Good idea or waste of $? Dual woofer line array: - diyAudio
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Old 3rd October 2005, 08:49 AM   #1
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Join Date: Jul 2004
Location: Columbus, OH
Default Good idea or waste of $? Dual woofer line array:

I purchased a few cases of these JBL buyout Vifas at PE a while back and made some line arrays with them: (10 woofers with a single Fountek JP-2.0 @ 2.5k 24db L/R DCX2496)

http://www.partsexpress.com/pe/showd...number=299-432

This was my first speaker project so the cabinets only came out fair. I'm thinking of gutting them and starting over and have been throwing around a few line array ideas. The most recent is a line of 9-12 woofers with a matching line next to it, accompanied by a line of 8-9 Dayton PT2B planars. I have a Behringer DCX2496 (I LOVE this thing) so I have full control over 6 channels. I was thinking, since these are only 4.5" woofers, that maybe a 3-way would work, with one line for bass, the second line for mids, and the last line for highs. Plugging in the T/S into Unibox here's what I get per driver:

0.707 Qtc [1.2L] F3 of 130hz / F10 of 75hz
0.600 Qtc [1.8L] F3 of 132hz / F10 of 69hz
0.500 Qtc [3.2L] F3 of 143hz / F10 of 63hz
0.450 Qtc [4.6L] F3 of 150hz / F10 of 61hz

As you can see, bass is not their strong point. I was considering doing the bass line up to 200-250hz, then letting the next line run from that up to 2.5k-3.0k, with a L-R 24/db slope. I can take care of baffle step within the DCX2496 so no need to worry about it here.

So, since I have a ton of these laying around (almost 60) do you think this design idea has merit? I was looking to get the best sound possible, and I'm thinking taking as much strain off these as I can would benefit them. I really enjoy the way they sound now with a line of 10 running up to 2.5k 24/db L-R, so I have no doubts doing a single line will sound fine, but hey, I have the extra so why not go all out, right? I am also considering letting the one line run full range up to the tweeters, and the lows line of woofers I can run only as bass and EQ them to flatten the bass out.

Lastly, I was wondering if I would experience any lobing or combing effects, even though I'll be crossing them low? The 200-250hz was just thrown out there; I'm flexible on those numbers.

As always, thanks for any and all input!
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Old 3rd October 2005, 05:21 PM   #2
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Join Date: Feb 2001
Location: Mars
This is what I would do. Simplify.

Make a line of 8-10 PT2's and run them at 1.7khz - 2.0khz,
LR48dB/octave. The PT2 is more 'magical' in sound at 1.7khz
vs. a higher crossover point and the power handling is insane too
with the steep slope.

This makes the midwoofer choice easy. Any midwoofer
can do up to 1.7khz. So the next question is bass.
You said the bass is weak so I would port the design.

Model the midwoofers ported and see what you like.
I would make a ported box with a hump in bass response,
3-6dB to get some extra umph in the midbass region with
very little strain on the drivers. If there is too much midbass
for you, use the DCX to attenutate it. It's easier to attenuate
the boom that to boost it.

One example, four of those drivers per chamber would be
nice. Maybe 1 cubic foot tuned to 75hz with a 4" rear flared
port. You can easily mate this with a subwoofer. Those are
just rough numbers, play around to see what you like.

How much SPL do you want in the midbass? I can generate
126dB peaks [c-weighting] at listening position with the cheap
NSB array ported by using this method. Mine are +6dB boosted
by box design around 100hz, these particular midwoofers you
have can go lower and should be able to excel in performance if
you do rear ported. I would do a four chamber, four rear port
design.

You don't need two lines of midwoofer using the same drivers,
that isn't an efficient design. Let the port resonance do the work
for you.

Make a four driver test box using cheap wood to confirm.
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