https://learn.microsoft.com/en-us/dotnet/api/system.speech.synthesis.speechsynthesizer.setoutputtonull?view=netframework-4.8
SpeechSynthesizer.SetOutputToNull Method (System.Speech.Synthesis) | Microsoft Learn
Configures the SpeechSynthesizer object to not send output from synthesis operations to a device, file, or stream.
speech synthesismethodsystemmicrosoftlearn