Tested with the latest Android and Ubuntu OS for XU4, C2 and C1+. You don't need any soldering. It is ready to go. 

If you have old version of OS, update it to the latest version first. 

This uses I2S as digital sound standard for audio output. 
It is super easy.  You'll be rockin' out in 15 minutes.
step1. Plug 2 x 2 Watt 4 ohm stereo speakers to the connector on the Boom Bonnet board and attach them with sticky glue. 
step2. Connect the GPIO ribbon cable one side to the boom bonnet board and the other side to ODROID board. 
step3. Update the OS to the latest version. 

You can easily adjust the audio output level with a potentiometer on the board.

Enjoy the stereo BOOM sound! 

A detail WiKi page for Software settings and Hardware schematics

Package include
- Stereo Boom Bonnet board
- 2 x 2Watt / 4 ohm mini speakers (28mm diameter, 11.5mm thickness)
- 3 x 5mm PCB spacers
- 3 x 5mm screws

and select one GPIO cable for your ODROID
- 7 pin GPIO ribbon cable(200mm) for C1+ / C2  or
- 12 pin GPIO ribbon cable(200mm) for XU4

- Download DXF Drawing File HiFi_Sheild3_REV0.1.DXF

Make a stereo quality sound system with ODROID-VU7
- I2S 2Watt Stereo Boom Bonnet Kit
- 7 pin GPIO ribbon cable
- ODROID-C2
- ODROID-VU7
- MicroSD Card 
- 5V/2A PSU

Connect the I2S 7pin cable