Never gotten around to watching it since I had to suffer through my daughter playing the album for months, then the Grease one plus 'mom' as one of the chaperons willing to suffer through the movies multiple times, so was at least spared that, though decades later was scanning channels and thought I noticed an A7 bass cab's shadow way at the back of the dance floor, but just now can't even find that when searching stills from the dance scene........

Regardless, good to know, at least someone involved in the dance club design had a clue; in my locale they typically used A7-8 since all the small neighborhood cinemas had them and only a mono system at that, ergo theoretically made it sound like the movies, which of course they didn't due to at least stereo and the DJ's used EQ to make it 'their' [horrible to my ears] sound.

- - - Updated - - -

OK, lacking any measured responses of a 311-90, came up with at least a close enough spec of ~5.44" to the bottom of the horn mouth, then remembered the whole sled/bracket had been discussed at least once here and wonder of wonders[!] actually found the 805 multicell bracket's measurements, which has near enough the same mouth diameter, ergo end correction, hence its bracket's slots falls in line with the 311-90/5.44":
https://audiokarma.org/forums/index....795.11707/full

Note that these assume mounted to a 3/4" thick sled, which ideally should be screwed to the bass horn to give it its much needed stiffness/mass loading rather than the 'floating' ones some folks prefer, though have to wonder if they've done any comparison to actually know if it's better overall for a HIFI/HT app: https://www.hostboard.com/forums/f70...light=brackets

This should put the horn mounting tab near enough right with the hardware at the bottom of the top slot.