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whats so special about planar magnetic headphones

post #1 of 9
Thread Starter 

Ive been reading up on some higher end headphones, and i have been noticing that higher end headphones like the HiFiMan HE500 and the Audeze LCD-2 are planar magnetic headphones. i really don't know what that means, and usually the ohm rating on the are really low like 38 ohms , can anyone tell me the main difference between regular headphones and planar magnetic ones?

post #2 of 9
Quote:
Originally Posted by missleman101 View Post

Ive been reading up on some higher end headphones, and i have been noticing that higher end headphones like the HiFiMan HE500 and the Audeze LCD-2 are planar magnetic headphones. i really don't know what that means, and usually the ohm rating on the are really low like 38 ohms , can anyone tell me the main difference between regular headphones and planar magnetic ones?

"ohm rating" angry_face.gif -> http://en.wikipedia.org/wiki/Nominal_impedance There is no "ohm rating" as a concept - there is nominal impedance (Znom) which by itself expresses nothing meaningful; it is not some sort of linear metric that conveys "easy to drive." Finally, 38 ohms is not "really low" for conventional headphones - it's about average (in that same 20-40 range you have most every Denon, Grado, and Audio-Technica headphone ever made); "really low" is <10 ohms imho (I'm aware of one current production model that is <10ohms Znom). Basically what the nominal impedance conveys is a component of figuring out what kind of amplification requirements you're looking at - lower Z = higher A/lower V; higher Z = lower A/higher V. You also have to consider sensitivity though; you can be super duper low Z (like the DT48A.00 - 5 ohms nominal) but super duper sensitive (like the DT48A.00 - 134 dB/V), which means very little actual input power is needed to get a usable output (so it doesn't matter if it demands relatively more current than an HD 600, it uses less power overall). Generally extremely low Z values present problems for some amplifiers (especially OTL tube designs), and extremely high Z values present problems for some amplifiers (they just want more voltage than the amp can deliver; apart from Beyerdynamic I'm not aware of anyone else still making headphones with Znom at 600ohms or higher though (and I'm convinced Beyer only does it to confuse the hell out of people)). The easiest way to figure out if XYZ headphone will work is to look at the nominal impedance, the sensitivity, and then compare that to the power output of whatever amplifier/thing you're going to use. In most cases, most amplifiers can drive most headphones. smily_headphones1.gif What I'd be more interested in is if the load is safe for the amplifier (for example Bellari makes a headphone amplifier that says to not connect anything lower than 16 ohms or the amplifier will be unstable (and perhaps more importantly, it will void your warranty); so I wouldn't try the DT48A.00 there - it just sounds like a recipe for trouble); rather than "can I get this loud enough to kill myself?" (Because in most cases the answer there is YES YOU CAN!).

Anyways, planar magnetic headphones use planar magnetic drivers (what did you expect? puppies? tongue.gif) as opposed to more traditional voice coil type drivers found in dynamic headphones (a random dynamic headphone example: Denon AH-D2000). Planar tells us that they're a big, uniform radiating surface - electrostats are similar in that respect (and *only* in that respect), which does a lot for how they sound (planar vs non-planar is a difference in radiation pattern and how sound hits the ear which changes how you perceive the sound, I'm not sure how best to describe the overall effect; one is not explicitly better than another). The current production ortho headphone models also seem to be able to take *a lot* of continuous input power, and generally tend to have very good (measured) bass response. This makes them stand-out against a lot of other headphones. The downside is that they're not the most sensitive headphones (meaning it takes more electrical power to translate to the same acoustic output) - they're still conforming to Hoffman's Iron Law.

To pick on a modern (and extreme) example, take the HiFiMan HE-6, which is around 40 ohms Znom, but something like 70-75 dB/mW; they need (compared to most any other headphone) a ton of power to run. Tyll measured them needing nearly 20mW/side to reach 90 dB (which is relatively loud, but not insanely so). Most headphones need a fraction of a mW, or perhaps 1 mW (some other random examples: the RS-1 is measured needing around .80 mW/side, the HD-650 around .15 mW/side, and the Beats Pro around .05 mW/side, to reach the same level (I rounded) - they will all be the same loudness (90 dB) but require different amounts of input power; 1 mW really isn't that scary for most headphone amplifiers (even non-dedicated devices), 20 mW is out of the reach of a good number of devices methinks (I've not personally tried it with an iPhone or something of the sort, but my suspicion is that it probably couldn't deliver)).

More technical good-ness:
http://en.wikipedia.org/wiki/Loudspeaker#Ribbon_and_planar_magnetic_loudspeakers

There are speakers that use similar operating principles (ribbons), like BG and Magnepan. They tend to be fairly well regarded. I think HiVi also produces some planar magnetic drivers, but I could be mistaken.
Edited by obobskivich - 6/27/12 at 8:32pm
post #3 of 9
post #4 of 9
Thread Starter 
Thank you both , you really cleared that whole thing up for me. Another thing I'm wondering is that planar magnetic drivers ; are they more expensive to produce , as you only see them in higher end headphones ?
post #5 of 9
Quote:
Originally Posted by missleman101 View Post

Thank you both , you really cleared that whole thing up for me. Another thing I'm wondering is that planar magnetic drivers ; are they more expensive to produce , as you only see them in higher end headphones ?

 

 

 

there is one that is much cheaper, fostex t50rp, fairly popular

post #6 of 9
Thread Starter 
Quote:
Originally Posted by reddragon View Post

 

 

 

there is one that is much cheaper, fostex t50rp, fairly popular

oh ok , i was looking at those,. aren't they a very popular set of cans to mod ?

post #7 of 9
Quote:
Originally Posted by missleman101 View Post

oh ok , i was looking at those,. aren't they a very popular set of cans to mod ?

 

 

they are, im planning to have mine mod when i have money to mod them

post #8 of 9
Quote:
Originally Posted by missleman101 View Post

oh ok , i was looking at those,. aren't they a very popular set of cans to mod ?

Yes, there's a huge thread about them. There's also some places that will mod them for you (I have no experience/knowledge about specifics btw) - I've heard of "Mr Speakers" and the "Thunderpants" as popular choices.
post #9 of 9

The good thing is that planar magnetic driver efficiencies can be increased drastically with some tweaks and design changes, cue the new HE400, which has 92.5 dB/mW, and is driven admirably with any amp big or small. I think it was done via reducing the driver tracing surface area (instead of covering the tracing over the whole circular diaphragm, here it's only within the square that takes up inside the circle), so it does lose some refinement, but all the planar magnetic character is still there if not more.

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