What occurred on Pentecost did not occur in an upper room of someone's home. The upper room of Acts 1:13 is where 11 of Jesus' male disciples were living at least 11 days before Pentecost. They slept there, changed clothes there, cleaned up there, etc. Women did not live there with them.
In verse 14 we are told: "These all continued with one accord in prayer and supplication, with the women, and Mary the mother of Jesus, and with his brethren." One accord here, homothumadon, is in regards to mind or mentality, whereas the one accord in Acts 2:1, homou, is in regards to place or time. Here is how the NASU reads:
Acts 1:14 These all with one mind were continually devoting themselves to prayer, along with the women, and Mary the mother of Jesus, and with His brothers.
Acts 2:1 When the day of Pentecost had come, they were all together in one place.
In verse 15 there are not just 11 people present, there are about 120 disciples! So, where was this? It was in the Temple, the "house" of God. Luke 24:53 says "and were continually in the temple praising God."
If this is not enough to convince you, let's read further in Acts 2:5-6
Now there were Jews living in Jerusalem, devout men from every nation under heaven. And when this sound occurred, the multitude came together, and were bewildered because each one of them was hearing them speak in his own language.