MLTL speakers with Jordan JX92 – part II – adding ribbon tweeter

My MLTL speakers project with Jordan JX92 was waiting for final touch with some paint or veneer, but it ended up with HiVi Research RT1.3 ribbon tweeters instead. As good as JX92 are, we all know that there is nothing perfect. It was absurd to think that 4-inch driver is capable of reproducing 30Hz perfectly and it is the same with the high end of the audible spectrum. That is why I decided to add ribbon tweeter to improve the highs after I cut the bass port to improve the lows, sacrificing those below 40Hz. The good thing is that I chose project which allows me to add second driver – second generation 35″ MLTL. Although I didn’t use Aurum Cantus G2 as Jim Griffin did, the final result is OK with me for now. The photo below shows the tweeter already mounted in the speaker. Its front panel isn’t the most beautiful but at least it sounds good.

Probably it looks strange that I didn’t use G2 and instead I chose HiVi Research driver. The first reason for my choice is that G2 can be ordered only from USA which means prob;ems with the customs, long time waiting, paying VAT and taxes. I didn’t like that idea at all. The second reason was the high price of G2, which is even higher than JX92’s. The third reason is that I can not listen to that driver and therefore I have to buy it blindly and if I don’t like it, I should try to sell it which is hard thing to do in Bulgaria. That is why I looked for alternative. After some research I ended my search with RT1.3. It’s frequency response according to the manufacturer is almost rectilinear in its usable spectrum. Moreover its price is a few times lower and even if I don’t like it it’s not a big loss. Additionally I got information that this driver is being used in speakers worth 3000 EUR, which gave me some hope that it deserves a chance.

After some consideration I decided to give it a chance and ordered two pieces and some components for cross-overs. This was my first cross-over design and like it often happens it wasn’t as easy as it looks. Thanks to good software and the help of some experienced friends I ended up with the following schematic.

I chose third order cross-overs for both drivers and I added resistor to the tweeter to compensate for its higher sensitivity (92dB compared to 85dB for JX92). I chose non-inductive metal-oxide film resistors polypropylene capacitors by Mundorf. The inductors I winded myself.

The software gave the results shown on the charts below. For the calculations I add not only the drivers TS parameters but also their frequency responses.

The results are not perfect and probably could be improved. The main target was achieved and it was to make smooth transition between the two drivers while keeping the phase shift as small as possible. Unfortunately I am not able to perform real-world measurements for now.

Finishing with the simulations I continued with building the filters and mounting the ribbon tweeters in the already built speakers.

For all inductors I used cylindric ferrite cores so I can have low DC resistance. This is subject with many pros and cons so I will not go into details. All components are mounted on peace of laminate flooring (remaining from the JX92 initial stands) and additionally secured by cable ties and some glue. I hope all that will keep the components in place and there will be no problems.

With the help of my drill and jigsaw I made the necessary cuttings for the new drivers.

I used T-nuts and bolts (M4 this time) with the right colour to mount the drivers. I already come across problems with ribbon tweeters in the same volume as the woofer and I was not able to put mine in separate volume, I used silicone to seal the back of the RT1.3 drivers. If the drivers are not sealed well enough some air pushed by the woofer starts to move through them, which causes audible sound distortion. It is not impossible that this causes damage to the tweeters.

This is all for now. I hope to be able to finish the project soon.

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