1)
Why does it say "Ki Kol Sha'on..."?
1.
Rashi (5): This is why they will be ashamed.
2.
Radak (5-6): This is in the days of Mashi'ach, when we will rejoice and they will be ashamed. It will be the tumultous voice of Gog and Magog - "v'Yatza Hashem v'Nilcham ba'Goyim ha'Hem" (Zecharyah 14:3).
2)
What are the three voices?
1.
Rashi (5): "Kol Sha'on me'Ir" is what they did in His city. "Kol Yotzei me'Heichal", and prosecutes those who destroyed it. Afterwards is "the voice of Hashem bestowing to His enemies."
2.
Malbim: First will be a voice from the masses in Yerushalayim. Then will be heard from the Heichal (Mikdash), and last when He pays His enemies. This is the Klal; the coming verses give details.
