It reminds me of a battle on another forum about 6 years ago. The subject was vertical line arrays and the woofers/mids/tweeters that feed them. The uninformed claimed that a bunch of inexpensive drivers will sound like a bunch of inexpensive drivers but just more of them. The driver in question was the Vifa TC9 which is a 3.5" driver full range that runs around $11 each. One guy took 25 of them, arrayed vertically about 8 feet tall and with heavy DSP and a CNC'd aluminum bezel--built a pair of the things. In total, he ran 50 drivers and took extensive measurements of the results. The distortion was very low, the SPL was respectible (for us "normals") and it worked very, very well! The distortion of those drivers when driven at less than a watt each was great as you would expect at such low power points. Mid-bass was amazing since you have two 8 foot columns to physically throw a line of pressure at you from the cranium to the tips of your toes. The DSP did it's job dealing with the chaos and both towers are corner loaded. It took him 2 years go build/tune and although "audiophiles" would not believe it, the distortion, FR, phase and polars proved otherwise.
I built a pair of 3-way line arrays (three times!) They use very basic 5" woofers in a sealed box with 1" voice coils, tiny neo magnets and stamped steel frames along with santropene surrounds--cone is paper with a poly coating and they vent through the fabric dustcap for cooling. I call them "mouth breathers" for front cooling which is nice when using sealed boxes. Built the boxes to match the Vas and when using 12 of them, I hit 10% over Xmax at 400 watts at 8Hz and they roll off at -3dB at 85Hz. Yes, they will acoustically roll off at the crossover point for the subs. This way I can use a PA amp that crosses them electrically at 80Hz or use any amp and run them full range and still roll in the subs at 80 to 100Hz and get decent response.
Initial testing with my "cheap as chips" 5" woofers? Well, they MSRP out at a staggering $18 each but thanks to China cornering the neodymium market in 2011--I got them close out at $2.50 each or $60 for a box of 24 in bulk. In a sealed box at Vas and crossed to subs at 80Hz they sounded clean up to 10 watts and decent enough to 16 watts but power compression started to show up at 20 watts each. They would ring but pipe dope and zip ties cured that quickly (go ugly early) Running 12 woofers per side, heavily stuffed and stiff sealed box and a pair of them I got 116dB at 200 watts per side in my garage at an 11 foot MLP. At that point, I was unable to have golden ears...more like ringing ears so I claimed that would work. The subs are dual 15's tuned to 24Hz in a push-pull slot loaded box at 2.2 to 1 compression with 7.5mm Xmax drivers so a pair of them would be 4 fifteen inch drivers. Each sub models out to 116dB (sealed) or 118dB (ported) and when corner loaded in the garage, it will shake the house, shake the neighbors house 30 meters away and attract the attention of law enforcement--I called it good (for now!)
Because I'm an idiot, I had to test those woofers at max so clipped my PA amp (hard) running them full range with the 1812 Overture with cannon fire that goes down to 8Hz. At 400 watts each side, I would say they really didn't like that but did not fail so I set the limiters to 200 watts which they can hammer away without too much distortion drama when crossed at 80Hz. The 21 three inch mids and 48 ten millimeter dome tweeters had an easy life and would burn the drums before ever showing signs of distress. The mids are at 16 ohms nominal so at max, they might get 3 to 4 watts of power worst case scenario each and 48 tweeters crossing at 6KHz even with +6dB of boost at 15KHz have never compressed, distorted or shown any sign of distress no matter what.
I am biased and after hundreds of hours of building/rebuilding over 18 months--my opinion does not matter. So, I enlisted the help of a drummer buddy of mine, a few other people and so on to evaluate my efforts. Basically, they loved the huge sound of them (arrays do that) and commented on the effortless bass response (drummer) and they can get to ear ringing levels without ever sounding harsh, distorted--just clarity that says that way until your ears give up. They also liked that they had great treble response over a block away and those things sure can "throw"!
They are "garage speakers" in that the point of them is to have a few beers, kick back and enjoy the sounds. 2 beers in, you don't notice the issues at 2 to 6KHz and the more beers you have, the better they sound! Although I tried, I have not blown up any of the 162 drivers or subs although 2 hours of Intersteller's no time for caution gave them a run. Switched out the PA amp for a 150 watt X 2 studio amp running full range and did notice a few things. Running at around 60 watt peaks per side, maybe a bump of +3dB at 63Hz with the subs on, I noticed very obvious chest slam at 11 feet. If I stood on top of the subs inline with the woofer lines--there was incredible chest slam over my entire body--the teenagers love to do that. Luckily, because they are line arrays the volume for mids/highs is slightly lower at 1 foot than they are at 11 feet so no hearing damage. No "horn burn" and so on... it feels like being inside a car getting physically pounded or getting near subwoofer stacks at concerts when the 12 five inch woofers starting to stroke. Yeah, I like to appeal to my inner 12 year old at time to time. For now, I just use the studio amp running full range to keep the dust off the two dozen 5" woofers
The PPSL subs kick in at 80Hz with the arrays doing acoustic roll off to match. It does sound a little different and feels different running the sealed boxes full range VS electronically filtering them at 80Hz. I like the energy field effect so run them that way.
For me, I'd much rather have multiples of drivers with lower Xmax and higher efficiency than a few drivers with low efficiency and high Xmax. Is it "the wall of sound" that I like? The energy field of 8 feet of woofers/subwoofers provide or purely psycho-acoustics because my eyes see it so my brain accepts it? I dunno, since they are garage/party speakers on a cement floor--I can't get all audiophile/OCD about them because they can never sound perfect because of their location.
In my house, I use Fusion 10 as left/right and an 88 Special center channel along with three 15" subs--I can get chest slam and my sound stage sounds larger than they should but... not as big as the garage arrays! This is a good or bad thing, the accuracy of the HT system is nice and line arrays give a larger than life sound which probably would not be a good thing for movies and sound effects. Two different systems, two different system designs, two different locations and they don't play well together.
Although I don't have 29 subwoofers like BTH, I do understand the draw! Technically, with 24 five inch woofers running full range and 4 fifteen inch subs that would be "28 subs"!
I do want to build a Quadhorn (22Hz knee tapped horn) for the garage because I always wanted a horn sub so that would make 29 "subs" as a perfect BTH wanna-be...technically....if you hold your mouth right.
As BTH put so well, the downside of low Xmax drivers is you do give up something--space, weight, complexity and many, many drivers to get there. You do gain massive efficiency from using such light weight mass drivers in multiples to really drive distortion down even if they are not the greatest things. No worries with 1" voice coil 5" woofers with 3mm of Xmax for inductance--they don't have much because they have tiny coils to start! No worries about power compression when you run 24 of the things either. The wimpy 85dB 1w/1m and 20 watts of power handling become 96dB 1w/1m and 240 watts (thermal) of power handling then you double them up by running a pair. Technically, that would be 99dB 1w/1m and 480 watts of power handling--PA territory so I can't and don't complain. I can run my studio amp to clipping at around 150 watts per side and the speakers don't give up...my amp will and my ears will force me out of the garage first.
Part of me wants to go all BTH and purchase sixteen 12" woofers and make 8 foot columns of woofers--one each side to match the arrays. I could put the two subs in the back or sides of the garage to improve sound quality
the sub boxes would be lashed to the arrays for safety and stability of the 100 pound 6 foot plus arrays to protect the children (they are attached to the walls with cables) Those JBL 12's are tempting to do just that. Eight of them per side would give me efficiency ratings of around 95dB 1w/1m to "match" the arrays but my wife would divorce me and the jury would agree. Never have a sub box that doubles as a coffin--the natural limit.
Realistically (because we have to go there on occasion) a single Quadhorn 22Hz tapped horn will give me 118 to 120dB on paper and when coupled with an additional two subs that punch 118dB each in a garage--that will work even in party mode. In the real world, my garage has issues structurally with the system at full chat so if/when I add a tapped horn--I'll need to fix a few things and stiffen my garage door etc. to not make a howling mess of structural complaints. My living room wall that is shared with the garage will need some green glue and additional drywall once I add the tapped horn and so on. Is the juice worth the squeeze?
As a cop out, get the driver's distortion charts at what power levels--determine your SPL needs and calculate multiples of each type of driver. As with BTH, he can hit 1% distortion at 150dB in the bass region and at that point--it don't matter anymore. Running 16 of those PA460's in towers floor to ceiling most likely never leaves a person wanting and in my pathetic opinion, I don't think "upgrading" the drivers to Neo B&C drivers would make any difference. When you are down into fractions of percent in bass, when the SPL is so high your ears go into survival mode--not accuracy mode so at a real, hard limit. I can't turn my house or garage into a bunker so my real limit is much lower although entertaining to ponder. At this point, I'm considered the villiage idiot with the garage system so I'll wear that crown proudly. My inner BTH bass head will just have to suffer.