I would like to use a kind of woven or embroidered speaker on the jacket to allow the person who is wearing it to speak loudly in front of an audience.
Unfortunately I don't believe such a speaker will have anywhere near the capability to produce clear and powerful sound.
The soft speaker is an innovative idea, great for wearable tech art where the type sounds and very low db and no quality is needed.
To have the person able to 'speak loudly in front of an audience', you will need the person to ware a large battery, a good quality and powerful audio amplifier with microphone input and a rather large speaker, all of which will probably weigh the person down quite a bit.
Maybe that is why lecterns with the complete audio works have been invented?