High pressure Brillouin scattering experiments on single crystal materials are an essential tool for determining their elastic properties and their variation with pressure and temperature. However, in order to obtain self-consistent data, it is important to measure the density of the material under investigation at the same conditions at which the acoustic wave velocities are obtained. This is not a trivial task, since the light path of the CO2 laser, used for heating the transparent samples needs to be completely enclosed up to the diamond anvil cell (DAC) containing the sample, limiting the movement of the DAC for X-ray measurements. In order to perform Brillouin scattering and X-ray diffraction experiments simultaneously at high pressure and high temperature, two important developments have been made in the Brillouin scattering laboratory at the Bayerisches Geoinstitut. A MAR345 image plate detector was installed at a distance of 410 mm from the centre of the diffractometer, leaving enough space around the sample for the incident laser beam lens of the Brillouin scattering system as well as for the power meter of the CO2 laser system. In this way, a resolution of about 1.6 Å can be achieved without moving the detector. In addition, experiments were performed using round table diamond anvils, which have two major advantages over flat table diamonds: first, the round table of the diamonds acts as a lens for the CO2 laser radiation, so that the laser spot at the sample position is less than 30 µm in diameter, allowing small crystals to be heated with relatively low laser power, and second, the laser heating was achieved using He as a pressure transmitting medium without damaging the diamonds. Acoustic wave velocities and unit cell volumes measured at high pressures and temperatures on single crystals of mantle minerals will be presented.