Series X-O help on centre channel

[Alex_B]

Hi guys and gals,

i've designed my prelim x-overs for my surrounds front and rear for my ht project.

But wondering what do i change in my design to change from one woofer+tweeter to Woofer+Tweeter+Woofer configuration.

i've used Andy Graddon's Series x-o spreadsheet to get so far with some help from him, here's my diagram for the surrounds:

.::C17's are 6.5" Woofers, D26 are 1" tweeters::.

[Alex_B]

can i just add another woofer off the same terminals for the first? i guess i need to change some components? some help please guys,

Alex

[kelticwizard]

Crossovers work off impedances. The impedance of the crossover, at certain frequencies, directs some frequencies to the woofer and the other frequencies to the tweeter, respectively.

For it to work properly, the impedances of the woofer, tweeter and crossover must work together.

When you take your Vifa 8 ohm woofer and connect a second Vifa 8 ohm woofer in parallel with it, you have made your woofer a 4 ohm unit. Therefore, the crossover will not work the same as it did for the 8 ohm woofer.

If you want to hook the second Vifa crossover in parallel, or even in series, with the first, you have to redesign the crossover for a 4 ohm woofer or a 16 ohm woofer.

If you use a spreadsheet, Re and Le should be divided in half if the second woofer is hooked up in parallel. Re and Le should be doubled if you hook them up in series.

[kelticwizard]

PS: This is the second series crossover for a center channel speaker that I have seen lately. Series crossovers tend to be fairly rare, not that there is anything wrong with them. Yet I am beginning to run into them used on the center channel only. Is this some kind of trend? If so, why the center channel and not the satellites?

[Alex_B]

Well myself, i'm using series X-O for the entire system!

thanks for explaination, so if i want the centre to siund extremely like my surrounds i should definatly deouble the Le and Re, correct? the thing is i'm not using that part of the spreadsheet, as andy instructred me to do so, for a simple x-o, i'll have a little adjusting with it and post my diagram,

merry xmas

Alex

[Alex_B]

hey, could i double the ohms to 16? i think it would do the job fine as it changes a few of the components,

Alex

[Alex_B]

well it look like it worked good, see below:

i just adjusted the ohms to 16 which in turn changed most of the other components.

[kelticwizard]

Well, I am not an expert on series crossovers, but if it worked for the single Vifa C17, a few changes of components will work for the two.

If you are hooking them up in series, then indeed it is 16 ohms.

I don't know that particular spreadsheet, but if it has a space for Le, (speaker inductance), generally given in mH, then double that too. And if it for some reason has a space for Sd (area of the cone), then double that as well.

Otherwise there is no reason not to simply change the components, unless your spreadsheet has a space for center-to-center spacing. I don't think too many do.

[Jimmy154]

I'm not an expert at x-overs by any means, but I think if you add another woofer AND x-over for the woofer like you have with your other woofer you'll be fine.

I know with a parellel filter logically, I think, it is like this. If you have 2 - 8 ohm woofers wired in parellel you get 4 ohms of course. So you design your filter for 4 ohms. But you can also go this way: 2 - 8 ohm woofers then 2 filters designed for 8 ohms and then wire the filters together to get 4 ohms and then to amp. Not sure if this applies to series wiring, though.

But in series the impedance works out perfect, if it works for series. Because you get a theoretical 3 db boost from the doubling of drivers or SD and a 3 db subtraction from the doubling of impedance (16 ohms) or halfing of power. Like I said I don't know if it works with series x-over, cause I don't know if the components for each driver work independently of the components for other drivers, like in a parellel x-over. Planet10 mentioned it in some post resently, but I forget if you change one component if it changes the way the filter works just for one driver or for all of them. It might still work even if this is the case. I use this link way too much, and I always say I use it way too much, but here it is anyway http://home.hetnet.nl/~geenius/ the guy at that link would know he's helped me before. He's a series x-over god or something.

[Andy G]

sorry aboutr not getting back to you on all your emails, I've been flat chat on a few other projects.

basically, if you run the C17's in parallel as shown, you will halve the coil value needed, you may need to adjust the resistor padding on the tweeter a bit. (I would avoid running them in series unless your amp has real problems with a 4 ohm load)

On the spreadsheet, enter the woofer resistance as 4 ohms, and up the sensitivity by 2 or 3 dB.

Hope that helps. !!