Body font family verdana geneva sans serif font size11px td font family verdana geneva sans serif font size11px hifiman he 400i open back full size planar magnetic headphones the hifiman he 400i is a full size planar magnetic headphone intended for high performance listening in the home or studio using single ended drivers he 400i delivers a lifelike soundstage and spatial imaging its increased efficiency of 93db allows it to be driven with a modest size amplifier or can even be