  The calculation of the acoustic field in or around objects is an important
task in acoustic engineering. To numerically solve this task, the boundary
element method (BEM) is a commonly used method especially for infinite domains.
The open source tool Mesh2HRTF and its BEM core NumCalc provide users with a
collection of free software for acoustic simulations without the need of having
an in-depth knowledge into numerical methods. However, we feel that users
should have a basic understanding with respect to the methods behind the
software they are using. We are convinced that this basic understanding helps
in avoiding common mistakes and also helps to understand the requirements to
use the software. To provide this background is the first motivation for this
paper. A second motivation for this paper is to demonstrate the accuracy of
NumCalc when solving benchmark problems. Thus, users can get an idea about the
accuracy they can expect when using NumCalc as well as the memory and CPU
requirements of NumCalc. A third motivation for this paper is to give users
detailed information about some parts of the actual implementation that are
usually not mentioned in literature, e.g., the specific version of the fast
multipole method and its clustering process or how to use frequency-dependent
admittance boundary conditions.

Numerical Analysis;Numerical Analysis