Planar magnetic headphones: how the driver works

How a planar driver moves the air

A planar magnetic driver has no voice coil and no cone. Its diaphragm is a thin plastic film with a flat metal conductor laid across it in a zig-zag pattern, stretched in a frame between rows of bar magnets on one side or both.

The magnets are arranged so their field runs across the surface of the film, and the zig-zag is laid out so that, at any instant, every run of the conductor is pushed the same way. When the music signal flows through it, the film moves forward and back largely as one piece. The sound leaves through the gaps between the magnet bars, so the bars sit directly in its path.

The Verum Audio Verum 1 gives a sense of the scale: an 82 mm diaphragm driven by 28 rare-earth magnets. Its review sets that against the roughly 50 mm most dynamic headphones top out at.

What spreading the force changes

A dynamic diaphragm is pushed at one ring and has to be stiff enough to carry that push out to its edges. A planar film is pushed almost everywhere the conductor runs, so it doesn't need that stiffness, and it can be far thinner and lighter for its size. HIFIMAN sells its films on that lightness: the HIFIMAN Sundara uses a NEO Supernano diaphragm meant to give a faster, more detailed response, and its review calls the $299 Sundara "just a really fast headphone".

Size helps in the bass as well. A large diaphragm moves less to push a given volume of air, which helps keep bass distortion low. The Verum 1's review hears its bass stay ruler-flat down to 20 Hz. Planar construction doesn't guarantee that extension, though: the HIFIMAN HE400se lacks bass below 60 Hz.

Why a planar's impedance stays flat

A dynamic driver's impedance jumps at its bass resonance and often climbs again in the treble. A planar's barely moves. Its conductor is a flat trace with very little inductance, and the load it presents is close to the same figure at every frequency.

That has a practical benefit. A source's output impedance and the headphone form a voltage divider, and with a flat load the division is the same across the band, so a source with a high output impedance lowers the level a little without tilting the tonal balance. The impedance explainer covers the output-impedance check for headphones whose curves do swing.

The cost in weight and size

Rows of magnets across the whole driver weigh more than one magnet behind a cone. Among the planars reviewed here that list a weight, the Sundara is the lightest at 342 g and the Verum 1 the heaviest at 475 g. The HIFIMAN HE1000se, a big flagship at 440 g, is praised in its review for being lighter than it looks.

Big drivers also need big cups. Most of the planars reviewed here are full-size open-backs, which means they leak sound and block very little of it, so they suit a quiet room better than a train.

Does a planar need a special amplifier?

It needs an ordinary one that suits its figures. Sensitivity, impedance and how loud you listen decide it, and the table further down this page works out the power every reviewed planar needs for 110 dB peaks.

Low impedance changes what kind of power matters. At 8 ohms the Verum 1 draws a lot of current for the voltage it gets, and its review warns that it "demands real current from the amplifier". It plays loud from modest sources, but the reviewer found it kept improving with more power and suggests starting at about 2 W per channel. The HE1000se sits at the easy end: 35 ohms and 96 dB/mW, a flagship that a good dongle or a modest desktop amp drives loud. The HE400se, at 32 ohms and 91 dB/mW, is one its review says wants an external amp, because from a phone it sounds thin and quiet.

Amplifier power ratings are quoted into a named load, so read the one at your headphone's impedance. A figure into 300 ohms says little about 8. The headphone power calculator does the sum for any pair and listening level.

Choosing between planar and dynamic

The technology settles a few things: the flat impedance, the weight, the size of the cups and, on most models, an open back. It doesn't settle the tuning. The Verum 1's review hears smooth treble that is almost impossible to make sibilant, while the HE1000se's describes a bright, peaky top end that can turn harsh on hot recordings. Those are two planars at opposite ends of the treble.

HIFIMAN makes most of the planars reviewed here, and many use its Stealth Magnets, bars reshaped to disturb the sound less on its way out through the array. The dynamic driver explainer covers what a coil and cone do differently, and the best planar magnetic headphones guide ranks the ones we'd buy.