18XR

ENCLOSURE RECOMMENDATIONS: 18XRX4-304B
Driver: 18XRX4-304B (18XR) — 18" XR sub-woofer / woofer, 4 ohm
Key T/S: Fs=21.0Hz, Qts=0.35, Qes=0.36, Qms=17.0, Vas=300L, Sens=92.07dB
Power: AES 1200W / Cont 2400W / Peak 4800W
Xmax=17.0mm, Xmech=36.0mm, Sd=1256.6cm², Bl=22.2T·m
Le=0.54mH | XR radial neodymium | 1 copper demodulation ring | SBR rubber surround

DESIGN HIGHLIGHTS:
  - XR (eXtended Range) patented radial neodymium motor: magnets run
    along the full voice coil winding, keeping the coil in the magnetic
    field through virtually the entire rated excursion — 17mm Xmax
    linear, 36mm Xmech mechanical limit. This directly eliminates the
    dominant source of high-order harmonic distortion in conventional
    18" drivers at high excursion.
  - Fs=21 Hz — free-air resonance at the threshold of infrasonic range.
    This is exceptional for a pro/cinema 18" driver and defines its
    capability for sub-20 Hz reproduction when properly loaded.
  - Vas=300 L — very large compliance volume; the suspension is
    extremely compliant, calibrated for maximum cone displacement at
    infrasonic and deep bass frequencies.
  - 4" (101.6mm) voice coil on glass fiber former — high thermal mass
    and mechanical strength for continuous 2400W operation.
  - Le=0.54mH — very low for an 18" driver of this power class, due to
    XR radial neodymium geometry + 1 copper demodulation ring.
    Extended high-frequency response; clean crossover integration up
    to ~500 Hz.
  - Double spider with spacer — two large Nomex spiders spaced along
    the former provide linear restoring force through the full Xmax
    without the progressive stiffening that limits conventional
    single-spider designs.
  - SBR (Styrene-Butadiene Rubber) surround — FEM-optimised geometry
    for constant cone geometry through large excursion, high durability
    for touring and installation environments.
  - Qms=17.0 — effectively zero mechanical losses; system damping
    is entirely electrical. Ideal for DSP-managed active systems where
    the amplifier's output impedance defines the damping behaviour.

RECOMMENDED ENCLOSURE TYPES:
  PRIMARY:   Bass Reflex (Vented) — for maximum LF extension, output,
             and efficiency. Pro touring, cinema, large install.
  SECONDARY: Sealed (Acoustic Suspension) — for hi-fi reference and
             large studio monitoring. Uniquely, a 100L sealed box gives
             a near-perfect Butterworth (Qtc≈0.70) alignment at fc=42Hz
             — exceptional for passive use or DSP correction baseline.

PORT DESIGN NOTE:
The very low Fs (21 Hz) combined with large box volumes and high Vd
(2136 cm³) means that port tubes are long regardless of aperture choice.
Slot ports built into the cabinet rear baffle or base are the practical
standard for cinema and large-install cabinets. Dual round ports are
the preferred option for touring. All port lengths given below are
achievable but require careful cabinet design; folded slot port
configurations are recommended where straight ports exceed cabinet depth.
VENTED ALIGNMENTS (Primary)
Vd = 1256.6 cm² × 17.0mm = 2136.2 cm³

  a) Pro Touring / Compact
     Net Volume: 100 liters
     Tuning (Fb): 35 Hz
     Est. -3dB: ~34 Hz
     HP Filter: 28 Hz (24dB/oct — essential for excursion protection)
     Slot Port: 300mm W × 80mm H × 584mm long (foldable in cabinet)
     Port Velocity (slot): 19.6 m/s ✓
     Notes: Maximum SPL in minimum cabinet size. Sub-30Hz extension
            below tuning requires HP filtering; without protection,
            17mm Xmax is consumed rapidly below Fb. Strong mid-bass
            punch well-suited to touring ground stack and flyware
            sub configurations. The slot port length can be managed
            by routing along the internal cabinet perimeter.

  b) Cinema / Studio Install
     Net Volume: 180 liters
     Tuning (Fb): 27 Hz
     Est. -3dB: ~27 Hz
     HP Filter: 20 Hz (24dB/oct recommended)
     Dual Round Ports: 125mm dia × 557mm each
     Port Velocity: 14.8 m/s ✓ (within professional installation limits)
     Notes: Reference cinema LFE alignment. -3dB at 27 Hz in the
            cabinet alone; room gain in a large cinema or studio
            space (+4–8 dB below 40 Hz) provides effective flat
            in-room response below 20 Hz. Dual 125mm ports at
            <15 m/s produce negligible port noise — appropriate for
            critical listening environments.

  c) Hi-Fi Reference
     Net Volume: 280 liters
     Tuning (Fb): 22 Hz
     Est. -3dB: ~21 Hz
     HP Filter: 18 Hz (24dB/oct recommended)
     Dual Round Ports: 125mm dia × 540mm each
     Port Velocity: 12.0 m/s ✓ (very low — inaudible port noise)
     Notes: Maximum low-frequency extension, approaching the driver's
            free-air resonance (Fs=21Hz). Anechoic -3dB at 21Hz —
            effectively flat through the infrasonic range in-room.
            Suited for dedicated listening room installations, large
            home cinema, and audiophile bass system designs where
            reproducing the full sub-bass register (16–30 Hz) is a
            priority. Port noise is acoustically inaudible at this
            velocity. Cabinet requires substantial internal bracing.
SEALED ALIGNMENTS (Secondary — Hi-Fi / Studio Active)
The relationship between this driver's Qts (0.35) and Vas (300L)
produces a remarkable coincidence: a 100L sealed enclosure yields
Qtc = 0.35 × √(1 + 300/100) = 0.35 × 2.0 = 0.70 — an essentially
perfect Butterworth (maximally flat) sealed alignment with fc = 42 Hz.
This is unusual in a driver of this size and power class, and makes
the 18XR highly suitable for passive sealed hi-fi use before any
DSP correction.

  d) Compact Sealed (80 liters)
     Qtc: 0.76
     fc: 46 Hz
     Est. -3dB (passive): ~43 Hz
     Est. -3dB (with Linkwitz Transform to 0.70/21Hz): ~21 Hz
     Notes: Slight warm character (+0.5dB region around 45 Hz).
            Smallest practical sealed alignment. Requires DSP for
            hi-fi sub use. Strong crossover platform for large
            2-way or 3-way systems crossed at 100–200 Hz.

  e) Hi-Fi Butterworth Sealed (100 liters)
     Qtc: 0.70
     fc: 42 Hz
     Est. -3dB (passive): ~42 Hz
     Est. -3dB (with Linkwitz Transform to 0.70/21Hz): ~21 Hz
     Notes: Near-perfect Butterworth alignment — maximally flat
            sealed response. Can be used entirely passively in a
            large 3-way system crossed below 100 Hz; the 42 Hz
            passive -3dB with room gain provides effective in-room
            bass to ~25 Hz in a typical large room. With DSP
            correction, extends to 21 Hz with exceptional linearity.
            This is the recommended alignment for studio and
            audiophile applications.

ROOM GAIN NOTE:
In large listening rooms, cinemas, and home theaters, acoustic
boundary reinforcement contributes +4–8 dB below 40 Hz. The in-room
response of alignment (b) vented or alignment (e) sealed is therefore
flat-to-room below 20 Hz in most large-room environments — without
any sub-bass DSP boost.
WOOFER APPLICATION NOTE
The 18XR's very low Le (0.54mH), XR motor linearity, and CF paper cone
support use as a high-power bass/woofer driver in large-format systems:
  - Crossover range: 100–400 Hz (to compression driver or midrange)
  - At 92 dB sensitivity, closely matched to 95–106 dB compression
    drivers; typically requires 3–14 dB attenuation or biamplification
  - The low inductance ensures clean, undistorted output through the
    upper bass — critical for music reproduction above 200 Hz
  - Suited for large-format horn-loaded woofer systems, cinema screen
    channel arrays, and high-power bi-amp studio monitor bass sections