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mberrync 30th November 2012 03:44 PM

Stereo-Lab cf400/cf250 Tactrix or Jabo KH-55 Exponential Horn for Radian 950PB
I have Radian 950PBs crossed at 475hz 24db slope in a Goldwood flat front bi-radial horns similar to P-Audio PH-4525 and JBL 2380A horns. These horns are in the center with two 15" Hawthorne Mid-woofers and Low-woofers in D'Appolito arrangement above and below. 950PBs are driven with Wright 3.5 monoblocks modified for .82 watt 45 tubes. Crossover is Marchand XM126 3 way with RCA 12AX7 black plate tubes on pre, high, and mid frequency boards.

I am looking first for others experience with the performance differences between flat front bi-radial horns and circular tractrix or exponential horns. The bi-radial horn closes down slightly before it opens up. I am curious what this does to help or hurt the sound and what the harder edge at the flat front does versus the gentle rounded fronts on the circular horns.

And secondly would like to hear experience and recommendations between the Stereo-Lab spherical/tractrix horns and the Jabo KH-55 modified exponential horn.

And finally recommendations on going with a horn useable frequency(as opposed to cutoff) down right to 475hz (Stereo-Lab cf400)or down lower to 350 (Stereo-Lab cf250 or Jabo KH-55). Does lower useable frequency help integration but maybe hurt high frequencies?

I have decided against expense and complications of going with additional higher frequency driver in 4 way set up.

I aplogize for the many questions and greatly appreciate any insight you can give.


Corvus corax 2nd December 2012 02:46 AM

I own the Stereo Lab 250, and the Jabo KH-55 horns, and have a pair of the Stereo Lab 400 horns on hand- I use them all with both the JBL 2450 and the TAD 4002 drivers, equipped with Radian diaphragms. The sound of the Jabo horns is quite a bit different than the Stereo labs, they are all articulate, but the Stereo labs seem to be more accurate overall. The Jabos have an enjoyable sound, but they should definitely be damped on the backside of the horn, because they do ring a bit- the sound is somewhat reminiscent of the Avantgarde horns- there is an immediate quality about them, but they have a definite color.

The Stereo Lab horns remain my choice- the build quality is superior, and there are virtually no bell resonances- the same cannot be said of the Jabos. The Jabos are a bargain if you get them at a good price, but having used them a while, I can say I'm not a fan of gelcoat/ styrene/ fiberglass horns, and will not be building any of my own in such a manner. The backside of the Jabos is unfinished, and the mat glass slivers are absolutely brutal. One of them also has developed a slight twist, meaning the mouth is no longer flat, and there are the usual issues with gelcoat- like the faint, but still horrid smell, that has thankfully faded with time…

The Stereo Lab horns cost more, and they look it. They are fully presentable as is, but with a coat of Line-X, so will be the Jabos. Of course, that will make up a good deal of the cost difference. I think my end choice would be the Jabo flare, rendered in the Stereo Lab's material, or even better yet- a good solid wood like the Zingali Omniray horn… At least the Jabos and StereoLabs were affordable enough I could go with both! It was an investment of sorts- I'm planning on spinning some horns of my own in the future, and I needed some accepted reference points to work with.

I have a pair of Avantgarde Duo HF horns in hand as well, but they are set up for a little driver I do not have as of yet, and they wont reach down to my midbass anyways.

I guess I would recommend the Stereo Lab 250 horns. Yes, they beam pretty strongly in the top end, as do all large midrange horns, but for my listening, it works out just fine. My 10 uF Jupiter caps will be here next week, so I can retire the old sprague bathtub paper in oil caps, and hopefully gain a bit more sparkle and coherency in the top end. Its great now, but we always want better…

mberrync 3rd December 2012 12:59 AM

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Thank you for the very helpful reply. With a crossover at 475hz would the cf250 Stereo lab horn be better at blending with the mid-woofers than the cf400 horn?

I have never heard circular horns. How will they sound compared to the 17" x 11" flat front 90 x 40 bi-radial 400hz cutoff horns I currently have shown in the pic below? The bi-radial horns have very little curvature and start out closed in before they open up to the curve.

When you write that the Jabo horns have an immediate quality do you mean that their sound more live, closer, or in the room? Do the Srereo lab horns shre this quality but just not as much?

I recently compared unshielded Volex power cords with Huffman shielded ones. Initially the Volex seemed to have more life but ultimately I decided that this came from "stuff" that should not have been there. Is this a workable analogy for comparing the sound of the two horns?


Corvus corax 4th December 2012 11:03 AM

The horns you currently are using are designed for coverage of a relatively wide listening area compared to round horns. The Jabos, because they are a relatively shallow horn, have a fairly "soft" sweet spot, which makes them a little easier to listen to both on and off axis. The Stereolab horns, because of their depth, have a more pronounced high frequency rise when listened to on axis, which means they need to be aligned carefully with the listening position for good tonal balance. The Jabos are still fun to listen to, because they are so shallow, you have the sense that the compression driver is speaking more directly to the listener. They are nearly as short as the Zingali Ominiray, which I liked for its low coloration back when I heard the HM15 system.

Ultimately I found BOTH horns to be good enough to keep, but I wish I could have the Jabos in something a little less plastic sounding. I wish Stereolab could make a pair in their cast material, they would behave a bit more. I'm going to fill the back of them with Line-X or similar coating, and paint the inside surfaces with a standard automotive base/ clear, because I want the tangerine pearl that Avantgarde offers on their horns. I'll have two horn systems then- one based on the Jabo and the JBL 2450 with maybe a Beryllium diaphragm, and one built around the Stereo lab horn, with horn loaded everything else.

Good rule of thumb on horns is to cross over at twice the Fh, so the 250Hz horns are going to be about right at 500hz. In my experience, you wont want to go much lower than 600Hz with that driver if you are using first order crossovers, which I would recommend based upon my experience so far. Buy the best caps you can get your hands on, and try running the driver with a current source (high source impedance). The capacitors make all the difference in the world, here. I tried a fairly large number before finding some I liked, and I was surprised how bad many of my previous favorites sounded. In the end, I settled on 8x 1uF of Sprague "bathtub" style oil filled paper capacitors, though I have some Jupiter wax caps on the way to try as well. The resistors used in the network are also immensely important, perhaps even more so than the caps. For me, there is only ONE choice here: The Duelunds. I tried pretty much EVERY other resistor out there, and the Duelund standard carbon/ silver were hands down the best. My advice would be to use regular cheap parts to get your ballpark values, and order the Duelunds once you have the values sussed out. I haven't tried the CAST parts, though I might in the future- the regulars were expensive enough…

mberrync 4th December 2012 05:11 PM

Thank you once again for the reply and help. My typical listening position is basically in 12 foot equilateral triangle. The slight complication is that I have a desk where I often sit which places my head about 3 feet farther back. Currently the speakers and horns are aimed directly at this second position and this slightly off axis from the first. There is a little wider soundstage at the first spot. Would the 3 foot difference be enough to lean to the Jabo horns?

I was looking for damping options and saw "Silent Runnings SR-500" ($100/gal) anti-vibration for boats and eDead V3 ($40/gal) sound deadening for cars. SR-500 is light gray and eDead is black. Good comments on both. I don't know if these would be better than truck liner.

I have changed out the coupling caps in the Wright 3.5, Quicksilver Mid-Monos, and Marchand XM126 pre, high, and mid filters to V-Cap CUTF caps. The values were mostly .33 and .22uF so expensive but not terribly so. Also changed power supply caps in Wright 3.5 to ASC motor run type. Using 24db slopes in crossover. I am okay at changing out parts but not that technologically savy. When changing resistors I have used Audio Note Shinkoh tantalum based mostly on reviews.

Corvus corax 4th December 2012 06:38 PM

I forgot you are using electronic crossovers. You will want to try a 20 Ohm series resistor between your amplifier and the Radian- it makes a world of difference with the TAD.

mberrync 4th December 2012 08:04 PM

I saw a chart of a TD-4001 with a dip with a bottom centered about 1.5K. The Radian 950PB has a less pronounced dip at least on the factory chart with a bottom at the same 1.5K point. What does the 20 ohm resistor do? Lessen the sound thereafter? Would a different value be used for 1.5K versus 2K?

Corvus corax 5th December 2012 06:32 AM

There is a response anomaly in the TAD that is helped along a bit by the series resistor, but I can't for the life of me remember why it is… I know using an approximated current source to drive compression drivers is said to reduce flux modulation, but I would think that would be occurring well above the power levels we are experiencing in home systems. However, for those of us running passive crossovers, the large series resistance has the side benefit of reducing the size of the required capacitor(s) in our networks.

Having used the drivers (JBL and TAD) with and without the series resistor, I can definitely say they both benefitted from the presence of the series buildout. The presentation had little to none of the "honk" that so typified every horn system I had experience with up to that point. AS soon as I removed the resistor, and ran direct, the nasality began creeping in, sometimes dramatically so. For whatever reason, it just seems to work…

One day, I'm going to get a pair of the Radians to play with, and see how they stack up against the TADs. If my experience so far is any indicator, they will probably sound very similar- I was amazed how similar the JBL drivers were to the TADs. The top end wasn't quite as crisp, but I wasn't missing out on a whole lot either.

My advice on the series resistor is to try a few different values and see what they do. 20 Ohms was what someone recommended for the TAD a while back, and I've simply stuck with it so far. It seems to work well on every driver I've used it on, but that doesn't mean there isn't another that would work just as well.

leifchristensen 5th December 2012 09:06 AM

having just sold my AG Trioīs and going for TAD4001 in JMLC270 nextel from Autotech Poland, I donīt understand why their very well made horns arenīt mentioned here?
of all the horns Iīve tested, the Trio midhorn was the second best for 4001
JMLC full rollbacks are even smoother and without the colorations
extremely well built and superbly finished as well

ARIYAHOOR 5th December 2012 06:53 PM

a couple months ago I had a chance to here a 250hz fc stereo-lab horn DIY speaker in Turkey, and Wow! almost blow me away. the sound was some sort like Avantgarde Trio. the CD was Selenium. Radian instead of Selenium is like jumping form a KIA into a Lamborghini so the sound should be far more accurate let's don't forget 950PB is the CD used in La Grande Castine

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