Regarding mid-woofers, Michael Børresen has delved even deeper into the subject: In his opinion, the traditional design applying iron to concentrate the magnetic flux on a narrow gap in which the voice coil moves, which has remained virtually unchanged since the invention of the loudspeaker, creates a lot of problems because the parameters of the system - and especially the inductance - vary with the position of the voice coil. These variances cause considerable "iron distortion". He encountered these obstacles with his patented, completely iron-free magnet motor, which uses four opposing neodymium-52 ring magnets to concentrate the flux lines over two solid copper discs that act like pole pieces. The Børresen magnet system features a high flux density of 1.1 tesla. As Michael Børresen explains, the solid copper pole rings also act as effective heat sinks, offering the driver unit a very high power handling capacity. The copper pole rings also reduce the voice-coil inductance to an exceptionally low value of 0.04 millihenry. This is less than ten per cent of the usual value of standard drivers. The lower inductance allows the driver to respond much faster and with almost no delay: The performance becomes much more refined and very detailed. A lower induction also curbs the impedance rise over system resonances: Bass performance becomes very tight, well focused and more authentic.

The Børresen diaphragm is made of a composite material: two layers of very thin carbon on both sides of a four millimetre thick Nomex honeycomb core. Therefore, it features a very good stiffness-to-weight ratio. The low weight of only 5.5 grams allows for a very high acceleration factor of the driver, which results in both excellent resolution and higher efficiency. But even with this patented high-tech bass/midrange driver, Michael Børresen discovered potential for improvement: The inductance of his drivers, which is already about ten times lower than that of conventional drivers, has now been reduced even further to a new, unprecedented minimum: it’s now about twelve times lower than that of traditional, iron-based drivers. Since silver has a six to eight percent better conductivity than copper, the copper pole rings have been replaced by silver rings handmade at Børresen in Aarlborg. The immense manufacturing effort required for this refinement is documented in the report on the visit to Aavik / Ansuz / Børresen starting at the bottom of page 7. In addition, Børresen subjects not only the magnet motor but also all other metal components of the driver to a cryogenic treatment. This is said to reduce their inductance by a further five to eight percent, thus setting a new and unsurpassed standard for the musical performance of the 01 model.

As with all Børresen speaker models, the crossover of the 01 is built in a serial configuration. According to Michael Børresen, this has the effect that the electrical current is phase-locked across the crossover range. A great deal of effort has gone into selecting the best state-of-the-art components for the crossover. The coils are foil types wound with paper insulation and impregnated with resin under vacuum to make them mechanically extremely solid and stable. As capacitors, arrays of small stack-foil types meeting military specifications are being used. They are said to have the best mechanical stability and the lowest inductance of any capacitor type on the market - and they do sound wonderful, too. For attenuating the ribbon tweeter, metal strip resistors are used, as they are having by far the lowest noise values by also showing a very low thermal variation.