Need Help: Crossover for Vifa 2-way

[jtsaudio]

Hi.

I have the following two speakers that I would like to use with a simple crossover (1st order?):

Vifa PL18WO09-04
PL18WO09-04 PL 6½″ Woofer Vifa Datasheet

Vifa XT25TG30-04
http://www.parts-express.com/pdf/264-1016s.pdf

Anyone used these together, or can recommend a crossover?

Thanks in advance -Joe

[SGregory]

Do you have any measuring equipment? I will let the experts really chime in, but my recent experience with building a first order isn't "simple"
From what I see in the woofer specs, the top the woofer curve natural roll off -3dB is around 5kHz. Particularly off axis. The tweeter at least looks like it goes low. Again from experience it may not play well there in real life.
Easiest solution is something like 3rd or even 4th order. (In this way you only have to deal with the rising impedance of the woofer and can avoid the resonant peak of the tweeter.

The other thing not noted in the spec sheet is the power handling of the tweeter. First orders crossovers, will eat them alive since they will be playing down into frequencies that is below their resonance. Be Warned.

From my recent build using first orders (Why.. because I like them), I would start with flattening out the impedance of the speakers.

For the woofer start with a CR circuit using C= 30uF and R = 4.25ohm. This goes in parallel with the woofer.

For the tweeter you should install a series notch filter LCR. With this you will have to guess a little but I would try L=1.0mH C=50uF and R= 5ohm.

At this point you should test and see the impedance plot. Regardless, this is a starting point to play with different crossovers using theoretical values. Again higher order will be easier even though it has more components. If you use a LR4 you may be able to eliminate the tweeter series notch filter.

Again based on recent experience, first order will take measurements to get it right and even then it may or may not be to your liking. I still have kinks in mine that need to be worked out, possibly by higher order crossovers.

With the impedances "close" to flat from above, there are several great resources on the web to play "what if" on the crossover design and give you approximate values for the components of different crossovers. Maybe someone else would chime in that has those links handy. At this point you need to decide were you want to go. Use cheap components first and when it is what you like, upgrade them. The soldering iron is your best friend in learning.

[Michael Chua]

The Vifa PL18 is a nice midwoofer. I have one in a 2-way. Not first order though. You can check it out here.

[twest820]

Sallen-Key Linkwitz-Riley is pretty simple, pretty cheap too if you buy a pro audio crossover. So is filter realization in Frequency Allocator. Active's probably not what you had in mind though. But, since you asked, my default crossover for two ways with typical drivers is LR4 at 2kHz.

All first order lowpass does is counter music's 1/f rolloff. SPL will roll off second order but excursion remains full range. Take a look at Zaph's XT25 distortion measurements, F2 in particular, and think about whether you really want to run the tweeter first order.

[Andy G]

A while ago, Ken Perkins used this series x-o (second order) on that combination



I never used that exact combination, but Ken knew his stuff, so I would assume it to be a nice speaker.

IIRC the PL18 was vented in a smallish volume around 15L.. but a vague memory at best.

ps.. use as low a dcr for the small coil as you can. say 15awg air.

[jtsaudio]

The Vifa PL18 is a nice midwoofer. I have one in a 2-way.

Mine is the PL18WO09-04- didn't you use the 8ohm driver??

Ken Perkins used this series x-o (second order) on that combination

Didn't Perkins also use the 8ohm version?

I'd like to stick with a simple parrallel crossover circuit on these (both) 4 ohm drivers.

[jtsaudio]

BTW, I have no measuring equptment, other than a cheap VOM.

How can the 8ohm crossovers mentioned be adapted for 4 ohm woofer?

Any help with 4 ohm 2-way crossovers is appreciated.

Do you have any measuring equipment?

[martinbls]

Hi Joe!

Perhaps I can help out with a few thoughts about this project, because I used the Vifa XT25 tweeter in some projects myself, and I played around with it for quite a while.

I can tell you, the Vifa XT25 with a simple 1st order x-over is either a no-go, or you have to search for a suitable midwoofer, which is a difficult task.
The problem with the XT25 is the fact that this beast wouldn't stop singing in the lower frequency range. What is a bit misleading is the resolution and size of the original frequency response graph from Vifa, which looks like this:

[martinbls]

Perhaps you get a better impression of the "real" behaviour with this image:

[martinbls]

There you can see that this tweeter has a nearly ruler flat response from something about 600Hz upwards! This is really not to handle with a 1st order filter. Most midwoofers tend to play up to something like, say, 3kH, and then they went to lower levels with 12dB or even 18dB by themself! So, you always end up with either a gap or a peak in the range of the x-over frequency. That's what I experienced, and there was no way. And I tried out quite a number of different woofers!

But, since it's not that difficult, just try it and find out if you are lucky. I never had the chance to try out the woofer you have, so perhaps this would be a match. But I wouldn't count on that...

Now, on to the impedance thing. If you wnat to give a 1st order a shot, you really have to look at the impedance courve of the XT25. Since this tweeter doesn't have ferrofluid, the impedance peak is rather highish and this really is audible! You will always have some kind of missbehaviour and distortion with nothing else than one single cap as x-over.
I made a few measurement myself (with a program called Arta Speaker Development) for the XT25, and then I tried some different values to achieve a proper designed LCR-filter.

This is the measured impedance courve of the XT25 without a LCR-filter: