In my HE-5LE review I also pointed out two possible drawbacks to orthodynamic designs: namely, relatively high construction costs and low efficiency (or low sensitivity). Let me elaborate on both these points.
If you’ve ever have a chance to see an orthodynamic driver taken apart, you’ll find (as mentioned above) that the thin driver diaphragms feature fine-pitch conductive traces arranged in specific patterns; during assembly, the diaphragms must be very precisely aligned vis-à-vis the driver’s magnet arrays. Getting the alignment spot-on typically requires specialized assembly tooling plus extra quality control steps to ensure that tight tolerances are maintained. While precision tooling and extra assembly work add costs, you may find—as I have—that the sonic benefits of good orthodynamic designs more than outweigh whatever extra manufacturing costs may be entailed.
The second point, relative inefficiency, is potentially a more serious concern.
Orthodynamic ‘phones tend, as a general rule, to be low in sensitivity. The power hungry HE-5LE, for example, carried a low-ish sensitivity rating of 87.5 dB (1 mW input)—a sensitivity rating much lower than ratings for typical top-tier headphones that use conventional dynamic drivers. The HE-6, in turn, quotes an even sensitivity rating of 83.5 dB (1 mW/input), despite the fact that it is equipped with a “super efficient magnetic circuit,” which means it’s not an easy headphone to drive.
In practical terms, there are several things prospective owners should understand about the HE-6. First, the HE-6 cannot be driven directly from an iPod, iPhone or any other low-powered digital device. As New Yorkers might say, “fuhgeddaboutit.” Second, while the HE-6 can be a phenomenally good-sounding headphone, it absolutely requires an adequately powerful, high-resolution headphone amp to give of its best. Lesser amps can, of course, get the HE-6 to product sound, but the fact is that they cannot and typically do not reveal the terrific sonic subtlety and nuance of which the HE-6 is capable.
But take comfort in this: once you invest in an appropriately good headphone amp, the HE-6 will deliver heightened levels of performance that are well and truly breathtaking. In fact, the HE-6 stretches the sonic performance envelope even further than the HE-5LE does, which is saying a mouthful. In the process the HE-6 establishes itself as one of the finest headphones now available at any price.