A fast and stable numerical solution for acoustic boundary element method equations combined with the Burton and Miller method for models consisting of constant elements. Theory and algorithm for the acoustic boundary element solver will be described. The solver represents the core of the package AField (acronym for acoustical field) and can be used for getting fast and stable solutions for huge as well as for small boundary elements models on PCs under Windows. The boundary element solver includes an early proposed GMRES iterative linear system solver (which can be used for big and huge models) and several traditional linear system solvers (for small and medium models). Implementation of the Burton and Miller regularization method for constant boundary elements will be discussed. Approximations in proposed boundary element solver and their influence on solution errors are investigated. Results for several models are included. Several possibilities of Afield package are illustrated.