The Sony sound system that came standard on the ST trim of the Fiesta is not a bad system for a subcompact car. That being said, with just the 6.5" speakers in all the doors and a pair of tweeters on the front doors, bass performance is limited. Surprisingly, despite the Sony branding this Fiesta didn't have a factory amplifier so to really give the speakers a rich and full sound we installed Sony's 5/6 channel amplifer. The plastic Sony speakers that came on this car were ok but we replaced them with Sony's top of the line GS series speaker which use a mica reinforced kevlar woofer for crisper sound and better power handling. The front speakers are a 2-way component speaker with a crossover and tweeter while the rear doors use a coaxial 2-way speaker.
The Sony XM-GS6DSP amplifier we installed is unique in that it has a DSP smartphone app where you can fine tune your system. It also has a subwoofer channel which we hooked up to an Alpine SWT-S10 tube loaded enclosure. This enclosure takes up a lot of the trunk space but pounds hard for the price point. To help with the powerful sound system we added Dynamat superlite sound deadening to reduce NVH and deliver a better car audio experience.