That would be a "certain ultra LOW frequency", below 20 Hrz. It's the amplitude (volume), at a frequency below the threshold of hearing, that causes severe distress.
How does that work ?
I have a question:when I was a bit younger,I went to see Mr. Malsteen (Guitarist) first row and while he was soloing w/ all the other band members taking a break, He hit a really Low E that was a Distorted "MMMMM" Sound,it sonded Compressed and man,I had to sit down,(felt like it was swooshing through the people 3-5 people to my left and right) I was sick to my stomach for a good 20-30 minutes and it ruined my whole show.This was before I drank Adult Beverages too.Is that what I felt coming out of those speakers for that brief time?I thought I was going to pass out.I wasn't the only one either.