A beat is a unit of time measurement that is used in the performance of a musical piece to pace the musicians.
Subsequently it is used to pace dancing that is influenced by the music.
However, on the listener's side, the beat is mostly arbitrary and new beats can be assigned.
Any sequence of beats can be ultimately considered a phrase comprised of 2 and/or 3 beats.
The beats are grouped by a musical container called MEASURES.
On the listener side, a "down beat" or initial repeating beat is intuited to determine the size and consistency of the MEASURES.
Has a composition of phases which alternate between MEASURES of 2 beats and MEASURES of 3 beats.
However, as a listener, you can not determine the "down beat" through some kind of repetition of "bass drum." You must infer the MEASURE repetition through the melodic lines.