If you were to randomly choose and listen to a pair of headphones, it’s almost guaranteed those headphones will have moving-coil dynamic drivers. The moving-coil dynamic headphone is by far the most common headphone type in existence.
What is a moving-coil dynamic headphone? A moving-coil dynamic headphone is defined by its moving-coil driver. It acts as a transducer, converting audio signals (electrical energy) into sound waves (mechanical wave energy) with electromagnetism. These HPs produce sound via conductive coils that move diaphragms in reaction to audio signals.
In this complete illustrated guide, we’ll discuss moving-coil dynamic headphones; their drivers and working principles; their pros and cons, and a few examples of these commonplace headphones.
What Is A Headphone Driver?
Before we get started, let’s go over the definition of the headphone driver.
Of all the elements that go into headphone design, the driver is the most important.
Headphone drivers are the transducer elements that allow the headphones to convert incoming audio signals into sound waves for the listener to hear. Without headphone drivers, a pair of headphones would not be able to perform.
Analog audio signals, which are used to drive headphone drivers, are electrical signals with alternating current.
To learn more about why the audio must be analog, check out my article Are Headphones Analog Or Digital Audio Devices?
Headphones are designed to pass these AC signals through their drivers by electrically connecting the drivers to the intended audio source. This connection is made via the headphone jacks in an assortment of different audio sources including smartphones, computers, mp3 players, mixing consoles, headphone amplifiers, audio interfaces, and many more.
To learn more about headphone amplifiers and headphone jacks, check out the following My New Microphone articles:
• What Is A Headphone Amplifier & Are Headphone Amps Worth It?
• How Do Headphone Jacks And Plugs Work? (+ Wiring Diagrams)
• Differences Between 2.5mm, 3.5mm & 6.35mm Headphone Jacks
Headphones nearly always have two drivers designed to convert two different audio signals and allow for stereo listening. This is why headphones are often referred to in a pluralized manner even if we’re discussing a single audio device.
For more information on how headphone drivers receive their intended audio signals (mono, stereo, unbalanced and balanced), check out the following My New Microphone articles:
• An In-Depth Look Into How Headphone Cables Carry Audio
• How Do Wireless Headphones Work? + Bluetooth & True Wireless
The driver is designed to allow the AC audio signal to flow and use the energy of this signal to move a diaphragm that will produce sound.
How does this happen? Well, there are multiple working principles for different headphone driver types.
To read about all the different headphone driver types, check out my article What Is A Headphone Driver? (How All 5 Driver Types Work).
Electrostatic headphones work on electrostatic principles while bone conduction headphones work with piezoelectricity.
The most common working principle of headphones, bar none, is electromagnetism. Planar magnetic and balanced armature transducers work on this principle. The moving-coil dynamic headphone transducer we are interested in in this article also work on electromagnetism.
What Is Electromagnetic Induction?
The principle of electromagnetic induction is the key to understanding how moving-coil dynamic headphones work.
Electromagnetic induction states that an electrical current flowing through a conductor will cause a magnetic field to be produced in and around the conductor.
Similarly, it states that a voltage (and, therefore, a current) will be produced across and electrical conductor in a changing magnetic field.
So with an audio signal and a conductive coil connected to a diaphragm, the moving-coil driver can produce a variating magnetic field in and around the coil.
This magnetic field interacts with permanent magnets in the driver structure to cause diaphragm movement and, therefore, sound waves.
How Do Moving-Coil Headphone Drivers Work As Transducers?
Now that we know the basics, let’s dive into the specifics of how moving-coil dynamic headphones work are transducers.
Remember that the moving-coil dynamic driver is the defining element of the moving-coil dynamic headphone and so we’ll be focusing our discussion on the driver.
Note, again, that headphones generally have two drivers (one for each ear) so even though we’ll be talking about the driver in singular, it’s important to note that a pair of moving-coil dynamic headphones will typically have two drivers.
The Moving-Coil Dynamic Headphone Driver
Let’s begin our in-depth discussion of the moving-coil dynamic headphone driver with a simplified cross-sectional diagram:
In the diagram above, we see 4 key components that make up a moving-coil dynamic headphone driver:
- Voice coil (moving-coil)
- Magnet (including pole pieces)
The housing is designed to keep all the elements together and allows the driver to be effectively incorporated into the body design of the headphone. It doesn’t play a major in the conversion of electrical energy (audio signals) to mechanical wave energy (sound waves).
The diagram, though not absolutely accurate in scale, shows us that the conductive coil is attached to the diaphragm and suspended in a cutaway within the permanent magnetic structure.
The coil is made of tightly-wound conductive wire (often copper) and forms a hollow cylindrical shape.
The oddly-shaped magnetic structure has a circular cutaway that is just large enough to fit the conductive coil.
There must be just enough space for the coil to move without touching the magnetic structure.
For optimal efficiency, the magnetic structure must be as close to the coil (interior and exterior) as possible. In other words, the magnetic flux lines must be concentrated at the coil. This involves having opposite magnetic poles to the immediate interior of the coil and immediate exterior of the coil.
This makes for a rather complex and oddly-shaped magnetic structure made of a primary magnet and magnetic pole pieces. This structure can be better understood via the simplified cross-sectional diagram below:
The main magnet is a ring magnet with its south pole facing upward and its north pole facing downward. These main magnets are often made of strong rare earth Neodymium (which we’ll get to later) but can be made of other magnetic material as well.
A larger ring-shaped pole piece is attached to the top of the main magnet to extend its south pole.
A plate-shaped pole piece is attached to the bottom of the main magnet to extend the north pole. Further extension of the north pole if made possible with a cylindrical pole piece shooting up out of it.
This shape allows the voice-coil to be suspended in the empty space.
As discussed above, by having opposite magnetic poles to the immediate interior and exterior of the coil, we maximize the magnetic field strength across the coil’s wire and, therefore, optimize the efficiency of the electromagnetic induction required to convert the audio signals into sound waves.
Here is a picture of two moving-coil dynamic headphone drivers:
For more information on the relationship between headphones and magnets, check out my articles Why & How Do Headphones Use Magnets?
So how do moving-coil dynamic headphone drivers work?
Let’s start with the audio signal and the connection of the headphones to an audio source. As we’ve discussed, analog audio signals are AC voltages.
Normally, the audio source sends an unbalanced stereo signal to the drivers of the headphones. One wire carries the left channel audio and another wire carries the right channel audio.
Each channel shares a common return wire.
The return wire is needed to create an electrical circuit between the driver and the audio source. This circuit includes the conductive moving-coil of the driver and passes the audio signal’s alternating current.
As the electrical current alternates within the coil, a coinciding varying magnetic field is produced in and around the coil.
This varying magnetic field interacts with the permanent filed of the driver’s magnetic structure and causes the coil to oscillate up and down within its cavity.
The coil is attached to the diaphragm of the driver. As this thin membrane vibrates with the moving-coil, it pushes and pulls the air molecules around it and effectively creates sound waves.
These sound waves are directly proportional to the audio signal applied at the coil, which effectively makes the moving-coil dynamic headphone driver a transducer!
Other Moving-Coil Dynamic Designs
This moving-coil dynamic driver design is not exclusive to headphones. In fact, most loudspeakers use the same design only at a bigger scale.
There are even moving-coil dynamic microphones that use this design, only in reverse. These mics covert sound waves into audio signals rather than audio signals into sound waves (like headphones and speakers do).
For more information on moving-coil dynamic microphones, check out my article The Complete Guide To Moving-Coil Dynamic Microphones.
What Are Neodymium Drivers?
Neodymium headphone drivers use rare earth Neodymium magnets in their design.
Neodymium magnets are permanent magnets made from an alloy of neodymium, iron and born (Nd2Fe14B).
These neodymium magnets are the strongest type of commercially-available permanent magnets and are preferred in headphone design because of their effects on improving the efficiency of the transducer.
Pros & Cons Of Moving-Coil Headphones
As is the case with anything in life, moving-coil dynamic headphones have their pros and cons. The advantages and disadvantages of moving-coil dynamic headphones are summed up in the following table:
|Relatively cheap to produce||Requires significant damping and tuning due to resonant frequencies|
|Rugged design||Poorer high-end response|
|Passive working principle||Less accuracy in transient response due to diaphragm mass and inertia|
|Somewhat humidity resistant||Spherical wavefront & distortion due to non-linear movement|
|Variety of form factors and sizes (headphones and earphones)|
|Often do not require headphone amplifiers|
Pros Of Moving-Coil Headphones
Relatively Cheap To Produce
Of all the different headphone driver types, moving-coil drivers are among the cheapest to produce. That is not to say that these headphones are cheap. There is a significant price variation between the cheap and high-end moving-coil dynamic headphones.
However, these headphones are often fairly prices and affordable to casual listeners and audio professionals alike.
For tips on choosing the right price point for your headphone purchases, check out my article Are Expensive Headphones (Or Cheap Headphones) Worth It?
The design of the moving-coil dynamic headphone is pretty reliable and durable. From the relatively thick diaphragm to the tough coil and magnetic structure, the moving-coil driver is likely to have a long lifespan.
Passive Working Principle
Dynamic drivers are passive, meaning they do not require power to function properly. This rids of the need for a power supply and lowers the price on the headphones.
Of course, the headphones require electricity (the audio signal) to function properly but their drivers are passive.
Note that wireless and noise-cancelling moving-coil dynamic headphones are active, though the power is required for their wireless receivers, amplifiers and ANC circuits rather than their dynamic drivers.
Somewhat Humidity Resistant
High humidity is unlikely to interfere with the performance of passive moving-coil dynamic headphones. Of course, I wouldn’t recommend dunking headphones in water unless they’re completely waterproof but moving-coil drivers are pretty resisitant to humidity.
Variety Of Form Factors & Sizes
Moving-coil dynamic drivers can be enjoyed in all the headphone form factors including:
- In-ear monitors
- Open-back headphones
- Closed-back headphones
- Supra-aural (on-ear) headphones
- Circumaural (over-ear) headphones
To learn more about the different form factors of headphones, check out my in-depth article How Do Headphones Work? (Illustrated Guide For All HP Types).
Often Do Not Require Headphone Amplifiers
Even though the coils in moving-coil drivers tend to have impedance resonances in the audible range, they still often do not require amplifiers.
Most moving-coil dynamic headphones have low enough impedances ratings and high enough sensitivity ratings to function well with a typical headphone jack.
Of course, there are plenty of high-impedance moving-coil dynamic headphones that require dedicated amplifiers. However, in the current market, there are more models that do not.
For more information on headphone amplifiers, check out my article What Is A Headphone Amplifier & Are Headphone Amps Worth It?
Cons Of Moving-Coil Headphones
Requires Significant Damping/Tuning Due To Resonant Frequencies
In the previous section we mentioned the resonances inherent in the coil. Add these resonances with those of the driver housing and these drivers actually require significant damping and tuning to achieve a natural frequency response.
Tuning and damping is built into the design of the headphones but may alter over time as the damping material ages.
Poorer High-End Frequency Response
The relatively large coil an thick diaphragm may have more difficulty than other driver types when producing the short wavelength vibrations required to make high-frequency sound waves.
Improved high-end clarity is often the first thing audiophiles notice when switching from a pair of miving-coil headphones to a pair of planar magnetic or electrostatic headphones.
Less Accurate Transient Response
The large coil and thick diaphragm also have more mass and more inertia, making moving-coil dynamic drivers a little bit less accurate when it comes to reproducing the transients of an audio signal.
An audio transient is a short-lived increase in amplitude (think of a tight snare drum hit as a coomon example).
Spherical Wavefront & Inherent Distortion
Planar magnetic and electrostatic headphones have the entire area of their diaphragms move according to the audio signal.
This causes a planar wavefront of sound with very little distortion, if any. These planar waves interact with our ears quite naturally.
Moving-coil dynamic drivers, on the other hand, only cause direct movement near the centre of their diaphragms where the coil attaches. Of course, the entire diaphragm moves when the coil does but it is only near the centre of the diaphragm that the coil is focused on moving, the rest of diaphragm follows.
This causes a spherical wavefront of sound with notable distortion as the outer area of diaphragm follows the excursions at the centre of the diaphragm. Spherical waves also reflect on our ears in relatively unnatural ways which, to a small degree, alters the way we hear the sound of the moving-coil dynamic headphone drivers.
Moving-Coil Dynamic Headphone Examples
To learn more about moving-coil dynamic headphones, let’s have a look at a few examples.
The Audio-Technica ATH-M50x (link to compare prices on Amazon and B&H Photo/Video) is a great prosumer moving-coil headphone that sounds awesome given its affordable price point.
The Apple Earpods (link to check the price on Amazon) are earbud-type earphones that utilize small moving-coil drivers, making them moving-coil dynamic headphones, too.
Related article: What Are The Differences Between Headphones And Earphones?
Grado Labs SR80e
The Grado Labs SR80e (link to compare prices on Amazon and B&H Photo/Video) is an example of a supra-aural (on-ear) open-back moving-coil dynamic headphone.
Related article: The Complete Guide To Open-Back & Closed-Back Headphones
Bose QuietComfort 35 II
The Bose QuietComfort 35 II (link to compare prices on Amazon and B&H Photo/Video) is a moving-coil dynamic headphone with Bluetooth wireless and active noise-cancellation technology.
This excellent headphone shows us that moving-coil headphones can have additional technology. Remember that it is the drivers that are the defining elements of moving-coil dynamic headphone drivers.
Moving-coil dynamic headphones are, again, the most common type of headphones on the market. There are plenty of brands that produce this type of headphone.
Audio-Technica, Grado Labs and Bose are all featured in My New Microphone’s Top Best Headphone Brands In The World.
For a list of all the headphone brands/manufacturers, check out my article Full List: Headphone, Earphone & Headset Brands/Manufacturers.
What’s better: 40mm or 50mm drivers? All else being equal, larger drivers are capable of producing greater sound pressure levels and more bass frequencies but require more power to do so. The best driver size for any given headphone is more than likely the driver size the headphone is designed with.
To learn more about headphone driver sizes, check out my article What Is A Good Driver Size For Headphones?
What specifications should I look for in headphones? The specifications sheets provided by headphone manufacturers give us important data. The most important specs include:
- Driver type
- Frequency response
- Power requirements
For more detailed information on the specifications listed above, check out the following My New Microphone articles:
• What Is A Headphone Driver? (How All 5 Driver Types Work)
• The Complete Guide To Understanding Headphone Impedance
• The Complete Guide To Headphones Sensitivity Ratings
• What Is Headphone Frequency Response & What Is A Good Range?
• How Do Headphones Get Power & Why Do They Need Power?