i want to plot a wave of spoken text ,how to store Speak command in a variable??

NET.addAssembly('System.Speech'); 
obj = System.Speech.Synthesis.SpeechSynthesizer; 
obj.Volume = 100; 
Speak(obj,'how are you');

i am initializing it like

a=Speak(obj,'how are you');

but it is not working.

[wala alzubaidi]

hi

what is role

obj.System.Speech.Synthesis.SpeechSynthesizer