A system for recycling planar objects including compressed mineral fiber material includes: a conveyor arranged to covey the planar objects through a number of stations at least including a thickness measurement station and a sound measurement station. The sound measurement station includes a sound reflecting surface arranged to back a first major surface of a planar object, a sound emitter arranged to emit sound towards the sound reflecting surface, a sound receiver arranged to receive sound reflected from the sound reflecting surface, and a converter arranged to determine a property related to sound absorption. A sorting station is arranged to sort the planar objects based on determined properties in to a plurality of fractions.

A system for recycling planar objects including compressed mineral fiber material includes: a conveyor arranged to covey the planar objects through a number of stations at least including a thickness measurement station and a sound measurement station. The sound measurement station includes a sound reflecting surface arranged to back a first major surface of a planar object, a sound emitter arranged to emit sound towards the sound reflecting surface, a sound receiver arranged to receive sound reflected from the sound reflecting surface, and a converter arranged to determine a property related to sound absorption. A sorting station is arranged to sort the planar objects based on determined properties in to a plurality of fractions.