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)

An externally hosted image should be here but it was not working when we last tested it.

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:

An externally hosted image should be here but it was not working when we last tested it.

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.

 

[AJ]

John,

When I first started thinking about the arrays and after reading Jim Griffin's paper, I thought of making the array in sections and stacking them. Use 4 drivers in a single sealed box with banana plugs to connect them and it would let me stagger the stacking - in effect a curved baffle although it would be a stairstep baffle and not a true curve. The cool thing about these cheap drivers is that once you have them, the possibilities for different enclosures is endless. they'll keep me busy experimenting for years.

 

[sqlkev]

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.

first of...thanks for the reply on the xover question...
so if I put 2 8ohms (mids + tweets) together in series...both have the same xover point (one is lowpass..the other is highpass) then the result would still be 8ohm??
sorry for the dumb question....i wished i took some of these classes in HS or something
I'll be sure to get an Lpad to do some padding as well

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.

as a matter of fact...I'll be running the OB with a 5.1 pioneer elite receiver...
I'll have to check on the manual to see where the HP would be...i assume its 80hz??

along the apex tweets..
i have 4 ribbons that i want to try out...
they sound beautiful above 6khz...

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

your project sounds fantastic...
let me know how the wide baffle works out for you..
i'm still confused about the baffles and spacing between drivers part..
yesterday i hooked up the mid and my ribbon up for testing..
the mid was LP around 5khz and ribbon was HP at 7khz (passives from my old 3 ways)
the combo sounded a bit thin...but i could tell that it had potential
yours should sound amazing with all the ribbons in place
once you've decided on the xover points...can you update me on that?
since I cant go active right now...I'll totally have to rely on passives..
cant wait for the pics

 

[AJ]

'm still confused about the baffles and spacing between drivers part..

From everything I've read so far, the bottom line is to keep everything just as close to each other as possible, or to at least know where the combing will start so you can choose an appropriate XO point. The main reason for keeping them as close as possible is to keep the XO point to the tweeters as high as possible, especially if you want to take advantage of the wide range capabilities of these 4 inch drivers.

Rule of thumb (or what I understand so far):

To find out where the combing will start (theoretically) divide the center-to-center distance into 13560 (speed of sound in inches) and you'll have a place to start wrt XO point. So for these 4 inchers, if you mount them edge to edge, the place to start thinking of crossing over would be 13560/4 = 3390Hz. An octave above that (~6.8khz) is where the effects of the combing will be evident. So if you figure a cross over at say, 3khz, you'll be in the ballpark, depending on the slope, the natural properties of the drivers etc. I'm going for a 4.25 center to center distance because of the shape of the driver flange and basket. A ~4 inch cutout would let you drop the driver right down to the flange, but because the square flange is the same size as the cutout, mounting them edge to edge would leave you with adjacent cutout holes. I'm using 4.25 just to leave some material between the holes. If you go with the second diameter on the baskets, you end up with a 1/16 inch gap between the baffle and the driver flange...it's always something isn't it?

So even if I'm not going for ideal, edge to edge placement, I can still know where the negative effects will begin. 13560/4.25 = 3190Hz so I'll lose a couple of hundred Hz on the XO point (not enough to worry about). the tweeters array needs to be done the same way and kept as close to the mid array as possible.

At least that's what I've read on the internet.

 

[johninCR]

SQLKEV,
The tweeter and woofers arrays are wired in parallel with each other. The XO blocks the lows from going to the tweets and vice versa to give you a steady impedance accross the frequency range.

AJ,
Yes close spacing is best especially for the tweets. My 1st array had 12 4's per side on 5" centers run full range and the comb filtering/lobing effects were almost unnoticeable. The theoretical impact is based on the spacing between where the sound originates which happens on different areas of the cone and there is some dispute as to exactly where this occurs, but it is not exactly in the center of the cone.

Regarding flexibility, fairly shallow boxes with no back will work fine.

 

[sqlkev]

From everything I've read so far, the bottom line is to keep everything just as close to each other as possible, or to at least know where the combing will start so you can choose an appropriate XO point. The main reason for keeping them as close as possible is to keep the XO point to the tweeters as high as possible, especially if you want to take advantage of the wide range capabilities of these 4 inch drivers.

Rule of thumb (or what I understand so far):

To find out where the combing will start (theoretically) divide the center-to-center distance into 13560 (speed of sound in inches) and you'll have a place to start wrt XO point. So for these 4 inchers, if you mount them edge to edge, the place to start thinking of crossing over would be 13560/4 = 3390Hz. An octave above that (~6.8khz) is where the effects of the combing will be evident. So if you figure a cross over at say, 3khz, you'll be in the ballpark, depending on the slope, the natural properties of the drivers etc. I'm going for a 4.25 center to center distance because of the shape of the driver flange and basket. A ~4 inch cutout would let you drop the driver right down to the flange, but because the square flange is the same size as the cutout, mounting them edge to edge would leave you with adjacent cutout holes. I'm using 4.25 just to leave some material between the holes. If you go with the second diameter on the baskets, you end up with a 1/16 inch gap between the baffle and the driver flange...it's always something isn't it?

So even if I'm not going for ideal, edge to edge placement, I can still know where the negative effects will begin. 13560/4.25 = 3190Hz so I'll lose a couple of hundred Hz on the XO point (not enough to worry about). the tweeters array needs to be done the same way and kept as close to the mid array as possible.

At least that's what I've read on the internet.

i think i'll copy you on the spacing as well
what would u use to cut out the holes??
my hole saw kit has the 4" missing...I guess I'll go pick up another and use the 4"...is 4" exactly what the cutout should be?
I'm afraid it might be a bit too big and would leave some gaps

aslo...I'm playing with the xover points right now (using winamp with independent channel EQ adjustment up to -92dB cut)
5k-6khz xover point sounds good so far....

SQLKEV,
The tweeter and woofers arrays are wired in parallel with each other. The XO blocks the lows from going to the tweets and vice versa to give you a steady impedance accross the frequency range.

AJ,
Yes close spacing is best especially for the tweets. My 1st array had 12 4's per side on 5" centers run full range and the comb filtering/lobing effects were almost unnoticeable. The theoretical impact is based on the spacing between where the sound originates which happens on different areas of the cone and there is some dispute as to exactly where this occurs, but it is not exactly in the center of the cone.

Regarding flexibility, fairly shallow boxes with no back will work fine.

thanks for clarifying on the parallel part
what would u think of a baffle that is 15" wide for my setup??
I have the mid playing on a 24" wide cardboard for the moment and the lowend is better than expected...
too bad i can't have 2 24" baffles in the living room..
that'd look too tacky

 

[johninCR]

Narrower with wings for stability images better. As long as the "wings" aren't too deep, you don't get cavity resonances. You could use something like strips of leather or material as hinges on the backside to make them adjustable to your liking. A 15" effective width only gets you down to about 210hz before the open baffle rolloff. See http://www.angelfire.com/electronic/DIY/OB-Speaker-concept-1b.html

 

[sqlkev]

Narrower with wings for stability images better. As long as the "wings" aren't too deep, you don't get cavity resonances. You could use something like strips of leather or material as hinges on the backside to make them adjustable to your liking. A 15" effective width only gets you down to about 210hz before the open baffle rolloff. See http://www.angelfire.com/electronic/DIY/OB-Speaker-concept-1b.html

210hz seems a tad high
i guess i could go with the wings on hinges...
What should be light enough that wont resonates??

my baffle should be around 90" in height...so the lighter the wings the better...

 

[johninCR]

I wouldn't go any lighter than 1/2" plywood.

 

[Chris8sirhC]

Just get out a ruler and measure it. You can use 1/8'' or 1/4'' hdf (found at almost all Lowes &or Home Depot) for mounting over the front of the driver since its got that little cardboard lip sticking out, then use 1/2 or 3/4 plywood for the back of the drivers. Get a good vibration absorbing glue to go inbetween the two layers and you dont even really need to worry about screws b/c the drivers are sandwitched and glued in place. The smooth side of the hdf is a great surface for painting. Sometimes if you use the cardboard lip to mount the drivers, if you have the hole cut exactly, it can be a real pain to get the drivers into the hole, on some of them i had to get out a clamp and force it in there.

 

[sqlkev]

thanks for the suggestions guys...i appreciate it


just an update...
for half of the day...I've been doing measurements and planning..
the final baffle should be 92" x 16"
with all 16 mids w/ 1/2" spacing...i have left on both top and bottom..(i figured i would go with this now and later on cut off the 10" from both sides and add subs under the baffle)

I used a 4" hole cutting tool...but of course the holes do not come out as expected...
I've already dropped by HomeDepot and picked up some foam sealant..I hope I can spray the foam from the back and seal up any airleaks

for now..the baffle is only 1/2 inches...I'll sandwich another layer tomorrow when I'm done...I dont feel like cutting 64 holes

Not sure where to cut the holes for the tweeters yet...is there a certain spacing from the mid ---> tweeter rule that i can follow?
Or do i just line the vertical line of tweeters as close to the mids as possible?

In the afternoon, I put 1 mid and 1 tweet on a cardboard with 3.5" c2c spacing between them and the result was quite pleasing..
is there any reasons for me not to do that in my final baffle?

I took some pics...but will post final product when im finished...