  Recent progress in the seismic interpretation of field {\beta} Cep stars has
resulted in improvements of the physical description in the stellar structure
and evolution model computations of massive stars. Further asteroseismic
constraints can be obtained from studying ensembles of stars in a young open
cluster, which all have similar age, distance and chemical composition. We
present an observational asteroseismic study based on the discovery of numerous
multi-periodic and mono-periodic B-stars in the open cluster NGC 884. Our study
illustrates the current status of ensemble asteroseismology of a young open
cluster.
