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Active Passive Bass Module

What is Power without Control? In developing one of the most powerful subwoofer solutions in the world today, our already successful VHD2.21 2x21" subwoofer has evolved to incorporate a revolutionary new Subwoofer Amplifier design unique to KV2 and featuring  Ultra High Current delivery, Immense Power, Exceptional Control, coupled with a class-leading 'Green Efficiency' low consumption power supply. Housing two newly developed large format 21" Woofers, the VHD4.21 Active can power an additional Passive VHD4.21 and deliver up to 14,000 Watts of peak power whilst being plugged into a standard 16A wall socket. The VHD4.21 is a truly Amazing product and demonstrates the Pinnacle of KV2's Pioneering Subwoofer technologies. There is also a flyable version available - VHD4.21R Active Passive Bass Module (KVV 987 480 / KVV 987 481) with additional fixings and requirements for the VHD4.21 Flybar (KVV 987 398). 


  • two purpose-designed 'Low Loss-Band Pass' enclosures, one Active and one Passive, 

  • each enclosure containing two specific custom-designed large format 21" woofers.

  • the Low Q design has been applied to attain the optimum Loudspeaker loading, enabling a high sensitivity of 109dB 1w/1m. 

  • new power management system enables the Active Power Amplifier to deliver peak output levels of 14kW whilst operating at a modest constant consumption of 3.6 kW from a 16A circuit

  • maximum 320V supplied (limited) peak to peak at 100A from the VHD4.21 Active Module 

  • a flyable version available - VHD4.21R Active Passive Bass Module (KVV 987 480 / KVV 987 481)


The Ultimate seismic Subwoofer to add to any KV2 Audio or third-party manufacturers system. 

  • Large-scale live music and playback performance

  • Dance Clubs and Nightclubs where Music comes first 

  • Hire and Production

  • Large Concert venues

  • Cinema

  • Fixed installation

  • Easily incorporated into multiple system projects with VHDSLES, and ESR 

System Acoustic Performance

Max SPL Long-term147dB

Max SPL Peak: 150dB

-3dB Response: 34Hz - 180Hz

-10dB Response: 28Hz - 240Hz

Crossover Point: 60Hz to 120Hz

Low-Frequency Section

Acoustic Design: Bandpass with low port losses

Woofer Size / Voice Coil Diameter / Design: 4 x 21" / 5.3"

Diaphragm Material: Epoxy Reinforced Cellulose with Carbon Fiber and Double Surround

Magnet Type: Neodymium Advanced Ventilated

Low-Frequency Amplifier Specification

Type: Direct power switching amplifier

Rated Continuous Power: 3500W

Short-Term Power: 14000W

Distortion: <0.05%

Signal Input

Input Sensitivity: 1.55V RMS

Input Impedance: 20 kΩ

Power Requirements

Power Connector: Neutrik PowerCon® 32A

Operating Voltage: 180V - 260V @ 50Hz | 60Hz

Recommended Amperage: 16A


Cabinet Material: Baltic Birch

Handles: 12

Color: Black (wear-resistant polymer coating)

Physical Dimensions

Height: 700mm (27.55")

Width: 1080mm (42.52")

Depth: 1200mm (47.24")

Weight (Active): 175kg (386lbs)

Weight (Passive): 155kg (342lbs)

Product code

KVV 987 333 - VHD4.21 ACTIVE 
KVV 987 336 - VHD4.21 PASSIVE

KVV 987 480 - VHD4.21R ACTIVE
KVV 987 481 - VHD4.21R PASSIVE 

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