S 21a

Touring high performance self-powered 21″ subwoofer

TransducersLF : 1 x 21″
SPL peak / 1m (measured)139 dB
Weight60kg / 132.27lbs
RiggingPole mount
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S 21a is a compact, high-performance self-powered touring subwoofer, designed to complement our FR-X, ARES 8 and ARES 12 series in sound reinforcement applications scaling to full stadium shows.

S 21a houses a long excursion 21″ neodymium driver and combines front diffusion, bass reflex, and transmission line design for maximum efficiency and outstanding SPL.

Rental companies favor S 21a as an alternative to industry-standard 2×18” subs, saving half the truck space and around 40% of the weight. The subwoofer can be deployed standalone, stacked or flown, making it a versatile, high-earning hire stock staple.

An advanced AUDIOFOCUS SCiO Class D amplifier module with integral DSP and versatile presets allows S 21a to be quickly deployed in any configuration, including cardioid and end-fire.

S 21a is built with pride in Belgium and coated in tough, weather-resistant polyurea to safeguard your investment. The cabinet front is protected by a rigid metal grill, backed by acoustically transparent foam.


  • Powerful bass-reflex T-line design
  • Lightweight and portable
  • Pole mount socket
  • Self-powered plug ‘n play
  • Dedicated presets

Technical specifications

DescriptionHigh-power self-powered subwoofer
Transducers LF: 1 x 21″
Frequency range (-6dB)28Hz-100Hz
SPL peak (1)139 dB
ProcessingDedicated AUDIOFOCUS SCiO omni and cardioid presets
RiggingPole socket
Audio ConnectorsIN: 1×3-point XLR
LINK: 1×3-point XLR
Network connectors1 x etherCON for control
Power ConnectorsIN: 1×3-point powerCON TRUE1 TOP
LINK: 1×3-point powerCON TRUE1 TOP
Dimensions (H x W x D)590 x 750 x 655 mm
23.22 x 29.52 x 25.78 inches
Weight60kg / 132.27lbs
FinishHighly resistant polyurea coating

CabinetHigh grade birch plywood

(1) Peak level measured at 1 m under free field conditions using pink noise with crest factor 5

Gll files for Ease and Easefocus

Gll file
S 21

Gll • 1.65 Mo • 06/01/2022

Gll file
S 21 Stack

Gll • 1.78 Mo • 06/01/2022

Quick Start guide
SCio Web Connection

PDF • 250 Ko • 13/06/2022

User Manual

PDF • 6.50 Mo • 10/07/2023

Firmware update SCiO
+ Procedure guide

ZIP • 5.9 Mo • 09/04/2024
PDF • 143 Ko • 09/04/2024

Technical sheet
S 21a

PDF • 732 Ko • 09/04/2024


Connect & Control your amplifiers

AUDIOFOCUS SCiO amplifiers can be securely monitored and controlled anytime, anywhere over the network.
Our intuitive Web UI network manager is web-based, eliminating the need for software downloads, and allows multiple amplifiers to be managed from your preferred device.

The network manager offers the comprehensive processing options you would expect from a high-end system controller.
For more detailed information please visit the AUDIOFOCUS SCiO page.


Note – this Quick Start Guide is for use with products manufactured from July 2022