When it comes to ferromagnetic powder cored inductors for passive speaker crossovers there are two material options most commonly used:
1. Powder cores made from a pressed non-ferrite (mainly) iron powder compound, for example our proprietary “Somaloy®” material.
2. Powder cores made from a pressed soft ferrite material, usually either a NiZn (nickel-zinc) or MnZn (manganese-zinc) based iron powder compound.
General thoughts:
All ferromagnetic cored audio inductors will introduce some level of audible noise / distortion (hum), but when this distortion will be audible to the human ear will depend on a wide range of factors, some of them listed below:
1. The properties of the specific core material used
2. The crossover design, hereunder at what frequency the coil position is crossed
It also comes down to the hearing ability of the listener if the audible noise / distortion is noticeable or not.
Even if there is a noticeable audible noise / distortion it is also a subjective decision if the noise is acceptable or not.
Non-ferrite versus ferrite versus cored audiocoils:
The two types can for certain low pass applications be interchangeable, but there are differences in how these core types perform relating to core saturation, the the level of audible noise (EMI), and other technical factors.
There are therefor pros and cons for both core types, which we will explore below:
Ferrite audio coils are generally a more efficient core type for high inductance and for filtering use.
This is due to their magnetic core, which concentrates the magnetic field.
However, they can saturate at high currents, potentially causing distortion and adding unwanted electromagnetic interference (EMI).
Non-ferrite coils will generally be able to handle higher power strains, have better pulse reproduction, and will saturate much later.
Depending on the exact material compositions, we can generally say that a ferrite core will saturate earlier than non-ferrite cores and that when saturation occurs for a ferrite core the inductance loss will be instant and the loss curve much more aggressive than for a non-ferrite core.
This means that non-ferrite cores will generally be better for higher frequency application, but they can be larger in size and more expensive when it comes to achieving the same inductance and DCR figures as a comparable ferrite core.
There are many options when it comes to the specific material (powder) composition for both ferrite and non-ferrite cores for audio grade inductors which means that it is not possible to say that all ferrite and non-ferrite cores are created equal.
It is one thing to look at initial permeability, EMI levels and other data from a more theoretical standpoint and then how coils will function and sound on actual crossover and when tested via live listening tests.
Why we produce coils made from non-ferrite Somaloy® powder cores and discs at Jantzen Audio:
The non-ferrite powder cores and discs used for Jantzen Audio iron core coils and iron core coils with discs uses a proprietary version of the material called Somaloy® and the exact proprietary composition of this material has been engineered specifically for us to give the best possible parameters when it comes to high power handling, low noise (EMI) and a high saturation point as well as a soft induction fall off curve, if the core saturates.
This means that although it is more expensive to produce audio grade powder cores from the non-ferrite Somaloy® material it simply makes for audio grade coils with better technical properties than the more commonly used and cheaper cores made from a ferrite compound.
Conclusion:
Both ferrite and non-ferrite powder cores can be used for audio grade coils, but one should be mindful of which core material to use depending of the various factors mentioned above.
In theory it is always best to use an air cored audio inductor, but in real life application using ferromagnetic cored audio inductors can be necessary due to the points mentioned below:
1. If an inductor with a low DCR figure and high power handling is needed and if there are any spacing and/or cost limitations it can be necessary to use a ferromagnetic cored inductor, as it takes a much larger and more expensive air core coil to reach as low a DCR figure and power handling of a ferromagnetic cored inductor with the same inductance.
2.) Cost of components matter and for audio professionals and DIY audio enthusiast alike, it makes a lot of sense to save on cost by choosing a significantly cheaper ferromagnetic cored inductor for the crossover positions where the inherit noise / distortion will not be audible.