Highschool dance speakers?

[Suprarick]

^^^ Great info.

[Bill Fitzmaurice]

The better way to add more speakers cabs is to stack them vertically(line array anybody), this doesn't eliminate comb filtering

Comb filtering by definition occurs when you go across the sound field, and line arrays do eliminate it. There is some lobing of response on the vertical plane close to the array, but well designed array won't have any lobing issues at normal listening distances. Much is made of the lobed response of not only line arrays but also MTM speakers, based solely on looking at a vertical polar plot taken in the nearfield, usually from six feet out or less. Lobing disappears a few wavelengths out from the source, this shows why:
http://www.acoustics.salford.ac.uk/f.../diffract4.htm

[ampnation]

The question of 12 vs. 15 inch tops was brought up a while back, and I don't think it was ever answered adequately. Probably too late, as I don't see the OP here anymore, but just in case, and for others...

USUALLY, if a company produces a 12 inch two way and a 15 inch two way, the 12 inch will be clearer above 100Hz.
The 15 will have better and lower reproduction 100Hz and lower.
And usually the 15 will be a few dB higher. Consider though, that the max SPL for a 15 INCLUDES the full range of reproduction. If you cross it over and lose the last few Hz, it won't be as loud, so it probably won't be much, if any, louder than the 12 once you pair them with subs.
Both however, will be louder in the highs and mids crossed over than when running full range.
When you consider all these things, the main advantage of 15s within the same model line, is that they can be run full range without subs for applications where a bass-heavy reproduction isn't needed. In other words, 15s are generally a Swiss Army Knife approach. They are a compromise when you either never quite need a sub, or sometimes don't, but DO need either a little more bass extension than the 12 gives, or a little more volume.

So really, 99% of the time, the only question that needs to be asked if someone is considering 15 inch tops AND subs, is, "Are you ever going to need to use the tops without the subs, and if so, will the 12s handle the volume and bass extension requirements?" If the 12s won't, you then need to ask, "Will THESE 15s handle the same requirements?" Sometimes, neither cabinet will handle the needs, but another 15, or even another 12, will.

[conanski]

Comb filtering by definition occurs when you go across the sound field, and line arrays do eliminate it.

I'll just have to disagree with you there, go to a live concert in a football or hockey stadium and walk up or down the seating area and you'll hear all kinds of comb filtering. Line arrays do a very good job of covering a large area with consistent sound levels but just because it's consistent doesn't mean it's intelligible.

[Bill Fitzmaurice]

I'll just have to disagree with you there, go to a live concert in a football or hockey stadium and walk up or down the seating area and you'll hear all kinds of comb filtering. Line arrays do a very good job of covering a large area with consistent sound levels but just because it's consistent doesn't mean it's intelligible.

That just means it's a bad install. Going to a live concert and walking up and down the seating area is what I did three or four times a week for four years as a consultant for an 8,000 seat amphitheater. Line arrays never had any issues. OTOH in the first two seasons, when some acts still were using cluster arrays, those ranged from barely tolerable to gosh awful.