Biot–Tolstoy–Medwin diffraction model
In applied mathematics, the Biot–Tolstoy–Medwin (BTM) diffraction model describes edge diffraction. Unlike the uniform theory of diffraction (UTD), BTM does not make the high frequency assumption (in which edge lengths and distances from source and receiver are much larger than the wavelength). BTM sees use in acoustic simulations. Impulse response. The impulse response according to BTM is given as follows: The general expression for sound pressure is given by the convolution integral where formula_2 represents the source signal, and formula_3 represents the impulse response at the receiver position. The BTM gives the latter  in terms of as an integral over edge positions formula_5 where the summation is over the four possible choices of the two signs, formula_13 and formula_14 are the distances from the point formula_5 to the source and receiver respectively, and formula_16 is the Dirac delta function. where