Line Array Help

[Bobcat19]

This is what I want, a speaker set up that has a lot of throw, maybe 30 metres or so. They will be used for house parties (sometimes outdoors, hence the throw) etc. Can someone point me in the right direction please, I was thinking about maybe doing a line array using 3 or 2 way 6x9 car speakers if I could get them cheap enough. Ill probably be using 18mm mdf by the way, just so you know, if it means anything. Are these bad ideas? Any contributions much appreciated.

[flg]

Well, I'ld like some help too, but I'm further along on my way anyway. I'm not going to tell you those ideas are "bad". But, that certainly is not the best approach Especially for your current expectations...
I havent found enough info here either but do some searching, there is some
Hi-Vi B3S for Line Array?
And the Jim Griffin paper they refer to is pretty much the Bible for builders at our level. It can be found here
http://www.audioroundtable.com/misc/nflawp.pdf
Audio circle I beleive has an archived thread or whatever you can still access
You should also search for this guy in Az who does alot of that. Don't have that link handy or remember his name???
There is a really good build article somewhere out there but I'll just have to check the bookmarks at home
JBL has an old but good paper too. I'm sure you can find that by youself.
Do some searching. D'Appolitto did one years ago you can still find info on. You might like that one?

With any luck we might get a good thread going here and generate more interest on this subject. Line arrays are amazing

[flg]

O.K. I breezed through my bookmarks for some more info for you. In addition to the links above, these links should get you up to speed a little.
I gotta tell you though, generally an outdoor system is 4X any indoor system. That's 4 times the power, 4 times the drivers, 4 times the size, , etc. etc.
I think someone like Cal Weldon should chime in here. I believe I've seen some of his toys that are the type of thing you need for open-air sound. Check out the Gallery maybe. Do some searching and reading.
Hope that helps

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[dublin78]

This is probably more your cup of tea.

The Murphy Corner-Line-Array Home Page

[Bobcat19]

Thanks for the help. Much appreciated. Will let you know what happens but it won't be anytime soon unfortunately.

[Scottmoose]

If it's outdoors, & with those kind of possible listening distances, a convex array will probably be needed. Most of the hifi arrays assume you're in the fresnel zone, with room reflections helping ~'mimic' an 'infinite' line source. Outside you don't have that luxury, so it's pro-audio / arena style that'll likely be what you need.

If it's for party etc. use, then expensive drivers won't be of much benefit, & you probably won't need extreme HF extension as nobody's likely to be 'listening' to it as such, unless you're talking piano recital style parties. Get whatever you can that's cheap & solid, with reasonable HF. Might not even be worth going multiway; in practice lobing isn't usually an issue, despite what the physics / measurements suggest, as our brains don't function like microphones & software, & the Haas effect tends to kick in, although admittedly, my experience on that score is limited to hifi indoor nearfield arrays, so how applicable it would be outside I don't know. The cheap car coax units you mention, might do the trick, so long as you can find a source of reasonably priced ones & they're not too large. Good luck with it all.

[tomi]

The basic sketch with line arrays seems to be:
a) to get the source - particularly at the HF end - as narrow as possible, in order to give a good horizontal disspersion, and
b) to get the amplutude & phase down the array as even as possible, in order to produce a flat wavefront and the required vertical directionallity.
It seems that you can go as far as you like (or not) to make your array behave like an ideal line source. Like most things, I suppose it depends upon your performance/price/complexity/size/etc tradeoffs.
The major problem will probably be the length of array you'd need to get good directionality (and hence throw) down to reasonably low frequencies. I've not done any summs, but it's certainly going to be a good few feet.

It's an interesting project though - halfway between a big HiFi and a small PA.

[flg]

The problem, No Offense, and Scotmoose seems to have ignored it, is that a 6x9, co or other axial, has a 6" dim that makes lobing happen at 2250hz or above or so. Personally, I think you need to go down to 3-3.5-4" before you start hoping the lobing won't be a problem. I think Bobcat would be better off with a seperate tweeter array than the units mounted center to center in a 6x9 co-axial... Just my 2 Cents.
You don't necessarily need a HiFi Tweet but 2250Hz isn't goin to get it! And yes, we're talking something far field not near field for 30m. Most everything we all do is nearfield

[Scottmoose]

Er, I didn't 'ignore' anything thanks:

in practice lobing isn't usually an issue, despite what the physics / measurements suggest, as our brains don't function like microphones & software, & the Haas effect tends to kick in, although admittedly, my experience on that score is limited to hifi indoor nearfield arrays, so how applicable it would be outside I don't know.

You don't want to be using drivers that are too large; up to 5 1/4in is about the practical limit for hifi purposes (I did some experimenting), but for house parties, possible use outside etc., a 6x9 on its side will likely be fine, above all if it's expected to project for 100' or so. We're not talking fine audio here by a long chalk.

[Cal Weldon]

If this is for parties as you describe, why are you considering line arrays? Seems like a bit of a different approach. Also, 6X9 car speakers would be way down the list of choices unless you have them already and are just looking to throw something together.