You're confused? So am I. Having trouble figuring out what you guys are doing, to be honest...
Look, that comment came about directly as to what was going on the Dimicatio, and basically how it applied here. But in the Dimicatio spells were being cast without words (and until I brought it up, no one was saying that they were shouting something at the end to get the spell to carry to the recipient, so how was I supposed to know what the intent was and what characters were doing, exactly?), which to me, suggested that there was an implicit understanding that Voice range wasn't determined based on the actual sound the voice could carry[1]. So if that was going to be the case, Perdo couldn't apply. Now that we have clearly established that Voice range is based on how far the voice carries, Perdo DOES apply, it must apply. When players start making assumptions and trying to game me, I'll take the assumptions and run with them.
So, yes, Perdo destroying sound in a room will cause any spell that relies on Voice range to fail. It has to, unless anyone wants to explain to me why it doesn't. My reasoning there was based on gamesmanship, where players were trying "beat" the SG. I don't play that way, until the players start playing that way. Decide how you want Voice Range to work. Meaning the sound must be carried to the intended recipient of the spell, or some range of about 15 paces/50 feet, whatever.
Getting whiplash? Good, so am I. You guys decide what's reasonable, and I'll just roll with it. You can't have both, you have to pick one or the other...
[1]Yes, but I could have reasonably presumed that they were shouting? I'm not going to play or SG like that. I want you guys to be explicit about what's being done. I dislike having to get into these discussions of the minutia when I have to fill in the blanks for you guys. If I fill in the blanks incorrectly, I lose. If I fill in the blanks because you guys forgot about something, well, that's not entirely fair, either, I might as well just lead you down a story that has no branching points, checking things off as you go along.