AUDIO NOTE UK Field-Coil Technology
The Pursuit of Perfect Sound
Field-coil drivers, using an electromagnet to generate the magnetic field with which the voice coil interacts, are a technology that dates back to the earliest days of electrical music reproduction. In this design, the magnet is powered by an external electromagnet, unlike permanent magnet systems that use materials like ferrite or alnico to maintain a constant magnetic field.
While permanent magnet materials like ferrite and alnico became the norm in speaker technology due to their cost-effectiveness and efficiency, field-coil systems offer potential advantages in terms of transparency, detail, and linearity. The development of permanent magnet materials led to the decline of field-coil systems in commercial audio equipment. However, the resurgence of field-coil drivers, as seen in Audio Note's work, is driven by a desire to capture the more subtle details of music—reducing distortion and providing a greater sense of depth and clarity.
Why Field-Coil Speakers?
In traditional magnetic speakers, materials such as ferrite often induce unwanted distortion due to magnetic anomalies like Barkhausen noise and hysteresis. These effects can cause unwanted "hash" or distortion in the sound, which may be imperceptible to the casual listener, but discerning audiophiles often find it detracts from the purity of the sound.
Field-coil systems, by contrast, avoid these distortions due to the softer nature of the materials used in their construction. In this setup, when current ceases to flow through the coil, the magnetic field disappears immediately, which contrasts with permanent magnets that "lock in" their magnetism, sometimes contributing to the unwanted effects.
The result is a calmer, more relaxed sound. Field-coil loudspeakers often deliver more natural tonal inflexions and a soundstage that’s expansive and richly detailed—offering listeners a more immersive experience. As Andy Grove, Senior Engineer at Audio Note (UK), notes, it’s akin to correcting long-held visual impairments, where previously unnoticed distortions fade into the background, revealing finer subtleties.
FIELD COIL
JOURNEY
THE AUDIO NOTE
Audio Note has embarked on a dedicated quest to develop their own field-coil drivers, with the ultimate aim of introducing them to the AN-E Ltd. series of loudspeakers. This venture began in 2019 with early prototypes, which, while promising, faced challenges related to heat generation and magnet efficiency. Over the years, the design evolved significantly, overcoming hurdles such as inefficiency in early magnet prototypes and issues with heat dissipation.
One breakthrough came when Audio Note investigated the casting of custom-made magnets with the help of a metallurgist, leading to improvements in both magnet efficiency and material properties. The company’s ability to combine scientific analysis with hands-on experimentation in their R&D lab, as well as their collaboration with a British foundry, led to the creation of highly efficient field-coil magnets that consume far less energy than earlier prototypes.
AN-E Ltd. Field Coil Power Supply
Technological Innovations and Power Supply
A key feature of the Audio Note field-coil loudspeakers is the specially designed active power supply that supports the field-coil drivers. Unlike passive supplies used in earlier models, which proved unstable under certain conditions, the active power supply has been engineered to ensure consistent voltage delivery to the speakers. This supply is crucial for maintaining optimal bass performance, as small fluctuations in voltage can lead to instability, making the sound either too "loose" or too "stiff."
The power supply is based on an in-house mains transformer and stabilizer circuitry, designed using insights from Audio Note’s preamp technology. It provides a stable DC operating point while allowing for slight adjustments in the audio band. This helps avoid a mechanical or “gripping” sound in the bass and ensures that the drivers operate within their ideal voltage range for natural sound reproduction.
Field-Coil's Future in Hi-Fi
While the current production of the AN-E Ltd. field-coil loudspeakers represents a significant leap forward, Audio Note plans to refine and expand on this technology further. Their work has already redefined expectations of what a field-coil loudspeaker can achieve; still, the potential for improvements in the power supply and crossover networks hints at even greater things to come.
In summary, field-coil technology’s return to the high-end audio space represents a quest to eliminate distortion and increase transparency. Audio Note's ongoing work showcases a deep commitment to this philosophy, and its field-coil loudspeakers are already generating excitement among audiophiles for their unparalleled sound quality. As this technology continues to evolve, there’s little doubt that it will play a significant role in shaping the future of high-fidelity sound reproduction.