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Full-range line array?
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Old 17th September 2004, 12:46 PM   #11
BillFitzmaurice is offline BillFitzmaurice  United States
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They are on an open baffle with 16 drivers and 18 tweeters (got sick of making holes).
That's the reason you need bass boost. I have 8 Pioneers in a TL and they run to 80 Hz room assisted.

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The speaker was placed ~3 feet from the wall.
That's OK open baffle, but NG with a closed box, giving a null at about 100 Hz where you least can afford it.

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Should I cross the tweeters over around 3-3.5k like suggested with the C-C calculation,
The C-C calc is not universally accepted as being accurate. It assumes that the driver is a true point source,whereas in reality a far larger portion of the radiating plane (cone) serves as the sound source. Real world measurements indicate and that you can go higher.

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They are mounted behind the 3/4" MDF and not much of the sound is getting out. They're also mounted about 2.75" apart as I haven't taken off any of the excess plastic yet.
That's why the highs aren't there.

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would it be better to let the 4" speakers go until say 5k or so, and let the tweeters take over after that?
The fours are OK to about 6Khz, but above that they have a nasty response peak on axis, while the off axis response falls off precipitiously. Therefore both response and imaging concerns dictate crossing over no higher than 6kHz. The falling off-axis response will be a problem with any full-rangers. Whizzers will help, but then the spacing becomes more problematic than with discrete tweeters. Don't knock the quailty of the Pioneers; their only deficiency is in power handling, and using eight or more of them takes care of that problem.
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Old 17th September 2004, 01:06 PM   #12
chipco3434 is offline chipco3434  United States
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I crossed with a second order at 5kHz. Like BillF says, it avoids all those nasty response bumps at 7kHz.

Glad you like 'em!
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Old 17th September 2004, 01:31 PM   #13
mazeroth is offline mazeroth  United States
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Thanks for the input!

This speaker was built just to let me see how a line-array sounds and if I want to pursue making a real pair of them. After my listening I DEFINATELY want to pursue this project.

As far as mounting the tweeters. Do you think I should use a router and recess the whole back of the MDF where the tweeters will mount say 1/4" or more, so the tweeter will be closer to the baffle? I can still roundover the tweeter hole but I'm not so sure having the tweeters 3/4" behind the baffle is a smart thing to do. What size tweeter hole should I use?

I'm still learning about crossovers and was wondering if I would benefit from stepping up to a 3rd order instead of a 2nd order like you did, Chipco? Or does this just add unneccessary cost and sound degredation? (I have no clue).

If you had this project to do over again, how would you make your speakers, learning from what you now know? Maybe this can help a speaker newbie like me out

Lastly, I messed up when I said I had 8w 9t. I really had 9w 8t to get the 8ohm load. If that matters or not.

Oh, and should I do 4, 6 or 8 ohms? Sorry for all the questions!!!

THANKS GUYS!
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Old 17th September 2004, 01:36 PM   #14
BillFitzmaurice is offline BillFitzmaurice  United States
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but I'm not so sure having the tweeters 3/4" behind the baffle is a smart thing to do.
You really have to get the faceplates flush with the baffle or you'll have all sorts of diffraction problems in the high end.

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3rd order instead of a 2nd order like you did, Chipco? Or does this just add unneccessary cost and sound degredation?
A 2nd order doesn't give adequate bandwidth isolation between the two lines and will lead to horizontal combing. The two lines have to be physically as close together as possible and a 3rd order crossover is the minimum.

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should I do 4, 6 or 8 ohms
8 is always safe.
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Old 17th September 2004, 03:01 PM   #15
chipco3434 is offline chipco3434  United States
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I will defer to BillF's experience because I'm new at all this. However, I will make the following statements:

1. On my first version I used the Onkyo's and drilled a 1 1/4" hole and rounded over the front of the hole with a 3/4" radius bit. The effect was like a little horn when I was finished. From the standpoint of physics, that didn't hurt it. Further, the appearance was improved over surface mounting the tweets. I used 24 of them.

2. On my second version, I used Dayton ribbons. One ribbon is placed at about 5' and the second at 3'. These correspond to on-axis heights of sitting and standing "ears". They are better if for only avoiding the forty eight holes.

3. V1 was wired at 8 ohms using straight series/parallel scheme. V2 used a staggered series/parallel scheme and came out to about 5 ohms on the woofer section. I think V2 sounds better.

4. As for the combing issue. I am sure I have heard it and seems more pronounced within the near field distance. Step back and it disappears. Does it bother me? No.

5. Bass. I added a sub box that I stole from my son. Good for classical but only adequate for rock. However, the most noticable effect of the line of 4" drivers is the "punch", like when a drum is struck. I guess this is not exactly bass but it hits you viscerally like bass.

6. Number of drivers. I think the Griffin paper is quite clear that if 8 are good, 16 are MUCH better to achieve the line array "effect". The graph does rise at an geometric level. In my particular circumstance, 2 to eighth power quantity drivers was too much freight cost and would not pass WAF standards.

7. Crossover frequency. This is the toughest question. There are two possibilities here. The first is to equip yourself with with a bandolier of caps and coils and have at it. I gave up that idea based on cost and I am presently preparing active filter MOX boards for biamping these arrays. IMHO, most of the listening is in the 200-5kHz range and I have avoided the cross in that area. The MOX will let me play for free.
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Old 17th September 2004, 05:17 PM   #16
mazeroth is offline mazeroth  United States
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2 questions...

Bill...you stated:
"You really have to get the faceplates flush with the baffle or you'll have all sorts of diffraction problems in the high end."

How can I accomplish this using the Onkyo $0.48 tweeters? I brought up the idea of plunging my router into the back of the baffle about 1/4" or more and routing out the whole tweeter section so the tweeter would only be 1/2" or less mounted to the back of the baffle. I would still like to use a roundover, like Chipco did, in order to eliminate the 90 degree cut and maybe apply somewhat of a "horn".

Chipco, you get question #2 =)

"3. V1 was wired at 8 ohms using straight series/parallel scheme. V2 used a staggered series/parallel scheme and came out to about 5 ohms on the woofer section. I think V2 sounds better."

I understand V1 as all of my plans have used a 4 or 8 ohm load on both w/t lines. When you say a staggered series/parallel do you mean something like:

8-8 = 16
8-8-8-8 = 32 }
8-8-8-8 = 32 } parallel these 2 to achieve a 16 ohm, then parallel these with the 8-8 to get an 8 ohm nominal? If not, then what do you mean? This is considered power tapering, right? Where you'd probably put the 8-8 in the center and the 32 ohm loads out the outsides?

Thanks!

-The newbie
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Old 17th September 2004, 06:47 PM   #17
chipco3434 is offline chipco3434  United States
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I should have explained myself better. By staggered I meant rather than a straight 4-4-4-4, I wired it up as (guessing now) 3-3-4-3-3 or 2-3-4-4-3. That scheme is somewhere out in the ether. Anyway, the measured impedance was about 5 ohms for the woofer array.
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Old 18th September 2004, 02:54 AM   #18
DonJuan is offline DonJuan
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hi mazeroth

i see you are using 4 inchers. how about 8 inchers?

so far, haven't heard anyone talking about the issue of using 8 inchers in a line array.

donjuan
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Old 18th September 2004, 04:15 AM   #19
mazeroth is offline mazeroth  United States
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I did purchase some 6.5" Vifa (Infinity) Buyouts from Parts Express to use in a line array. Problem is I don't have the $$$ right now to get tweeters that will do those drivers justice. With a 6.5", and even moreso with an 8", you'll have to cross the tweeter over much sooner (in most cases). I also think it's more difficult to achieve good midrange from a large woofer, like an 8" in your case. I'm even a little reluctant to try it in a line array.

I was thinking of making a set of bookshelfs first, before I jump into the line array project. Maybe a set of MTMs with (2) of the 6.5" Vifas and a nice tweeter. Do you guys think these drivers will work well in an MTM speaker?

http://www.partsexpress.com/pe/showd...number=299-493

If not, how could I use them? And is there something more desirable than an MTM?

Thanks!
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Old 18th September 2004, 01:01 PM   #20
BillFitzmaurice is offline BillFitzmaurice  United States
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My cab used the round Onkyo's, which I mounted in holes using silicone sealant. Flush mounting is the best method, but a radiused faux horn is the next best option.

The problem with large drivers isn't so much the C-C as it is dispersion, and with eights that pretty much forces you down to 2kHz, which is OK, you just won't get tweeters that go that low for $.32.
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