Abstract: New design formulae are presented for the Tchebyscheff array, which afford straightforward computation in the design work. It is proposed to use the energy concentration factor and directivity factor as indication of the directivity of the array, and formulae as well as the way of using them are presented. Finally, the application of the Tchebyscheff arrays in the diffuseness measurements for room acoustical investigation is discussed, the method is more sensitive to the change of diffuseness than those heretofore suggested.