line array xover question

[sqlkev]

hi...i got all my drivers today..
32 4" full range from partsexpress
32 apexjr tweeters

both are 8ohm

I will be wiring the mids and tweeters up like this (12 drivers wiring diagram)



my questions are:

1. if the tapered wiring makes the final impedance load = 6ohm...
do I calculate the crossover with the resulting final load?
i would only need one set of passive xover b4 all the drivers correct? or do I need to have 12 sets of passives b4 every driver?? (that would cost me a whole lot)

2. how would i combine both wirings of tweeters and mids together??
do i just parallel the tweeters (add more rolls) to the wiring above?

I know these are very basic questions..
but I cant seem to find the answer through searching..
thanks

[johninCR]

First, I don't think 6ohms is correct. 16, 32, and 48ohms wired in parallel is more than 6 ohms.

Second, I think your power tapering plan is going to be problematic. Those 4"ers are only 5 watt speakers with a sensitivity of only 86db. You're planning to send over half of the power to the 2 center drivers. It seems to defeat a major benefit of an array and that is for the work load to be spread among many drivers. While power tapering may be ideal for an array of good drivers, I'd bet it will sound better, bigger, and louder by sharing the power equally using those cheap drivers.

Third, the good thing is that you only need 1 crossover component for the woofer network and one for the tweeter network.

[sqlkev]

thanks for the good news on the passive

the tapering wiring is actually made up of 3-4 lines of series parallel to achieve a low final impedance..(thats what i got from Dr. Griffin's paper)

about my plan on tapering...i think i want to try it out anyway...just to see how the idea works out
if it doesnt work well...i can always rewire back to uniform feed...
I'm planning an open back anyway...so wiring won't be a problem...

a few more questions..

do you guys need an Lpad at all??
i think i may need one since I don't even know the sensitivity of my tweeters...
would i need more tweeters than the number of mids??
finally...what should the horizontal distance should the line of tweeters from the line of mids?? was that ever discussed?

thanks again for the knowledge ive gained on this site

[sqlkev]

I'm doing some calculations on my scrapbook and realized that power tapering with these lesser sufficient drivers isnt a good idea afterall (as suggested earlier )

how should i wire to get a final impedance right around 8 ohm with all 32 drivers per side (16 mids + 16tweeters)?

next up...crossover design...
this is a bit tougher than i though

[johninCR]

4 in series then the 4 groups in parallel or vice versa get you to 8 ohms each for the woofers and tweeters. As long as your high pass and low pass are at the same xover point, you get 8. I'd xo just below that 7khz peak on the 4"ers, so they run as full range as possible. You might even want to set the tweeter high pass higher than the low pass cutoff due to that peak.

I'd add a high pass on the 4"ers at 200hz if you run dual subs or 100-125hz if you run a single sub, to protect them from the low frequencies that they can't play anyway. That will enable you to play them a lot louder without burning them out.

Yes, definitely, on the tweeter Lpad question to match the overall sensitivity of the woofers and tweets.

[BillFitzmaurice]

You don't have to worry about a HP on the fours if you have a 5.1 or 7.1 receiver. If you are running passive throughout or active with a separate crossover the Parts Express fours are fine to 80 Hz. I use eight per box to 80 Hz with no problems at 115dB. Make sure you don't run the fours higher than 6kHz and use a 3rd order or better LP filter on them to tame the 7kHz peak, and also a third order or better HP on the tweeters to minimize driver overlap that would lead to horizontal combing.

[AJ]

hey sqlkev,

Sort of OT, but we're both working toward the same end on these arrays so I thought I'd give you an update on where I decided to go with mine. I'm going to start with an open baffel too, with 16 four inchers per side and 8 PT2 planar tweeters per side. I'm wiring the 4 inchers for a straight 8 ohms and the tweeters will be wired for 4 ohms. If you go by the numbers, that will put the 4 inchers at ~98db sensitivity and the tweeters at about 95db, assuming there won't be any appreciable array gain from the tweets.

I'm looking at optimizing everything for a sitting position, so I'm making the baffle 75 inches tall - it's the same height as my subs even though I won't actually need that much height. It'll just blend better. I'll be using as wide a baffle as I can fit in the space I have so it'll be somewhere between 18 and 24 inches wide and I'll be setting them right next to the subs so I can use the width of the sub as an extension of the baffle. The extra coupla feet of baffle from the sub won't hurt to help keep the 4 inchers extended on the low end.

I just rebuilt my whole source too. I replaced the two amps and 2-way active XO I had with an Outlaw 7 channel amp and added an Ashly XR2001 3 way active XO. The Ashly turned out to be a very nice component - absolutely dead quiet and the functionality is terrific. The level controls will be all kinds of useful for blending the mid/tweeter array and it's hard not to like the dial-a-point for the XO.

I should be able to get started this week sometime. The PT2's were just ordered yesterday so they should be here by Wednesday. I still want to order two JP-2 ribbons and make another version with a single tweeter centered between two sets of 8 four inchers just to see what the difference is. I really don't listen to music standing up, and I'll never be more than 8-9 feet from the speakers, so I have a feeling that setup may be adequate for me. If these show some promise, I'm gonna go ahead and buy some "real" drivers for the woof/mids and do a final version aimed at better sound quality. OTOH, I may like these 69 cent drivers just fine.

I'll take some pics as the project progresses.

Bill - the 5.1 or 7.1 amp and active XO is a terrific idea. You can get a ton of flexibilty in a very small package.

Allan

[johninCR]

Allan,

I don't think 4 4's per side is going to be enough. I use 5 per side OB for my desktop at about a 4' listening distance to good effect. You've got plenty of baffle height to go with more. With more drivers and a fixed listening position, you may want to think about a concave baffle. Check out Dmitry's at http://www.geocities.com/dmitrynizh/labaffles.htm
Before you build the permanent baffle, try the 4's on cardboard with just 4 vs 8 before you finalize your plan.

SQLKEV,
If you are going OB, it is even more important to be sure that the 4's are protected from the low frequency stuff, so if your amp doesn't do it actively, you'll need an LP filter on the 4's.

[AJ]

John - I'm using 16 4 inchers per side. It'll look something like this:



I thought about the curved baffle too, but I read that it will focus the sweet spot pretty tightly. I'd rather have some room to at least move my head around. Still, it may be worth looking at. I'm not going to spend any time making these first coupla versions look good, I'm just wanting to hear the options. Since nothing's cast in stone. I could still try a curved version. Thanks for that link.

[johninCR]

Sorry Allan, I misread you post. With 16 per side you'll get impressive results. Concave will give you better imaging and even greater dynamics, but would require a sitting position. Dmitry found that that a curved concave made too small a sweet spot and that groups of three on flat baffles with each unit focused at the listening position was less problematic. Going with units of 4 in your case would give you the option of straight or concave with minimal work to make the change. Adjustable is even a simple possibility.