How do I turn the volume down on Announced alerts?

My Mac speaks aloud the various Reminders and Calendar events. In System Preferences' Dictation & Speech pane, I have turned on "Announce when alerts are displayed". I generally find this useful. Unfortunately, in Mountain Lion the alerts are simply too loud. Excessively loud. Over loud in relation to the system volume. It is as if they are set on 10 while all other sounds are at 5. If I raise the volume to hear music or videos better, the announced alerts sound like they're being played over a megaphone. This is a problem early in the morning and late in the evening because I live in an apartment surrounded by others. Announced alert volume is separate from system volume and separate from alert volume. The only way to lower the announced alert volume is to either shut that feature off or to shut off the sound. Neither solution addresses the problem. I simply want the announced alerts to not shatter glass and vibrate the foundation of my apartment building when they go off.

I originally started a similar thread here. I excitedly marked the question as answered, but it turns out my excitement was mislaid. The solution offered there didn't help. In fact, even with alert volume set to 0, the announced alert volume remains unchanged and loud. So now I know that there is a difference between alert volume and announced alert volume. Maybe this will help somebody help me.

I summary,

• I know I can lower my system volume in the Sounds pane. I want to adjust announced alert volumes.
• I know I can adjust the alert volume in the Sounds pane, but the announced alert volume remains high.
• I know I can set spoken alerts to off. I want to keep this feature on, but not at its current volume level.
• I know I can adjust the clock voice volume, but announced alert volume is not affected.

Got any suggestions? I hope I was thorough enough. This Mountain Lion issue is driving me crazy.