Active High-End Immersive
Audio Subwoofer


ACTIVEBuilt in Amplifier

The THE21 Sub PRO ACTIVE SEALED is a jewel in the pool of subwoofers designed for the highly educated customer that is on the quest for the highest performance and understands how to differentiate sound quality. When this customer experiences the THE21 SUB PRO AS’s unparalleled output and uncolored sound, the measured test results we publish translate perfectly to realized performance. ASCENDO’s policy is to be completely transparent and publish measurements done by independently certified third-party labs to provide factual data, thereby enabling informed, educated decisions. The THE21 SUB PRO AS is so far above and beyond the competition in every aspect; refined musicality, tightness, and output levels suitable for a 21"" driver. It is also engineered to operate perfectly in sync (in phase) with our Infrasonic subwoofers; THE24/32/50/80 SUB PRO SEALED when there is a desire to reproduce movie content below 20Hz with the same authority, precision, and musicality.

Compared to conventional subwoofer motor concepts, the ultra-modern double-gap motor of this custom-made 21" driver with two outer and two inner voice-coils enables more linear travel and much faster directional changes with higher sound power and significantly lower power compression.

Enormous power is achieved with the integrated powerful DSP and amplifier unit. The immensely powerful 3kW amplifier and even more powerful 6kW Power-supply handle any musical or movie attack with ease. 

Specifications (selection)

Speaker type

21-inch forward-firing, dual gap motor structure with 2 inner and 2 outer voice coiles, neodymium motor.


18 mm excursion each direction (36 mm linear), voice coil remaining in homogeneous magnetic field, linear and lowest distortion

Passive | Active

Active, built in DSP Amplifier

SPL (peak / half space 2pi)

Measurement Data
139 dB @63 Hz and up 

Frequency Range

Measurement Data (without DSP)
55 Hz - 500 Hz / -3 dB
28 Hz - 500 Hz / -15 dB

Air volume displacement 

2,88 L / in comparison 21" standard cinema subwoofer 1,76 L

Directivity horizontal x vertical in Deg°


Output power

3.000 W

Power voltage range

85 V - 265 V

Input sensivity, balanced input impedance

2.7V (with gain 32dB), 10k

Damping factor (20-500 Hz @8Ω)

> 400


High Performance 96kHz/24 bits AD/DA converters, 64 bit double-precision 96kHz DSP process

Input IIR EQ section 

Gain, Mute, Phase inversion, Delay (up to 116ms, 40m), 10 EQ filters (Parametric, Shelving, LP, HP, BP, SB, AP)

Analog Input Amplifier

1 x XLR balanced

Power connector

Neutrik powerCON True 1 in-out

Automatic power off


Network Switch

2ports Ethernet switch for daisy chain


OCS Software control


Internally braced birch ply and MDF


23,62 " | 600 mm


43,31 " | 1100 mm

Hight with feet 

44,29 " | 1125 mm


14,57 " | 370 mm

Depth with plug

14,96 " | 380 mm


125,66 lbs | 57 kg


Structural paint black

Custom colour options 

Piano lacquer, colour of choice, matt or other finishes upon request

Shape customization 

Upon request 


Floor standing with feet


The21 SUB PRO ACTIVE SEALED is supplied with a front cover as standard

Technical modifications subject to change without further notice