An MMTMM isn't really a line array. A real line array in a home would be an array
where the driver line is close to the floor and up close to the ceiling. Anything
else is a compromise, which is ok. Alot of people are making compromised
line arrays because their budget doesn't support the big line array or other
reasons why they can't have a tall tower in the home. I prefer to call these
hybrid arrays as their performance will be different than a real line array, but it
doesn't make the design bad, just different.
I had plans to make a hybrid array, two tower array using four pro planars,
four 8" midranges flanked by three 15' wideband woofers, but after
experimenting with the budget array using 49 cent modded 4" midwoofers
{PE buyout drivers}, and PT2 planars, I realized that the big array even using
cheap drivers, optimized design, has huge performance capabilities and I only
imagined what a real line array could do if you were to use high end drivers. Since
then I changed my mind completely and will only make full line arrays, no hybrids
even if using quality drivers.
You will find many arrays where they use alot of midranges and only one tweeter.
You will find short line arrays where they use 4-6 midwoofers and a small line of
{small center-center spacing} dome tweeter or planar/ribbons. I haven't found
any DIY or commercial line array except my budget array that is wired for low
impedance to gain maximum performance. These folks who have high end line
arrays have not seen the full power of what they can do. lol ..... yet they are completely amazed by them.
The hybrid array in your case would be a minimum requirement of MMMMTMMMM
design. The general rule is that the distortion would be 1/8 of the single driver
distortion at the same SPL level - because you have 8 drivers. My budget array is
16 4" midwoofers and distortion is 1/16 of the single driver. As you see, more
drivers, less distortion = sweet. More drivers also means line array midrange
sensitivity rises. Wire them up for lower impedance, you get another higher
sensitivity boost. This hybrid array has a tweeter bottleneck. The overal
performance of the line array is limited to the performance of the single tweeter.
Because you have to match the tweeter to that big midrange line, you will reduce
gain on the midrange line so it's not overpowering the poor ole' tweeter so
you will never really realize it's full potential, all you get is very low midrange distortion. A better design would be to make the tweeter line equally as uber
as the midrange line so you can push performance to it's limit. It would be like
building a muscle car with an uber 500 horsepower engine, but you are using
a weak transmission and skinny tires. The engine looks impressive when you
show it off, but the car isn't going to perform to it's full abilities.
I'd arrange them in a MMTMM vertical alignment. Would I have issues with the outer mids being farther from the tweeter than the inner mids?
It's a compromised design so you have to accept the gremlins that may manifest
because the top array segment is spaced further apart from the bottom segment.
In the real world, you have no choice unless you move the tweeter to the right
of the baffle and make the midrange line with no break. The speaker will look
fugly and this is where art takes priority over sound theory. I'd choose the compromise and just live with it.
Also, with non-linear distortion and linear distortion taking into consideration. Would 4 of these RS180s outperform a Seas Excel W18E or W15CY?
When you line source drivers, distortion drops alot and it's easy to beat
out single drivers. My 49 cent midwoofers, all 16 of them would beat a single
Seas Excel when you crank it up loud, no contest. The power of the large
quality of drivers just rule.
If you want to make a line array, select the tweeter first as you are limited by
choice. Make a full line of tweeters, then choose 4" - 5" cheap midwoofers
and performance will be huge. SQ will be defined by the tweeters and less by
the midranges.
Here's a Dayton RS/PT2 array that someone started to build last year
based on my recommendations.
pics in numerical order.
http://home.pacbell.net/lordpk/ew/
If you want to order sample drivers to audition, then just buy one driver
and return the ones you don't like. If you want to make a big line array,
you really don't need to sample any midrange drivers -- because -- you will
not be pushing the midrange to it's performance limit in an array as much
as you will in a standalone design. Gremlins manifest when you push the driver
hard and you want to identify which ones take the abuse while sounding clean.
For an array, it's hard to push each driver to it's limit unless you have some monster kilowatt proamps in bridge mode, even so, distortion of the array is
uber low so the midrange candidates can realistically be any cheap driver
especially if you use a LR8 crossover under 2khz crossover point.
If it was me, I'd either make a quality 3 way speaker using one tweeter, one
midrange, one woofer, subwoofer seperate.... OR I'd chose to make a tall line
array using PT2 planars with cheap midwoofers. If you have bigger bucks,
use $100 ribbon tweeters and Dayton RS or higher brand. If you want to use
domes, there is little choice on the market, the Dayton Neo $4 dome is the
one typically chosen, but you need alot of them for a big line.
~100dB with 4 of them.
