There have been some great discussions on this subject, here's a quick link.
As I understand it, convolution algorithms work on the principle of common frequencies being reinforced. Example, if you have a source sound with a lot of midrange frequencies and you process it through an impulse response which also has a lot of midrange, the resulting sound will be…wait for it…heavy on the midrange! Knowing that, you can push voices through metallic IRs, glassy/crystal IRs, or doors through IRs that are chock full of low end, like tunnels, cisterns or other large spaces.
If you're looking for a soft-type of timbre, I'd try some of the smaller spaces like closets or boxes. Also remember that you can craft your own IRs using simple sounds like a finger snap run through a multi-tap delay, or a gunshot echoing through a canyon.