The tiny speakers also arrived. These Visaton BF 32 3.2 cm 2 W 8 Ω speakers are perfect for the prototype because they can be fitted nicely in the case. They have a Powerful neodym drive and so be powerful enough to be driven by a small amplifier.

For the prototype we decided to drive the speakers with a mono amplifier. These modules are widely used and produce acceptable sound quality for this prototype. 

Picture of the 3D printed casing with wiring and electronics. 

The speaker module is half the size of the normal base module. The module can be powered from both sides and will pass the i2c data to the other side(connector). This enables the end user to place a speaker module in between two hand detecting modules, a couple of speaker modules in series or even a speaker module alternately to other modules. That's the beauty of a modular design :)

The picture below shows all the needed components fitted nicely in the module.

Some of the parts needed protection from touching other components.  The Buck converter and amplifier are therefore encased with heatshrink.