Echo Sub will be a Subwoofer for Echo According to Pocket-Lint, New Products to be Announced Today

Echo subwoofer and Alexa-capable smart plug may be on the way

A Week With The New Echo Plus & Echo Sub

Echo Sub: A Subwoofer Whose Time Has Come

Echo Sub: a $129.99 subwoofer that pairs with Echo speakers - The Verge

Echo Sub Review

Is it possible to use an echo dot as a speaker? - Quora

Review: The tiny $129 Echo Sub is a huge audio upgrade