How did they make the Inception sound?

Question

I've noticed that deep bwaaah sound from Inception in several movies and trailers.

Apparently others have too--hear a montage of similar sounds (collected by Gregory Porter). I found some info on Wired about Inception's other (crash) sounds, but nothing about the bwaah sound, specifically.

1. It seems similar to Star Trek The Motion Picture's Blaster Beam instrument. Anyone know how was the Inception sound was made?
2. Also I think "that Inception sound" works but would "musical stab" be the right term for such a sound/effect?

Edit: I've seen it spelled or referred to as:

• "BRRRRRRRAAAAAWWWWRWRRRMRMRMMRMRMMMMM!!!"
• "BWONG"
• "Inception Trailer Horn"

Answer 1

In the featurette The Sound of Inception sound designer Richard King talks shortly about recording sounds from an oscillator that are played through subwoofers.

That's when you can hear that bwaah sound, as you call it.

 

 

Mix Magazine has an article in which Richard King explains a bit more about using subwoofers and oscillators to create certain sounds for the movie.