The problem asked by Mark Kac in the paper “Can one hear the shape of a drum?” (1966) will be well-known widely as an initiation of spectral geometry and analysis (after Hermann Weyl ?). Since then, many counterexamples are found or constructed.

In this talk I will give a new example of infinite series of pairs of such manifolds, isospectral but non-diffeomorphic. They are constructed by making use of Clifford algebras with respect to quadratc forms with arbitrary signatures and their modules. [<6>]