https://www.techradar.com/news/the-new-moto-z-stereo-speaker-gives-you-more-smartphone-sound-for-less

You'll now be able to pump up the volume in a new way on your Moto Z and Moto Z2 smartphones thanks to a more affordable speaker Moto Mod attachment.

The new Moto Stereo Speaker is now available in the US for $59 (about £42, AU$76), giving you a cheaper way to outfit your Moto Z with loud stereo sound out the back.