If you've ever taken apart a pair of headphones or researched how headphones work, you've likely seen (or read about) headphone drivers. These drivers are the transducer elements in headphones responsible for converting audio signals into sound waves and come in a wide variety of sizes.
What Is A Good Driver Size For Headphones? The best driver size depends on the design of the particular headphones. Earphone drivers are usually 8mm – 15mm in diameter, while headphone drivers are typically 20mm – 50mm. A larger driver produces stronger sound waves (particularly in the bass/sub-bass), but this doesn't mean they sound better.
In this article, we'll discuss headphone driver sizes in more detail and investigate the correlation between drive size and headphone performance.
What Is A Headphone Driver?
Let's begin by defining the headphone driver.
A headphone drive is the transducer element in the headphones. In other words, it is the component within headphone design that is responsible for converting audio signals (electrical energy) into sound waves (mechanical wave energy).
Moving-coil dynamic headphone drivers, which we'll discuss in detail, are by far the most common driver type in headphones today. However, there are other notable headphone driver types, including planar magnetic, electrostatic, balanced armature and magnetostriction (bone conduction).
Generally speaking, when buyers and audiophiles are concerned with driver size, they are discussing moving-coil dynamic drivers. More specifically, they are considering the diameter of the diaphragm of the moving-coil driver.
That being said, the headphone specifications influenced by diaphragm diameter in a moving-coil dynamic driver are often the same in the other driver types.
Let's quickly discuss how a moving-coil headphone driver works. We'll use the following simplified cross-sectional diagram for reference:
The audio signal passes through the voice coil (moving-coil) of conductive wire. Since audio signals are alternating currents, this causes a varying electromagnetic field in the coil.
As we can see, the coil is attached to the diaphragm, so any coil movement means diaphragm movement.
The oddly-shaped magnetic structure has a cylindrical cutaway in which the coil is suspended. Note that the coil does not touch the magnet.
To the interior of the coil, the magnetic pole is north, and to the exterior, it is south. This concentrates the magnetic field around the coil.
So, as the coil experiences a changing electromagnetic field from the audio signal, it is effectively pushed and pulled by the permanent magnet's field. The result is the diaphragm movement and, therefore, sound waves that represent the audio signal.
Below is a picture of a pair of moving-coil dynamic headphone drivers:
Note that the vast majority of loudspeakers, studio monitors and subwoofers use this same design, only with larger and stronger components. This should give us a hint as to how driver size affects the sound of headphones.
To learn more about moving-coil dynamic headphone drivers, check out my article The Complete Guide To Moving-Coil Dynamic Microphones.
For your additional information, moving-coil dynamic microphones also utilize the design described above; only the energy flow is reversed. Rather than converting audio to sound, moving-coil microphone transducers convert sound to audio.
Size-Dependent Factors Of Headphone Drivers
The most significant factor having to do with driver size is the amount of air the driver is capable of pushing.
A small diaphragm can only move so much air even when it vibrates to the extent of its physical limitations.
Larger diaphragms can push and pull much more air, and they need to move less to do so.
The more air that gets moved, the greater the variation in sound pressure level; the stronger the sound waves, and the louder the perceived level. This is particularly true of bass frequencies.
So do larger drivers produce more bass? Though it is one factor, it is not the only one. Impedance, damping and tuning; frequency response; driver positioning relative to the ear, and the headphone signal amplifier all play roles in bass response.
We can argue that larger drivers require more energy to move. However, this is not necessarily true.
Of course, all things being equal, a larger body of mass requires more energy to move. However, things are not always equal in different headphone drivers.
The impedance and sensitivity of two equal-sized drivers may also differ and cause the two drivers to sound vastly different from one another when the same audio signal is sent to both.
A driver with a higher impedance will require more voltage to induce the same diaphragm movement. Headphones with lower sensitivity will also require more voltage (and power) to move their diaphragms.
For more info on drive impedance and sensitivity, be sure to check out my articles The Complete Guide To Understanding Headphone Impedance and The Complete Guide To Headphones Sensitivity Ratings, respectively.
To summarize, the headphone driver size directly affects the amount of air, and therefore the “loudness” the driver can push.
But if we're concerned with perceived loudness, this is not enough.
The distance from the eardrum is not always the same. This is critical because the sound pressure level of sound waves follows the inverse-square law. This states the sound pressure level is quartered (drops 6 dB) for every doubling of distance. Therefore, the closer the driver is to the ear, the less air it must move to sound as loud.
Similarly, in-ear headphones may actually seal the ear canal and cause direct coupling between the driver's diaphragm and the eardrum. In this case, the driver really shouldn't push much air at all to avoid damaging the ear.
An important aside about earphones is that their drivers must be small by the nature of their intended positioning.
But that's about it in terms of the factors that are significantly affected by driver size.
Typical Driver Sizes In Various Headphone Types
As mentioned in the introduction, earphone drivers are usually 8mm – 15mm in diameter, while headphone drivers are typically 20mm – 50mm.
Planar magnetic headphone driver sizes are typically around 30 mm for in-ears and range from 50mm (Blue Ella) and 106mm (nearly all Audeze models) for headphones.
Electrostatic headphone specifications typically do not suggest driver size.
Balanced armature headphones are used in earphones. The driver size itself is independent of the diameter size, though BA headphone diameter sizes roughly span in the 8mm – 15mm range.
To learn more about these headphone types, click on any of the following likes to check out the appropriate My New Microphone article:
• Planar Magnetic Headphones
• Electrostatic Headphones
• Balanced Armature IEMs/Earphones
Is Bigger Better?
Bigger is not always better. For example, some small in-ear monitors outperform large closed-back headphones and vice versa. There are plenty of other factors we must take into consideration.
The way in which the driver is built into the headphone is important. Tuning and damping are typically required in moving-coil dynamic headphones to achieve the intended frequency response.
Driver proximity to the eardrum, magnetic field strength, and driver sensitivity and impedance all play major roles in determining the sound quality of headphones. It is not nearly a question of “is bigger better?”
What Is A Good Driver Size For Headphones?
The best driver size for a pair of headphones/earphones is nearly always the designated driver size in any headphone/earphone design.
Remember that the drivers are the transducer elements, and the entire headphone design is centred around the drivers. From the damping and tuning of the frequency response to the material and form factor of the pads, everything in a high-quality headphone design is there to enhance the chosen drivers.
I know this is a sort of lacklustre answer, but it is the truth.
Sure, the size of the drivers in your headphones is good to know, but it is not a determinant of whether the headphones will sound perfect, terrible, or anywhere in between.
What determines sound quality in headphones? Though sound quality is somewhat subjective, certain factors determine the objective sound quality and accuracy of headphones. These factors include frequency response, impedance, sensitivity, driver type and driver size, and passive and active noise-cancellation capabilities.
Which headphone brand is the best? There are plenty of excellent headphone brands on the market today. Here are a few worth mentioning:
- Bang & Olufsen
- Bowers & Wilkins
- STAX (notable for electrostatic headphones)
- Audeze (notable for planar magnetic headphones)
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.