How Planar Magnetic Headphones Work

Many will be aware of Magnepan and their speakers, for which they’ve coined and registered the name “Magneplanar” referring to their planar magnetic operating principle. Most won’t know, however, that Yamaha similarly branded their planar magnetic headphones as “Orthodynamic” headphones, with a U.S. introduction in 1976. Just like with planar magnetic speakers, Yamaha’s Orthodynamic headphones (and those by Fostex, MB Quart, and others) have never gathered a wide following. On the other hand both planar magnetic speakers and headphones have gathered cults of rabid fans … with good reason, as it turns out.

Terminology!
The correct term to refer to this type of headphone is planar magnetic. Unfortunately, all of Headphonedom calls them Orthodynamic, a Yamaha marketing term. Well, I call a facial tissue a Kleenex, so no big deal I suppose, but it’s not technically correct. Likewise Magneplanar (not often used) is a registered mark of Magnepan.

The other less used common term is Isodynamic, which means, “having equal force,” and refers to the zones of evenly distributed magnetic force in the driver within which the electrical conductors are immersed. Isodynamic magnetic systems exist in numerous types of devices. For example, isodynamic separators can sort streams of powders of mixed materials having differing magnetic permeability.

So, in the world of headphones, Orthodynamic, isodynamic, and planar magnetic all mean the same thing. I’ll probably use them somewhat interchangeably here to be sure people Googling for the terms will find the info … but planar magnetic is the correct term.

The Planar Magnetic Operating Principle
You can think of planar magnetic drivers as a sort of crossbreed between dynamic and electrostatic drivers. Like a standard dynamic headphone, planar magnetic headphones use the magnetic field around a conductor that has electrical current flowing through it to drive the diaphragm. Like an electrostatic driver, the diaphragm of a planar magnetic speaker is a thin sheet of flexible transparent film, but unlike an electrostat, the film has very thin, flat electrical conductors (wires ... but very flat ones) in it.

An array of magnets is placed in front of and behind the diaphragm such that the conductors are immersed in a very even field of magnetic flux (isodynamic magnetic field). When current is passed through the conductors, the magnetic field created by the current flow interacts with the isodynamic field created by permanent magnets, causing the conductors, and therefore the diaphragm, to move. The importance of the isodynamic field is to ensure that the relationship of current flow to force exerted on the diaphragm is constant regardless of the position of the conductor in its excursions through the field. The quality of the isodynamic field partly determines the linearity, and therefore contributes to the harmonic distortion content of the reproduced sound.

ARTICLE CONTENTS
Share | |
COMMENTS
JIGF's picture

Very informative, thanks Tyll.

I took the liberty and posted a link to this article over here (http://www.head-fi.org/forum/thread/493214/hifiman-he-6-planar-magnetic-...). Hope you don't mind.

Tyll Hertsens's picture
Not. One. Bit! In fact, I love it. I think this site should be a gateway for people to find out about headphones; see that there's more than meets the eye; and develop (if it feels like something they might be interested in) a desire to find out more. Readers providing links to further information is a service to folks not familiar with the community of enthusiasts. So thank you very much for the link, JIGF!
LFF's picture

Very informative and loved how you broke them down in the video. Pun intended. Thanks!

kwkarth's picture

Good show Gov!

svyr's picture

so um, he-500 = 1/2 a sandwich = still ortho?

PMM's picture

"My guess is that the high-end planar magnetic headphone makers (Audez’e and HiFiMAN) need to move the drivers a little forward and angle them back towards the ear to make improvements here."

It saddens me a little bit that so few headphone manufacturers understand that. It's something that a number of Sony's headphones have been doing for a long time now (I enjoy this chaotic writeup by the inimitable Leonard Lombardo: http://www.sonicstudios.com/mdr-f1.htm ), and obviously the Senn HD800 and AKG K1000 benefit greatly from the angling.

If by any chance at all some folks from Audez'e and/or HiFiMAN are reading: Please do your best to implement this! You guys are AWESOME for reviving planar magnetics while all of the old dog companies rested on their laurels, but you can still bring 'em closer to the promised land.

Tyll Hertsens's picture
... I just got a new pair of LCD2s and it does look like the padding creates more of an angle to the ear (and is somewhat softer) than my previous one. I'll take pix and go into more detail in my upcoming review.
PMM's picture

That's great news. Looking forward to it.

jrkong's picture

Now if my 11th grade education is correct, the conductive trace would be attracted to the top field and repelled by the bottom field unless the motor principle I learned was wrong.

Pappabetalar's picture

Was at a hifi-store listening to the LCD 2's while I was reading this informative article. Thank you for taking the time to write it!

Insatiable's picture

This article mentions the high end of HiFiMAN's product line. What about the HE-400? It is lower on their product line. I was wondering what you think about it, if you have heard it before. Would you say it would fit the general description of the higher end models, just a little less so? I am looking to buy these as an upgrade from my old ATH-M50.

X
Enter your InnerFidelity username.
Enter the password that accompanies your username.
Loading