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12″ Bass reflex 2-way Stage monitor

Celestion CKT-FM-FTX1225

2-way coaxial stage monitor from Celestion with 12″ FTX1225, passive crossover and measured frequency and dispersion data – build plan from the manufacturer.

Partially verified Last checked: 13 September 2026 What does this mean?

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 × Celestion FTX1225 Manufacturer
Enclosure type
Bass reflex
Low-frequency extension
65 Hz (-3 dB) · 44 Hz (-10 dB) standing on the floor Manufacturer
Sensitivity
97 dB 2,83 V / 1 m Manufacturer
Max. SPL
123.5 dB continuous · 129.5 dB peak Manufacturer
Power handling
450 W EIA · 1,800 W Peak power · 300 W AES (Woofer) Manufacturer
Impedance
8 Ω (min. 6.5 Ω) Manufacturer
Dimensions (H × W × D)
430 × 426 × 610 mm Manufacturer
Volume
48 L (Internal volume (deductions not stated)) Manufacturer
Tuning frequency
48 Hz Manufacturer
Weight
not available
Recommended high-pass
55 – 75 Hz Manufacturer

External dimensions according to the specification table. The dimensions in the enclosure drawing (p. 7) have not yet been cross-checked.

Description

Link to section “Description”

In brief

A vented wedge monitor with a 12-inch coaxial driver. Celestion supplies a drawing, passive crossover and measured frequency and dispersion data with measurement conditions.

The CKT-FM-FTX1225 is a reference design by Celestion for a medium-sized stage monitor. At its heart is the 12-inch coaxial driver FTX1225: woofer and high-frequency driver sit on a common axis. According to the manufacturer, this arrangement provides wide and even dispersion – horizontally as well as vertically.

Construction

Link to section “Construction”

The enclosure is a bass reflex wedge with 48 litres of internal volume and two round ports. It can be set up so that the driver axis points upwards at 30° or 60°. For the tuning, Celestion names two alternatives in addition to the standard ports (shorter/narrower and longer/wider). This lets you adapt the low-bass reproduction to the stage without changing the enclosure.

Why this plan is well documented

Link to section “Why this plan is well documented”

Celestion gives not only dimensions and components but also measured frequency and dispersion data – including measurement distance, normalisation and placement. This is rare for manufacturer plans. Only the smoothing of the curves and the weight are missing.

Passive or with a controller?

The plan describes a passive crossover at 1.7 kHz. The recommended high-pass of 55–75 Hz is set on the mixing desk or controller. It protects the woofer from excessive excursion below the tuning frequency of 48 Hz.

Drivers

Link to section “Drivers”

Enclosure

Link to section “Enclosure”
Enclosure type
Bass reflex · How does it work?
Shape
Wedge (monitor) · Angle 30° / 60°
Ports
  • 2 × round port Ø 75 mm length 160 mm
  • Variant kleiner: 2 × round port Ø 70 mm length 135 mm
  • Variant larger: 2 × round port Ø 80 mm length 183 mm
Material
  • Birch plywood, 18 mm – specified
  • MDF, 18 mm – alternative: possible according to the manufacturer if the internal volume is retained; less stiff and less durable
  • Birch plywood, 15 mm – alternative: possible according to the manufacturer if the internal volume is retained

Build plan

Link to section “Build plan”

We link to the original plan and do not host other people’s drawings.

  • CKT-FM-FTX1225 System – Bauplan (PDF, englisch)

    Official source · 8 pages · accessed on 13 September 2026

    Published by the manufacturer

    Open original document
    Checksum (SHA-256)eba768b4054d188b83e13e89436326d058a5b630d4fe72d75cc72ee1b4c0306d

Plan access: Free

Measurements

Link to section “Measurements”

Measurements with their conditions. The curves themselves are in the original document.

  • Measured · Manufacturer limited comparability

    Frequency response

    Low-frequency range measured twice: on the floor and free-standing at 1.5 m distance, each normalised to 2.83 V / 1 m. Smoothing not stated.

    Environment
    Standing on the floor
    Distance
    not stated
    Normalisation
    2.83 V / 1 m
    Smoothing
    not stated

    Location in source: PDF p. 3 · CKT-FM-FTX1225 System (build plan PDF)

  • Measured · Manufacturer

    Impedance

    Impedance response as a graph in the original document.

    Environment
    not stated
    Distance
    not stated
    Normalisation
    not stated
    Smoothing
    not stated

    Location in source: PDF p. 3 · CKT-FM-FTX1225 System (build plan PDF)

  • Measured · Manufacturer limited comparability

    Horizontal directivity

    Horizontal on axis, 30° and 60°; vertical on axis, 15° and 30°. Measured at 2 m in free field, normalised to 2.83 V / 1 m. Smoothing not stated.

    Environment
    Free field
    Distance
    2 m
    Normalisation
    2.83 V / 1 m
    Smoothing
    not stated

    Location in source: PDF p. 4 · CKT-FM-FTX1225 System (build plan PDF)

  • Measured · Manufacturer

    Beamwidth (−6 dB)

    Coverage angle at the −6 dB point according to the manufacturer’s table. The table does not state the plane (horizontal/vertical).

    Environment
    Free field
    Distance
    2 m
    Normalisation
    not stated
    Smoothing
    not stated
    Beamwidth (−6 dB) by frequency
    FrequencyValue
    500 Hzüber 120°
    800 Hzüber 120°
    1,000 Hzüber 120°
    2,000 Hz90 °
    5,000 Hz80 °
    8,000 Hz80 °
    10,000 Hz80 °
    15,000 Hz40 °

    Location in source: PDF p. 4 · CKT-FM-FTX1225 System (build plan PDF)

Crossover & controller

Link to section “Crossover & controller”
Crossover
1.7 kHz · Passive crossover: 3rd-order low-frequency section, 2nd-order high-frequency section; according to the manufacturer this results in an acoustic 4th-order crossover. Schematic, parts list and assembly notes are in the original document.
Recommended high-pass
55 – 75 HzSource: “High Pass Filter: 55-75Hz”

Pros and cons

Link to section “Pros and cons”

Pros

  • Manufacturer’s measurement data with stated conditions (distance, normalisation, placement)
  • Passive crossover with schematic and parts list in the original document
  • Two tilt angles (30° and 60°) and three port variants for adjusting the tuning

Cons

  • No controller or DSP settings documented, passive operation only
  • Weight not stated

Sources

Link to section “Sources”
  1. Tier A · primary source

    CKT-FM-FTX1225 System (build plan PDF)

    Celestion · 5 July 2018 (Date from file metadata) · accessed on 13 September 2026

    8 pages: description, measured frequency, impedance and dispersion data, specifications, crossover circuit, enclosure drawing, damping.

  2. Tier A · primary source

    BUILD THIS! 12-inch Coaxial Floor Monitor

    Celestion · accessed on 13 September 2026

Usage rights of the plan: Published by the manufacturer. Added on 13 September 2026, last updated on 13 September 2026.

Further reading

Link to section “Further reading”