In this talk we present a method for computing quasi resonances in acoustic scattering based on a discretization of a boundary integral operators of the second kind. Quasi resonance is a minimum point of the function mapping the real wave number to the minimal singular value of the Calderon operator. We adaptively approximate this function by a piecewise rational function satisfying Hermite interpolation conditions in a weak sense. Hermite information is readily available in this setting since the main computational effort consists in assembling the discretization of the Calderon operator and the cost of assembling its derivatives is only a postprocessing task. The main algebraic effort consists in solving a family of SVD problems using a subspace accelerated randomized algorithm. The randomized algorithm is a further development of the standard approach in that we solve for the smallest singular value and we need to balance this error with the error in the construction of the rational surrogate function. We use BICGSTAB algorithm with H-matrix based preconditioner to this effect. This is a joint wotk with Luka Marohnic, TVZ.