I have an idea - somebody please tell me if it's a good one!
If I clap my hands in an acoustically dead space it sounds a lot quieter than if I do in a tiled bathroom.
Sure, there's a long reverb tail in the bathroom but I don't think this affects perceived loudness. I'm guessing it's to do with a blizzard of loud ERs in effect putting a sustain on the sound. Although they won't increase the peak level I'm guessing that one perceives a multi-peaked, sustained sound as louder than one with just a single initial transient.
Does that sound true? And in practice does anyone use this effect (eg with Altiverb) to make percussive type sounds seem bigger?
The decay has a little to do with it, but I'd wager that the frequency content has more. In a true dead space a lot of high freq content gets absorbed. Part of what makes a room sound live is it's reflectiveness, which affects higher frequencies first. So I'm guessing the early reflections' hf content makes it seem louder, as it is adding power to the original signal.