Deliver Better Phone Calls & Siri
The Apple Watch 4 speaker is 50% louder than the Apple Watch 3, and it includes better microphones as well.
This upgrade means that making and taking phone calls on the new Apple Watch Series 4 is a much better experience. It's easier to hear the caller, and they can hear you better thanks to the new microphones.
These upgrades also help when using Siri. The Apple Watch 3 already could speak back to you, but it was hard to hear Siri sometimes. The new model should allow Siri to hear you better and be loud enough for you to hear answers in noisier environments.