Emacsvox needs a speech-server process. For a new installation, use Omnivox. Omnivox is the server that Emacsvox talks to; the engine that produces speech underneath it is platform-specific. The normal engine is eSpeak NG on GNU/Linux, AVSpeechSynthesizer on macOS, and WinRT SpeechSynthesizer on Windows.
For a first installation, follow the linear procedure in Getting Started: Installation and First Speech. Return here when you need platform-specific build details, compatibility servers, or deeper diagnostics. Omnivox build internals, engine behavior, and versioned protocols are documented and maintained in the Omnivox repository.