What are the key features of the REDCATT 21XR?

The REDCATT 21XR features: linear cone excursion 60mm peak TO peak !!; unparallel low distortion at low frequencies; patented design, innovative magnetic structure & venting system.

What are the power handling and sensitivity specifications of the 21XR?

The 21XR has an AES power rating of 1800 W, continuous power of 3600 W, peak power of 7200 W, and a sensitivity of 95.70 dB (1W/1m).

What are the Thiele-Small parameters of the 21XR?

Key T/S parameters: Fs=32.30 Hz, Qts=0.500, Vas=194.45 liters, Sensitivity=95.70 dB, Bl=29.37 T·m, Xmax=22.83 mm. Magnet type: Neodymium.

21XR - Sub-woofer - Professional Loudspeaker Engineering

Name: 21XR
Brand: REDCATT
SKU: 21XRX8-347A

Design Notes

The 21XR is a high efficiency, (96 dB 1watt / 1 meter) 21-inch woofer with incredibly linear frequency response characteristics. Our new and patented ground up motor design is a new approach to high-excursion woofers. The voice coil winding is always in the magnetic gap that is extremely wide. This feature ensures extremely low distortion across whole working range of this unique driver.

Motor Design
The magnetic design incorporates large neodymium magnets placed along the voice coil winding. This has allowed us to push the cone excursion to 50mm peak to peak. Unique gap venting ensures good air circulation and greatly improves the reliability of this driver. We have also developed a new technique for manufacturing deep copper caps that are implemented in this design and covering the whole voice coil movement..

The design further utilizes triple, uncommonly large, spiders, spaced with spacers, hot-pressed tinsel wires onto the top spider, reinforced cone edge, reinforced surround to cone joint, reinforced spider to basket joints, etc.

Specifications

General Specs

Nominal Diameter 21"

Rated Impedance 8 Ohm

Magnet Neodymium

Basket Material Aluminum

Power Handling

AES Power 1800 W

Continuous Power 3600 W

Peak Power 7200 W

Voice Coil

Diameter 134.6 mm

Winding Wire Copper

Former Glass Fiber

Winding Height 21 mm

T/S Parameters

Resonant Frequency (Fs) 32.30 Hz

Re 4.50 \u2126

Qes 0.510

Qms 16.79

Qts 0.500

Vas 194.45 liters

Sd 1662.00 cm\u00B2

Mms 488.58 grams

Rms 5.90

Cms 0.0500

Bl 29.37 T\u00B7m

Le 0.650 mH

Sensitivity 95.70 dB

Design Details

Surround Material fabric

Cone/Dome Material Paper CF

Spider Nomex

T-Plate 66.66 mm

Xmax (peak) 22.83 mm

Xmech 89.49 mm

Overall Diameter 549.00 mm

Bolt Circle Diameter 525.00 mm

Baffle Cutout Dia. 503.00 mm

Mounting Holes 8

Depth (flange to rear) 287.00 mm

Net Weight 23.80 kg

Ordering Codes

Product Code 21XRX8-347A

Downloads

2D Drawing (PDF) 3D Model (STEP)

Frequency Response & Impedance

2D Drawing

Technical Summary

This design is particularly effective in single or multi-driver bass reflex systems used in touring, installation, and high-SPL applications, where consistent performance, durability, and output capability are critical.

Enclosure Recommendations

ENCLOSURE RECOMMENDATIONS: 21XRX8-347A
Driver: 21XRX8-347A (21XR) — 21" Sub-woofer
Key T/S: Fs=32.3Hz, Qts=0.5, Vas=194.45L, Sens=95.7dB
Power: AES 1800W / Cont 3600W / Peak 7200W
Xmax=22.83mm, Sd=1662.0cm², Bl=29.37T·m
RECOMMENDED ENCLOSURE TYPE: Bass Reflex (Vented)
PORT RECOMMENDATION: Slot port (full-width or L-shaped internal duct) — provides large cross-sectional area needed for high air displacement; reduces port noise at high SPL
  a) High SPL
     Net Volume: 130 liters
     Tuning (Fb): 37 Hz
     Est. -3dB: 34 Hz
     HP Filter: 29 Hz (24dB/oct recommended)
     Round Ports: 3× 150mm dia × 771mm long
     Slot Port: 402mm W × 90mm H × 445mm L
     Port Velocity: 16.7 m/s
     Notes: Strong mid-bass impact, reduced cone excursion, maximum output
  b) Balanced Response
     Net Volume: 165 liters
     Tuning (Fb): 33 Hz
     Est. -3dB: 30 Hz
     HP Filter: 23 Hz (24dB/oct recommended)
     Round Ports: 2× 150mm dia × 464mm long
     Slot Port: 402mm W × 90mm H × 431mm L
     Port Velocity: 22.4 m/s
     Notes: General-purpose PA/subwoofer, even response, good transient behavior
  c) Extended Low Frequency
     Net Volume: 200 liters
     Tuning (Fb): 29 Hz
     Est. -3dB: 25 Hz
     HP Filter: 20 Hz (24dB/oct recommended)
     Round Ports: 2× 150mm dia × 530mm long
     Slot Port: 402mm W × 90mm H × 498mm L
     Port Velocity: 19.5 m/s
     Notes: Deep bass extension, requires proper system protection below tuning
--- Summary ---
The 21XRX8-347A is a 21-inch high-output sub-woofer driver designed for professional subwoofer systems requiring high sensitivity (96 dB 1W/1m) and controlled low-frequency behavior. The driver features a compliant suspension design suited to moderate-volume enclosures with extended low-frequency response.
In bass reflex enclosures, the driver performs best in net internal volumes of 130 to 200 liters, tuned between 29 and 37 Hz. This alignment provides a balanced combination of low-frequency extension, cone control around resonance, and efficient port loading. Lower tuning improves deep bass extension but increases excursion below tuning, requiring appropriate high-pass filtering. Higher tuning increases sensitivity and output in the upper bass region while improving mechanical control.
The driver is intended for use with high-power amplification (approx. 1800 W AES / 3600 W continuous) and DSP control. A high-pass filter in the range of 20–29 Hz is recommended depending on enclosure tuning, along with proper limiting to manage thermal and mechanical stress. Typical operating bandwidth is 25–100 Hz, making it suitable for integration with mid-bass or full-range systems.

Frequently Asked Questions

- linear cone excursion 60mm peak TO peak !!
- unparallel low distortion at low frequencies
- patented design, innovative magnetic structure & venting system

ENCLOSURE RECOMMENDATIONS: 21XRX8-347A
Driver: 21XRX8-347A (21XR) — 21" Sub-woofer
Key T/S: Fs=32.3Hz, Qts=0.5, Vas=194.45L, Sens=95.7dB
Power: AES 1800W / Cont 3600W / Peak 7200W
Xmax=22.83mm, Sd=1662.0cm², Bl=29.37T·m
RECOMMENDED ENCLOSURE TYPE: Bass Reflex (Vented)
PORT RECOMMENDATION: Slot port (full-width or L-shaped internal duct) — provides large cross-sectional area needed for high air displacement; reduces port noise at high SPL
  a) High SPL
     Net Volume: 130 liters
     Tuning (Fb): 37 Hz
     Est. -3dB: 34 Hz
     HP Filter: 29 Hz (24dB/oct recommended)
     Round Ports: 3× 150mm dia × 771mm long
     Slot Port: 402mm W × 90mm H × 445mm L
     Port Velocity: 16.7 m/s
     Notes: Strong mid-bass impact, reduced cone excursion, maximum output
  b) Balanced Response
     Net Volume: 165 liters
     Tuning (Fb): 33 Hz
     Est. -3dB: 30 Hz
     HP Filter: 23 Hz (24dB/oct recommended)
     Round Ports: 2× 150mm dia × 464mm long
     Slot Port: 402mm W × 90mm H × 431mm L
     Port Velocity: 22.4 m/s
     Notes: General-purpose PA/subwoofer, even response, good transient behavior
  c) Extended Low Frequency
     Net Volume: 200 liters
     Tuning (Fb): 29 Hz
     Est. -3dB: 25 Hz
     HP Filter: 20 Hz (24dB/oct recommended)
     Round Ports: 2× 150mm dia × 530mm long
     Slot Port: 402mm W × 90mm H × 498mm L
     Port Velocity: 19.5 m/s
     Notes: Deep bass extension, requires proper system protection below tuning
--- Summary ---
The 21XRX8-347A is a 21-inch high-ou...

This design is particularly effective in single or multi-driver bass reflex systems used in touring, installation, and high-SPL applications, where consistent performance, durability, and output capability are critical.

AES Power: 1800 W, Continuous: 3600 W, Peak: 7200 W. Sensitivity: 95.70 dB (1W/1m).

21XR

Key Features

Quick Specs