The plane of the strings lies perpendicular to the resonator’s surface.
322.1 Open harps – The harp has no pillar.
322.11 Arched harps.
322.12 Angular harps.
322.2 Frame harps – The harp has a pillar
322.21 Without tuning mechanism.
322.211 Diatonic frame harps.
322.212 Chromatic frame harps.
322.212.1 With all strings in one plane.
322.212.2 With strings in two planes crossing each other.
322.22 With tuning action.
322.221 With manual tuning action.
322.222 With pedal action.