Is it permissible for a woman to use a loudspeaker in school even though her voice is 'awrah?

The preponderant opinion is that a woman's voice is not 'awrah (something that must be covered or concealed), but she must avoid softening her speech or making it melodious; this is based on the Almighty's saying: "Then do not be soft in speech [to men], lest he in whose heart is disease should covet, but speak with appropriate words."