Line array help

[Fazorcat]

I don't know much about this project, but it was cheap and seemed cool. So I am gonna give it a shot. Here is what I have...

I have 16 of these mid-woofers: http://www.partsexpress.com/pe/showd...number=269-570

I have 2 of these tweeters: http://www.partsexpress.com/pe/showd...number=275-035

And 2 of these woofers: http://mcm.newark.com/NewarkWebComme...KU=55-1480&N=4

I plan on making two line arrays... 1 tweeter, 1 woofer, and 8 mid's per cabinet. Is it possible to have them wired to be 8 ohms? They are all 8 ohms except the tweeter, which is 4.

Should I use all these speakers? I figured it'd be best to put that woofer in there. Any opinions or advice is appreciated. Thanks

[Fazorcat]

Or....

Should I ditch the tweeters and woofers, and just make a array including the mids. The mids frequency response is 75hz to 15000hz. Do I need the top and lower end if I have a subwoofer and center and rears? I can get the low end out of the sub and the high end out of the rears and center. It would seem easier to do without the tweeter and woofer. Lemme know if that would be a bad idea. Thanks

[dhenryp]

You can't wire eight, 8 ohm mids to get exactly 8 ohms. You can wire them in series parallel to get ~6.9 ohms with a little power tapering (the two in the first group would be a db or two louder than the rest):
------------------------
| | |
8 8 8
| | |
8 8 8
| | |
| 8 8
| | |
-------------------------

You would put the two speakers in the first group in the center of the line with the other six, three above and three below.

You realize that you can't just wire the woofer and tweeter in with the mids without some kind of a crossover don't you? The question for the tweeter and the woofer is: is their efficiency high enough so that they can keep up with 8 mids? I have not looked closely at them but it seems likely they can't keep up. If that's the case, then you might have to pad down the mids to get them in line with tweeter and woof. This works against one of the advantages of a line array: high efficiency.

If you do use the tweeter, you would put it in the center of the line of mids and presumably you would put the woofer at the botton. This would require a three way crossover so if you don't have a lot of crossover experience, my inclination would be to try it with just the mids first to see how you like it. You can then add the tweeter and woof later on.

Good luck

[Hennie]

A combination of line and point sources can only be in balance at one listening distance. Here is a good white paper about line arrays by Dr Griffin.

http://www.audiodiycentral.com/resource/pdf/nflawp.pdf

[thylantyr]

Cheap projects are cool. But sometimes it's not worth spending
the money if the project is not balanced well. Consider adding
more money to your project to make it worth your time.

After playing around with those mids, 8 mids have the potential
to drown out the single tweeter and woofer. You can lower the
level of the 8 mids but then why bother using 8 of them ?

Those NSB mid have the potential to give you really good
sound quality if you do the lacquer modification ($5) and you can
boost power handling with the ferrofluid modification ($30).
The phase plug modification is over $1.5 per driver and is audible
at higher frequency. You can ditch this mod if you crossover the
mid lower, around 3khz. You don't have to do any mod either,
but if you want to make that 50 cent driver sound like a $25
one, then put some effort into the mod.

Those tweeters appear to be good candidates for a line array
project because you can get the center to center spacing
very low.

Ideas;

A line of 8 4" mids = 32" line
A line of 8 1.5" tweeters = 12" line

That is what I consider a starting point where the system might
achieve some balance. This is just a guess, I haven't worked
with those tweeters.

If you can make the tweeter line bigger then I would consider it.
Cost for the 12" tweeter line is $32. Not bad.

A tweeter line of 24" is $64, use an Lpad to control the tweeter
if needed.

Another idea. Use a low cost compression driver w/small horn lense in the center of the box, then have 4 mids above, 4 mids
below. The cost is also cheap.

The best idea is use to use some form of 'ribbon' tweeter
for the array but the cost goes up alot. The Dayton PT2 mates
very nice with those mids and you can crossover the design
around 3khz. You can mate 4 PT2 with 8 mids pretty well
and this would give you nice results. Cost is higher.

You can get some decent boom out of those 4" mids if
you tune the box around 80-100hz and then mate to a subwoofer. But don't expect monster midbass from
those 4 inchers. If you desire alot of bass then you need
more than one 10" woofer.

What you should do is make a test box.

reference;
http://www.caraudioforum.com/vbb3/sh...d.php?t=210115

http://www.caraudioforum.com/vbb3/sh...d.php?t=212800

[Fazorcat]

Thanks guys for the reply's. I think I am going to try just the mids. I tried 4 mids last night (just sitting on the floor) and they sounded decent. Then I took one of those out and put in the tweeter... couldn't even hear the tweeter, and it sounded worse. Then i tried with the woofer, still lost some sound quality. So overall, just the mids themselves sounded the best. So I think I am gonna take the easy way out and not use a crossover or other speakers. I also believe I am gonna put all 16 mids in one cabinet, and then buy 16 more. So that will be a tall array. I'd like to slope the tops and bottoms of this, but I don't have the skill to do that well. Is that gonna suck now if it is straight? So with 16 of them, there shouldn't be a problem with getting 8 ohms total then, right? Also, how big do I need to make this box? I didn't plan on porting it, but would that help some? I assume with a ported box there will be a better chance to blow the mids cause the cone will move easier. Well hit me back with another reply please and straighten my thoughts out Thanks guys.... o yeah, I was thinking like 6" wide, 8" deep, and however tall. Does that sound ok?

[ralph-bway]

I'm not at all familar with the ferrofluid mod for the NSB's?
Could you explain or point me in the right direction.

Thanks.

BTW I've done a 13 driver per side Line Array with the NSB's, I wound up at 6.5 Ohms. Very pleasing for an inexpensive project.

[thylantyr]

Ferrofluid

http://www.teachersource.com

FF-310

$30 a bottle.

Since I plan to use phase plugs I cut off the dust cap and
used a small eye dropper to place the ferrofluid in the gap.

All you do is place the fluid in the dropper and the magnetic
field will suck the fluid out by itself. When you see it fill up,
stop and remove the eye dropper.

If you don't want to cut the dust cap you probably need a syringe
and poke a hole in the center of the dust cap but you need to
pre-measure the correct amount. Perhaps sacrifice one NSB
to do the test.


******* NSB Torture Test No ferrofluid *************
Setup: Adcom 555II, 200w/ch amp, band pass 220hz - 6khz,
18db/octave, free air.


The driver was being tortured by Slayer and I can smell the fine
aroma of 'I'm hating life, help me'...

Four songs and the driver died.

The metal cup in the back of the driver was warm.

****** Ferrofluid Test *******
How many songs can the driver survive if I redo the test
with ferrofluid ?

The driver was being punished and it survived many Slayer
songs with no aroma. The metal cup is warm and it is
happy

<Captain Kirk>'We need more power Scotty....'

Time to crank the tunes and push the driver into death.
The heavy clipping LED's are working overtime and the
driver is outputings some crazy SPL listening
to some serious guitar jams. The metal cup is getting
warmer and warmer, then hot.. hot enough that I can't
touch it for more than a second. The SPL is driving people
out of the garage, the paint on the phase plug is melting
and then I see smoke coming from the front.....

Kaput...
Toast...

The voice coil is fused, the driver is toasty hot... 5 watt
driver taking 400 watt peak before dying.

***************************************

Update on the ferrofluid mod.

Right now the test box has the NSB dust cap removed.
I've been cranking the tunes for a while now and I
noticed some spatter on the cone. It's the fluid
that is being sprayed at high excursion

Reminds me of water stains on the car on a hot day.

Perhaps the phase plug with a metal slug (wood screw)
installed will help contain the fluid :unsure:

Most of the fluid is still there, this is just little sprinkles
and if you are into the 'eye candy' thing, you may not
like it.

If you didn't cut off the dust cap then you should be ok.
If you did cut off the dist cap and don't abuse the speakers
like I do, you could be ok.

The stains don't affect the sound quality. It's cosmetic.

I'm thinking of placing less fluid in the NSB for the next test.

[Fazorcat]

So I am gonna put 16 mids per cabinet.... What should the distance be between each speaker?

[thylantyr]

Originally posted by Fazorcat
So I am gonna put 16 mids per cabinet.... What should the distance be between each speaker?

The general rule;

13400/driver space = crossover frequency.

13400/4" = 3350hz

People cheat and crossover higher than the 'rule', perhaps
as high as 4khz to 6khz.

That is if you chose a center to center of 4". As you space
them out further the crossover should be lower.

I chose a center to center spacing of 4.375" to allow to me
to sneak in a piece of 3/4" thick wood between the NSB's
to create four chambers (groups of four NSB). Also, I chamfered
the back of the front baffle 45 degrees (3/4" thick baffle) for
each NSB hole to let the driver 'breath'. Even with 4.375", it's a
tight fit to sneak in that piece of wood and the chamfer is large
which requires me to 'fill the gap' with some type of glue
to seal off the chambers. If you are not doing anything fancy, do
4" ctc give or take.