( ( ( The ( beat frequency ) ) ( of ( the ( resultant wave ) ) ) ) ( ( will ( be ( ( the difference ) ( in ( ( the frequencies ) ( of ( the ( two sources ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN beat) (NN frequency)) (PP (IN of) (NP (DT the) (JJ resultant) (NN wave)))) (VP (MD will) (VP (VB be) (NP (NP (DT the) (NN difference)) (PP (IN in) (NP (NP (DT the) (NNS frequencies)) (PP (IN of) (NP (DT the) (CD two) (NNS sources)))))))) (. .)))
The beat frequency of the resultant wave will be the difference in the frequencies of the two sources.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS waves)) (PP (IN of) (NP (CD two) (JJ different) (NNS frequencies)))) (VP (VBP interfere)))) (, ,) (NP (NN beating)) (VP (VBZ occurs)) (. .)))