P-core inductors – Ferrite and non-ferrite powder cores

When it comes to ferromagnetic cored inductors for passive speaker crossovers, various core materials are used.
The three most popular core types used are:

1. Soft ferrite cores made from a pressed ferrite (mainly) iron powder compound (P-cores)
2. Non-ferrite cores made from a pressed non-ferrite (mainly) iron powder compound (non-ferrite P-cores)
3. Laminated steel cores (I-core)

In this article, we will only look at the properties and differences between soft ferrite and non-ferrite P-core audio inductors.

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 which are listed below:

1. The properties of the specific core material used
2. The crossover design, hereunder, at what frequency the coil position is crossed
3. The specific driver(s) used

It also comes down to the listener's hearing ability, whether 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.


Ferrite versus non-ferrite cored audio inductors:

The two types are largely interchangeable when used for low-pass filtering, but there are differences in how these core types perform when used, for example, for the lower midrange. There are, therefore, 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, like air-core coils, handle higher power, have better pulse reproduction, and will saturate much later.

Depending on the exact material compositions, we can generally say that ferrite cores will saturate earlier than non-ferrite cores and that when saturation occurs for a ferrite core the loss of inductance will happen instantly and much more aggressively than for a non-ferrite core.

This means that non-ferrite cores will generally be better for high-frequency applications, but they are larger and more expensive when it comes to achieving the same inductance as a 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 will follow the general notions mentioned in this article.

It is one thing to examine permeability, hysteresis graphs, and other data from a theoretical standpoint, and then to consider how coils will function in actual crossover and when tested via listening tests.

Conclusion:

Both ferrite and non-ferrite powder cores can be excellent audio inductors when used correctly and when their inherent noise/distortion do not degrade the sound of the speaker system to a level audible to human hearing capabilities.

In theory, it is always best to use an air-cored audio inductor, but in real-life applications 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, it can be necessary to use a ferromagnetic cored inductor, as it takes a much larger air core coil to reach as low a DCR figure and power handling of a ferromagnetic cored inductor with the same inductance.

2. Unless there are no space restraints on the crossover board, using a ferromagnetic cored inductor will be needed to reach the desired properties while fitting on the crossover board.

3.) Cost of components matters, and for audio professionals and DIY audio enthusiasts 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 inherent noise/distortion will not be audible.

ARTICLE SUBMITTED BY JANTZEN AUDIO