Magnets and microphones play huge roles in our everyday lives. You may have read somewhere that magnets play a central role in microphones. Is this true?
Do Microphones Need Magnetism To Work Properly? Dynamic mics (moving-coil and ribbon) convert energy via electromagnetic induction and have magnets built around their diaphragms. Additionally, any mic with a transformer also requires magnets to function as designed. Transformerless FET condenser mics, conversely, do not require magnetism.
So the answer is sometimes yes and sometimes no. It really depends on the microphone in question. In this article, we’ll discuss in detail why some microphones need magnetism and why some others do not. I’ll share mic examples to help illustrate.
Related article: Why & How Do Headphones Use Magnets?
Magnetism And The Dynamic Microphone Transducer
As mentioned, dynamic microphone transducers work on the principles of electromagnetism. This means that dynamic microphones, in particular, require magnetism to work properly.
Before talking about the two main types of dynamic mics (moving-coil and ribbon), let’s define the main working principle, which is electromagnetic induction.
What is electromagnetic induction? Electromagnetic induction is the creation of a voltage (electromotive force) across an electrical conductor as the conductor experiences a changing magnetic field.
Dynamic microphone transducers have permanent magnets built into their cartridges or baffle. These magnets provide the magnetic field required for electromagnetic induction.
Dynamic mics, like all other microphones, have diaphragms that move according to sound waves. The diaphragms of dynamic microphones contain the electrically conductive material required for electromagnetic induction.
As the diaphragm of the dynamic mic moves with varying sound pressure, so too does the conductive material.
The stationary magnets provide a permanent magnetic field. However, as the conductive material changes position within this field, the magnetic field according to the conductive material changes.
In other words, the magnetic field is permanent, but the diaphragm experiences it differently depending on its position within the field.
So then, the electrical conductor experienced a changing magnetic field. There, electromagnetic induction happens and a voltage is created across the conductor.
Because the diaphragm moves back and forth (in alternating directions), this induced voltage is AC.
Ultimately, this AC voltage is our microphone audio signal!
For more info on microphone signals, check out my article What Is A Microphone Audio Signal, Electrically Speaking?
As promised, let’s talk about the moving-coil dynamic mic and the ribbon dynamic mic.
Moving-Coil Dynamic Mic Transducer
The moving-coil dynamic microphone has a non-conductive diaphragm membrane. However, attached to this diaphragm is a conductive coil (typically copper) that sits within a cylindrical slot in a magnetic structure.
A simple digram of the moving-coil mic transducer is shown below:
The diaphragm and attached conductive coil move according to the sound waves they are subjected to. This movement happens within a permanent magnetic field and so a voltage (mic signal) is induced across the conductive coil.
Note that the interior magnetic pole piece has the opposite magnetic polarity of the exterior magnets.
For a complete description of the moving-coil dynamic mic, check out my article The Complete Guide To Moving-Coil Dynamic Microphones.
Ribbon Dynamic Mic Transducer
The diaphragm of a ribbon microphones is, itself, the conductor (often made of aluminum). It sits in a permanent magnetic structure known as a “baffle.”
The conductive ribbon diaphragm moves back and forth about its resting position according to the sound waves it encounters. It does so within a magnetic field and so an AC voltage (mic signal) is induced across it.
Note that along one side of the ribbon’s length, the magnet has a north polarity and that on the other side of the ribbon’s length, the magnet has a south polarity.
For a complete description of the ribbon dynamic mic, check out my article The Complete Guide To Ribbon Microphones (With Mic Examples).
Magnetism And The Transformer
In addition to all dynamic microphones, any mic with a transformer, by default, requires magnetism to work.
What is a transformer? A transformer is a passive electrical device that uses electromagnetic induction change the voltage, current, and impedance of a primary circuit and introduce these changes in a secondary circuit. It does so without electrically connecting the two circuits.
Transformers are made from a single magnetic core and two (or more) conductive windings that wrap around the core without touching one another. In microphones, the transformers are fairly basic and typically only have windings.
These two windings are known as:
- Primary winding (the transformer “input”): this winding is part of the circuit that carries the AC voltage generated by the mic transducer.
- Secondary winding (the transformer “output”): this winding is usually part of the mic output circuit and carries the adjusted mic signal.
Below is a diagram of a step-up transformer. The primary winding is on the left and the secondary winding is on the right. They both wrap around the magnetic core.
In microphones, transformers are often put at the microphone output. These mic are referred to as having “transformer-coupled outputs.”
These output transformers are used for multiple reasons:
- To adjust the impedance of the microphone output.
- To block DC voltage (phantom power, DC bias, etc.) from reaching the parts of the mic that are not designed for DC voltage.
- To boost the voltage (step-up transformer).
- To reduce the voltage (step-down transformer).
- To balance the signal (requires with tube microphones).
Note, too, that in some microphone designs (like active ribbon microphones), there are transformers between the transducer element and the active electronics.
Depending on the microphone design, these transformers could be step-up or step-down transformers.
Step-up transformers increase or “step-up” the voltage between the primary and secondary winding while decreasing the current. The impedance is also stepped up in a step-up transformer
Step-down transformers decrease or “step-down” the voltage between the primary and secondary winding but increase the current. The impedance is also dropped between the primary and secondary windings.
Transformer Turns Ratios
To wrap up our brief discussion on transformers, let’s talk about the equations of the turns ratios.
As mentioned, the transformer has a magnetic core (which is why we’re discussing it in this article). Wrapped around this magnetic core are coils of conductive wire. One coil is the primary winding and the other is the secondary winding.
A “turn” refers to each time a winding is wound around the magnetic core. If the primary winding has fewer turns than the secondary, we have a step-up transformer. Conversely, it the primary winding has more turns than the secondary, we have a step-down transformer.
In an ideal world with no losses, we have the following turns ratio equations:
- Voltage ratio = number of turns in primary winding vs. number of turn in secondary winding.
- Current ratio = number of turns in secondary winding vs. number of turns in primary winding.
- Impedance ratio = square of the number of turns in primary winding vs. number of turn in secondary winding.
For more information on transformers and their role in various microphones, check out my article What Are Microphone Transformers And What Is Their Role?
Condenser Microphones And Magnetism
The condenser microphone transducer works on electrostatic principles. The capsule’s main elements are a diaphragm and backplate that create a sort of parallel-plate capacitor.
These plates require an electric charge between them in order to function properly (via external polarization or electret material). However, there is no need for any magnetism in a condenser microphone capsule.
For an in-depth read on microphone capsules, check out my article What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules).
That being said, condenser microphones often have output transformers. This is particularly true of tube and “true” FET condensers (though there are plenty of transformerless condensers on the market).
Therefore, it is safe to say that many condenser microphones do, in fact, require magnetism to function properly.
Those with transformers need magnetism whereas transformerless condenser mics do not.
To learn more about condenser microphones, check out my article What Is A Condenser Microphone? (Detailed Answer + Examples).
A Recap On Magnetic And Non-Magnetic Microphones
To recap, the elements of a microphone that require magnetism to work are the dynamic mic capsules (moving-coil cartridges and ribbon elements/baffles) and the transformers.
So if a microphone has either of these components, it needs magnetism to work properly.
To provide more information, I’ve assembled the following list to help determine, in general, if a given mic type need magnetism or not:
|Mic Type||Does It Require Magnetism?|
|Passive ribbon dynamic||Yes|
|Active ribbon dynamic||Yes|
|FET condenser||If there is an output transformer|
|Electret condenser||Not unless there is a transformer|
|Lavalier||If it has a dynamic capsule|
|USB mic||If it has a dynamic capsule|
Related article: How Do Microphones Work? (The Ultimate Illustrated Guide).
Do magnets affect microphones? Dynamic mics are designed to convert energy via electromagnetic induction and have magnets inside their cartridges/baffles. Although a magnet may attract a dynamic mic, it likely won’t effect performance, nor will it disrupt the components of a condenser mic unless its magnetic field is enormous.
What are condenser microphones? Condenser mic transducers work on electrostatic principles rather than dynamic electromagnetic principles. Condenser capsules work like parallel-plate capacitors and must be electrically charged to function. Condenser mics also require other active components in order to output a healthy mic signal.