Line arrays are not for everyone. I think their strong points are;
1. Potential for a big sound stage.
--> you can implement power tapering to reduce the image size but max SPL
is less and distortion can be higher than a non power taper setup.
2. Potential for very low distortion.
3. Potential for very high SPL.
4. Potential to be expensive as you need many drivers.
5. Potential to be heavy and take up alot of space in the room.
You should only seek a line array design if a standard design is boring. If
you find satisfaction with a standard design then it might be a better choice.
Model performance in an open baffle design, ideally prototype it first using
a hunk of cheap wood. Verify.
If the line array is for a typical room in a house, lets say 5-20 feet listening
distance, then there is little to be worried about other than having the normal
room treatments on the walls and carpet/rug on the floor. Maybe add some heavy drapes behind you.
You are analyzing way too much. This is simple stuff. A stack of drivers near
the floor up to the ceiling, following the common rules and even cheating the rules, plus a fully active setup with DCX,
anyone can make it work great.
The hard part is opening up your wallet and taking money out. The next hard part is choosing midwoofers and tweeters,
selecting OB, sealed or ported enclosures, then you figure out how much SPL you want by wiring the
array for higher SPL {lower impedance} or normal SPL {normal impedance},
choosing amplification, and fine tuning with your DCX. The fact that you will use
a fully active rig with DCX gives you so much flexibility to make this work well,
unlike a passive crossover design where you will use one amplifier to drive the array. There is more obstacles in your path using that method.
I dont understand your point about cheating...if I cheat I get comb filtering and/or poor performance. Its black and white...nothing subjective. I cant *bend* science...lol.
The line array math gives you a guideline to follow, it's not written in stone
as it must be that way. If your crossover is theoretically suppose to be 1khz,
setting it to 2khz doesn't guarantee bad sound. In fact, you might think it sounds better as you balance the lesser of the evils.
That's why you have an adjustable crossover, you sweep the vast frequency range to understand the audible effects. For instance, if I turn off
my tweeter array and just listen to my midwoofer array and sweep a crossover
frequency of 1khz all the way up to fullrange, it's not like the sound is horrible.
Most people would probably like the sound full range over 1khz because they
don't know any better. I can tolerate a high crossover from the midwoofer line
no problem. The real issue is the tweeter line.
tweeter line
Your tweeter line will define the SQ. You will perceive better SQ if you concentrate
the bulk of your money into getting a good tweeter line built and use cheaper
midwoofers.
The way I adjust my array is;
1. I turn off the midwoofer line.
2. I turn on the tweeter line. I sweep the crossover frequency from a low
starting point and sweep up while listening to my favorite music. Do this at
medium SPL so you don't damage your tweeters if you have a low crossover point. You will hear things as you sweep and
eventually you will favor a certain crossover point that sounds sweet. For sake of argument, lets say you like
the sound of your tweeter line at 1.2khz LR8 at low SPL, but at medium SPL the tweeters sound nasty and
you need to raise this closer to 1.7khz. For high SPL you may need 2.5khz. I make a mental note of these
three crossover frequencies; 1.2khz - low spl, 1.7khz medium to high spl - 2.5khz very high spl ..
3. Next, listen to the midwoofer line only and determine how your midwoofer
line sounds in the 1.2khz - 2.5khz range. If nothing bad is heard, then you
are good to go.
4. Listen to the midwoofer and tweeter line from 1.2khz - 2.5khz and you will see
imaging improve at the lower crossover point, but if it's too low and SPL is raised,
the sound degrades. For me, I do 90% of my listening at 1.7khz LR8, at extreme
SPL I will take it to 2khz, maybe 2.5khz to protect the tweeters and lower tweeter distortion.
For very low leveling listening [backround music], 1.2khz works fine, but so does 1.7khz and
2.5khz.
DCX has the ability to store settings. A huge bonus. Make different settings and
store them in memory. Recall your settings from memory on the fly.
Basically, I cheat. I cheat the theoretical crossover point because gremlins
that may manifest aren't audible, therefore no need to worry about it. I cheat
by choosing different crossover frequencies for my listening mood, SPL level I listen at and even the song
I listen to may sound better with a different setting to compensate for recording issues. DCX = ultimate cheater processor for $250.
Why should I worry myself about wiring for low impendances? It seems pointless and I'd risk ruining my amplifier. As long as I deliver the power necessary to the line array...then Its going to reach the same SPL no matter the wiring configuration.
Low impedance wiring can raise sensitivity. You get higher SPL for the given
watt until you reach the drivers limits. I have four PLX3402's in bridge mode
wired like so;
PLX #1 - tweeter array, left side, 0.8 ohms.
PLX #2 - tweeter array, right side, 0.8 ohms.
PLX #3 - midwoofer array, left side, 2 ohms.
PLX #4 - midwoofer array, right side, 2 ohms.
3400w per ampliifer rated.
If I flick a switch on the back panel.
http://home.pacbell.net/lordpk/robarray/Control_Panel-2.JPG
I can select a higher impedance to make it more amplifier friendly.
0.8 ohm tweeters are now 3.2 ohm. 2 ohm midwoofers are now 8 ohm.
I lose 6dB sensitivity in higher impedance mode and even though I drive
the array with four 3400w amplifiers, I do notice the lack of SPL. The reason
I notice the lack of SPL is because the amplifiers have reached their clipping
headroom first before the line array hit it's performance peak. Unless
you have an amplifier with unlimted headroom and power, then you don't
need low impedance wiring. Low impedance wiring is a neat trick to boost
performance and nobody, not even commercial line arrays use this method because the audio industry doesn't do fully active systems with 10kw of headroom. lol ...I'm just telling you the best kept secret in line array design.. shhhhhhhh...
If your amplifiers can't handling low impedance, then you have no choice
and can't wire it up this way. My design has a switch to select low and high
impedance to make the line array user friendly. I had a four channel
chipamp running this array in high impedance mode. LM4780 based system.
It works fine, you get sound, it's going to satisfy everyone, but it's not going
to push the line array to it's peak performance like the proamps do.
If you plan your line array wisely, you can make a killer system if you
think ahead. Implement an impedance switch so you can use low powered amplifiers, later if you want to exploit more potential, get some monster amps,
flick the switch and you are good to go.
Good amplifiers can drive low impedance tweeters with ease because tweeters
won't be a difficult load. PLX is rated for 4 ohms in bridge mode, no less. It runs
the 0.8 ohm tweeter load. My Adcom 555 was driving 0.8 ohm per channel,
it's not rated for less than 4 ohms per channel. At very high SPL for a while
cranking metal music, it did go into thermal mode as there is no fans to cool off
the heatsinks. I run the midranges at 2 ohms, I think the amplifiers might have
some issues at under 2 ohms in bridged mode. Woofers; use manufacturer
recommendation and don't cheat by driving lower than recommended. Chipamp
systems; they are not robust enough in design to allow impedance cheating.
