When the swarthmore folkdance club holds contra dances in upper tarble they like to make a single really long line. The hall is quite large, and it's nice to dance with everyone. I remember liking doing this when I was a student there. One thing I didn't think very much about at the time was how difficult it is to deal with sound when you have a large live hall with a really long line. If you put your speaker at the front, it's too loud in front and to quiet in back. If you put it in the middle it doesn't disperse properly. If you put a second one at the bottom of the hall facing back up dancers lose their location cue of the music coming from the top of the hall and the band. If you put a second speaker halfway down you need a delay and the bass being non-directional will sound bad (a little muddy and unclear) up the hall from the second speaker. All of these that use a second, remote, speaker suffer from the annoyance of running longer cables (and having an additional speaker). Getting the main speaker higher would help a lot help, but the school wouldn't let you hang anything and the speaker system the club usually uses puts the speakers a little below head height.

When we played there in march (which was really fun!) we switched to using one of our monitors (a QSC K10) as the only speaker near the beginning of the night, and that worked well. I think much of it was just getting the speaker to be a few feet above head height. There was still too much of a volume difference between the top and the bottom of the hall, but it was better.

A real solution would be to convince people to dance in two shorter lines. But the dancers don't see it as being worth it.