Add the Voice of Siri to Mac OS X:
Via OS X Daily
- Launch System Preferences from the Apple menu and click on "Speech"
- Click the "Text to Speech" tab and then click the pulldown menu next to "System Voice"
- Choose "Customize" from the dropdown menu
- Check the box next to "Samantha", a notification will be added to the window saying the voice will be automatically downloaded, click "OK" to start the voice download
- Confirm at the next screen to install the Samantha voice by clicking "Install"
- When finished, verify that the voice is selected to use it as your default text to speech voice in Mac OS X, click "Play" to hear the voice sample