Originally Posted by Russell Burrows
60 to 3000 will be 6 inch poly mid woofers
3000 and up will be soft dome tweeters.
No crossover points in the problematic vocal zone .
No passive crossovers.
Welcome to the line array crazy train--all aboard!
So there I was, it was about 8 years ago and I had a dozen 5" woofers per side (85dB efficiency) and 48 tweeters per side (90dB efficiency) I was crossing at 4,200 Hz so it should be good. My main concern was that having 5dB more efficient tweeters and having four times as many, conventional math indicates they should be +11dB louder. No problem, had plenty of L-pad resistors to getter done. Those wee little tweets extended past 22 KHz so all is well. So I built the thing, put an L-pad on the tweets and gave it a listen. Hmmmm, I had bass, lower mids, the upper mids were gone and no treble to speak of. I then shorted out the L-pad, had a bit of treble but nothing real to speak of over 10 KHz--my measurements were terrible, the speakers sounded bad and my wife had no problem letting me know I took a ride on the fail whale.
In desperation, I did more reading about line arrays--the upper mids and treble issues are a constant in the design dating back to the 1950's--did more reading. After hundreds of pages of reading, it is math equations with center-to-center distances and coupling being the law that governs how they work. Did the calculations, my measurements agreed with the equations so I was on to something. Yeah, now I can predict failure before starting--a good thing. As A9X stated, you want the center-to-center distance (C2C) to be at a 1/4 octave at the crossover point. If you do the math, that means you need tweeters that have less than a 1/4 inch between them at around 20 KHz. The math being brutal, basically informs you what you are attempting to do is impossible. So, if you are the OCD type--run, run away fast and far!
Since I was stupid and already built the boxes, already had 48 tweeters per side with a 1.35 inch C2C distance--and my wife to remind me how much all that stuff costs--I was in and had to keep fighting. Did some more reading, learned about psycho-acoustics, the precedence effect and how poor human hearing really is. The name of the game is to exploit our hearing weekness, fudge it with EQ and do things like curved arrays (Keele's "broke back" arrays or floor-to-celing arrays and so on. Polish the turd! Looking at what JBL does with their "sticks", they use 2 inch full ranges, subs and EQ to make them work. Faital Pro makes speakers specifically for line arrays, they are 3 inch full ranges and can really hammer it out but EQ is required. IF you put a gun to my head and told me I had to build another pair or two of them, I'd use the Faital Pro 3" Neo full ranges, use 9 of them per box (wired 3 series/3 parallel) and seal off each 3 driver segment of parallel drivers away from each other then wire the segments in series. I would use the 16 ohm drivers so each "box" would be about 2.5 feet or less than a meter tall then put three boxes in parallel for a 6 ohm load--at around 7.5 feet tall or 2.5 meters to fit in most rooms. They will beam and comb filters--but that is what arrays do. At least with rows of 3 inchers, I can cross them at 160 Hz to subwoofers or kick bins and be done with it.
To "fix" my problem, I added twenty 3" full ranges and bumped the crossover at 350 Hz LR and 5700 Hz Bessel filters (passive) The woofers were wired at 6 ohms, the mids at 13 ohms and the tweets at 7 ohms so they would smoothly cross at those points without L-pads. If you do the math, the tweeters were already outside the 1/4 octave rule and my 10 KHz, they had completely decoupled and SPL started falling. Each tweeter by itself made it to 22 KHz flat--but stack 48 of them and their frequency response starts dropping off at 10 KHz--weird how that works. I did put a +6dB boost at 16KHz to get them even but if you use conventional math for point sources, the 16KHz band would run +17dB HOT!
It don't, it won't because it is a line array and the domes have decoupled--the way it goes. The good thing is you have huge power handling with 48 tweeters, driving them 4 times harder is not a problem when you have 48 of the things.
My 3 inch full ranges even at 13 ohms really belted it out, at around 1.5 KHz the output was screaming so I did an EQ cut to compensate. I pondered building some passive filters in the crossover but by then, my OCD was blunted, kicked around and crushed so EQ is fine. I did try supwer tweeters, they worked but sounded weird--EQ to the rescue. My acoustic problems with the 3 inchers was at around 3KHz and up, my C2C was 3.3 inches. If I went completely anal, I'd look to replace the tweeters with those DAyton 5/8th inch ones that I coupld pack in at 3/4" C2C. I would then cross them at 3 KHz to solve that problem. All I need is 96 of them per side which forces you to ponder "Is the juice worth the squeeze?" They are garage speakers, I can "cheat" a bit with EQ and after a beer or two, I generally don't notice the sins anymore so I passed.
So if you want to build line arrays for fun, education, like the idea of the weird things they do go for it! Personally, I would recommend the Vifa 3.5" TG9 series, the one with the fiberglass cones. Run 25 of them per side, 5 series/5 parallel with the paralleled segments sealed from each other. Leave about 3 inches of space on one side of the bezel if you want to add a tweeter line later. The TG9 when using 25 of them can handle some power, they are quite efficient and at 17 buck each--the total driver cost would be less than 1,000 dollars US. Build them, wire them, EQ them and enjoy... if you want to add tweeter lines, I found some Tang Band 1/2" dome tweeters that can do 4 KHz and have a rising response (good thing with arrays as the higher they go, the boost is good because SPL naturally goes down) They are 0.77 inches in diameter or a 0.8 inch center to center distance. Get around 110 of them to match the Vifa line and wire them 10 series/22 parallel. They cost less than 8 bucks each so mulitiply that by 220 and it gets expensive fast! The other option is the Dayton 5/8ths dome tweeter which allows crossing down at 3 KHz with a steep filter and a 1.375" center to center distance--good to over 10 KHz. They run 9 bucks each and pack in 64 of them (8S/8P) so a bit over 1,000 bucks for the tweeter line each box. Yeah, although $17 full ranges sound reasonable and $9 tweeters are easy--it piles up to 4,000 bucks when you have 89 drivers per box. Are you sure?
Just some ponderings, I lucked out by purchasing boxes of drivers when the price of nedodymium went through the roof and manufacturers were drumping their stocks at 90 percent off. Figured it was a good time to find about line arrays, I did and am glad I built them for the garage. However, I won't do it again because I'm content with their performance--including the beaming, colmb filtering, EQ demands and the space they take up. The thing DIY'ers always do, no matter if it is speakers, dog houses, classic car restoration or old bicycles--if you had to do it again, knowing what you know now...would you do it again? My anser is no, IF I had to do it again--I would use the Vifa full ranges and EQ...if I could of started over I'd of gone with point source for garage sound. Sure, I can change the tweets to the Daytons and cross at 3 KHz--I could add passive notch filters to the mids--I could but I won't. At the end of the day, they are garage speakers and I'm screwed because it is in a garage. Now if I had to have them in my living room for life, I'd be seriously thinking about the Daytons and noth filters--I would! My garage speakers provide sound everywhere when I work on stuff--they also provide the goods for parties and "barley processing" tames the sins of the arrays so I call it good.
IN summation, I offer this--line arrays are not more accurate than point source because they can't--the rules won't let them. So if you are going for acoustic nirvana, run away now! However, if you want something different, something with a huge sound field, something really cool looking--loud and proud--they perform that function well. Very educational, I learned a ton about acoustics, comb filtering, beaming and psycho-acoustics in the 17 moths and three revisions building them. The 1/4 octave rule is sound but it can be pushed to a full cotave--but once beyond that our imperfect human hearing ability will pick up on it. You will learn what EQ can and can't do and gain knowledge of infinite line theory VS point source real world. In reality, there is no infinite line and there is no point source--just flawed concepts of both of them. That is the biggest thing I took away building those things, living proof that human hearing sucks...it is not golden in any way! It proves that math and measuring equipment agree with each other, there is no magic. The biggest things it proves, at least with the local population is that people hear with their eyes. I've been told my arrays are the best sounding speakers or in the top 3 of any speaker system they have heard. Yes, a jazz drummer that has been playing for over 50 years told me they were in the top 3 PA speakers he has ever heard. In a garage... uhhhh.... you need to get out more! When people see a speaker sitting on subs that stands 7 feet 10 inches tall, notice the two dozen woofers, the 40 mids and 96 tweeters all playing at once--the visual swamps their senses and it must sound great!
It sounds great because it sounds huge, it sounds great because it has very low distortion, it sounds great because there is no floor/ceiling bounce and it has very wide dispersion--very true. However, the measurements show the problems, the math points out the problems and I KNOW what the problems are, I can hear them. They get more comments and love than alll of my other audio systems combined by far--because they are huge, they sound different, they look cool and very unique. A lady I know loves the things, she calls them "The Compensators" .... the only speakers I have ever owned that women get a kick out of. Who knew? They are the most "fun", sinane speakers I have ever owned and teenagers think they are the ultimate--but they are not.
Last piece of advice, learn about infinite line theory, learn center-to-center spacing of acoustic drivers, learn about comb filtering, lobing, horizontal VS vertical arrays, precedence effect, psychoacoustics and issues with series wiring of drivers. This will allow you to make an educated decision if you want to move forward in your quest. You don't want to be like this guy Steave Meade--He built arrays with 7" woofers and 1" tweeters and completely jacked up the math, did the crossover points wrong, did the tweeter lines wrong (center to center was around 4 inches so) Spent a fortune on the drivers, big bucks on the box and supporting electronics. Yeah, they are huge, they are LOUD but the "sounds good" part is the details. Big sound, high SPL and cool looking only last so long and eventually, that newness fades but sound quality always takes over. Know the theaory, understand the limits and accept the compromises before going in. If the design is wrong, you have to start over even if you throw the most expensive drivers in the world in the box. The array system is more design strict VS what drivers you use. Not hard to get great treble response with low distortion when you might be putting a tenth of a watt into each one max. Even very basic drivers will give you low distortion when driving them at one watt. Since EQ in manditory, you can fix a lot of problems going in. That is the upside, you don't need expensive speaker drivers because quantity helps you there just like it helps with multiple subs. The downside is the design must be correct, it must follow the rules as close as possible and they are a pain to build that way. You can also curve them and there are all sorts of configurations that might help for you, your room, your space and your needs. So, read up on the various types and figure out what design works best for you FIRST.
However, if it is your "only" sound system--I'd stick with point source. Line arrays are like having a crazy date--a lot of fun, very educational and always a good time--but not a good long term solution.
At least with audio systems, they won't super glue body parts because of the other audio system... you have that bonus!
They do make a great "Speaker B" on the old receivers--just make sure Speaker A is selected for sound quality. Good luck and enjoy the read!