Full Stacks?

[Joe P]

You also want the speakers to be as vertical as possible. I forget the technical reasons (maybe someone that knows more about speakers can help me here) for this but it's alwasys better to have the speaker as close to up to down as possible, side to side is not good.

YES.

You get usually-objectionable phase cancellations any time speakers are side-by-side. Picture it: if you're standing right in the middle, both drivers are exactly in-phase - the waves from each speaker coincide and reinforce each other. As you move off to the side, one speaker is closer to you than the other, and now there are time diffferences, meaning that the waves aren't in-phase - this effects High freqs first, as you move the speakers apart a little, but as more and more drivers get spead wider and wider horizontally, this line of speakers literally 'smears' the sound - causing like overlapping comb-filters that really eat-up the sound.

It gets worse with distance, because when you're really close the cancellations can't be exact because the closer speaker is louder than the farther one (according to the square law), but as you get farther back their realtive volume is nearly the same (because your distance from each of them is much greater than their distance from each other), so any 'comb filtering' is in full effect; as you get off to the side, and the longer the line, the more these cancellations dip down into lower and lower freqs. This is all exacerbated by the natural 'beaming' that even a single speaker exhibits - the beaming itself is a product of the speaker cone being a finite width.

The reason it's OK for speakers to be stacked vertically - and therefore 'smear' vertically - is that we're all terrestrial beings who tend to move around on a horizontal plane (because we're 'stuck to the floor' by gravity). If the vertical array of speakers is standing on the same floor that we are, then it works-out right. The resulting cancellations that now occur above and below the array are actually a benefit, and assuming that the stack is purpendicular to a flat floor (almost always the case, right?), then any reflections from the floor esentially make the stack looke twice as long acoustically. Even more freaky is considering that theoretically-speaking, if you had a highly reflective floor and ceiling that were parallel to each other, and perpendicular to a line of speakers that went from floor-to-ceiling, it would acoustically simulate a VERY long line array that's many times longer than the actual stack! It'd be like standing in the middle of a hundred-foot line array.

I've been fascinated with this subject. I just recently did a search and found some information on the subject. I'm planning on studying more to better understand the geometry and trig and physics involved.

Here's a great quote from billfitzmaurice from where he was answering a question posted by someone who was concerned about how directional their 4X10 cab was:

You're off-axis response sucks because you've got drivers mounted side by side and one above another, and that narrows midrange dispersion severely. You can cure that on the vertical plane by simply lifting the cab to ear level, as you've discovered on your own, but there's nothing you can do about it on the horizontal. A properly engineered 4x10 would have the four tens vertically aligned to address both horizontal and vertical dispersion issues, but neither Harkte nor anyone else is likely to market something like that because it wouldn't 'look right' and therefore wouldn't sell.

That's why I'm going with a VERTICAL array for my dream-rig. I'm thinking four Avatar 1X12s for now (that'd stand almost six feet tall), but I'm wondering if they're coming out with a Neo version soon (anyone know??).

Joe

 

[IvanMike]

thanks joe, you beat me to it. and thanks to the ox for that nifty read. now the bad news. the read on the "stack" the ox gave us explains somewhat why so many cabs have speakers placed horizontally. It looks cool, and more to the point, it's traditional. PA gurus have known about the advantage of vertical arrays for some time now, one look at the grateful dead's wall of sound shows a good deal of experimenting with vertical arrays way beyond the norm (i still want a stack of eighteen 15" cabs)

 

[merrill1]

The above replies about phase cancellation are right on, having worked with PA stuff quite a lot, I can say it does make a diference. For the stack though it just looks cool. I do the water on the top deal too, with a 1x18 and 4x10. two on the floor is boomy on a lot of stages, and with a full stack you get BOTH, the cool pantleg moving thing, and the sound right at your back. Thats always been my love.
I've recently downsized to a 2x10 combo, which I have to tilt a little or raise up. Sometimes I miss the stack (though I still have the 18 to put under if needed)
later guys