( ( However ( ( the ( fundamental difference ) ) ( is ( ( that whereas ) ( ( electromagnetic waves ) ( can ( travel ( through space ) ) ) ) ) ) ) ) ( , ( ( sound waves ) ( ( ( require ( a medium ) ) ( through ( which ( to travel ) ) ) ) . ) ) ) )
(ROOT (S (S (ADVP (RB However)) (NP (DT the) (JJ fundamental) (NN difference)) (VP (VBZ is) (SBAR (IN that) (IN whereas) (S (NP (JJ electromagnetic) (NNS waves)) (VP (MD can) (VP (VB travel) (PP (IN through) (NP (NN space))))))))) (, ,) (NP (JJ sound) (NNS waves)) (VP (VBP require) (NP (DT a) (NN medium)) (PP (IN through) (SBAR (WHNP (WDT which)) (S (VP (TO to) (VP (VB travel))))))) (. .)))
However the fundamental difference is that whereas electromagnetic waves can travel through space, sound waves require a medium through which to travel.
(ROOT (S (NP (NNP Medium)) (VP (VBZ is) (NP (NP (DT the) (NN matter)) (SBAR (WHPP (IN through) (WHNP (WDT which) (NN sound))) (S (NP (NNS waves)) (VP (VBP travel)))))) (. .)))