https://www.cnet.com/news/black-friday-2018-amazon-deals-sale-starts-now-fire-tablets-tomorrow-fire-tv-sunday-echo/

The Amazon Echo Sub adds an instant bass upgrade to the Echo line of smart speakers -- and you get two of the latter as well, making for a better overall music experience.

One Echo Sub and two Echo smart speakers make for a great combination. If you want to raise the ante, opt for a pair of Echo Plus instead. They add a temperature sensor and smart-home hub to the mix.