Ferrite magnets: Hard and Soft Ferrite Magnets Explained

Ferrite magnets (also known as ceramic magnets) are one of the popular types of permanent magnets used in subwoofers and speakers to create an opposing magnetic field which further results in vibration thus resulting in boomy sound.

They are a type of ceramic magnets composed of iron oxide mixed with other elements such as barium, zinc, copper, or strontium. 

Furthermore, they are also known as alpha-iron and symbolically it is presented as α-Fe (α-Ferrite) which is a scientific material term for pure iron.

Key Takeaways

  • Ferrite magnets are also known as ceramic magnets.
  • They are not as strong as Neodymium (Rare Earth Magnets) but make a good fit for low to mid-range speaker designs.
  • The main benefit of these magnets is that it does not corrode easily if used properly.
  • Even though they are brittle, high coercivity, low cost, and high resistance to demagnetization make them an excellent fit for speakers and subs.
  • They are made by combining iron oxide and strontium carbonate and are typically popular in larger driver assemblies.

How are ferrite magnets for subwoofers and speakers made?

Ferrite magnets are man-made products and are produced by heating a mixture of elements (iron oxide, strontium carbonate, barium carbonate, etc.) at high temperatures (over 2000° F). Upon heating under high temperatures, a chemical reaction converts the mixture into a ferrite material with a strong magnetic force.

Depending on the use case, magnets are created in a variety of forms and sizes for use in subwoofers and speakers.

Here’s a general overview of how ferrite magnets for speakers are made

Raw materials preparation

Ferrite magnets are made of ceramic material main components being iron oxide and strontium carbonate or barium carbonate. These raw materials are finely ground into a powder form to ensure a homogeneous mixture.

Forming the magnet shape

The powdered mixture is then pressed into the desired shape using molds or hydraulic presses and the shape is typically a ring or a cylinder with a hole in the middle, as required for speaker applications.

Sintering

The formed magnet shapes are heated to high temperatures in a sintering furnace, usually around 1000 to 1300 degrees Celsius.

During this process, the particles fuse together, and the magnet’s crystalline structure is formed, resulting in a solid and durable magnetic material.

Cooling and cutting

After sintering, the magnet is allowed to cool gradually to room temperature to avoid any cracks or structural defects.

Once cooled, the magnet is cut into individual pieces, ensuring they match the specific requirements of the speaker.

Magnetization

The cut magnet pieces are then magnetized in a strong magnetic field.

This process aligns the magnetic domains within the material, giving it its magnetic properties.

Surface treatment

In some cases, the magnets may undergo surface treatment to protect them from corrosion or improve their performance.

Quality control

Throughout the manufacturing process, quality control measures are implemented to ensure the magnets meet the desired specifications for use in speakers.

Diagram explaining the process involved in making ferrite magnets

Diagram explaining the process to make ferrite magnets

Also Read: How to build a subwoofer box for deep bass?

Types of ferrite magnets used in Speakers and subwoofers

In speakers and subs, the most common types that are used are barium and strontium ferrite magnets, which are standard in many designs due to their cost-effectiveness and suitable magnetic properties.

Both strontium and barium ferrite magnets offer sufficient magnetic strength for most speaker requirements, making them popular choices in the audio industry for their performance and cost-effectiveness.

Also Read: Active vs Passive Subwoofers (Differences explained)

What are the two types of ferrite magnets?

There are mainly two types i.e., hard and soft ferrite.

Hard Ferrites

Hard ferrite magnets are ceramic magnets that have a high coercivity and are used in subwoofers, loudspeakers, and other applications such as refrigerators and electric motors.

When the hard ferrites are exposed to an external magnetic field it tends to retain the magnetism due to high coercive properties.

Also, they have stronger magnetic properties when compared to soft ferrites.

The most common types of hard ferrite are Strontium ferrite (SrFe12O19) and Barium ferrite (BaFe12O19).

Soft Ferrites

Soft ferrite magnets are often termed as more temporary magnets because they tend to lose their magnetism when exposed to extreme temperatures or strong magnetic fields.

In other words, they have low coercivity,  meaning they have a lower resistance to changes in their magnetic orientation or magnetization.

Common Soft Ferrites with formula

Soft Ferrite TypeFormula
Manganese-zinc ferrite (MnZn)MnaZn(1-a)Fe2O4
Nickel-zinc ferrite (NiZn)NiaZn(1-a)Fe2O4

These types of magnets are typically used in transformers, inductors, several components of a microwave, etc.

Finally, there is also a semi-hard ferrite known as Cobalt ferrite (CoFe2O4) which stands between the hard and soft ferrites.

These types of ferrites are magnetostrictive and are typically used in applications like sensors and actuators.

A table to understand the difference between hard and soft ferrites

PropertyHard FerriteSoft Ferrite
CoercivityHard ferrite magnets have a high coercivity (difficult to demagnetize)Low coercivity (easily demagnetized)
Magnetic StrengthHigh magnetic strengthRelatively lower magnetic strength
Permanent MagnetizationRetains strong permanent magnetizationMinimal permanent magnetization
ApplicationsCommon applications of ferrite magnets include speakers, motors, magnetic sensors, etc.Transformers, inductors, high-frequency applications
MagnetizationRequires strong external magnetic fieldEasily magnetized by weak magnetic field
Use in InductorsNot suitable for inductorsIdeal for inductors and transformers
DemagnetizationMore resistant to demagnetizationEasily demagnetized under changing fields
Temperature StabilityGenerally good temperature stabilityGood temperature stability
CostTypically more expensiveGenerally more cost-effective

Note: The properties listed above are general characteristics and may vary depending on the specific type and composition.

What is a bespoke ferrite?

The term “bespoke ferrite” simply means that it is a ferrite magnet that is custom-built or made-to-order, rather than a standard, off-the-shelf product.

Bespoke ferrite magnets are created to match precise specifications, such as specific dimensions, magnetic properties, or performance characteristics, that may not be readily available.

Manufacturing a bespoke ferrite is a complex process as it typically involves close collaboration between the magnet manufacturer and the customer to ensure that the final product meets all the required specifications and performance criteria.

What are the characteristics of ferrite and the benefits of using subwoofers with ferrite magnets in them?

Benefits of using subwoofers with ferrite magnets in them:

  • Ferrite magnets have high resistance to corrosion.
  • They are available at lower costs thus making them affordable.
  • They are easier to produce in various sizes and large rings.
  • They may perform very well in damp conditions and last longer.
  • They are ideal for many applications in the sound system, especially marine sound applications.
  • It is highly versatile as it balances performance and affordability for various audio setups.
  • Practical choice for bass production with larger drivers.

With all that said, when we look into the drawbacks, the major drawback is the size and weight of these magnets.

This is because the magnetic power of a ferrite magnet is not as strong as a neo magnet (neodymium magnet). Hence, speakers with ferrite magnets have to be built larger to produce better output.

Also Read: Subwoofer placement ideas for deep bass

Difference between rare earth and ferrite magnets

Rare earth magnets are a type of permanent magnet made from alloys of rare earth elements, such as neodymium, praseodymium, and dysprosium, combined with other metals like iron and boron.

They are known for their exceptionally high magnetic strength, making them the strongest type of permanent magnets available.

Due to their strong magnetic fields, they are used in various high-performance applications where high magnetic strength is critical, such as electric motors, wind turbines, and high-efficiency speakers.

Rare earth magnets have a higher energy density compared to ferrite magnets, which means they can generate stronger magnetic fields with smaller volumes.

On the other hand, Ferrite magnets are typically characterized by their high magnetic permeability, which makes them ideal for magnetic shielding applications and magnetic assemblies.

Since they are made from a combination of iron oxide and either strontium or barium carbonate and are less expensive to produce than rare earth magnets, they are a more cost-effective option for many applications.

That is one of the reasons why these types of magnets are commonly used in electronic inductors, transformers, speakers, and various consumer electronic devices.

Furthermore, they have moderate magnetic strength compared to rare earth magnets, but they still offer sufficient magnetic properties for many applications.

Table explaining the key differences between rare earth and ferrite magnets

CharacteristicRare Earth MagnetsFerrite Magnets
CompositionAlloys of rare earth elements and other metals.Magnet Example: Neodymium and samarium cobalt magnets.Iron oxide combined with strontium or barium ferrite.Magnet Example: Ceramic Magnets
Magnetic StrengthMuch stronger, providing higher magnetic fields and energy densityModerate, sufficient for many applications, used in electronics and barium ferrite magnets
CostMore expensive to manufactureLess expensive, cost-effective option
ApplicationsUsed in high-performance applications where stronger magnetic fields are required, commonly used in the electronicsSuitable for a wide range of applications, including electronic devices and low to mid-range speakers
Energy DensityHigher energy density generates stronger magnetic fields with smaller volumesLower energy density compared to rare earth magnets, magnets are permanent magnets
CorrosionMay be prone to corrosion, especially in damp environmentsFerrite magnets are corrosion free in most cases

Can temperature affect ferrite magnets?

The change in temperatures can influence the performance of a magnet including ferrite magnets.

Additionally, due to the inherent coercivity of ferrite magnets, their resistance to demagnetization increases at higher temperatures or when they get hotter.

Generally, an increase in temperature by every degree will increase the inherent coercivity of ferrite magnets by about 0.04% whereas on the downside, it decreases by 0.02% for every degree.

Note – Although ferrite magnets can perform at higher temperatures ranging around 180 degrees Celsius, they are less effective at cold temperatures, especially, below 0 degrees Celsius.

However, depending on how they are designed and the applications they will be used for, ferrite magnets can work efficiently at temperatures as low as -40 degrees Celsius.

Do ferrite magnets corrode?

The material iron-oxide within the magnet material is already in oxide form (rusted iron), therefore it is difficult to be oxidized further.

Therefore ferrite magnets have excellent corrosion resistance.

Final Thoughts

If you want to go for an affordable yet reliable source of magnetism, then a subwoofer using a ferrite magnet might be just what you need.

On the other hand, if you looking for more stronger and compact sound set-up then neodymium is your best bet.

Finally, whatever you decide, just remember that each type has its own set of pros and cons that should be considered before making a final decision.

Frequently Asked Questions

When was the chemical composition of the first ferrite synthesized?

The first ferrite magnet was synthesized in 1930 at the Tokyo Institute of Technology by two Japanese professors Dr. Yogoro Kato and Dr. Takeshi Takei.

Which type of ferrite magnet is used in a subwoofer?

Hard ferrites are used in Subwoofers and speakers whereas soft ferrites are used in transformers and inductors.

Do ferrite magnets react at room temperature?

Technically ferrite is one of the allotropes of iron and remains stable at room temperature.

What color is a ferrite magnet?

Ferrite magnets can be found in dark gray shades.

Are ferrite and alnico magnets same?

No, ferrite and alnico magnets are not the same. They are two different types of magnets with distinct compositions and magnetic properties.

Armed with a Diploma in electrical engineering and a remarkable 12 years of expertise, he excels in rejuvenating music systems, washing machines, dryers, and laundry-related appliances. Manish's profound insights and practical know-how establish him as a credible authority in appliance and music system repairs. Contact: manish.singh (at) subwooferblog.com. He's always ready to lend a helping hand!