Choke Coils

Our choke coils are primarily developed for use in crossovers for loudspeaker cabinets. Inductors have the property of conducting low frequencies better than high frequencies. Because of this property, inductors are used to split the frequency spectrum between the different drivers such as tweeters or woofers. The focus here is especially on supplying the bass and midrange drivers with information and energy. Loss-free and distortion-free transmission of these signals is the prerequisite for contoured, impulse-stable and powerful bass reproduction. The music thus receives its vital foundation – precise, thrilling and alive.

Core materials

The uncompromising reference is the air-core coil: it shows no core-related distortion whatsoever; but because budget and space set limits in practice, we use carefully selected core materials optimized for specific applications.

• Air-core coils: the uncompromising reference when space and resistance allow it
• Ferrite: precise cleanliness at moderate currents and in clearly limited applications
• Aronit: robust current-handling and stable control under high loads
• Feron: maximum control, highest reserves and no sonic compromises

Any distortion caused by inductors has an effect across the entire frequency range due to its harmonic spectrum. The quality of all inductors used – including those connected in parallel with a driver – is therefore of great importance for the entire frequency range, including the mid and high frequencies. Inductors that work free of distortion are not only the basis for optimal bass reproduction, but also essential for natural, differentiated and lively mid- and high-frequency reproduction.

Macro-microphony: when the coil winding vibrates along

Alternating currents flow in a coil and generate an alternating magnetic field. This magnetic field exerts forces on the conductor itself and on the entire winding. If the winding is not sufficiently stabilized mechanically, it can start to vibrate as a whole. These vibrations extract energy from the signal and additionally couple back electrodynamically into the music signal – this is referred to as macro-microphony.

Macro-microphony always manifests itself as a loss of energy, calm, precision and control. Dynamic signal components are particularly affected: bass impulses lose contour, fine details are masked and become inaudible, and the sound image appears more restless and diffuse. These effects are also caused by inductors connected in parallel with the drivers: just as cabinet edges create secondary sound sources in acoustics, vibrating coil windings act as secondary electrical signal sources that corrupt the music signal.

Our countermeasures

To effectively suppress macro-microphony, we deliberately employ mechanical stabilization techniques. These are a central component of the sonic optimization.

Rigid winding geometry

The winding itself is already designed for mechanical stability. Defined winding tension, clean layer guidance and controlled geometry reduce the winding’s degrees of freedom from the very beginning.

Bake-varnish wire

With baked varnish wire, the conductors carry an activatable varnish layer. After winding, the turns are thermally bonded together and form a rigid composite. This effectively reduces vibration of the winding.

Resin soaking

As an alternative to baked varnish, we use resin soaking for certain designs. The resin penetrates the winding and fills cavities. Curing under temperature fixes the winding as a unit. Mechanical stability increases significantly, and vibrations are strongly damped. Choosing the right resin is essential for an optimal result.

Foil coils – maximum calm by design

Foil coils are inherently the mechanically calmest. The flat, dimensionally stable winding structure is mechanically extremely stable and shows practically no tendency to vibrate along. This is why foil coils exhibit very low macro-microphony even without additional measures.

Resin-soaked foil coils – maximum stability

Additional resin soaking further stiffens the already very stable foil winding. This represents the highest level of macro-microphony suppression.

Micro-microphony – the sound of the metals

Micro-microphony describes material-specific processes within the conductor itself: the music signal couples via the electron flow to the natural vibrations of the metal lattice. This interaction modulates the tiniest parameters such as resistance, inductance and timing behavior. This becomes audible not as a tone, but as calm or restlessness, focus or diffusion, refinement or nervousness in the sound image. Micro-microphony cannot be switched off – it can only be shaped, damped and stabilized.

Metals: how are they structured, why do they conduct current, and what happens to the signal in the process?

Copper (Cu)

After silver, copper is the second-best conductor – highly conductive and mechanically robust. Due to its microstructure, however, it shows a certain activity and restlessness at grain boundaries. Sonically, this results in a balanced, full-bodied precision with good substance and a natural foundation. How finely and calmly copper plays in detail depends on the respective copper quality and its internal structure. That is why we use high-purity, thermally post-treated copper grades and select them so that the signal remains stable, faithful in timbre and free of fine restlessness.

Angelique copper (Cu with Ag/Au content)

Our patented Angelique copper is copper with deliberate silver/gold additions (Ag/Au). These additions stabilize the boundary regions in the metal and reduce the temporal micro-restlessness typical of copper, so that the noise spectrum is reduced. This is heard as a calmer, clearer reproduction with more stable timbres and better focus – without copper losing its full-bodied character.

Silver (Ag)

Technically: silver is the best conductor and possesses a very long mean free path of the electrons and few active micro-contact points. This reduces the structural noise of the conductor and creates an impression of luminosity, transparency and fine texture. Silver plays openly and with microscopic precision, but without additional stabilization it can also sound cool.

Silver-gold (Ag-Au)

Technically: a small gold content stabilizes the interfaces in the silver and reduces temporal drift. The transparency of silver is retained, while the reproduction appears calmer and more relaxed. This is heard as more natural, more stable timbres and a clear presentation

Angelique silver/gold with copper content

Combines the transparency and tonal fidelity of silver/gold with more warmth and body. The gold content stabilizes the material and reduces fine temporal restlessness, while a copper content gives the sound more substance and natural fullness. The reproduction thus remains clear and transparent, yet at the same time appears calmer, more relaxed and more stable in timbre.

Conductor shapes

Round wire

Round-wire coils are the proven standard design: a solid conductor is wound into a coil. Sonically, what matters here is that the DC resistance (RDC) suits the application. It directly influences efficiency and control – especially in the bass. Depending on wire cross-section and area of use, the skin effect also plays a role. The mechanics are also crucial: a loosely built round-wire winding can vibrate under load and impair the calm. Our round-wire coils are therefore optimized for a tight winding and fixed with damping so that they remain mechanically calm. Correctly dimensioned, round wire is thus a very strong all-rounder.

Bake-varnish wire / resin-soaked round wire

Bake-varnish wire and resin soaking are two paths to the same goal: a mechanically calm, firmly fixed winding. With baked varnish wire, the turns “bond” into a composite – this significantly reduces macro-microphony and makes the coil audibly calmer and more precise. Alternatively, a resin soaking can transform a winding of ordinary enameled wire into a rigid composite. Both lead to more contour, less “working” in the winding and thus more punch and cleanliness in the sound. The reduced macro-microphony means a considerable gain in detail and fine dynamics across the entire sound image. In this respect, a fixed, bonded round-wire winding is clearly superior to ordinary round wire.

Hepta-litz (7 individual wires, baked varnish)

Hepta-litz consists of seven individual wires, each of which is already baked varnish wire and can therefore be stabilized mechanically very well. Splitting the conductor into several individual strands favors the current distribution in the conductor bundle as frequency increases and can thus reduce additional losses in certain applications. Typical fields of use are correction networks and equalizer branches as well as selected midrange tasks.

Foil

Foil coils use a flat, dimensionally stable conductor made of copper, silver or silver-gold. The decisive feature, besides the winding’s low capacitive component, is the mechanical stability: while round conductors touch and stabilize each other at only very few points, the turns of a foil coil lie flat on top of each other with 100% contact area and are mechanically extremely stable. Even under high loads they vibrate significantly less than bonded round-wire coils. The further reduced macro-microphony means a considerable gain in detail and fine dynamics across the entire sound image. This makes the reproduction appear exceptionally composed, precise and controlled.

Resin-soaked foil

A resin-soaked foil coil takes the already very high mechanical calm of foil to the extreme. The impregnation further reduces remaining degrees of freedom in the winding and makes the composite even more stable. The result is maximum composure under current and a particularly “black” background calm. Especially in the bass and lower midrange, this can deliver audibly more contour, punch and composure, without harshness or restlessness. Resin-soaked foil is thus the logical choice when, in addition to a low RDC, maximum mechanical stability and thus minimum macro-microphony have priority.