If you are new to audio and headphones, in particular, you may not be very familiar with the various types of headphones drivers that are available in the market. This is a topic that can also get a bit confusing even for audio enthusiasts.
So, what are the main types of headphone drivers available for audio consumers today?
There are 6 main types of headphone drivers, namely;
- Dynamic or Moving coil drivers
- Planar magnetic or Orthodynamic drivers
- Balanced armature drivers
- Electrostatic drivers
- Bone-conduction or Magnetostriction drivers
- Hybrid drivers
All these drivers are transducers and at the basic level, they all serve the same purpose and that is to convert electrical sound signals into audible sound waves through variations in sound pressure (acoustic pressure) that can be received by our ears and get processed by our brains.
But before we can look at each of these drivers in more detail, you should first get familiar with common phrases and jargon that you may encounter when deciding which type of driver is best suited for you.
Headphone driver glossary (Meaning of common terms)
|Transducer||Is a device that converts energy from one form to another. A speaker or headphone driver is a transducer.|
|Neodymium magnet||Is the most common type of permanent magnet used in most drivers mainly due to their efficiency, power, and how small they can be made.|
|Diaphragm||Is a thin but semi-rigid material used in all drivers to create waves through back-and-forth movement.|
|Sound pressure||Is the variation in atmospheric pressure that is caused by soundwaves. It is measured in decibels|
|Voice coil||Is a coil in a headphone driver that is induced by a current to create an electromagnetic force that drives the diaphragm.|
|Electromagnetic force||Is a magnetic force that is created by electrically charged particles.|
|Transient response||This is the ability of a headphone driver to start and stop as fast as possible per the analog sound signal|
|Bass response||Ability to reproduce low audio frequencies|
|Distortion||These are unwanted artifacts in sound mainly caused but the non-linear movement of a headphone driver|
|Imaging||This is the ability of a headphone driver to reproduce the best possible replica of the recorded soundtrack to space and stereo balance|
|Piezoelectric effect||The ability of a material to produce an electric charge under mechanical stress. Can also include sound vibration. The reverse can also occur where sound vibrations are generated by applying an electric charge on the material which is known inverse piezoelectric effect|
|Electrostatic effect||This is the effect of electric charge fields where similar charges repel and opposite charge attract|
1. Dynamic or Moving coil drivers
This is the most common and oldest type of headphone driver that is also found in the majority of conventional cone speakers.
These drivers are made of;
- A permanent magnet, usually a neodymium magnet
- A voice coil which is a thin wire wound over a former
- A spider to support the voice coil
- A diaphragm directly connected to the voice coil
- A suspension for the diaphragm
- A dust cap that prevents dust and other particles from getting into the voice coil
The technology behind dynamic drives is highly developed and they are, therefore, easy to manufacture and mass-produce ranging from small-sized drivers that can fit in IEMs to large concert PA systems.
The larger the driver the more air it can displace for louder sound (higher SPL), especially when playing lower bass frequencies. However, a larger driver does not always mean better sound or better bass.
How dynamic drivers work
It all starts when an audio signal is fed to the driver through its leads that connect to the voice coil.
This is usually an analog and varying electrical signal that varies depending on the frequency being played.
Once the signal is applied to the voice coil, an electromagnetic field is formed by electromagnetic induction around the voice coil which changes depending on the kind of AC signal cycle being received whether it is negative or positive.
Due to this changing electromagnetic field, the voice coil can either be attracted or repelled by the permanent magnet in which the voice coil is suspended. This is why this type of headphone driver is also known as a moving coil driver.
As the voice coil is attracted and repelled, it moves the diaphragm back and forth rapidly per second. These movements vibrate the diaphragm which creates sound waves due to compression and rarefaction of air.
The soundwaves created by the drivers reach our ears where they are translated by our brains.
Pros and cons of moving coil drivers
|Cheaper compared to other driver types which makes dynamic headphones more affordable, especially for the average consumers||Has a higher total harmonic distortion, especially at higher volumes|
|Can produce deeper and punchy bass as it can move large amounts of air||Poorer bass response at the roll-off points|
|Highly available||Poorer transient response due to the mass of the diaphragm structure|
|Does not require a lot of amplification power to be driven||May lack accurate precision|
|Have a sound signature that most audio enthusiasts find pleasing|
2. Planar magnetic headphone drivers
These drivers are also known as Orthodynamic drivers. The name Orthodynamic drivers are attributed to the popularity of the Yamaha planar magnetic headphones that appeared in the 1970s.
But contrary to dynamic drivers, planar magnetic works on different principles which we will discuss below.
These drivers are made of the following parts;
- A thin flat diaphragm in which thin flat conductive wires are embedded
- One or two powerful and permanent magnet arrays
These are the two main components that make up a planar magnetic headphone driver but the magnets need to be evenly arranged with respect to the conductive wires for linear, near-perfect pistonic motion.
They are known to sound better than dynamic drivers due to low distortion which is brought about by the linear movement of the diaphragm. However, they require more power and are heavier when compared to moving coil drivers found in most headphones.
How planar magnetic drivers work
Similar to dynamic drivers, planar magnetic headphone drivers also use electromagnetic forces to move the diaphragm.
This occurs when a varying audio signal flows through the conductive wires on the diaphragm. The current (alternating current) makes the diaphragm an electromagnet, but since audio signals are not a perfect sine wave, the electromagnet also varies depending on the signal.
Diaphragms on planar magnetic drivers are suspended between the magnetic arrays. This means that the diaphragm can either be attracted or repelled by the magnetic array and in the process, it moves/vibrates rapidly to create sound waves with planar wavefronts that we can perceive.
However, the magnetic arrays also need to be perforated to allow air to pass through and for sound waves to escape.
Pros and cons of planar magnetic drivers
|Faster transient response due to the effective and lightweight diaphragm||Require more amplification power and often need to be paired with a headphone amplifier|
|Better and more open soundstage then moving-coil headphone drivers and open-back design found on most of the planar magnetic headphones||Costlier than dynamic drivers|
|More accurate bass response||Not widely available for the audio consumer market|
3. Balanced armature drivers
The next driver on this list is the balanced armature headphone driver or BA driver that also uses electromagnetic induction for audio playback.
These drivers are arguably the smallest drivers on this list and are usually used in IEMs due to their small sizes. They are small enough that multiple drivers can be fitted into one IEM enclosure with drivers ranging from as low as 1 to as high as 7 in some high-end IEM models.
Balanced drivers use technology borrowed from hearing aids with some modifications for sound reproduction with the help of the following parts;
- A balanced miniature arm or balanced armature (is centered between 2 permanent magnet poles with a net force of zero)
- A conductive coil wrapped around the armature
- A thin diaphragm membrane
- A driver rod that connects the diaphragm to the armature
- A permanent magnet with two poles namely: north and south
All these components are put in one small isolated enclosure which is then put in the main headphone housing where other drivers can also be added depending on the design.
Where multiple-way armature drivers have been added in a certain IEM design, a crossover also has to be added since the different drivers can only handle a specific frequency band. The crossover is responsible for assigning the right signal to the respective driver that can best handle a certain frequency range.
For example, in the case of an IEM with 4 armature drivers, usually, one driver will handle the bass and sub-bass frequencies, one will handle the mid-range frequencies, another will be responsible for the upper-mids and the last driver will playback the highs or trebles.
How do balanced armature drivers work?
As I mentioned earlier, balanced armature drivers also apply principles of electromagnetic induction to produce sound but unlike the other two drivers discussed above, armature drivers do not displace air. This means that balanced armature drivers are not great at reproducing low frequencies.
All this begins when a varying signal is fed through to the driver from the source. This signal induces the coil that is wrapped around the miniature arm to create a changing electromagnetic field.
These changes in the electromagnetic field cause the balanced armature to be attracted by either of the poles causing it to move rapidly moving the driver rod which, in turn, moves the light diaphragm with it, reproducing sound.
Pros and cons of armature drivers
|Has great noise isolation||Does not reproduce punchy bass|
|Is efficient and does not draw a lot of power||They are costlier to manufacture than dynamic drivers|
|Great at reproducing accurate and precise upper mids and high frequencies||Most armature drivers can only handle a narrow frequency range hence the need to use multiple drivers|
4. Electrostatic headphone drivers
Electrostatic drivers are different from the 3 drivers we have discussed above in that they use electrostatic principles to playback audio other than electromagnetic induction.
Electrostatic principles are the same physics principles that get your hair attracted to a static surface such as a balloon that has been rubbed on some sheets. This is essentially the same principle that these drivers use for operation.
This is accomplished when the following parts work in tandem;
- A thin diaphragm usually made of mylar (BoPET)
- 2 perforated stator plates in which the diaphragm is sandwiched
- Spars to separate the stator plates from the diaphragm
These headphone drivers are accredited for being super accurate and precise as they reproduce every single detail of an audio signal. This is why electrostatic headphones are highly relished by audiophiles.
However, this level of detail can also be detrimental to your listening experience if your audio signal has any forms of artifacts that the drivers will faithfully reproduce.
These headphones are also known for having a wide frequency response which does not really matter that much but lacks the bass punch that moving coil drivers are known for.
Additionally, there is also the question of price when it comes to investing in electrostatic headphones. This is because these headphones are super expensive with most of them retailing at the $3000 price range or above without even factoring in the fact that they need electrostatic headphone amps (energizers) to drive them due to their over-the-top impedances which range at the kilo-ohms region usually above 100 kΩ (100,000 Ohms). This makes the cost of owning one of these headphones extremely high.
Weight can also deter potential buyers from picking up one of these electro-acoustic transducers.
With all that said, these are probably the best headphones you can buy for the best lifelike audio playback. There is little distortion of the sound by the driver, high acoustic accuracy, the transient responses are super-fast and the sound signature is great if you do not mind the lack of punchy bass which some may find boring.
How electrostatic drivers work
For electrostatic drivers to work, the diaphragm needs to be electrically charged which is usually done through DC biasing. To accomplish this the diaphragm is coated with a conductive coating that enables it to hold a charge.
DC biasing entails applying a fixed DC and voltage to the conductive material on the diaphragm. This ensures that the diaphragm is electrically charged when in use which is usually a positive charge.
Remember we mentioned that electrostatic drivers also have perforated stator plates. The main function of these stator plates is to either attract or repel the positively charged diaphragm once an audio signal is applied.
These stator plates essentially act as fast-discharging capacitors that can either have a negative or a positive charge.
So, when an audio signal is applied to the plates, one of the plates will hold a positive charge while the other will hold a negative charge at any given point.
When one plate is positively charged it repels the positively-charged diaphragm and at the same time, the other plate attracts the diaphragm which doubles the net force on the diaphragm allowing it to move air which escapes through the perforations to reproduce sound.
And since audio signals alternate thousands of times a second, the stators rapidly shift between negative and positive charges either attracting or repelling the diaphragm causing it to move linearly as the force is applied evenly across the entire diaphragm surface.
However, for this to work flawlessly, the diaphragm should not touch either of the plates. This is where spars come in to ensure that there is enough separation between the plates and the diaphragm.
Something else to also keep in mind is that electrostatic headphones produce sound waves with planar wavefronts similar to those produced by planar magnetic headphones.
Pros and cons of electrostatic drivers
|High levels of accuracy which gives high-quality sound||Any artifacts in the audio signals are also reproduced resulting in a poorer experience if the signal is not too clean|
|Fast transient response||They are super expensive|
|They have a low distortion||They are not portable since they require an external amplifier due to their high-power consumption|
|Do not have the best bass effects|
5. Bone conduction drivers
Bone conduction drivers are a whole different beast by themselves in that they do not operate like other convection headphone drivers but directly vibrate the listeners’ skulls to make audible sounds.
They do this by completely bypassing the eardrum and effectively sending vibrations directly to the cochlea and stimulating it before the vibrations are sent to the brain for interpretation. This means that bone conduction headphones are used without any direct contact with the listener’s ear canals.
Bone conduction headphones are especially useful for individuals that want to hear what is going on around them, especially when outdoors, and for individuals with conductive hearing loss since they do not require the eardrum to stimulate the cochlea.
All this is accomplished by one key component found in these headphones and this is a moving coil/moving iron or a piezoelectric transducer.
The piezoelectric transducer found in some bone conduction headphones uses reverse piezoelectric effect when a potential difference (audio signal) is applied across it.
This potential difference causes the transducer which is essentially a crystal element structure to change shape depending on the applied signal producing vibrations that are sent through the cheekbones and stimulating the cochlea structure so that we can hear the sound.
Pros and cons of bone conduction headphones
|Great for people with hearing loss||Does not have the best audio quality when compared to other drivers|
|Great for audio playback when outdoors as they do not mask the sound around us||Lacks in bass|
|Can be effectively used underwater since most of them are virtually water-resistant to a certain degree||Has to press the bone structure and is, therefore, uncomfortable for extended use|
|Has audible distortion at high listening levels|
6. Hybrid drivers
Hybrid headphones combine both electrodynamic and balanced armature transducers with the dynamic drivers primarily being used for the low-frequency bass frequencies.
This is because as we mentioned earlier armature drivers do not reproduce sound by displacing air and are, therefore, not effective at playing back the bass effects which require displacement of a lot of air to sound rich and deep.
Most hybrid headphones will have a single dynamic driver to handle the bass frequencies which can be paired with about 3 miniature arm drivers to playback the higher frequencies.
How to choose the right headphone driver
Choosing the right kind of headphone driver will come down to three main things and these are;
- Personal preference
- Listening habits
Depending on how you like to listen, whether you are a bass-heavy person, whether you are interested more with the details in the critical frequencies, noise isolation, portability, comfort as it pertains to the headphone’s weight, and so on, you can decide to go for one headphone driver over the other.
The other important thing that most people tend to gloss over when advising on the right headphone driver for different uses is the cost of the headphone.
Moving coil headphones will probably offer you the most bang for your buck depending on your budget, especially with the entry-level and mid-range products. You can also spend as much as you want on high-end audiophile-grade headphones if your budget allows you.
Conversely, if you are well-off and are very interested in the precision and accuracy of the audio playback, you can decide to purchase yourself a pair of electrostatic headphones for several thousand dollars that you can be used in your listening room. But it is important to note that these headphones need to be driven by “energizers” and are the least portable of all the headphone drivers.
For audio enthusiasts that suffer from conductive hearing loss, bone conduction headphones will offer the most value but they can also go for quite a premium with prices ranging over $300 for high-quality products.
The other options are also great and as I mentioned above you have to take several factors and personal preference into consideration.
Does the size of the headphone driver matter?
The size of the headphones’ drivers does not matter as much, at least where audio quality is concerned.
Larger drivers do not necessitate a better listening experience but are important for displacing more air which can come in handy for people the love to listen to high levels and for punchier bass. You should also keep in mind that punchy does not mean great bass.