Open Baffle 4 way Lii Song F15/W15 Bliesma T25B-6/M74B-6 Part 4 

@@jazzboy 😀

Thanks Thommy for the nice comment! Yes, of course I tried the combination of the two Lii Song's together for several days. Compared to my Magnepans, the F-15s have less definition as well as a less holographic presentation. On the other hand, the bass and dynamics are superior. For me, the F-15s can't compéte with planars for sound quality. Combined with the two Bliesmas, the resolution and dynamics in the upper midrange and treble are quite different: it's hyperdefinition, you can simply hear everything, with endless layers. Placement is very important, as always with Open Baffle. And without the use of a DSP, it's impossible to obtain a satisfying sound. It's all a question of choosing the right type of filtering and the right slopes. The Bliesmas are exceptional in terms of clarity, a step above what the Magnepans are capable of, and they're also very linear, so it's easy to get the best out of them. On the other hand, the Lii Songs, which operate in the low frequencies, have strong interactions with the listening room, and the frequency response of these babies requires quite a lot of correction, without which the low frequencies are very powerful but not sufficiently controlled. I'm still exploring new DSP settings, but I don't think I'm too far from a good compromise. I'd like to add that these aren't speakers that will appeal to everyone, there's nothing “romantic” about the sound, it's the naked truth. For this, Bliesma has other drivers, such as silk, paper, aluminium or Textreme, choose your poison.... Berylliums are no longer in the catalog, as the supplier has stopped production. But, if like me, you like spooky sound, try to find ASAP these drivers!

@@Pierre-Leloup Thank you very much for the detailed explanation. Have to dig deeper into active crossovers and DSPs

Hello and welcome to the small club of owners of these Bliesma drivers which are no longer produced for lack of a supplier. In this baffle, the center distance is 110mm. Because of the overall configuration of the different drivers, a waveguide on the T25B would have complicated this project without any prospect of benefit, especially in active applications where the difference in sensitivity is not a problem. Staying as close as possible seemed more appropriate to me. Speaking of the M74B's ringing, which occurs very high up in the spectrum, blocking the two peaks with notches via the DSP is a valid solution, because if you block these incoming frequencies (-20dB attenuation), they create much less ringing either. In any case, I filtered both drivers at 48dB/octave (L-R) around 4-4.5kHz and none of the ringing showed up on the measurements, with or without notch filters. Of course, I filtered lower too, and preferred the M74B over the T25B up to 4,5kH. Even at 24dB/octave, ringing doesn't seem to cause any problems, it's a straight line down measured to 20kHz without disturbance. I think we lose more resolution by adding passive components, unless this is the aim to “romanticize” the sound rendering, why not if you like it better? Now, as far as the rendering of these beryllium drivers is concerned, we're closer to high-resolution photography than to an impressionist painting. When the recording is excellent, it's really very realistic. On the other hand, as soon as it becomes average, it's unforgiving. My Magnepans are more forgiving, and the character remains warmer. They are also true dipoles, the soundstage is deeper and as they are line sources, there seems to be more “height” and 3D. My 2 cent.

@@ABC-rh7zc No it's the classic F-15/W-15 combo paired with Bliesma domes I had waiting for another project.

That's called PLLXO (passive line level xover). If you can stand with a first order xover, it sound very good (with excellent capacitors and resistors). But it's not that easy and it's depending on the input impedance of your power amps, plus you'll lose some gain. www.t-linespeakers.org/tech/filters/passiveHLxo.html You can get much better results with a DSP, they also have much highter slopes and PEQ, I mostly use 4th order and above, that's not realistic to do with PLLXO.

@@Pierre-Leloup Why only first order because more parts in the signal path or other reasons? Im considering building 2x firstwatt f5m and trying this out. I could get a variable resistor and try adjust it for proper phase coherence and testing crossover points. Silver mica and just generic carbon films should do right. Also do you think that High pass filter RL or RC filter sounds best. Im interested in this topology because i suspect its much superior to normal passive crossover

@@williammeincke9071 Yes, PLLXO sound better than classic xovers. If you only need first order, it's ok, above you'll lose a lot of amplification gain. I didn't use RL, only RC. I first used low quality components and once the expected result was obtained, they were replaced by excellent ones and it overal made the sound better, but then the cost become of the same level as my actual DSP, with less flexibility and SQ. DSP wins, no doubt about that, and it's far easy to make filters on the fly, plus they have LS, HS and PEQ, individual phase cantrol and delay...

@@Pierre-Leloup thanks for ur reply u know too much :) Have you build any tube preamps?

@@williammeincke9071 No, on my tube preamps I only made minor modifications myself. I was lucky enough to meet a real tube guru, a real enthusiast capable of making his own transformers and chokes, he's the one who modified all my tube-based projects.