A time-aligned top end for the Khorn

[Al Klappenberger]

I have always maintained that there is no good reason to go to a 2-inch horn to replace the K400 in the Khorn. A 1-inch horn is by far the best bang for the buck. 2-inch horns are for movie theaters but there is some advantages to upgrading the K55 driver. The problem with that is there is simply no 1-inch driver in current production that will operate cleanly down to 400 Hz where the Khorn must be crossed over. Evan the 1-inch JBL 2426h will start making distortion at 450 Hz let alone down at the 400 Hz required by the upper limit of the Khorn woofer. It was designed to be crossed over at 800 Hz but JBL says that it will operate down to 500 at reduced power. That's fine for the Belle or LaScala, but not the Khorn. Only a 2-inch driver will go down to 400 Hz. If you are ready to make the leap to a 2-inch horn and driver you might as well go a step further and make it really worth doing. B&C Speakers makes a coaxial version of their DCm50 driver, which is exactly what the doctor ordered for the Khorn squawker, a design specifically for a 400 Hz crossover. It's the DCx50. It uses the same midrange "guts" as the DCm50 but has a tweeter built right into the throat that extends the frequency range to 16 KHz. That's the same upper limit as the K77 tweeter that most of us have been listening to for years. A response that extends above that is nice but chances are only your dog is going to appreciate it! The big plus with a coaxial is that it's as close as you can get to having the midrange and tweeter occupy the same place at the same time. That means the propagation time from both drivers to you ears is virtually equal! That's TIME ALIGNMENT!

Time aligned drivers let you use a far less aggressive crossover than the extreme-slope networks needed to eliminate the driver interference caused by two sources of sound located in two different places. The interference between drivers is significantly reduced. Another advantage here is that the DCx50 requires a crossover at 9 KHz rather than the 6 KHz required by the K55. This adds up to a far less aggressive network with fewer parts of smaller size. It will cost less than an extreme-slope network. Another advantage of the time alignment is the opportunity to use a phase-coherent type of network called a 4Th order Linkwitz-Riley. This type of network is usually only appropriate for sub-woofers as active filters where the wavelength is extremely long.

Dave Harris (Gethover) and I have worked together to develop a 2-inch horn of comparable quality to the Martinelli Trachorn 420 that is no longer available. Dave calls it the Fastrac K2. I have posted a paste-up of pictures of the Fastrac K2 side-by-side with the Martinelli Trachorn 420. The two are identical in all the important ways. The one with the nicer paint job and all the screws down the edges is Dave's Fastrac K2.

I have used the K2 horn to take frequency response and impedance measurements on the B&C DCx50 to develop the 4th order Linkwitz-Riley network at 9 KHz specifically for this driver. The new network will be designated the LR24-9000. The design is complete and the parts are on order to build the prototype. Until the parts come in, I'll share the measurements.

[Al Klappenberger]

The impedance of the new network will be determined by the lowest impedance of the two drivers. In this case, that turned out to be the tweeter. At 9 KHz, the resistive part of the complex impedance is 5.8 Ohms. That is in series with about 0.03 mHy of voice coil inductance. I normally don't use a Zobel on tweeters, but since 4-5 dB of attenuation will be needed and the netwrok will be dedicated to a single driver, a transformer attenuator modified for 6 Ohms will be part of the network. The Zobel can be built right on the network as well. The values for the Zobel turned out to be 6.8 Ohms in series with a 0.68 uF capacitor. That transforms the load to a nice 6 Ohms resistive impedance for the attenuator and network tweeter channel.

[Al Klappenberger]

The impedance of the DCx50 midrange is close enough to 11 Ohm resistive that a simple 12 Ohm swamping resistor will transform it to the needed 6 Ohms for the network.

[Al Klappenberger]

The frequency response. The mid-range response is nice and flat. The tweeter is not quite as nice, but still flat enough though. It's about 4-5 dB hotter than the mid-range.

The sensitivity of the mid-range is about 110 dB SPL at 1 meter. That level will be cut down to the 99 to 100 dB of the Khorn by the woofer to squawker network. The the AP12-350 or ES400 strapped for 2-way operation will do that easily.

[Al Klappenberger]

Here's the B&C dcx50 driver. Notice the tweeter mounted right in the middle of the throat.

Until the parts get here to build the prototype network there isn't much I can add. It will probably take about 2 weeks to get everything together. Stay tuned!

Al K.

[jwc]

Wow. So you will be selling the Fastrac K2 as a two way setup with a coaxial driver? I sure didn't see that coming.

I'm curious to what the top end does when you move the mic off-axis.

jc

[dkalsi]

Al,

I think this is an excellent idea. To date, the best system I have ever heard (by a long shot), is the Oris Horn Orphean system by BD Design

I beleive the 2" co-ax driver mated to the Khorn bassbin - would be equaly good - but even if it isn't, I'm hoping it would be 90% there at less than half the cost of the Orphean system.

Listening to the Orphean system was the number #1 reason why I gave up my Khorns (which I tried with all upgrades including V-trac+2"BMS driver, etc. etc.). But despite all the upgrades - my system was nowhere near as good as the Oris. Granted they are very expensive - but the performance was there.

That is percisely why I am looking forward to your next project. I wish you best of luck.

[Al Klappenberger]

JC,

I will be doing at least one set of the LR24-9000 networks. How many I make depends on the amount of interest there is in it! The horn will be Dave's product. The one I am using for testing is simply a loaner. If there is any interest in the combination, I might offer it as a package deal along with the DCX50 driver.

Dkalsi,

I had never heard of the Oris speaker. I suppose I'll have to look for it.

...........

Update: I take it back.. I have seen the Oris. They use the large round Tractrix horns in the midrange. That is had to beat. You got to like that look though! There might be a WAF issue to those to consdier!

Al K.

[Al Klappenberger]

Jc,

Here are tweeter plots off-axis horizontally by roughly 30 Deg and 45 Deg. I'm surprised. The off axis plots are flatter than on axis!

Al K.

[Guest " "]

So Al, we talking 2 smaller horns next to each other?

[Al Klappenberger]

So Al, we talking 2 smaller horns next to each other?

No. They are mounted one inside the other, or have I misunderstood the question?

Here's a view down it's throat lit with a flashlight.

Al K.

[SSnyder]

If anyone has issues with my posts, please take them to the forum
moderators. This forum is the property of Klipsch, I will neither
address complaints nor defend myself to anyone other than them.

what is this about

[Al Klappenberger]

It's about people who accuse me of abusing the forum by allegedly using it as a sales tool. It was written word-for-word by Amy Unger.

AL K.

[IB Slammin]

If anyone has issues with my posts, please take them to the forum moderators. This forum is the property of Klipsch, I will neither address complaints nor defend myself to anyone other than them.

what is this about

You will need to spend about two days reading old posts to know the real answer. No big deal.[H]

tc

[IB Slammin]

It's about people who accuse me of abusing the forum by allegedly using it as a sales tool. It was written word-for-word by Amy Unger.

AL K.

Some of the guys here offer things to help you out in this quest for better audio. One that offers his designs on line for no charge .......Hard for me to see that as a sales tool or a ploy to make money. Like I said, no big deal. [H]

[BE36]

Would this fit in a La Scala Cabinet?

I have Dave's Fastracs and JBL Tweeters sitting on top of La Scala Cabinets.

If this sounds at least as good as that combo with out having tweeters sitting on top of my cabinets -- count me in.

Modifying the motor board would not be an issue as long I could keep the exterior of the cabinet in tact.

[Al Klappenberger]

Please change the subject! I would rather argue religion or politics than this sales abuse thing!

BE36,

The main thing here is the coaxial driver and phase-coherent network. The DCX50 driver would fit on any 2-inch horn. The Fastrac K2 is larger than the Fastrac Lascala that I think you have. I think it's a 1-ich horn. You would probably need to cut the cabinet, The Fastrac K2 has the same mounting as the original Martinelli 1-inch Trachorn 400 which had a larger mouth than the Klipsch K400.

Al k.

[jwc]

Nice off axis plots.

There are two peaks with the on-axis curve. I wonder if this is the driver....not the horn. Is there a plane wave curve of that driver?

So Al...I don't know the exact details of your scale...but what would you say is the dB loss at 30 degree off axis at 15000Hz? -3,4,5,6,7 dB?

jc

[Al Klappenberger]

JC,

I did a series of plots using the Martinelli Trachorn 420. It's the only other 2-inch horn I have here. The on-axis plots looked exactly the same. I think it's the driver.

The plots are done using a 2-channel analyzer with a reference attenuator in channel A equal to the mikes output at 100 dB SPL. This means ZERO dB on the plot represents 100 dB SPL at the mike. The mike is exactly 1-meter from the mouth of the horn. That means the top line marked 30 dB is actually 130 dB SPL at 1-meter.

It looks like the entire response at 30 degrees drops about 5 dB and smooths out. It's normal to drop like that but the fact that it smooths out surprises me! At 45 degrees the curve side of the horn obscures the driver throat from the view of the mike. The picture below is looking at the horn as the mike sees it. The blur in the foreground is the mike itself. The other side of the horn must be acting like a reflector to disperse the highs. I don't know much about acoustics so I really don't know. Something is bending the sound to make it fan out horizontally. Listening to the sound of white noise through the horn as I slowly move off axis clearly tells me the dispersion is far better that I expected. I'm impressed!

Al K.

[dkalsi]

I now regret selling my Khorns (which I sold just last week).

I would be shocked if this does not turn out to be one of the best upgrades to the Khorns.

-D