enclosure type
- Bass reflex
- Low-frequency extension
- not available
- Sensitivity
- not available
- Max. SPL
- not available
- Power handling
- not available
- Impedance
- not available
- Dimensions (H × W × D)
- 520 × 419 × – mm (incomplete) from drawing, PDF p. 9 Manufacturer
- Volume
- not available
- Tuning frequency
- not available
- Weight
- not available
- Recommended high-pass
- not available
Front 419 × 520 mm (W × H) according to the front view (p. 9). The depth is not given as an external dimension in the drawings.
Description
Link to section “Description”In brief
A compact bass reflex top with a 12-inch coaxial driver and the manufacturer’s passive crossover. The document includes measurements and polar plots.
A compact coaxial top for the 12-inch neodymium coaxial driver 12NCX750. 18 Sound supplies its own passive crossover for it, which according to the manufacturer is ready-tuned. The coaxial driver is meant to combine high power handling and wide dispersion with low weight.
Build notes from the source
Link to section “Build notes from the source”- Baltic birch plywood, 15 mm
- Four ports made from PVC pipe with 74 mm inner diameter
- M5 × 35 mm screws with T-nuts
- Damping as shown in the document, with dense synthetic fibre material
The measurements comprise frequency, phase and impedance response with the crossover as well as horizontal and vertical polar plots from 1.25 to 16 kHz. According to the document, the polar maps are normalised to 0° and smoothed to 1/3 octave. The document does not say whether the enclosure is also suitable as a stage monitor. We therefore list it as a top.
Drivers
Link to section “Drivers”- Original driver
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Original driver
18 Sound 12NCX750 XOVER
Crossover · Dedicated passive crossover from the manufacturer
Enclosure
Link to section “Enclosure”- Enclosure type
- Bass reflex · How does it work?
- Shape
- Rectangular box
- Ports
-
- 4 × round port Ø 74 mmPVC tube, 74 mm inner diameter; parts list: “Vent 80x185 mm”, 4 pieces
- Material
-
- Birch plywood, 15 mm – specified: Baltic Birch
Build plan
Link to section “Build plan”We link to the original plan and do not host other people’s drawings.
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Open original document
12″ Coax – Application Note (PDF, englisch)
Official source · 16 pages · version v0 · accessed on 13 September 2026
Published by the manufacturer
Checksum (SHA-256)
b3932f14d56a7b6d81eafa3a562d5a6543980fcba44fb56d1a823ecfb3fc483f
Plan access: Free
Measurements
Link to section “Measurements”Measurements with their conditions. The curves themselves are in the original document.
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Measured · Manufacturer limited comparability
Frequency response
Amplitude, phase and impedance response with 12NCX750 and crossover. Measurement conditions not stated.
- Environment
- not stated
- Distance
- not stated
- Normalisation
- not stated
- Smoothing
- not stated
Location in source: PDF p. 4 · Application Note – General Purpose 12″ Coaxial Loudspeaker System (18_Sound_12_Coax_v0.pdf)
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Measured · Manufacturer limited comparability
Horizontal directivity
Horizontal and vertical polar plots (1.25–16 kHz) and polar maps, normalised to 0°.
- Environment
- not stated
- Distance
- not stated
- Normalisation
- not stated
- Smoothing
- 1/3 Oktave (Polarkarten)
Location in source: PDF p. 5–7 · Application Note – General Purpose 12″ Coaxial Loudspeaker System (18_Sound_12_Coax_v0.pdf)
Crossover & controller
Link to section “Crossover & controller”- Crossover
- Passive crossover “12NCX750 XOVER” from 18 Sound; crossover frequency not given in the document.
- Recommended high-pass
- not stated
Pros and cons
Link to section “Pros and cons”Pros
- Passive crossover from the manufacturer
- Horizontal and vertical polar plots
- Simple PVC tube ports
Cons
- Enclosure depth not dimensioned
- Measurement distance and measurement environment not stated
Sources
Link to section “Sources”-
Tier A · primary source
Application Note – General Purpose 12″ Coaxial Loudspeaker System (18_Sound_12_Coax_v0.pdf)
Eighteen Sound Srl · 28 August 2017 (Date from file metadata) · accessed on 13 September 2026
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Tier A · primary source
Eighteen Sound – Enclosure Designs
Eighteen Sound Srl · accessed on 13 September 2026
Overview of the enclosure designs with short descriptions and PDF downloads.
Usage rights of the plan: Published by the manufacturer. Added on 13 September 2026, last updated on 13 September 2026.