Hi Niwantha, While it is true that "speak up" is used to encourage someone to speak more audibly, both "speak up/out" are used to mean expressing one's views, especially in a public setting. There are usually some things which we perceive as unjust and would like to make them publicly known when we "speak up/out". Examples: Could you speak up, please? (raise your voice) We must speak up (publicly voice our support) for these indigent communities. Someone has to speak up for the marginalised. If we do not speak out (publicly highlight some issues such as unfairness) against the system, the ones to suffer will be our future generations.

Speak up = to speak louder, but it also means to defend yourself verbally, to not let people bully you. To say more clearly and forcefully what you want. To not let people "queue jump" <-- this would be very British. "HOYE there's a clue mate" is speaking up. Speak out= same as speak up, speak louder or defend yourself, often like this "speak out/up for yourself" so basically they are the same. But you have to grasp the context and the tone of voice to know which one is being spoken. It is also just personal preference, some people say "speak up' some say "speak out" AND I agree with chuck speak out would be more for political protest.

Just personal preference. To me, speaking out is more associated with the concept of protesting political in nature, while speaking up is more associated with either encouraging the speaker to increase the volume of his/her voice or to say what is on their mind. Others may see things differently.

They both actually mean the same thing which is to adress your opinion in a controversial setting, however the main difference would be that you can also use "to speak up" in order to ask someone to raise their voice. I also guess "to speak out" would be more often used in a formal setting with a lot of people.