X-ray diffraction and transmission electron microscope (TEM) measurements were performed on icosahedral AlMn and AlMnSi samples. Quasicrystallbe order was obtained via different sample treatments : quenching, laser annealing and furnace annealing of amorphous samples. In quenched bulk AlMn samples, the icosahedral grains are embedded in a crystalline Al matrix. The Al matrix is strongly reduced or rendered noncrystalline by the addition of Si. Samples prepared by laser annealing and quenching show a high degree of disorder. This shows up, in x-ray diffraction, as a large average peak line width. The furnace annealed samples show apparent homogenous grains by TEM darkfield methods, and the smallest peak widths in x-ray diffraction. However, the grain sizes are much larger than the x-ray correlation lengths. The variations of the line widths and their values can be understood in a Hendricks Teller mode1 as a consequence of interferences between projected lattice spacings in a disordered sequence