The stress should be on the penultimate, exclamátis, as the vowel is long. Not exclámatis like the audio seems to be saying.
I also opened this page because I was wondering in general about word stress. Is there any way to know where to put it? In Spanish there are rules and accent marks. In Italian, no. Sometimes even mother-tongue Italian news reporters make a mistake on where word stress is supposed to fall (usually on names of small villages).
Here's a page with a description of Latin's accent rules.
The basic rule seem fairly straightforward.
"Accent the second-to-last syllable, unless that syllable is short. Accent the third-to-last syllable if the second-to-last syllable is short."
(The design of the webpage is , um, a little retro. Sometimes that's not a good sign. But it is from respected university, so I hope it's all good.)
There is more about Latin here: