Tale Of A Headphone — Dynamic vs. Planar, Magnetic vs. Electrostatic

A quick read on three different types of headphones.

It’s the best of the times to be an audiophile. Its the worst too. The market has been flooded with a smorgasbord of aural delicacies, so confusing that even Bach might have ended up befuddled — had he ever wanted to listen to his Magnificat.

One needs things to be simple. And in the world of audio, they are anything but!!

Basically, there are three types of headphones available in the market, based on the type of technology used to create their sound i.e. the transducer principle used.

Okay, don’t let your head start swimming just yet… We’ll try and keep this interesting. So, the transducer principle is the technique that’s used by headphones to convert the electrical signal from a media source (read: audio player) into sound waves that can be heard by our ears.

Currently 3 standards exist in the market:
 1. Dynamic
 2. Planar Magnetic or Orthodynamic
 3. Stax or Electrostatic

Dynamic

Dynamic drivers are the hoi polloi of the headphone universe. They’re also known as moving coil drivers, and are the headphone equivalent of the full-size drivers you probably have in your hi-fi speakers or portable speaker.
 If you don’t know what kind of driver your headphones use, they almost certainly have dynamic drivers. This is by far the most common style, and there’s no chance of that changing in the foreseeable future.

In this kind of driver, the signal is sent through a coil of ultra-thin wire, creating a magnetic field that reacts with a magnet that it’s set into. It’s an electromagnetic relationship, in physics terms. This causes the voice coil to rapidly move backward and forward, in turn moving the speaker diaphragm the coil is attached to.

On a hi-fi speaker this is the cone-shaped part you tell the kids not to touch (and they inevitably do). But in headphones or a small Bluetooth speaker it’ll generally be hidden behind a grille so you can’t see it.

This movement rapidly compresses and decompresses air, causing the sound waves that make up the audio you hear.

Planar Magnetic

These are far less common than dynamic range ones, and also more expensive — for only few companies make them.

There are three important names in planar headphones right now: HiFiMAN, Audeze and Oppo. Hardly the biggest names, but worth taking note of if you haven’t already.

These headphones work on a principle similar to dynamic driver headphones — using the interaction of two magnetic fields to cause motion. However, instead of moving the voice coil, pulling the diaphragm in and out from one ring within the driver, here, the charged part is spread across the driver, which is a thin, largely flat film.

So instead of focusing the force on a small part, it’s spread across the diaphragm. This generally requires larger magnets than a dynamic driver array, and they’re needed on both sides of a diaphragm, which is why a lot of planar magnetic headphones are quite big and heavy.

Headphone veterans out there may also know this kind of headphone as Orthodynamic, a term popularized by Yamaha. However, that’s actually a marketing term that only really referred to Yamaha headphones.

Electrostatic headphones

Now we’re onto the grandaddy of headphones — electrostatics. Not because they were being worn by caveman back in year X, but because greatest headphones are made using this technology (okay I couldn’t think of a really humorous parable).

Electrostatic drivers consist of a thin, electrically charged diaphragm, typically a coated PET film membrane, suspended between two perforated metal plates (electrodes). The electrical sound signal is applied to the electrodes creating an electrical field; depending on the polarity of this field, the diaphragm is drawn towards one of the plates. Air is forced through the perforations; combined with a continuously changing electrical signal driving the membrane, a sound wave is generated.

Electrostatic headphones are usually more expensive than moving-coil ones, and are comparatively uncommon. In addition, a special amplifier is required to amplify the signal to deflect the membrane, which often requires electrical potentials in the range of 100 to 1000 volts!

Due to the extremely thin and light diaphragm membrane, often only a few micrometers thick, and the complete absence of moving metalwork, the frequency response of electrostatic headphones usually extends well above the audible limit of approximately 20 kHz.

The high frequency response means that the low midband distortion level is maintained to the top of the audible frequency band, which is generally not the case with moving coil drivers. Also, the frequency response peakiness regularly seen in the high frequency region with moving coil drivers is absent. The result is significantly better sound quality, if designed properly.

Electrostatic headphones are powered by anything from 100v to over 1kV, and are in proximity to a user’s head. The usual method of making this safe is to limit the possible fault current to a low and safe value with resistors.

I know this sounded like a physics lesson — and honestly, there’s not a much easier way to explain such stuff. But I know for a fact that if you go back and read this article again, it’ll make more sense.

Hope you enjoyed reading this article, and that you’re wiser now about the vast world of technology behind the humble headphones. I know this is just a primer of an article, but any more and we’d have both needed an Aspirin! But, if you need more advice on choosing/buying a good pair of headphones, we’d written a really nice article on the topic a few months ago. You really should read that too.


Originally published at Chip-Monks.