For those of you who may be into or considering DIY speaker projects, one of the newer tweeters that's been getting a lot of notice is the Vifa XT25 in it's various configurations. Manufacturers as diverse as Krell and Polk Audio are using it in new products.
I've had some reservations about this speaker because the published response curves seem to show a glitch in the impedance and response curve in the 1.5 kHz region, possibly due to decoupling between the outer "concentric ring radiator" and the center radiator. (It is an, uh, unusual looking tweeter....)
MarkK sent me a pair to look at in a measurement round robin, while he's waiting for his CLIO WIN to come in. Naturally, this is when my mic preamp decided to get uppity on me. With some effort I worked around the problems, but wasn't able to do absolute SPL measurements, just relative dBV. However, they're still interesting and useful.
On my standard 2' X 4' test baffle with offset mounting to spread the diffraction effects, it's clear the XT25 has a smooth extended low end, as tweeters go, even just listening to the MLS test signal.
The directly on axis response isn't super smooth, and it shows a typical slight shelving below 3 KHz- which is often desired in speakers, to create the "audiophile dip". I'm fairly certain the slight dip in the 7-8 kHz region is partly my test baffle.
The 30 degrees off axis response looks quite interesting -
As might be expected, the response above 12 kHz is rolling off somewhat. However, the overall response is quite smooth and flat up till then, again with a very slight shelf below 3 kHz.
The impedance curve of the samples I measured showed no untoward behavior, revealing a very low Fs for a tweeter (600Hz), and a benign curve free of any glitches indicative of mechanical decoupling or breakup.
The impedance curve shows an undamped (no ferro fluid) primary resonance at 600 Hz. With most crossover configurations, you'll want to use an LCR zobel to tame the impedance rise, and prevent interaction with the crossover network which could cause a bump in the response at resonance, as well as added distortion from the driver.
You might notice this is a 4 ohm tweeter; it's optimized to be a little more efficient for a nominal voltage drive by cutting the voice coil impedance, not by using a larger magnet. This keeps costs down; on the other hand, at typically $60 each for the DIY market, I think Vifa or someone is making money hand over fist on this well designed driver. Build quality is *not* in the Focal TC90 or TC120 category.
But nevertheless, it's an excellent performing design, with wide, smooth frequency response, one you may definitely want to consider for your next project. It would be a natural (with an Fs zobel) for a series crossover in a minimonitor, as it would be easy to integrate with midwoofers. It also looks like a very good candidate to be used quite successfully with a relatively low frequency high order crossover, such as in my M8 two way system.
Hmmmm. Looks like I have work to do in the lab. See you guys and gals later.....
Regards,
Jon
Earth First!
_______________________________
We'll screw up the other planets later....
I've had some reservations about this speaker because the published response curves seem to show a glitch in the impedance and response curve in the 1.5 kHz region, possibly due to decoupling between the outer "concentric ring radiator" and the center radiator. (It is an, uh, unusual looking tweeter....)
MarkK sent me a pair to look at in a measurement round robin, while he's waiting for his CLIO WIN to come in. Naturally, this is when my mic preamp decided to get uppity on me. With some effort I worked around the problems, but wasn't able to do absolute SPL measurements, just relative dBV. However, they're still interesting and useful.
On my standard 2' X 4' test baffle with offset mounting to spread the diffraction effects, it's clear the XT25 has a smooth extended low end, as tweeters go, even just listening to the MLS test signal.
The directly on axis response isn't super smooth, and it shows a typical slight shelving below 3 KHz- which is often desired in speakers, to create the "audiophile dip". I'm fairly certain the slight dip in the 7-8 kHz region is partly my test baffle.
The 30 degrees off axis response looks quite interesting -
As might be expected, the response above 12 kHz is rolling off somewhat. However, the overall response is quite smooth and flat up till then, again with a very slight shelf below 3 kHz.
The impedance curve of the samples I measured showed no untoward behavior, revealing a very low Fs for a tweeter (600Hz), and a benign curve free of any glitches indicative of mechanical decoupling or breakup.
The impedance curve shows an undamped (no ferro fluid) primary resonance at 600 Hz. With most crossover configurations, you'll want to use an LCR zobel to tame the impedance rise, and prevent interaction with the crossover network which could cause a bump in the response at resonance, as well as added distortion from the driver.
You might notice this is a 4 ohm tweeter; it's optimized to be a little more efficient for a nominal voltage drive by cutting the voice coil impedance, not by using a larger magnet. This keeps costs down; on the other hand, at typically $60 each for the DIY market, I think Vifa or someone is making money hand over fist on this well designed driver. Build quality is *not* in the Focal TC90 or TC120 category.
But nevertheless, it's an excellent performing design, with wide, smooth frequency response, one you may definitely want to consider for your next project. It would be a natural (with an Fs zobel) for a series crossover in a minimonitor, as it would be easy to integrate with midwoofers. It also looks like a very good candidate to be used quite successfully with a relatively low frequency high order crossover, such as in my M8 two way system.
Hmmmm. Looks like I have work to do in the lab. See you guys and gals later.....
Regards,
Jon
Earth First!
_______________________________
We'll screw up the other planets later....
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