The term “dynamic” is used quite a bit with audio gear, including headphones, microphones and speakers. In musical terms, “dynamics” refers to the range of intensity/loudness of a performance. The dynamic range should be considered when it comes to headphones, but the term “dynamic” typically means something different.
What are dynamic headphones, and how do they work? Dynamic headphones have electromagnetic drivers that convert audio signals into sound waves via electromagnetic induction. Conductive coil/wire is connected to a diaphragm and suspended in a magnetic field. As audio signals pass through the coil, the diaphragm moves and creates sound.
That's the simple definition and the defining characteristic of dynamic headphones. In this article, we'll get into greater detail about dynamic headphones and how they function.
Related article: What Is A Dynamic Microphone? (Detailed Definition + Examples)
What Are Dynamic Headphones?
When it comes to musical performance and playback, dynamics refer to the differences between quiet and loud passages. For example, the difference between the loudest and quieter part of a live performance or recorded audio is known as the dynamic range.
However, when it comes to audio transducer devices (headphones, speakers, microphones), the term dynamic refers to the method in which the device converts audio to sound or vice versa. Dynamic transducers work on principles of electromagnetism.
So then, dynamic headphones are headphones that convert analog audio signals (electrical energy) into sound waves (mechanical wave energy) via electromagnetic principles.
The transducer element of headphones is called the driver. A dynamic driver is built with a movable diaphragm and conductive voice coil and features a magnetic structure.
I've made a note about the driver being the dynamic component for this reason: dynamic headphones can be wired or wireless; open-back or closed-back; on-ear or over-ear; headphones or earbuds; stereo or mono, etc. That is to say, the only determining factor of a dynamic headphone is the driver element.
The majority of headphones on the market today are dynamic, so it's often safe to assume a pair of headphones will be dynamic unless otherwise labelled. So then, this article will explain not only how dynamic headphones work but how the vast majority of headphones work.
How Do Dynamic Headphones Work?
So we know that dynamic headphones work on the principle of electromagnetism, but how do dynamic headphones really work?
Before we answer this question, it's important to note that various headphone driver designs utilize electromagnetism. The most common is the moving-coil dynamic headphone driver. Planar magnetic and balanced armature headphones also work on electromagnetism and are, therefore, dynamic, too.
Before we get into each of the aforementioned designs, let's first discuss electromagnetic induction. This will give us a strong idea of the working principle of dynamic headphones.
What Is Electromagnetic Induction?
Electromagnetic induction is the production of a voltage across an electrical conductor in a changing magnetic field.
This phenomenon was first discovered by Michael Faraday in 1831 and has since been utilized in many electrical components, including dynamic headphones, loudspeakers and microphones, along with motors, generators, inductors and transformers.
Although electromagnetic induction is defined as an induced electrical signal across a conductor in a changing magnetic field, it can be used to explain the reverse process. In other words, a varying voltage in a conductor will cause an effect in a magnetic field.
When dealing with permanent magnets and conductive material, electromagnetic induction will cause relative movement between the two components in an attempt to maintain equilibrium.
So electromagnetic induction can occur within a fixed conductor and a varying magnetic field, a stationary magnetic field and a moving conductor, or any situation where the relative movement between a magnetic field and a conductor changes.
In the case of dynamic headphones, the conductive coil has an AC voltage (audio signal) sent to it. This changing voltage in the conductor wants to cause a change in the magnetic field, but the magnets are permanently set into the design. Therefore, the conductor, which is free to move, does do.
With that primer out of the way, let's look at how each dynamic headphone type works. We'll discuss:
- Moving-coil dynamic headphone drivers
- Planar magnetic dynamic headphone drivers
- Balanced armature dynamic headphone drivers
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How Do Moving-Coil Dynamic Headphone Drivers Work?
Moving-coil dynamic drivers are the most common type of headphone driver. As their name suggests, they have a moving coil. This coil of conductive wire is attached to a diaphragm.
As the audio signal passes through the coil, the permanent magnetic field that surrounds it causes it to move up and down within its cylindrical cutaway. This movement causes the diaphragm to push and pull air around the driver, creating sound waves that represent the audio signal.
There are really 3 key components in a moving-coil dynamic headphone driver with 2 other components worth mentioning:
- Conductive coil
- Magnetic structure (magnets & pole pieces)
- Electrical lead wires
- Housing & spacers
Here is a simplified and labelled diagram of a moving-coil dynamic headphone driver for better understanding.
Note that the dynamic headphone driver is essentially the same design as a dynamic loudspeaker (the vast majority of loudspeakers are dynamic as well). This design is also very similar to a moving-coil microphone design though the signal flow is reversed.
To learn more about dynamic microphones and moving-coil microphones, in particular, check out my articles What Is A Dynamic Microphone? (Detailed Definition + Examples) and The Complete Guide To Moving-Coil Dynamic Microphones.
Now back to the moving-coil headphone driver.
Two lead wires carry the audio signal from the audio output device to the conductive coil. Typically with headphones, this is an unbalanced audio signal. The left driver will get the left unbalanced signal, while the right driver will get the right unbalanced signal.
So the coil effectively becomes part of an electrical circuit with the audio device's output. The AC nature of audio signals causes the electrical current to flow in alternating directions within the coil.
This alternating current through the conductive wire produces a magnetic field in the coil that coincides with the signal. A change in the coil's field causes it to be repelled or attracted within the driver's magnetic field, which makes the coil move back and forth according to the audio signal.
Since the coil is attached to a diaphragm, the diaphragm moves with it, pushing and pulling air as it does. This diaphragmic movement produces sound waves that are representative of the audio signal.
The moving-coil dynamic headphone driver can be found in all headphone form factor types.
The famous Sennheiser HD280 Pro are moving-coil dynamic headphones.
The Sennheiser HD280 Pro is 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
For an in-depth article on moving-coil dynamic headphones, check out My New Microphone's Complete Illustrated Guide To Moving-Coil Dynamic Headphones.
How Do Planar Magnetic Dynamic Headphone Drivers Work?
Planar magnetic headphone drivers also convert energy based on the principle of electromagnetic induction. However, the conductive element in a planar magnetic driver is incorporated directly into the diaphragm rather than being attached to the diaphragm, as with the moving-coil driver.
In a way, the planar magnetic headphone driver is kind of like a mixture of the moving-coil dynamic and electrostatic driver designs. It works on the same principle as the other dynamic drivers but has a form factor similar to an electrostatic driver: a very thin diaphragm placed between two closely spaced slotted discs.
The discs of the planar magnetic driver are actually made of magnets. The diaphragm in between the discs is made of a thin film with a flattened conductive wire incorporated within its design. The flat magnetic discs and the flat thin diaphragm yield the name planar magnetic since the magnets work on a plane.
Let's have a look at a cross-section of a planar magnetic headphone driver. This simplified diagram with help us to better understand this type of driver:
Note that there are many different designs with varying sizes and numbers of magnets in planar magnetic driver design.
So as the audio signal (AC voltage) passes through the conductive wire, an alternating magnetic field is produced, which causes the diaphragm as a whole to vibrate between the two magnetic discs at either of its sides.
Because there is space between the magnetic discs, the sound created by the diaphragm can be outputted from the driver. Due to the nature of the design, the magnets in the planar magnetic driver must be either stronger, heavier or both compared to those used in moving-coil designs.
Planar magnetic dynamic headphone drivers are also typically found in open-back, circumaural (over-the-ear) headphones. That being said, Audeze and other manufacturers produce closed-back and even in-ear headphones with planar magnetic drivers.
Though bulkier and more expensive, the planar magnetic design yields greater transient precision, range and overall sound quality since the audio signal vibrates the diaphragm directly.
The Audeze LCD4 is a great pair of planar magnetic dynamic headphones.
For an in-depth article on moving-coil dynamic headphones, check out My New Microphone's Complete Guide To Planar Magnetic Headphones (With Examples).
How Do Balanced Armature Dynamic Headphone Drivers Work?
The balanced armature driver is somewhat more confusing than the two dynamic drivers mentioned above. So long as we remember that it works on electromagnetic induction, we should be alright in understanding its inner machinations.
As the name suggests, balanced armature drivers have balanced armatures. In modern designs, these armatures are U-shaped, with the top portion being stationary and the bottom part being movable in a bending fashion (think of a diving board).
The armature is electrically conductive, but it is the coil of wire that wraps around the armature that is directly connected to the audio source. Regardless, the audio signal effectively induces a magnetic flux in the armature, which causes the lower part to move toward one of the poles of the permanent magnets.
A drive pin connects the bottom of the armature to the diaphragm. As the signal causes the armature to move up, the diaphragm moves up, pushing air. Conversely, as the signal causes the armature to move down, the diaphragm moves down as well, this time pulling air. The main takeaway is that the signal causes coinciding sound waves via the diaphragm movement.
Here is a simplified diagram of a balanced armature driver design.
Note that there are plenty of different designs for balanced armature drivers. For example, the above-drawn diagram could be improved by moving the diaphragm toward the sound outlet and having the drive pin toward the end of the armature. This would, in theory, make the driver more efficient since the end of the armature is likely to have the greatest amount of movement.
The entire driver is enclosed for protection, and a sound outlet allows the sound waves to move out of the driver.
The armature is balanced and relatively unstable, making it very easy to move with low-level audio signals.
Due to the small size and the protective requirements of balanced armature drivers, they are only available in in-ear monitors (IEM).
Overall, the balanced armature driver design is not overly effective. These drivers require extensive tuning and dampening due to high resonances and typically fail at reproducing the entire audible spectrum. Several balanced armature drivers are often needed in a single pair of IEMs to produce a complete wide-range sound.
For example, the Audio-Technica ATH-IM04 are excellent in-ear monitors with 4 balanced armature drivers.
For an in-depth article on moving-coil dynamic headphones, check out My New Microphone's Complete Guide To Balanced Armature IEMs/Earphones.
The Popularity Of The Dynamic Headphone Design
I'll reiterate that the moving-coil dynamic headphone driver is by far the most common in headphones on the market today.
Planar magnetic headphones are heavy, expensive and require headphone amps but are sought-after for low distortion, accurate transient response, and superior bass response. However, they are quite rare for day-to-day use.
Balanced armature dynamic headphones are somewhat common with in-ear monitor designs but the balanced armature design is never used in larger headphone designs.
So yes, dynamic headphones are incredibly popular, but it's the moving-coil variety that makes up the majority of the headphone market.
A Note On Dynamic Range
I'll reiterate that the term “dynamic headphones” has nothing to do with the dynamic range of the headphones themselves.
The dynamic range of headphones refers to the difference between the loudest possible sound pressure level the headphones can produce and the quietest sound pressure the headphones can produce. Note that headphones will begin to distort before they reach their absolute maximum SPL output. The low-level noise a headphone produces is difficult to measure versus the noise in the audio signal itself.
Dynamic range, therefore, is not typically discussed and never shows up in a specifications sheet.
Dynamic drivers do not necessarily mean the headphones will have a wider dynamic range or higher max input level.
What are the different types of headphones? Headphones come in many different varieties. We can distinguish between headphone types by their form factor, driver type, transmission method and noise-cancellation. Note that some factors overlap, and headphones can belong to multiple types within a distinguishing factor.
Headphone form factors include:
- Supra-aural (on-ear)
- Circumaural (over-ear)
Headphone driver types include:
- Dynamic moving-coil
- Planar magnetic
- Balanced armature
- Magnetostriction (bone conducting)
Headphone transmission method:
- Infrared wireless
- Radio-frequency wireless
- Bluetooth wireless
- Analog wireless
- Digital wireless
- True wireless
Headphone noise-cancellation method:
- Active feedback
- Active feed-forward
- Active hybrid
Does a bigger headphone audio driver mean better sound? Bigger is not necessarily better when it comes to headphone driver size. Larger drivers are more capable of producing lower frequencies, but headphones do not rely on size to produce bass since they work in a closed tunnel with ears. Sound quality depends on build quality much more than driver size.
Related article: What Is A Good Driver Size For 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.