Best answer: The Amazon Echo Sub adds richness and depth that you just don't get with an Echo or the Echo Plus. If you already have an Echo and stream music through it, you'll know that the bass is flat. That's where the Echo Sub comes in — the companion device is designed to pair to compatible Echo devices to offer room-rumbling sound.
Amazon: Echo Sub ($129)
The Echo Sub makes your music come alive
With the Echo Sub, Amazon is taking a different approach from that of Google or Apple. Instead of launching a standalone device to take on the likes of Google Home Max or the HomePod, Amazon is offering a piecemeal solution in the Echo Sub. You'll be able to configure the Echo Sub with a single Echo or Echo Plus or pair it with two Echo devices to turn it into a 2.1 system.
The Echo Sub is hefty at nine pounds, but its fabric finish — designed to complement that of the Echo and Echo Plus (2nd gen) — allows it to stand out.
Coming to the hardware, the Echo Sub offers a six-inch woofer with a 100-watt class D amplifier, and it manages to deliver an impressive amount of bass. Pairing the Sub with an Echo device (or two) leads to a vastly superior experience when streaming music, and if you already have an Echo or Echo Plus and are looking to improve its sound quality, then the Echo Sub is a natural addition.
Add some bass
Booming bass for your Echo
The Echo Sub adds much-needed bass to the Echo or Echo Plus. The ability to create a 2.1 system from two Echos paired to the Sub makes it an interesting choice for those looking to stream music, and it costs less than Google or Apple's offerings in this segment.
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Harish Jonnalagadda is a Senior Editor overseeing Asia at Android Central. He leads the site's coverage of Chinese phone brands, contributing to reviews, features, and buying guides. He also writes about storage servers, audio products, and the semiconductor industry. Contact him on Twitter at @chunkynerd.