The ν6 + ν8 combination band of diacetylene has been remeasured at 0.0019 cm-1 resolution with a Fourier transform infrared spectrometer. Analysis and assignment of the improved data sets were carried out with an interactive Loomis-Wood fitting program. Altogether more than 1400 assignments were made and band origins, rotational and distortion constants for the main band and associated hot bands were determined. The band centre was found to be 1241.060828(37) cm-1 and the ground-state rotational and distortion constants, B0 and D0, were found to be 0.14641021(52) cm-1 and 1.6085(49) × 10-8 cm-1, respectively. The experimental values of B0 for diacetylene, triacetylene and dicyanoacetylene are compared with values predicted from ab initio calculations, and with values obtained from estimates derived from the known structural parameters of HC3N and HC5N. Several very weak difference bands, 110901, 110801 and 410601, and combination bands, 510610 and 110910, in the region 3600-2600 cm-1 were also assigned.