To me, the Wall of Sound was the giant wall with speakers stacked up to 32’ high (I’ve been told the 32’ stack was for Phil’s E string which put out a 32’ foot wave, crest to crest, and Phil wanted to put out the whole wave, not just a piece of it. I don’t know if that’s true, but it sure is a great story).
That was the reason because it was a line array, as originally theorized by Harry Olson in the 1930s in his book/treatise (of which I would be happy to send anyone a pdf copy- warning: lots of math). The way it works is that when you have a stack of speakers one wide and taller than the longest wavelength you want to throw, the physics of the propagation changes. Normal speakers propagate as a sphere or portion thereof and fall off exponentially (twice as a far is four times quieter) and send the sound all over the place. With a line array, the sound falls off linearly (or closer to it) and spreads horizontally, but far less vertically (so less spill into the rafters and reflecting off the floor). They were years ahead of their time and now all major PAs are designed as line arrays, EXCEPT for the bass, which seems sad. The low end benefits the most from the use of a line array, but it's still a little less than efficient to cart around 40 foot stacks. I've heard it done once, with the PA the GD brought to Oxford Plains in 1988. The low end was profound.
Dave Rat, the sound guy from the Red Hot Chili Peppers, did a bunch of experiments with how to project low end efficiently, including low end line arrays, and came up with something that requires fewer boxes that operates like a cardioid mic does, by having additional subs behind the regular subs and playing with the phase to cancel the sound behind the subs and focus the propagation to the front.
I don't doubt that the speakers for sale here are GD speakers, but I don't think they are the ones shown behind Keith in the pictures. Lining up the 2x12 cabs next to it, there's no way that 4 12s could fit. However, Jerry and, I think, Bobby, used 4x12 tie dye cabs in '72 for their guitars. As SkyPilot notes, there were many cabs that came and went. I don't know of any new cabinets after 1972 that were put onstage with tie dyes. Those, AFAIKT, all were made in 1971 into early 1972. By the end of 1972, the new cabs that were introduced were all open faced.
