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Gradient NERO is an intelligent add-on dipole bass concept to any conventional passive speaker system.

The NERO offers clean and fast bass down to 20Hz with minimum effects of standing waves in the listening room. 

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Already 30 years ago Gradient developed an add-on dipole bass systems for the legendary Quad ESL-57 and ESL-63. The Gradient SW-63 for the ESL-63 was a module with two 12 inch drivers which also acted as a stand for the Quad. 

Later with the design of Gradient Revolution Active, we  came up with a scalable add-on dipole bass system for use with any Quad ESL. The models were called Gradient SW-S and SW-D. The SW-S (a Single Pair of modules per side) or SW-D (‘d’ for “double”, i.e., two SW-S modules stacked vertically for a total of four 12 inch drivers per side).

Now we have extended Gradients add-on dipole bass concept to any conventional box speaker system.


In addition to the add-on bass modules, the Gradient NERO consists of Gradient XO-AMP unit. The XO-AMP is an active crossover with four power amplifiers based on the high-performance Hypex Ncore®-technology. Features like extremely flat frequency response irrespective of load impedance and practically frequency independent distortion behaviour make the power amplifier one of the very best in the market.

The crossover sends the bass below 200Hz to the dipole modules and above 200Hz to the main speakers. 


Since the add-on bass modules take care of the lowest tones, there is an added advantage of better mid-range and less cabinet and port artifacts form the main speakers.


Due to the dipole radiation pattern (figure of eight). The Gradient NERO delivers only 2/3 less energy into the room for a given sound pressure level. The result is most uncoloured bass with minimum effects of standing waves in the listening room. 


The level of the signal, feeding the bass amplifier can be adjusted continuously by a trimmer adjustments at the back of the unit. The adjustment range is +/- 10dB for both channels separately. According to the personal taste and listening room acoustics the bass is easy to adjust. Once found the correct balance, there is little need for further adjustments. 

Data sheet
Make and modelGradient XO-AMP
Output power240 W/Channel
Input impedance40 kohm
Output impedance100 ohm (line-level output)
Crossover frequency200Hz (Version A), 110Hz (Version B)
Bass level adjustement+/- 10 dB for left and right channels separately
AC mains110-250VAC, automatic detection
FeaturesHigh-end analog signal path, Extremely low, frequency-independent THD performance, true dual-mono design.
Dimensions (WHD)465 x 60 x 412mm
FinishChassis: black. Frontplate: Alpine white acrylic stone.
Made inFinland