Smart Speaker with Volumio, Raspberry Pi 3 and Adafruit MAX98357
Volumio is an open source music player designed to play all your music. It is available as a whole GNU Linux distribution for popular development boards such as Udoo, BeagleBone Black and my favorite Raspberry Pi.
As a weekend hobby project I built my own smart speaker powered by Volumio using a Raspberry Pi 3 Model B, an amplifier, a breadboard and a lot of wires. The power rating of the loudspeaker is 2 Watts and the impedance is 4Ohm. The same setup should work fine with any other version and model of Raspberry Pi with 40-pin header.
The amplifier is Adafruit MAX98357A. It is class D and it is just a mono amplifier using MAX98357A. In other words it is definitely not for audiophiles. I have connected it to the standard I2S digital audio input of the Raspberry Pi.
Volumio has a user friendly web interface which provides features for playing audio files or directly playing online radios. The back-end is written in Node.js.