A (Long) Stroke of Genius: Designing Drive Units Without Compromise
When we designed our flagship 360 loudspeaker, we set out to drive distortion down to unprecedented levels. Breakthrough technologies like Adaptive Bias Control and Power DAC, paired with a revolutionary cabinet design and our Exakt phase-linear digital crossover, deliver its signature wide dispersion and low distortion. Yet for us, this wasn’t the end of the journey...
We were still fundamentally constrained by 360’s off-the-shelf low-frequency drive units. They were the most significant remaining source of distortion and noise in the whole system. Magnetic field modulation; inductance variation; acoustic compression within the motor; thermal compression – each distorting element could theoretically be tackled and overcome.
So we dedicated three years to designing our own 6” upper bass and 8” woofer units from first principles. At the heart of both lies a unique motor system: Pistonik. Innovations throughout its design engineer out magnetic, mechanical and thermal factors which together conspire to defeat linearity.
Now fitted as standard to 360 speakers – and available as an upgrade – these new units featuring Pistonik move awesome volumes of air, with absolute control, and the widest truly linear excursion of any low-frequency drive units ever created.
Flawless Linear Force
In most drive units, force delivery isn’t constant as the cone moves. As excursion increases, the voice coil exits the magnetic gap. Field strength changes. Inductance shifts. The restoring forces of the suspension become increasingly non-linear. The audible consequence of this is high levels of distortion – particularly at higher output levels.
With Pistonik, our drive units achieve ultimate linearity across a prodigious excursion range, thanks to its very long-stroke, underhung topology. The compact, multi-layer voice coil is contained within a specially extended magnet gap across its range of travel.
To lower distortion further and reduce magnetic drag, we immersed the entire motor assembly in permanent magnetic saturation. A uniquely profiled inner structure, combined with a full-length copper sleeve, stabilises flux density within the gap and reduces the impact of eddy currents in the surrounding steel. This provides the drive unit with exceptional speed, agility and responsiveness.
In this animation, you’ll see the force plot remain impeccably flat across the vast majority of its extremely wide operating range. No asymmetrical behaviour, no abrupt transition into instability. Force only begins to taper slightly at the extremes – at practically unlistenable volumes. Linear force means consistent motion. Consistent motion means lower distortion.
Magnetic linearity is only one part of the equation, however. At high excursion, the cone assembly acts like a plunger. Air trapped within the motor structure can compress and decompress rapidly, generating turbulence and audible noise. Simultaneously, voice coil temperature rises, increasing resistance and reducing output — a phenomenon known as thermal compression. Pistonik addresses both.
A triple-layered ventilation network allows air to move freely and silently through the motor structure, eliminating acoustic compression and whistling/chuffing as sources of distortion and noise. A smoothly flared central vent is supported by several tributary airflow routes in the pole piece, voice coil former, and cone assembly. These paths are engineered to maintain supple and smooth motion of the driver’s moving mass, and prevent turbulence even under extreme drive conditions.
At the same time, those ventilation paths draw heat directly from the heart of the drive unit into the aluminium voice coil former and the surrounding steel via the copper shorting sleeve. Warm air is continuously exchanged for cool inside the cabinet. The voice coil remains stable. Resistance doesn’t creep upwards. The amplifier behind the drive unit remains firmly in its comfort zone. Performance doesn’t sag after hours of high-level listening.
Bespoke Suspension to Mirror the Motor
A highly linear motor is nothing without an equally advanced suspension.
Because we design and control the entire 360 system — including its amplification and cabinet loading — we have intimate knowledge of the forces acting on the drive units under all conditions. This gave us the freedom to develop a bespoke suspension far more extreme than the norm using advanced multi-physics simulation.
This finely tuned, bespoke suspension mirrors the linear performance of the Pistonik motor system across the operating range, before confidently applying the brakes at the last moment – stiffening rapidly and predictably only at the outermost limits of travel and not before.
The suspension stiffness remains stable and linear until the final region of maximum excursion, where it rises sharply to preserve control and protect the system.
This behaviour allows maximum usable excursion with total stability and without interfering with the linearity of the motor, ensuring maximum output capability without loss of composure.
Optimised Materials for Resonance Control
Both drive units utilise hard aluminium diaphragms. Aluminium provides a useful combination of low mass and high rigidity, allowing us to push break-up modes well beyond the operating band.
The coupling between diaphragm, surround and Pistonik motor system was carefully optimised to push resonance frequencies higher still and reduce their amplitude.
The outcome is a moving mass that behaves as a rigid piston throughout its working range — maintaining clarity and efficiency without introducing colouration.
Exakt – Measurement and Correction
Even the most advanced manufacturing processes produce microscopic variations. This is where our proprietary Exakt technology extends the performance envelope further still.
Every individual drive unit is laser-measured at the Linn factory. Its unique characteristics are logged against its serial number and used to generate a tailor-made Exakt profile for that specific drive unit. When installed, your Linn system retrieves this data before calculating and applying a correction filter to all drive units in the speaker – accurate to within 0.0625dB of the reference.
Rather than designing around tolerance bands, we correct to an exact target. In practical terms, the loudspeaker performing in your home conforms precisely to the reference design – not statistically, but individually. You have the reference speaker in your room.
Advancements in Assembly
To reliably and repeatably achieve this level of linearity, we also redesigned the assembly process.
Ten precision-machined aluminium and steel jigs were developed to expand the build sequence and enforce exacting tolerances. Additional alignment stages ensure that components are positioned perfectly perpendicular and concentric to the voice coil former, reducing off-axis stresses and microscopic asymmetries. Manufacturing variance is significantly reduced.
The Outcome
We’ve pushed the performance of the first-ever Linn-designed drive units to the very edge of what’s possible; a freedom earned through complete understanding of how they are driven within our systems.
With our proprietary Exakt technology, every individual drive unit performs precisely as designed. Light, rigid aluminium diaphragms with optimised coupling banish resonances far beyond what you’ll ever hear whilst maintaining efficiency. An advanced suspension system, designed to mirror the motor’s linearity, allows motion to be pushed to extremes yet remain closely controlled.
At the core, our unique Pistonik motor system delivers flawless linear force across its prodigious excursion range. Immune to magnetic, mechanical, and thermal factors, every element works together in service of ultimate linearity.
These 6” upper bass and 8” woofer units redefine the state of the art – delivering deeper, cleaner, more controlled bass, with total accuracy, and the widest truly linear excursion of any low-frequency drive units, ever.
Read all about the flagship 360 speakers which feature these new drive units here.
