FreeTTS.jar in Eclipse you can not hear text to speech

I'm trying to learn text-to-speech conversion, using FreeTTS .

I use Ubuntu 16.04 , Java 1.8 and Eclipse Oxygen .

I tried the demos with freetts.jar and if I run them from an Ubuntu terminal the voice of the text is heard, but if I execute them from Eclipse you do not hear anything.

I suppose it should be some configuration of Eclipse but I do not know what it is.