When HiFiMan refers to the single-sided planar magnetic driver in the HE-400i headset they are describing the positioning of the magnets within the drivers, single sided only have magnets on the side of the driver that is facing away from your ear.  As you might expect from this design decision this is not an inexpensive gaming headset but a high end audiophile headset and the $500 price tag further emphasizes this.  TechPowerUp had a chance to don these earphones and try them out, connected to JDSLabs C5D and O2 headphone amps and were more than impressed.  Indeed the bass reproduction of the HE-400i came near to matching the HE-560 which is twice the price.  If you have a decent headphone amp and discerning ears then HiFiMan is brand to take under consideration.

"HiFiMAN has always been known to produce some pretty interesting high-end headphones. Today, we take a look at the new HE-400i. It uses the same magnet array technology HiFiMAN introduced with the critically acclaimed HE-560."

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