He spoke into the microphone.

He spoke at the microphone.
He spoke on the micrphone.
He spoke through the microphone.

(Which preposition do I have to use? Are they all correct?)

It depends on the situation, but the first one makes sense.

the first one makes the most sense

Angie and jojo are correct.

When describing how someone speaks using a microphone, the most common preposition to use is "into". Therefore, the correct sentence is: "He spoke into the microphone."

The preposition "into" suggests that the speaker is directing their voice towards the microphone, as if they are speaking directly into it. This usage implies that the microphone is being actively used to amplify or transmit the speaker's voice.

On the other hand, the preposition "at" can also be used in certain contexts to describe speaking with a microphone. For example, if someone is speaking from a distance and their voice is being projected through the microphone to the audience, you could say: "He spoke at the microphone." This suggests that the speaker is aiming their voice towards the microphone, but not necessarily speaking directly into it.

The preposition "on" is not typically used when talking about speaking into a microphone. Instead, "on" is often used when referring to physically placing or resting something on a surface. Therefore, "He spoke on the microphone" would not be the most appropriate usage in this context.

Lastly, "through" is used when describing the transmission of sound or communication. For instance, you might say: "He spoke through the microphone" if the speaker's voice is being transmitted to a larger audience or to a different location using the microphone as a means of communication.

In summary, "He spoke into the microphone" is the most common and appropriate prepositional choice in this context.