Yes, SPEAKER is a Scrabble word!

Letter values in Scrabble US: S 1, P 3, E 1, A 1, K 5, E 1, R 1.

Is it a valid word?

SPEAKER is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

someone who expresses in language; someone who talks (especially someone who delivers a public speech or someone especially garrulous)
electro-acoustic transducer that converts electrical signals into sounds loud enough to be heard at a distance
the presiding officer of a deliberative assembly

Also: speaker unit, loudspeaker system, speaker system.

Not playable in Scrabble US: VERBALISER.