We have been using the ST MP23DB01HP microphone to measure the shockwave signature of assault rifles. When comparing the time signal with measurements performed with other microphones (e.g. B&K model 4948), we noticed that the typical N-wave signature looks different with the ST microphone. The initial compression wave of the shock appears negative when measured with the ST microphone, which is counter intuitive. Also, the expansion phase of the shockwave, which appears relatively clean when measured with the B&K microphone, is severely perturbed when measured with the ST microphone. Could it be that the perturbation observed with the ST microphone is of internal nature, e.g. caused by some internal flow due to the shockwave and not properly vented out of the casing? What other possible causes would you see? Exceeded acoustic overload point? Tthe shockwave has very strong gradients, that might interact negatively with the ST microphone.
