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In Reply to: RE: Oh yeah, what ever happened to the line array? posted by AJinFLA on May 22, 2007 at 14:04:37
aj: ""
Chip amps eh? Large power supplies to avoid multiple cords like me?""
Actually, I wasn't worried about the cords too much, I know how to keep em "honest".
I'd been tossed as to how to array them. I have 128 4 inch drivers and 211 3/4 inch dome tweets. I was thinking of 11 cabinets of 10 drivers each plus 10 cabinets with 20 tweets in each. (leaves me spare drivers). 10 drivers allows a 5 by 2 connection, which presents at 20 ohms to the amp..this was simplest as I can parallel 5 arrays on one amp channel, it'll draw about 450 watts outta the rmx1450 channel max, which works well with the driver max power limit of 10 watts. This was the origional intent for the drivers, as I was putting together a rear panel set for the auditorium, and the seats are only 6 feet away from where the panels would go. Spreading the power out that much area lowers the spl that the people in the nearby seats would experience. The fronts are 12 inchers at 300 wpc, but they are about 25 feet from the front row of people, so the intensity is down by the time it hits em..
Going with 9 drivers per line allows 8 ohm op in a three by three config, total of about 90 watts capability per line. This arrangement is what I'm looking at the LM4780's for, as it requires 12 independent amplifier channels, a monster power supply is easier than 12 smaller ones.
Independent control of timing and amplitude of each array channel is gonna be the big problem, so I'm concentrating on that.
But, as I said, this is the fun stuff...and it is second (always) to my enjoyment of life (well, yah, and the honeydo list...) :-)
Cheers, John
That sound rather complex to say the least. I guess I would have to see the layout of the array itself. Will there be forward steering/directionality in the bass region (I'm assuming these are boxes)? You are using these in your basement IIRC. Acoustics a bit different than the auditorium including first reflections and modes to be sure.
Hey, maybe the wife and kids will like how they sound too and wish ya had built them sooner had you not had all that "other" stuff to-dew :-).
Oh yeah, be careful how you mention QSC amps around here. No good for "Hi-end" street cred LOL.
cheers,
AJ
The threshold for disproving something is higher than the threshold for saying it, which is a recipe for the accumulation of bullshit - Softky
I designed the lines to be physically independent. That way I only have to carry 9 or 10 drivers in one cab at a time...gettin too old to carry big stuff anymore. It allows me to bring as many as I need for the app. I have a 3D line drawing showing the array setup as 8 tall by 4 wide curved, with three 16 tweet lines in between. Tis not a jpeg I can post, I'll hafta convert when I get the chance.
Each line array cab will have a buried t-nut in top and bottom, allowing me to attach them to a to and bottom mount plate. If I use a straight plate, the array is flat. A curved plate of course, gives a cylindrical array, either convex or concave.
No directionality is planned, the boxes will be too small for lots of bass extension..I have some 15 inch bass cabs for that if I wish, plus a coupla bass horns with 18's.
But your right, the electronics for phased array work is the complex nut.
I was just thinking of going 1 bit conversion, and sticking the stream into ram, with 10 or more latched addies to pull the needed time info outta the ram.
As for wife and kids, they are the reason my priorities are what they are.
Cheers, John
What approach to perform acoustic measurements? From where? What listening distance in the basement?
cheers,
AJ
The threshold for disproving something is higher than the threshold for saying it, which is a recipe for the accumulation of bullshit - Softky
Why the heck would I want measurements??
Simple...Entire array behind a screen. When the signals are processed to produce something, like targeting a specific location in space for an image, the human will determine where in space it is coming from. Given the computerized nature of the information processing, the computer can be set to randomly shift parameters, and the human gets to point to where it seems to come from..pointing can be as simple as a scale printed on a 2 by 4 across the field, human inputs to the computer the number on the scale that the image appears to be at.
This allows trivially computing the uncertainty in localization, I would expect a gaussian distribution.. The distribution sigma (presumably), can be used as a scoring mechanism for determination of the accuracy of the algorithm to targeting, with the center of the distribution also of use.
What I really want to do is determine the localization capability of humans and the effect of alcohol on that capability. However, that by nature, will require Lots and Lots of trials (one can never be too sure, now can one?)
My prediction for the future...lots of martini's...in the name of science of course..
Cheers, John
ps...lots of trials...:-)
is the only sane way of doing that:
"Independent control of timing and amplitude of each array channel is gonna be the big problem, so I'm concentrating on that"
Do your remeber how sampling scopes produce a time delay? ('bet you do :-)
Only need a DC voltage .....
Scope delay...holy mackeral, I''m dustin off the cobwebs on that one.
I seem to remember a linear sawtooth feeding a comparator, with threshold based on a DC voltage on the other comp terminal. Tis hazy enough that I'm not quite sure bout the memory, though.
I used to play with a ghz sampling scope a while back (in my TRR fixture days), the horiz trigger started the upslope of the sampling timer sawtooth, and they used the comparator to drive a pulse forming line, that line energizing a diode bridge input switch. They had a slope to slowly alter where in the input waveform the sample occurred, for example, moving the bridge pulse 100 picoseconds farther from the horiz trigger every cycle.
Man, those were the days...seat of the pants scoping..
Cheers, John
We must be about the same age - i used to use a built-in HP sampling scope in a Fairchild semi test system.
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