  We performed parallel measurements of the high-frequency shear modulus $G$
and relative volume $\Delta V/V$ for high-entropy
Ti$_{20}$Zr$_{20}$Hf$_{20}$Be$_{20}$Cu$_{20}$ and
Ti$_{20}$Zr$_{20}$Hf$_{20}$Be$_{20}$Ni$_{20}$ glasses upon heating from room
temperature up to the complete crystallization. The changes of these properties
due to structural relaxation both below and above the glass transition
temperature are singled out. It is shown that these changes for both initial
and preannealed samples can be well described within the framework of the
Interstitialcy theory. It is found that the whole relaxation process in the
full temperature range of the experiments for both samples' states can be
characterized by a single dimensionless temperature-independent parameter
$K_i=dln\;G/dln\;V$, which equals to -44 and -53 for the above glasses,
respectively, and strongly points at interstitial-type defects as a source of
relaxation. We also show that the relaxation of the relative volume linearly
depends on the defect concentration. This behavior can be described by another
dimensionless temperature-independent parameter, which is related with the
relaxation volume of defects. Possible contribution of vacancy-like defects
into the relaxation is discussed.
