The text specifically states, "And they [the disciples] were filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance" (2:4). Here, the miracle is clearly in the speaking. The disciples were able to speak languages they had not previously learned.

But was there also a miracle in the hearing that took place that day?

As you have discovered, Acts 2:6 could easily be interpreted to mean that "each of the different linguistic groups was hearing all the disciples speaking his own native language at the same time." If that's what was happening, then it would seem that the miracle was in the hearing, at least in part.

But Luke (the writer) is not attempting to provide a highly detailed description of the events of that day. He tells us that "everyone heard them speaking in his own language," but he does not tell us whether or not all the disciples were together in one place the whole time; nor does he describe the exact format (or whether there was one) the disciples followed in addressing the crowd. Did they speak one by one from a platform? Were they moving about freely in the crowd, speaking separately to individuals and small groups? Luke doesn't provide all the details of this event.

So let's consider a couple of possibilities as we try to envision what that day must have been like and how the events Luke describes unfolded.

In Acts 2:14, Peter is "standing with the eleven," indicating that the twelve were all together in one place. But does this mean they had been standing together in that one place for the entire time? If so, were they all speaking at the same time? It seems more likely that if they were all together during the entire time, they would have been speaking one after the other. So if each of the disciples were speaking in turn—one followed by another—from one location, then we might logically conclude that the miracle was in the hearing. This would mean that if a Galilean disciple who knew only Aramaic and maybe a little Greek miraculously began addressing the crowd in Latin, but the Jews from Arabia heard that speech in their own Arabian language, then the miracle would be in both the speaking and the hearing.

However, it is possible that, before the scene described in 2:14, the disciples (individually or by twos, not as a group) were moving about freely speaking to individuals and small groups. In a large multi-lingual setting, we would naturally expect to find people grouped together according to their cultural and linguistic backgrounds. So when a disciple spoke to a group (perhaps a family) of Latin-speaking Jews, the Spirit enabled him to speak in Latin; when the same disciple later spoke to a group from Mesopotamia, he was miraculously able to communicate with them in their Sumerian language.

Remember also that when Peter addressed the crowd, it was "the third hour of the day" (2:15), or about 9:00 am. Perhaps the Spirit had come two or three hours earlier. This would allow enough time for the disciples to individually address different groups and for word of the strange "tongues" phenomenon to spread through the crowd. Within a short time, reports quickly circulated about these Galileans (known for their peculiar accents) speaking fluently in the languages of the different groups that were present that day. Responses to this phenomenon were mixed. Many "were amazed and perplexed, saying to one another, 'What does this mean?' But others mocking said, 'They are filled with new wine'" (2:12).

The mockers' statement—"They are filled with new wine"—is not a statement one would make after witnessing the miracle; it is rather a statement one would make after hearing about such a miracle. This would suggest that, prior to Peter's message (2:14ff), the disciples were individually addressing groups within the assembly, and not speaking one-by-one from a shared platform.

So, in the final analysis, it is possible that the miracles of Pentecost included a miracle in the hearing, but we know for sure that there was a miracle in the speaking, for when the disciples were "filled with the Holy Spirit" they "began to speak in other tongues as the Spirit gave them utterance."