First DIY: WMTMW cc build: Help!

**Jed** · 06 July 2009, 16:13 Monday

Can you design a crossover? That's the hard part and already done in the 2CC design. Also I don't have a problem with lobing in these designs because the drivers are pushed next to eachother to minimize CTC spacing. The power response is very flat. Now, if you were to do an WMTMW with them all in a row on the same axis; then yes, you would have problems. There is more than one reason for the layout I used in the 2CC and 4CC.

**smitty611** · 06 July 2009, 23:38 Monday

I don't doubt your prowess one bit! Your designs are gorgeous and really the reason I looked into this at all. I'm afraid my crossover abilities are severely lacking for this project. I had even considered the sin of a prefab network from PE (the 375hz/3k 3way) as at least a starting point. Then figured if I could wrap my head around at least some of the ins-n-outs a little more I'd be further ahead building a custom crossover. I was afraid the dual 8ohm mids would present a roadblock. And I assumed the crossover you had designed would be dramatically different for my driver combination. Am I off base there? If you'd be willing to offer any major pitfalls you foresee with this driver combination I would greatly appreciate it. I'll put in the time to figure it out.

**HareBrained** · 07 July 2009, 01:07 Tuesday

Hi Smitty,

The drivers you have can certainly be made into a WMTMW but the quality may not be what you expect. It's sorta a joke around the DIY audio sites that a newbie asks if someone can help him design a 3-way. You could probably search for "newbie" and over half will be about a 3-way design needing help. You've gone one better in tackling a CC 3-way with 2 woofers and 2 mids.

MTM centers are difficult to get right. They're often "aimed" off axis since their placement is less than optimal. And the horizontal combing caused by the two mid drivers must be addressed. And you can double that for the woofers.

I'm guessing you haven't designed a set of speakers yet, correct? Do you have surrounds? Perhaps you should consider getting your feet wet there? You can learn a lot from designing a simple 2-way as the problems are easier to solve but the process is the same.

Since you've chosen some older drivers, you're going to want to measure their performance. There's a very good chance that none of your drivers will have the T/S parameters even close to that published data. Deviations occur from batch to batch. If you design to the spec sheets, the probability of it sound good is very low.

This doesn't mean you can't give it a shot. In the end, your first efforts may cost only $50 in xover components and $50 in wood. Don't start with the PE canned xover because you'll just end up swapping out all the components for ones of different values. There are several design thru simulation threads here and on Parts Express's Tech Talk forum. I suggest you start there.

**ThomasW** · 07 July 2009, 09:20 Tuesday

It's difficult if not impossible to match a point source dynamic driver center to line source planar mains. It becomes a situation of trying to make apples and oranges taste the same.

IMO as a 20+yr user of planar mains, the best solution is to use one of the Maggie centers, or make a center using lines of the B&G Neo3/Neo8 flanked by dynamic driver woofers operating open baffle.

**smitty611** · 07 July 2009, 09:44 Tuesday

John ---
Haha! Yeah, I know. And I normally don't post such horribly noob questions. I think I just wanted to know from some seasoned vets if they thought the drivers I have "in stock" would even work for this particular application. If so then I'm sure I can put something together that will at least suit my tastes/expectations. Honestly, at this point I probably won't go the extent of measuring the drivers...which means I'm more or less flying blind (if you don't think the spec sheets are reliable)...which means I'll probably end up spending more time/money revisiting the crossover components than I would have otherwise...but that's the journey, yeah? By the time I get the box built I will likely change my tune. I'm much more confident in my woodworking/finishing abilities so I intend to spend the time making this sucker look sharp...which means I'll probably by then want to take the measurements and whatnot so everything sounds as sharp as it will hopefully look. I'm very pumped about the external after seeing many of the designs out there. Is that like the cart leading the horse? That story didn't end well, I don't think...

Thomas ---
Yeah, I wasn't really holding out much hope that the maggies would work well with this center channel. I don't really have the room/setup right now for a maggie center, I don't think. The wifey wants them out of the room anyway. :cry: And I've just grown away from the maggie's sound for movies. That's in large part to not having an active sub currently though. This is just the beginning of a makeshift HT setup which will undoubtedly never end.

Thanks for the replies

**ThomasW** · 07 July 2009, 10:58 Tuesday

Roman has a good tutorial on using the FRD tools to design speakers

FRD Consortium tools guide

http://www.rjbaudio.com/Audiofiles/FRDtools.html

**smitty611** · 07 July 2009, 11:03 Tuesday

I read that actually, but I couldn't get SPL Trace to run on Windows XP Pro. I did manage to finally get FRD and ZDA data from another spreadsheet to import into Jeff Bagby's Passive Crossover Designer spreadsheet. I couldn't get much info on the Vifa tweeter though. Guess that's what I get for using older drivers!

This is probably a dumb question but how can I wire the two 8ohm mids optimally? Do I just go parallel for a 4ohm load? I was going to go series on the 4ohm woofers and pad the tweeter to 8ohm.

**ThomasW** · 07 July 2009, 11:36 Tuesday

If your amp will drive a 4 ohm load that's the way to go

First DIY: WMTMW cc build: Help!

First DIY: WMTMW cc build: Help!

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