As we may know, headphones convert audio signals into sound waves that we can listen to. Without a proper driver, headphones would not be able to function.
What is a headphone driver? A driver is the headphone's transducer element responsible for converting audio (electrical energy) into sound (mechanical wave energy). Each pair of headphones has a pair of drivers. Drivers typically utilize a movable diaphragm to produce sound waves, and most rely on electromagnetism to function.
This quick answer is, of course, overly simplified. In this article, we'll get into the finer details of how each of the 5 headphone driver types works to deepen our knowledge of these excellent audio devices.
The 5 Headphone Driver Types
There are 5 noteworthy types of headphone drivers. They are:
- Dynamic Moving-Coil
- Planar Magnetic
- Balanced Armature
- Magnetostriction (Bone Conducting)
Let's discuss each of these driver types and the working principles that allow them to act as transducers.
Before we get started, if you'd like a primer on the differences between audio and sound to better understand the headphone drivers' role as transducers, check out my article What Is The Difference Between Sound And Audio?
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Dynamic Moving-Coil Headphone Drivers
The most common headphone driver type, bar none, is the dynamic “moving-coil” driver. We'll find these drivers in most earphones/earbuds, all types of headphones, and in-ear monitors (though IEMs also often utilize balanced armature drivers).
Dynamic headphones work on the principle of electromagnetic induction.
Electromagnetic induction states that a changing magnetic field will induce a voltage across an electrically conductive material. Similarly, a changing voltage across a conductor will cause a changing magnetic field around the conductor.
Let's talk about design.
Like most headphone drivers, their designs include a movable diaphragm that pushes and pulls air, producing sound waves for our ears to hear. The diaphragm is typically circular and is attached to the driver's housing around its circumference.
The diaphragm of a moving-coil driver is attached to a moving coil, hence the name. This coil is electrically conductive and is designed to be part of the electrical circuit with the audio output device.
The coil is suspended in a cylindrical cutaway in an oddly-shaped magnetic structure. This structure has its north magnetic pole to the interior of the coil and its south magnetic pole to the exterior. The design allows for maximum magnetic flux density through the coil, which is paramount in creating an efficient and effective dynamic headphone driver.
Here is a simplified cross-sectional diagram of the moving-coil dynamic headphone transducer to better visualize this driver type.
The moving-coil dynamic driver in action.
Two electrical lead wires carrying the audio signal are connected to the conductive coil. One wire is connected to each end of the coil.
When the headphones are connected to an audio source (wirelessly or via cable), these lead wires carry audio signals to the coil. More specifically, the coil becomes part of the audio circuit.
Audio signals mimic the energy of sound waves and are, therefore, alternating currents.
Electromagnetic induction states that as an electrical current passes through a conductor, a coinciding electromagnetic field is produced in and around that conductor. Since the audio signal is AC, the magnetic field induced across the coil as audio passes through it alters direction.
However, the magnetic field produced by the dynamic driver's magnetic structure is permanent. Thus, any change in the coil's magnetic field would cause attraction and repulsion with the permanent magnet. This means that the coil will move back and forth according to the sign and amplitude of the audio signal.
Because the coil is attached to a diaphragm, the diaphragm will also move according to the audio signal. The diaphragm is able to push and pull the air required to produce sound signals that emulate the audio signal.
And that's how dynamic moving-coil headphones function!
Note that the term dynamic, when it comes to audio transducers, means that the transducer works on the principle of electromagnetic induction.
Planar magnetic and balanced armature headphone drivers are also dynamic, though “dynamic” typically refers to the moving-coil variety.
Moving-coil dynamic microphones share the same basic design as moving-coil dynamic headphones. The major difference is that the microphones are designed to work in reverse, converting sound waves into audio rather than the other way around.
For everything you need to know about moving-coil dynamic microphones, check out my article The Complete Guide To Moving-Coil Dynamic Microphones.
Loudspeakers, monitors and subwoofers also almost always utilize moving-coil dynamic drivers as well. The difference here is that speaker drivers are generally larger than headphone drivers (but not always).
To learn more about dynamic headphones and their relationship to magnets, check out the following My New Microphone articles:
• What Are Dynamic Headphones And How Do They Work?
• Why & How Do Headphones Use Magnets?
• Are The Magnets In Headphones/Earbuds Bad For You?
Pros And Cons Of Moving-Coil Drivers
The pros and cons 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
|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
Moving-Coil Dynamic Headphone Examples
There is an overwhelming amount of different moving-coil dynamic headphone models on the market today. They range from cheap consumer-grade products to top-of-the-line studio professional products. They include all form factors from in-ear monitors to earbud to over-ear closed-back wireless active noise-cancelling headphones.
Let's have a look at a few examples of popular moving-coil dynamic headphone designs:
Sennheiser HD 280 Pro
The Sennheiser HD 280 Pro is a popular pair of headphones. They are a closed-back circumaural (over-ear) design and have moving-coil dynamic drivers.
The Sennheiser HD 280 Pro is also featured in the following My New Microphone articles:
• Top 5 Best Moving-Coil/Dynamic Headphones Under $100
• Top 5 Best Closed-Back Headphones Under $100
• Top 5 Best Circumaural (Over-Ear) Headphones Under $100
Beyerdynamic DT 990 Pro
The Beyerdynamic DT 990 Pro is another well-known and respected pair of moving-coil dynamic headphones. These headphones have an open-back circumaural design.
A particular point of interest with Beyerdynamic's DT 990 headphones is that there are 3 variations of the product with different impedances:
- 80-ohm: for professional mixing/mastering and compatibility when listening to consumer audio devices (smartphones, etc.).
- 250-ohm: for professional mixing/mastering with the use of a high-end headphone amplifier.
The Beyerdynamic DT 990 Pro is also featured in My New Microphone's Top 5 Best Open-Back Headphones Under $200.
The Apple AirPods is a wildly popular pair of wireless Bluetooth earbuds. I've included these common earbuds to offer an example of a wireless earphone moving-coil dynamic model.
There are numerous other examples of moving-coil dynamic headphones out there. Chances are, if you were to pick a random headphone model, it would have moving-coil dynamic drivers. This goes for in-ear monitors, active noise-cancelling headphones, supra-aural (over-ear) headphones, and many other design types not included in the above-mentioned examples.
For a more in-depth article explaining how moving-coil dynamic headphones work, check out My New Microphone's post titled How Do Headphones Work? (Illustrated Guide For All HP Types).
Planar Magnetic Headphone Drivers
As suggested above, planar magnetic headphone drivers are also dynamic and work on the principle of electromagnetic induction.
Planar magnetic headphones can be considered a middle-ground choice between moving-coil dynamic headphones and high-end electrostatic headphones. In general, we'll find that planar magnetic headphones have the low distortion advantages of electrostatics without needing any extra hardware (though headphone amps can help improve the performance of planar magnetic headphones in certain situations).
So how do they differ from their moving-coil dynamic counterparts?
To start, planar magnetic headphone drivers have their conductive elements embedded within their diaphragms. The thin conductive material traces are part of the diaphragm rather than being attached to the diaphragm.
Strong flat magnets are positioned directly to either side of the diaphragm.
There must be space between the magnetic planes in order for air to escape the driver and sound waves to move out of the driver. Note, too, that the magnets are designed as close as possible to the diaphragm for maximal magnetic field strength around the diaphragm but must be positioned far enough away that the conductive element with the diaphragm doesn't stick to either of the two magnetic planes.
Here is a simplified cross-sectional diagram of a planar magnetic headphone driver:
The name “planar magnetic” comes from the plane of the diaphragm and the flat magnetic structure to its front and back and from the fact that the transducer works on the principles of electromagnetism.
Let's break down how the planar magnetic headphone driver works.
As with all headphone drivers, two electrical lead wires bring the audio signal to the conductive element. As discussed, in the case of the planar magnetic headphone driver, this conductive element is embedded into the diaphragm.
So the diaphragm itself, in essence, becomes part of the audio circuit. As the alternating current passes through the diaphragm, a coinciding magnetic field is produced in and around the diaphragm.
This magnetic field is constantly changing. At one instance, it is attracted to the front side magnets while being repulsed by the back side magnets. At another, it is attracted to the backside magnets while being repulsed by the front side magnets.
This attraction and repulsion of the diaphragm mimics the audio signal. As the diaphragm moves back and forth, it pushes and pulls air, creating sound waves that pass through the spaces between the magnetic structure that sandwich it.
Pros And Cons Of Planar Magnetic Drivers
The pros and cons of planar magnetic headphones are summed up in the following table:
|Very accurate and transparent
|Wide frequency response
|Often require a headphone amplifier
|Passive working principle
|Somewhat humidity resistant
Planar Magnetic Headphone Examples
Planar magnetic headphones are much less common than their moving-coil dynamic counterparts. That being said, there are still plenty of options to choose from when it comes to planar magnetic headphones:
HIFIMAN HE1000 V2
The HIFIMAN HE1000 V2 is a high-end pair of over-ear open-back planar magnetic headphones for home, studio and portable devices.
Monoprice Monolith M1060
The Monoprice Monolith M1060 is a more affordable pair of planar magnetic headphones. Like the aforementioned HE1000s, the M1060s have an open-back circumaural (over-ear) design.
The Monoprice Monolith M1060 is also featured in the following My New Microphone articles:
• Top 5 Best Open-Back Headphones Under $500
• Top 5 Best Circumaural (Over-Ear) Headphones Under $500
The Audeze iSINE10 is a rare example of planar magnetic earphones. Typically planar magnetic drivers are only found in headphones, but Audeze's iSINE line features excellent planar magnetic earphones like the iSINE10s.
For a more in-depth article explaining how planar magnetic headphones work, check out My New Microphone's post The Complete Guide To Planar Magnetic Headphones (With Examples).
Balanced Armature Headphone Drivers
Balanced armature headphone drivers are also dynamic and work on the principle of electromagnetic induction.
These driver types are precise but generally limited by their narrow frequency response and physical size limitations. They are typically found in in-ear monitors, which often host up to 4 different balanced armature drivers with varying frequency responses along with a moving-coil dynamic driver for improved bass response.
The design of balanced armature drivers is a bit involved compared to the other headphone driver designs. Let's begin our description by looking at a simplified cross-sectional diagram of a balanced armature driver.
So as we see, the BA driver also works with a conductive coil. However, unlike the popular moving-coil design discussed earlier, the balanced armature conductive coil is stationary.
This coil is wrapped around a conductive armature that is balanced (hence the name) between two magnets. The poles of the magnets are opposite to the top and bottom of the armature. Note that the armature does not touch the magnets.
The armature, designed to move upward and downward, similar to a diving board, is mechanically coupled to a diaphragm via a drive pin. As the armature moves up, so too does the diaphragm, pushing air upward. Similarly, as the armature moves down, the diaphragm follows and pulls are back.
This pushing and pulling of air produces sound waves.
As we see in the diagram above, the BA drivers have an outer case and soundhole. These features do not only protect the relatively sensitive driver mechanisms but also concentrate the sound of the driver out of a single point which helps with directionality.
Let's quickly run through how the balanced armature driver works.
The coil of the BA driver is effectively connected to the audio source. This allows the AC audio signal to pass through the coil, which causes a coinciding alternating magnetic field within and around the coil.
This alternating magnetic field is passed on to the balanced armature that the coil is wrapped around.
As the magnetic field alternates back and forth according to the sign of the audio signal, it is attracted to one of the magnets and repulsed by the other. This consistent changing of the magnetic field in the armature causes it to move back and forth about its balanced resting position.
Due to the mechanical coupling of the armature and diaphragm, any movement in the armature causes proportionate movement in the diaphragm.
By this design, the audio signal will cause sympathetic sound waves to be produced by the BA driver.
The sound waves produced by the diaphragm movement pass through the case of the driver and escape via the sound port.
Pros And Cons Of Balanced Armature Drivers
The pros and cons of balanced armature headphones are summed up in the following table:
|Narrow frequency response
|Excellent transient response
|Passive working principle
|BA earphones typically require multiple BA drivers
|Do not require dedicated amplifiers
Balanced Armature Headphone Examples
To learn more about balanced armature headphones, let's look at a few examples:
1More Quad Driver
The 1More Quad Driver is a pair of balanced armature earphones. Each side has three balanced armature drivers and one moving-coil dynamic driver to complete its 20 Hz to 40 kHz frequency response.
The FiiO FA7 is a pair of in-ear monitors with four Knowles balanced armature drivers per earpiece.
Westone UM Pro 30
The Westone UM Pro 30 are in-ear monitors with triple balanced armature drivers designed for personal listening and professional stage monitoring applications.
For a more in-depth article explaining how balanced armature headphones work, check out My New Microphone's post The Complete Guide To Balanced Armature IEMs/Earphones.
Electrostatic Headphone Drivers
The electrostatic headphone driver is the first non-dynamic design on this list. Rather than working with principles of electromagnetic induction, these drivers work on electrostatic principles.
How are electrostatic headphone drivers constructed?
Electrostatic headphone drivers are built with a movable diaphragm set very closely between two perforated stator plates. The diaphragm and stator plates are insulated from each other.
Proper electrostatic driver designs offer just enough space for the diaphragm to move without getting stuck to one of the stator plates. It's critical that the diaphragm and plates are spaced closely together to ensure accurate and efficient reproduction of the audio signals as sound waves.
The electrostatic headphone driver's electrostatic nature makes it quite similar to a rugged capacitor with a diaphragm sandwiched in between the plates.
Let's have a look at a simplified cross-sectional diagram of an electrostatic headphone driver:
To understand electrostatic headphone drivers, we must also understand the specialized amplifiers required to drive them properly.
The electrostatic headphone amplifier has two major roles to play in the proper functioning of the electrostatic driver:
- To electrical bias/charge the conductive diaphragm of the driver.
- To greatly increase the voltage of the audio signal while dropping the current before sending the signal to the stator plates.
The biasing voltage is required to positively charge the diaphragm so that it can be moved by applying opposite charges on the stator plates at either side of the diaphragm.
Note that electret technology has made it possible to quasi-permanently charge the diaphragm to render the need for an external biasing voltage supply obsolete. There are both “true” electrostatic and electret electrostatic headphones on the market.
The other main role of the amplifier is to boost the voltage of the audio signal across the stator plates while dropping the current.
The charge across the stator plates, which is ultimately responsible for the diaphragm movement, is a function of the capacitance of the stator plates and the voltage across them. By cranking up the voltage of the audio signal, the electrostatic driver becomes more efficient.
This is typically done, in part, by a step-up transformer that works to “step up” the voltage while reducing the current.
To learn more about headphone power requirements, check out my article How Do Headphones Get Power & Why Do They Need Power?
So the audio source is sent to the headphone amplifier. The audio output of the amplifier connects one lead wire to each of the stators. When the audio signal is positive, one stator has a positive charge, and the other has an equal but opposite charge. The reverse is true when the audio signal is negative.
The large voltages across the stator plates allow for strong electrical charges on the plates. Remember that the stators have equal but opposite electrical charges at any given moment (when an audio signal is in the circuit).
Because the diaphragm is positively charged, it will be attracted to one stator and repelled by the other at any instant. The direction in which the diaphragm is pulled changes many times per second (within the audible frequency range of 20 Hz – 20,000 Hz and beyond).
The movement of the diaphragm causes air to move, producing sound waves that represent the audio signal applied across the driver. The perforated stator plates allow this air to pass through and the sound waves to travel outward from the driver.
Pros And Cons Of Electrostatic Drivers
The pros and cons of electrostatic headphones are summed up in the following table:
|Excellent transient response and clarity
|Requires dedicated headphone amplifiers
|Wide frequency response
Electrostatic Headphone Examples
There aren't many manufacturers of electrostatic headphones. To learn more about these rare headphone types, let's run through some examples:
STAX SR007-A MK2
STAX is an industry-leader in electrostatic headphones. Their STAX SR-007A MK2 open-back circumaural model is an excellent example of a pair of electrostatic headphones.
The Stax SR-007A MK2 is also featured in My New Microphone's Top 5 Best Electrostatic Headphones.
HIFIMAN Jade II
The HIFIMAN Jade II is another excellent example of a pair of open-back circumaural electrostatic headphones.
The HIFIMAN Jade II is also featured in My New Microphone's Top 5 Best Electrostatic Headphones.
The Shure KSE1500s are a rarity in headphone design in that they are a pair of electrostatic earphones. You'll see in the picture below that the earphones require their very own dedicated power supply/amplifier.
For a more in-depth article explaining how balanced armature headphones work, check out My New Microphone's post The Complete Guide To Electrostatic Headphones (With Examples).
Magnetostriction (Bone Conducting) Drivers
Magnetostriction headphones are the odd-balls of the headphone driver types. This is because, unlike the other driver types, they do not have a diaphragm that produces sound waves for our ears to hear. Rather, they cause vibrations that are transmitted to the bones in our heads and act to stimulate our inner ears rather than our outer ears.
Magnetostriction headphones do not work on electromagnetic or electrostatic principles but rather on piezoelectric principles.
Essentially, rather than the audio signal being sent to a conductive coil or diaphragm, the bone conduction driver has its audio sent to a piezoelectric crystal.
The piezoelectric crystal is placed between two metal plates that are connected to the audio source. These plates become part of the audio circuit.
As the alternating current of the audio signal passes through the plates, it is applied to the crystal. The crystal shrinks and expands accordingly.
As the crystal’s structure expands and contracts, it converts the electrical energy (audio signals) into mechanical energy in the form of vibrations and sound waves.
If the crystal is touched to a solid, like over the listener's jaw or cheekbones, the vibrations will extend into the solid. With bone conduction headphones, this means the bones of the skull will vibrate along according to the audio signal.
These vibrations will reach the inner ear, bypassing the ear canal completely and cause the inner ear to send electrical impulses to the brain that represent the audio signal.
Pros And Cons Of Magnetostriction Drivers
The pros and cons of magnetostriction (bone conduction) headphones are summed up in the following table:
|Do not produce much airborne noise
|Relatively poor audio quality
|Can be listened to without obstructing the listener from hearing their surroundings
|Passive working principle
Magnetostriction (Bone Conducting) Headphone Examples
Bone conduction headphones are becoming somewhat popular on the consumer market today though they are nowhere near as common as moving-coil dynamic headphones. To learn more about the magnetostriction headphones, let's have a gander at an example:
Aftershokz is the stand-out brand/manufacturer of bone conduction headphones. Their Xtrainerz model is a great example of this headphone type.
What is a good driver size for headphones? The best driver size for a pair of headphones is generally the size of the drivers the headphones are designed to have. Earphones generally have driver diameters between 8-15mm, while headphones are between 25-50mm. Quality headphones are designed, tuned and damped to accommodate the driver size within their designs.
For more information on headphone driver sizes, check out my article What Is A Good Driver Size For Headphones?
How do you read headphone specs? Headphone specifications give us a good idea of how the headphones will function. Key specs to look for on headphones data sheets include:
- Frequency response: the frequencies the headphones are capable of reproducing.
- Sensitivity: the relative loudness the headphones are capable of producing relative to the power supplied to their drivers.
- Impedance: the electrical impedance in the headphone driver that affects the voltage of signal required to drive the drivers.
For more information on the headphone specifications mentioned above, check out the following My New Microphone articles:
• What Is Headphone Frequency Response & What Is A Good Range?
• The Complete Guide To Headphones Sensitivity Ratings
• The Complete Guide To Understanding Headphone Impedance
Choosing the right headphones or earphones for your applications and budget can be a challenging task. For this reason, I've created My New Microphone's Comprehensive Headphones/Earphones Buyer's Guide. Check it out for help in determining your next headphones/earphones purchase.