opinions on the new VIFA dual conc. tweeter XT25

Hi!

The local vifa dealer in my town sells a "kit" including the XT25 and rest of the parts for a nice 2-way speaker. My dad bourght it and are in the process of building the cabinets. For what I can tell the crossover network suggested is quite complicated. It's a -24 dB containing three coils, two 68uF caps plus some more. I was by the store today asking for a datasheet on some other drivers and mentioned the XT25 crossover. He told me the complex network is "necessary to get it going"...

Later this week i will upgrade my own speakers (D27tg tweeter) with the XT25 and will be able to tell more at that time.

Btw. they cost 400 Dkr. (47US$) a piece.
 
Yea I've had a pair for several months now...

They are quite good on detail but they have a nasty resonate peak and are difficult to integrate with the mid’s, the low FS of 500hz suggests that it will work well in a MTM which I am using along with a pair of SS 8530-K00 Mid woofers and a Marchand Active 24db L-R crossover. Right now (actually tonight) I'm adding a conjugate network to the XT per the suggestion of Peter at Acoustic Reality (he has a lot of experience with this tweeter) to remove the resonate peak, a simple .1mh in parallel and a 4 to 8 ohm 20W resistor in series in conjunction with the active network should help according to Peter. I'll post my listening evaluation later this week if anyone’s interested, also I'll try posting pictures of my SST8 DIY MTM's that use these drivers, quite a unconventional design that some might be interested in being a dual tapered octagon with separate tilting mid enclosures and a telescoping tweeter mount for time alignment.
 
Hi!

A while ago I promised to post some more information. I didn't upgrade my speakers as I said, but decided to build new ones. -This explains the extra time.

The design is my own MTM config (had an eye on the VSS eros, though). I also did measurements with JustMLS for designing the crossover. There has been some consern about measurements provided by the factory, but I'm glad to tell I got 'the same'. The resonanse peak realy is at 500hz. 3.3ohm, 0.68mH, 140uF in parallel should take care of this.

I'll post the data I got from JustMLS below:
 

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Brett

Member
2002-01-07 6:02 pm
<b>And the new Scanspeak...this is seriously expensive, I'm heard around $US1000 each!</b>

Are you serious? For a glorified dome tweeter?
Wow, some cables are beginning to look like bargains.

<img src=http://www.d-s-t.com/scs/data/foto_r2904_700000.jpg>

Looks like on of Madonna's old designers had something to do with it.
 

Bryan G

Member
2002-05-31 9:20 pm
These things are great. I just put to gether a pair of speakers that use the xt25, and what a nice sound. I'm not done tweaking it, but they already sound great. If you are thinking about useing one I would go for it.


I have some pictures here

http://members12.clubphoto.com/bryan583504/769972/owner-3059.phtml


I haven't finished them yet. I am thinking about an ash with maybe a wild dark green stain and a marble top..... hehe :)


-Bryan
 
XT-25 an interesting part, using it in two new designs

I've worked with a variety of metal and ceramic tweeters in some two and three way designs, and recently did some evaluations of the XT25. It's a pretty nice piece, and I'm trying it in two new designs- the test box for one is playing right now, with "Frateres" composed by Arvo Part, on Telearc.


[IMGDEAD]http://server2045.virtualave.net/ttriff/XT25.jpg[/IMGDEAD]


From measurements, I think it would be most accurate to characterize it as a three ohm tweeter. If you choose to use zobels to achieve a flat impedance curve (which I recommend in most cases to assure the expected crossover behavior, and the ability to scale output level with a pad without changing the contour of the filter), you'll find that to be the maximum impedance you can achieve a flat impedance plot.

The raw impedance curve shows an undamped resonance at about 600 Hz. No ferrofluid in this tweeter....


[IMGDEAD]http://server2045.virtualave.net/ttriff/XT25_Z.jpg[/IMGDEAD]


I tested it initially on a two foot by four foot baffle, with asymmetrical mounting, to distribute the affects of baffle diffraction, which can particularly show up in the lower end of the tweeter pass band. Though I agree the on axis response is important, I think the performance at 15 degrees and 30 degrees off axis is much more important, as this correlates much more strongly with the total power response into the room. Both the power response and the axial response are important to the subjective balance, especially the former if you aren't listening in the on axis "sweet spot"- which is most of the time for non-critial listening.

Here's the performance at 30 degrees off axis, with the expected HF roll off above 15 kHz, but overall with exemplary behavior.

[IMGDEAD]http://server2045.virtualave.net/ttriff/MLS1-30.jpg[/IMGDEAD]

Note that there was no smoothing done with this curve, and with the small test room, there are some early reflections present.


It appears that the raw response of the tweeter even has a slight "BBC dip" built in between 1 kHz and 3 kHz, so making a pleasing sounding crossover will be fairly easy.

Measurements show that it is subject to even order distortion when driven hard in the lower frequency ranges; I'd suggest either a crossover around 3 kHz or higher with conventional topologies, or using a high order crossover if one wants to take some advantage of the nice repsonse below 3 kHz.

In the current test system, it's crossed over with a network which produces an an acoustical 8th order L-R response down to -50 dB; crossover frequency is 1.25 kHz. It's being used with a metal cone woofer, which has a complementary high slope crossover, modified slightly from 8th order L-R to account for the phase shift from the difference in acoustic centers.

For the money, I think it's a exceptionally good driver, and certainly one to be evaluated in it's price range. ;)

Regards,

Jon