A new impulse-response model for the edge diffraction from finite rigid or
soft wedges is presented which is based on the exact Biot-Tolstoy solution.
The new model is an extension of the work by Medwin et al. [H. Medwin et a
l., J. Acoust. Sec. Am. 72, 1005-1013 (1982)], in that the concept of secon
dary edge sources is used. It is shown that analytical directivity function
s for such edge sources can be derived and that they give the correct solut
ion for the infinite wedge. These functions support the assumption for the
first-order diffraction model suggested by Medwin et al. that the contribut
ions to the impulse response from the two sides around the apex point are e
xactly identical. The analytical functions also indicate that Medwin's seco
nd-order diffraction model contains approximations which, however, might be
of minor importance for most geometries. Access to analytical directivity
functions makes it possible to derive explicit expressions for the first- a
nd even second-order diffraction for certain geometries. An example of this
is axisymmetric scattering from a thin circular rigid or soft disc, for wh
ich the new model gives first-order diffraction results within 0.20 dB of p
ublished reference frequency-domain results, and the second-order diffracti
on results also agree well with the reference results. Scattering from a re
ctangular plate is studied as well, and comparisons with published numerica
l results show that the new model gives accurate results. It is shown that
the directivity functions can lead to efficient and accurate numerical impl
ementations for first- and second-order diffraction. (C) 1999 Acoustical So
ciety of America. [S0001-4966(99)02111-6].