Mostly to satisfy my curiosity at this point; I'm still a long way from actually building one.
I've thought for a while about a true-full-range, single-point-source PA speaker, that can produce comparable volume to a modern concert, and actually use it as such. Say, within 1dB of flat between 30Hz and 15kHz, and 140dBA continuous at 3 feet, measured with pink noise, all from a single acoustic point.
And enough directional control to not feed back easily to the stage mics. Say, 90deg absolute max for that, at 200Hz (high-ish highpass for vocals), which dictates a radiator size of almost 5 feet. (Keele's Constant)
The original idea was to make it easily portable - unload from the truck and set up at least two of them in no more than 10 minutes total, with no local infrastructure at all - while keeping that performance. But those are massively conflicting requirements!
I keep coming back to a horn design, specifically a multiple-entry horn to easily satisfy the "single acoustic point", with sealed-back drivers and a DSP to manage it all. But a horn would have to be about 10 feet long to comfortably support 30Hz. (it can be folded, but the total length through all the folds must be at least that) Building it out of 1/2" or 3/4" cabinet grade plywood would almost require straight sides, to avoid the headaches of bending (thick) wood, and then a coverage angle between 45 and 90deg would dictate a 5 to 10 foot mouth, not to mention the weight of all that solid plywood! And any homogeneous span of that size and relatively small thickness would still have panel resonances that need to be damped.
To try and get some portability back, the overall dimensions can be modified using hinges or disassembly, which also create possible places to rattle, and doesn't help the weight at all.
Then I got to thinking, "What about fiberglass-covered foam?" I remember doing that in a high school robotics program, with 1" insulation foam and fiberglass fabric, to make a robot arm that was easily more than strong and stiff enough for what we needed and barely weighed anything. A single panel wouldn't even have to be a single sheet either. It could be "boards" of 'glass-wrapped foam that are then "glued" together with more fiberglass, which creates an internal brace at the edge of each "board". And these "boards" don't even have to be straight or uniform, just as long as they fit together. If it ends up with internal braces (edges of pieces) going every which way, that might actually be a good thing for acoustic stiffness. All that really matters is that the acoustic surface doesn't move appreciably at any audible frequency.
If that solves the weight problem without creating resonances, then the portability part becomes less constrained...
And it might also be easier to create curves that way too, like for a folded exponential horn instead of a strictly-straight one...though that would make it harder to pack into a small truck with other gear...
Thoughts?
I've thought for a while about a true-full-range, single-point-source PA speaker, that can produce comparable volume to a modern concert, and actually use it as such. Say, within 1dB of flat between 30Hz and 15kHz, and 140dBA continuous at 3 feet, measured with pink noise, all from a single acoustic point.
And enough directional control to not feed back easily to the stage mics. Say, 90deg absolute max for that, at 200Hz (high-ish highpass for vocals), which dictates a radiator size of almost 5 feet. (Keele's Constant)
The original idea was to make it easily portable - unload from the truck and set up at least two of them in no more than 10 minutes total, with no local infrastructure at all - while keeping that performance. But those are massively conflicting requirements!
I keep coming back to a horn design, specifically a multiple-entry horn to easily satisfy the "single acoustic point", with sealed-back drivers and a DSP to manage it all. But a horn would have to be about 10 feet long to comfortably support 30Hz. (it can be folded, but the total length through all the folds must be at least that) Building it out of 1/2" or 3/4" cabinet grade plywood would almost require straight sides, to avoid the headaches of bending (thick) wood, and then a coverage angle between 45 and 90deg would dictate a 5 to 10 foot mouth, not to mention the weight of all that solid plywood! And any homogeneous span of that size and relatively small thickness would still have panel resonances that need to be damped.
To try and get some portability back, the overall dimensions can be modified using hinges or disassembly, which also create possible places to rattle, and doesn't help the weight at all.
Then I got to thinking, "What about fiberglass-covered foam?" I remember doing that in a high school robotics program, with 1" insulation foam and fiberglass fabric, to make a robot arm that was easily more than strong and stiff enough for what we needed and barely weighed anything. A single panel wouldn't even have to be a single sheet either. It could be "boards" of 'glass-wrapped foam that are then "glued" together with more fiberglass, which creates an internal brace at the edge of each "board". And these "boards" don't even have to be straight or uniform, just as long as they fit together. If it ends up with internal braces (edges of pieces) going every which way, that might actually be a good thing for acoustic stiffness. All that really matters is that the acoustic surface doesn't move appreciably at any audible frequency.
If that solves the weight problem without creating resonances, then the portability part becomes less constrained...
And it might also be easier to create curves that way too, like for a folded exponential horn instead of a strictly-straight one...though that would make it harder to pack into a small truck with other gear...
Thoughts?
