Complex sentence: The researchers presume that today's headphone solutions are limited by a form of standardization of the acoustic restitution linked to the fact that the shape and size of a person's skull and ears are not taken into account.
Split into simpler sentences: The researchers presume that today's headphone solutions are limited due to the fact that they are all standardized in terms of the acoustic restitution. This is linked to the fact that the shape of each individual's ear and the size of their head are not taken into account.