A stock assembly for attachment to a firearm assembly is described. A chord profile is provided at each triangulation point and two corners of the triangular cross-section are situated at the same level with the third corner situated above the corner. Operation of the drive will cause rotation of the lifting head, the stack of flats and the drive engagement device simultaneously. During scheduling of reads, the earliest received read whose target memory module is not busy is immediately issued at a next command cycle. A signal processing module is in communication with the sensing arrangement and processes the recorded data for the purposes of at least one of estimating the sparsity of the recorded sound field and obtaining plane-wave signals to enable the recorded sound field to be reconstructed. Similarly, beneath the belt are mounted flat, elongated strips made of a high density plastic.