You'll notice when adding Sparks to your event the settings will ask you for a Sparks Count. The Sparks Count is the multiplier of X. If X equals "the audience is angry", which is a collective representation of the words that the audience is typing in chat, then the trigger count is the number of times the anger needs to be expressed before we consider "the audience is angry".
Much like the Word Cloud, this number depends on how big your audience is. If you have 10 people watching your broadcast, you probably want to have a lower number than if you had 1000 people watching. We don't have a great number for you but our current hypothesis is 30% of the total number of viewers. Also like the word cloud, this is probably figured out with some trial and error.
You can change your Sparks Count at any time, even while the broadcast is live. So if you notice changes in the audience number, or you really want to set off a spark and it's taking a while, then simply raise or lower the count to get the results you need.