How do I delete some of the system voices that I find in System Preferences/System/Speech/

If you go to System Preferences/Settings/Speech/Text To Speech you will find a list of voices that you can choose to have the computer speak to you in. I believe these voices can be as large as 400 Mb each. I would like to delete the ones I don't care for but I can't find their files. Does anyone know how to perform this operation?

Thank you,

rmbarr (Richard)