How Planar Magnetic Headphones Work Page 2
Advantages of Planar Magnetic Drivers There are so many advantages to this type of driver in a headphone that I’m surprised it hasn’t caught on more. Let’s work our way down the list.
Planar Sound Wavefront --- In my opinion, this may be the most important characteristic advantage of Orthodynamic headphones. Standard dynamic drivers are fairly small and essentially operate as a point source of sound radiating a spherical section wavefront. When a spherical wavefront hits your ears it reflects on the outer ear in a geometrically different way than a planar wavefront. This causes the focusing of sound entering your ear to behave somewhat differently than it would normally. It is surmised that this disturbance of the reflective characteristics of your ear may inhibit normal localization of sound, and therefore disturb the audio image heard.
Headphones like the Stax electrostatics, AKG K1000 earspeakers, and Sennheiser HD 800 with it’s large ring-radiator, are known for their excellent audio imaging likely due to the more planar wavefront they present the ear. I find the imaging (such as it is on headphones) to be quite good on the latest crop of planar magnetic headphones, though possibly not quite as good as those mentioned above. 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.
Low Distortion --- Unlike dynamic drivers that are driven from the point at which the voice coil is attached (usually near the center), planar magnetic drivers are forced to move over their entire surface. This means they don’t suffer from modal break-up found on traditional drivers when the cone surface starts wobbling in undesirable ways at higher frequencies.
Large and Powerful Diaphragm --- Getting powerful, tight bass response is difficult for most dynamic headphones as the driver surface area is relatively small and would have to make large excursions to move the volume of air that good bass response requires. The force used in electrostatic drivers (the static force the makes your socks cling together out of the drier) is relatively weak compared to the electro-magnetic force in planar magnetic drivers. Electrostatic drivers have trouble delivering the horsepower needed for big bass notes. The large surface area of the planar magnetic driver coupled with the powerful drive of the electromagnetic force permits large amounts of air to be moved with authority. My experience with planar magnetic cans is that they offer the best bass response of any type of headphone.
Responsiveness --- The diaphragm in an Orthodynamic headphone is very light, and the electromagnetic force is very strong, so the ability for the signal to accelerate the diaphragm is very, very good. Like electrostatic speakers, planar magnetic headphones tend to sound very coherent and spacious.
Easy on the Amplifier --- Unlike the coiled winding of a dynamic driver, which creates inductive peaks in the impedance characteristics of the headphone, current planar magnetic headphones use a serpentine pattern for their voice coil, which makes their impedance characteristics almost purely resistive. Though they sometimes need quite a bit of voltage to drive them, they are not difficult loads to drive at all.