Help a noob with a center channel

[jjminch]

First off this seems like a really good forum. So much so, I realize I'm really over my head. I'm going to have to go to the library and get some books on this stuff.

Anyways here is the plan. My dad needs a center channel build that is no taller than 5" or deeper than 8", width can be as long as 49". It needs to go between a flatscreen and an fireplace mantle. He is really good at woodworking, but I need to do the electronics bit. We can't seem to find a commercially built one to suit the space requirements that isn't garbage. The budget is at $200.
He doesn't even have a center channel right now, and is just going to run this with some bookshelf speakers.

Ideally we want four 4" drivers and two 1" tweeters.
I found these

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=264-817

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=276-154

How should the sequence of these be? WTWWTW? Or do I really need two tweeters? Also ported or sealed?

The speakers are all 8 ohm. I've done car stereos and whatnot, but I cannot figure out how to wire all the speakers into a crossover and one terminal and still have the proper independence. Is it even possible?
I found this crossover, will this work for this application?

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-142

[Marzen]

Hi JJ, have you looked at the Cynosure center speaker on PE's Project Page? You'd have to modify the dimensions of the cabinet to meet your Dad's space requirements & still have the same amount of internal volume. Darren even mentions going with a wider cabinet and moving the ports to the front baffle. This is the only DIY speaker I've seen that's designed around the narrow constraints of your situation, and at $200.88 w/o shipping it meets your budget criteria.
Unfortunately, going with your orig choice of drivers would require some considerable amount of time, software, & measuring. Not impossible, but fairly involved for a one shot specialty design. :E
Cheers,
-Ward

[jjminch]

Actually I just found it. It is a great link, and I really like the setup. If I don't do this one, then I am going to have to change the original design. I was thinking 2 three inch 4ohm woofers, a midrange, and a tweeter with an out of the box three-way crossover.

Question on the Cynosure... Do I really need four ports, or could I get away with two on the front? And since the box will be considerable wider, is 1/2" MDF board with some bracing going to be adaquate?

[Mazeroth]

If it helps, I heard the Cynosure at the Dayton 2005 DiY event and was thoroughly impressed by it. It has excellent extension for its size, and it's off-axis performance is great.

[joetama]

You could go down to 2 ports if you kept the total port opening area the same(4*x=A=2*2x where A= Total Area and x= one port area), otherwise you could have to make the port deeper to bring the tuning back down here it was designed. But, that can cause other problems with air flow in/out of the ports which could be very audible....

[jjminch]

Thanks guys, it looks like this is our winter project. Now I have to find some bookshelf speakers to match. Any ideas? Looking for a 6" 3 way setup.

Also I understand the wiring diagram they provided for the crossover somewhat. My question is, how do you actually wire everything up? Do these have to be mounted on some sort of circuit board? Or can I simply solder them (inductors, resistors, etc) in-line with the wiring?

[Marzen]

...If I don't do this one, then I am going to have to change the original design. I was thinking 2 three inch 4ohm woofers, a midrange, and a tweeter with an out of the box three-way crossover.

JJ, I think you'd be hard pressed to beat this 2.5 way with a 3 way using a stock crossover.

Question on the Cynosure... Do I really need four ports, or could I get away with two on the front? And since the box will be considerable wider, is 1/2" MDF board with some bracing going to be adaquate?

I would stick with 4. They're only 4" long which meets your required box depth w/o restricting the ports inside opening. As Joe mentioned, going with a pair of 1-3/4" ports will require a longer tube length; stepping up to 3-1/2" ports might be a problem when you consider the flared section on the outside might be to large a diameter to fit your front baffle height.
With a PPWWWTWWWPP front baffle layout; you're at around 29" wide for just the drivers & ports.
I don't think you'd have any significant issues with 1/2" stock. I've used it for test enclosures for dual 8" drivers.
-Ward

[jjminch]

Marzen, thanks for the help. I think we'll stick with this route then since the crossover guesswork is already done. How to you wire these capacitors and whatnot? Can I simply solder them inline with the speaker wiring as shown in the diagram?

Also check out this advice I received on the parts express board

I agree with Johnny about not needing an extra mid. I can't even quite picture how it could work without either looking really ugly while screwing up the lateral dispersion or popping over 5" high.

If I were doing anything along the lines of what you're talking about, I'd use four of the Tang Band drivers and one tweeter. I've recently had good experience with Audax's 1" domes (both the textile and titanium domes) which are quite small and would look quite nice set between any of Tang Band's 3-inchers while also allowing super-close spacing. I'd have the tweeter crossed over as low as possible, with only the middle two Tang Band drivers reaching up to the tweeter's X-over. The two that are farther to the sides would come in to help at a lower frequency, say 400 Hz, so all four drivers would operate from there on down. This would basically be a 2.5-way x-over, you won't get any deep bass at all and I would strongly encourage that your HT setup never sends lower bass frequencies to this CC, ESPECIALLY if you go ported. But you'd get a super small enclosure with very little comb-filtering, which would make for a slick little design.

If you really want this thing to be able to make bass, you could make it a true 3-way by using only two 3-inchers flanked by a couple of more capable 4"s, or better yet, four 4"s with only 2 3"s, basically a WWMTMWW setup. With four 4"ers you can more safely use a ported enclosure AND wire them in as an 8-ohm load in the bass frequencies where it's most important. I like to go ported when I can, not just for more bass extension but I also feel it has lower harmonic distortion. Sealed enclosures are no-brainers to tune though, and are better protected against accidental deep bass pulses. If you're attracted to Tang Band you can look at their 4" "subwoofers".

The 3"ers should share a chamber separate from the 4s. Wire the 3s in parallel and stick a 2-ohm damping resistor in series with them to create a 6-ohm load within their operating range. This will help even the impedance somwhat as well as the frequency response. The tweeter is a self-contained enclosure so you don't need to worry about it.


I like the concept of having four of the drivers be 4", since we have the room. Then the middle two would be 3". I assume I can use the same crossover specs as the original design. Do you think it would sound better than the original design?

Thanks again
Josh

[Marzen]

Josh,
Yes, you're correct about wiring the crossover in line per the diagram. Here's a xo for the RS180 MT that has some close up photos on page 1 for an idea of how it's done.
However, if you change any of the drivers from the published design you have a completely different speaker. Well, at least in regard to some of these factors:
Power handling
Impedance rating
Sensitivity
On & off axis frequency response
Crossover frequency
Box volume
Port tuning (length)
You could always go that route using some freeware like Speaker Workshop and a microphone/preamp. I don't know what kind of time frame your looking at for completing this project 'tho.
-Ward

[jjminch]

Thanks for the link, it really doesn't seem that hard to do.

It makes sense how I would have to redesign everything. I just didn't think going to a slightly larger driver would completely change everything. I suppose it's better to just keep things simple, and go with an idea that works.
Thanks again

[Marzen]

True, but you could build another from scratch, or some mains for yourself. I suppose like most things - it's as difficult & complicated as you wanna make it. Lemme know how it turns out; I have a friend with similar space constraints, only he has a window above his tv.
-Ward