Typically the driver is modelled using Thiele-Small parameters to keep computation time down but full mechanical models can also be used.
The air volumes surrounding the driver and the holes, leakages and meshes to the outside world are modelled and so is skin- and eardrum impedance of the head.
Using a virtual model allows for trying different speakers by changing the associated speaker parameters. This can speed up the development process considerably compared to building physical prototypes.
Example of Thiele-Small data of a 8x15mm speaker used in a pair of glasses with a built-in speaker.
The OWR-1653T-20 driver is an excellent driver with good compromise between size and performance that will work well in applications such as smart glasses.