The sonic modulus of a multifilament yarn can be measured with our pulse propagation setup (PPM). The pulse propagation speed in a medium in a multifilament yarn depends on the crystallinity and the orientation of the amorphous phase. The higher the crystallinity or the more orientation in the amorphous phase the faster the pulse propagation speed (expressed in m/s). By measuring the pulse propagation speed structure parameters can be elucidated. The sonic modulus (Eson) can be calculated once the density of the specific yarn is known as well (see Davenport gradient column). The orientation of the amorphous phase (FAS) can be determined once the crystal orientation is known as well (see XRD).