Børresen BM2

Unique Crossover Topology

While the Børresen BM2 is engineered to perform exceptionally on its own, optimal results depend on seamless integration with the existing audio system. To support this, our sister company Aavik develops amplifiers with advanced crossover networks specifically designed for loudspeaker systems complemented by subwoofers.

The BM2 is a self-powered active design featuring an integrated low-pass crossover derived from the analog filtering topology used in selected Aavik electronics. Unlike many conventional subwoofers that rely heavily on DSP, the BM2 employs a fully analog crossover architecture built around carefully selected high-grade components. This avoids DSP-induced latency, helping preserve timing accuracy and system coherence.

The crossover frequency can be adjusted between 30 Hz and 170 Hz, allowing the BM2 to integrate naturally with a wide range of loudspeaker systems and room configurations. Frequencies above the selected point are attenuated at a 24 dB/oct. slope for effective low-frequency integration.

Adjustable gain control enables further fine-tuning of bass response to suit system characteristics, room acoustics, and personal preferences. For systems using the crossover functionality built into selected Aavik amplifiers, the BM2’s internal crossover can be bypassed entirely, allowing the external crossover network to manage integration directly.

Resonant-mode power supply

Although linear power supplies remain highly regarded in audio, they are not without limitations. Their large capacitor banks draw current from the transformer in short pulses, generating unwanted current transients and switching noise. For this reason, the Børresen BM2 instead relies on a significantly faster and quieter switching power supply architecture.

The UMAC Class D amplification stage incorporates a switching power supply engineered specifically for this application. Operating in power-factor-corrected resonant mode, it generates sine-wave behavior rather than conventional square-wave switching. As power demand increases, the operating frequency rises accordingly, enabling higher power density and greater peak current delivery.

The result is an exceptionally low-noise power supply that remains stable under demanding dynamic conditions. Equally important, it places no practical limitations on the amplifier stage and helps maintain extremely low output impedance—an essential factor for precise driver control and accurate low-frequency reproduction.

Mechanical Grounding

Avoiding unwanted vibration transfer from the floor to the loudspeaker is essential to performance. Bass modules generate substantial mechanical energy and must therefore be effectively decoupled to prevent vibrations from spreading into the floor, cabinet, and sensitive electronics elsewhere in the system.

Although the folded dipole architecture of the Børresen BM2 produces lower vibration levels than conventional subwoofer designs, it still benefits significantly from effective resonance control. Proper mechanical grounding helps reduce structural resonances and vibrational feedback, improving clarity, precision, and low-frequency articulation.

For this reason, Ansuz offers optional Darkz resonance-control devices for the BM2. They help limit external vibrations entering the cabinet while providing a controlled path for internally generated energy to dissipate without returning as delayed resonances.

As a result, Darkz represents a highly effective upgrade for the BM2, improving cabinet stability while preserving the precision, speed, and articulation required for high-performance low-frequency reproduction.