Choosing the right coil core

The sound characteristics of a coil are not only determined by the coil wire and the manufacturing quality but also by the coil core used. As the use of different cores results in coils with different advantages and disadvantages we offer four core materials and a total of seven core types. This enables us to manufacture exactly the right coil for each application.

In order to avoid microphonic effects, all Mundorf coils are wound on a coil body. This ensures mechanical stabilisation of the winding, decoupling of the coil from the board and, in addition, facilitates the manufacturing process.

Air coils

The ideal core material for coils is air. Air cored coils are, for physical reasons, superior to all metal core coils as far as accurate pulse reproduction and freedom from distortion are concerned. They can be used in all areas; either as highpass filter in the middle frequency range, as bass coil (with large conductor cross section) or in correcting components (with thin wire cross section).

Precision, dynamic, subtle tonal gradations, great detail and liveliness distinguish coils with air core from all others. In high-quality speakers, they are thus the basis for realistic and harmonic musical enjoyment.

Core coils

Core coils have a metal core which reinforces the magnetic field. Compared to air coils, smaller, cheaper coils with higher inductivity and lower ohmic resistance can be realised. However, the metal core also affects the music signal (among other things due to unwanted distortions).

Ferrite cores are sintered from a metal plastic powder. The German-made ferrite material HP3616 used by us offers a significantly higher performance than the Asian cores used in many other products. It is characterised by low basic distortions and rapid magnetic reversibility (= change of field direction). The music signal is hardly delayed so that coils with ferrite cores are perfect for use in correcting components (as so-called peaking coils) and in the middle frequency range. So far the only ferrite material tested by us HP3616 meets our high demands regarding resilience and distortion making it suitable even for use in the middle-low frequency and bass range for lower amplifier performance.

Aronit cores (also known as P cores) consist of high-density metal-ceramics-powder. The Germanmade Wicon ferrite rods produce extremely low distortion, even at very high loadings. Due to their highly compact dimensions, their low internal resistance and their excellent price/performance ratio they are particularly suitable as bass and subwoofer coils and for PA applications.

Feron cores consist of an iron-silicon alloy (also called electrical sheets). Our high-performance transformer plates are rolled and tampered several times using special procedures so that all crystals are oriented in the same direction (grain oriented) and a uniform crystal-lattice structure is obtained. Mundorf Feron core coils thus differ from conventional, similar looking coils in a measurable and audible way. They stand out due to minimum basic distortion, magnetic reversal losses and distortions while having a high performance and are thus suitable for flexible applications.

Zero-Ohm-Coils (ZOC) are a speciality of our company. In the ZOC, an air gap is calibrated and precisely adjusted by hand between two sheet metal packages made of Feron. The air gap determines the inductivity of the coil and demands great care in the manufacturing process. The high production costs of the ZOC are always justified when maximum faithfulness in pulse reproduction of the playback is required. This special form of the Feron core coil helps to realise lower internal resistances as compared to other core types.