Try the following to end the sound in the middle of running a speak action. In order to preserve the indentation of your code use the code tags the next time you post some code.
Code:
import viz
viz.go()
viz.clearcolor(viz.SKYBLUE)
viz.add('tut_ground.wrl')
teacher = viz.add('vcc_female.cfg', pos = [0,0,5], euler = [180,0,0])
teacher.state(14)
speech = vizact.speak('carousel.wav')
teacher.addAction(speech)
def clean():
teacher.clearActions()
teacher.remove()
viz.playsound('carousel.wav', viz.STOP)
vizact.onkeydown(' ', clean)