Stojek Horns - DIY round BLH

[marekst]

It is not a new project, it is not practical for cabinetmakers, but people asked me for info so I am opening dedicated thread for my horns.
Warning, I am not a horn “expert”, I did some modeling, but I took plans for these horns from the top of my head therefore the dimensions of horn may not be optimal for the driver used. Although I like the sound of Lowther drivers I can not recommend them because of materials that disintegrate after a few years and shoddy workmanship.

To calculate profile of the horn I used Hipex calculator, courtesy of James Melhuish. I have education in material technology so to build the horns I was able to design material with desired mechanical and acoustical characteristics. I used metal powder, polyester, fiberglass composite with micro boundaries of various densities. Because I wasn’t making a shiny toy for sale I could use an inexpensive male mold. I partially broke the mold during removal from finished horn and threw it away after one pair of horns was made. Each horn was made in one continuous process, no “stitches” etc.

Baffle rings and phase plugs are made from oak; compression chamber and horn material is custom composite, content of metal powder in composite is 60% of weight, content of metals in powder is 55%W, 40%Cu, 15% Pb.
Because my horn is not folded, to limit midrange output from the mouth, horn had to be filled with some wool.
Baffle ring diameter is 0.35m; CC volume is ~0.003m^3; throat surface 0.0075m^2; effective length is 3.5m; mouth surface is 0.8m^2; horn profile is Hipex with M=0.8;
Drivers are stripped and modified Lowther EX3.
Dimensions: W-1.3m, H-1.05m, D-1.8m; weight ~ 90kg each without supports.
The frequency response is excellent from 50 to 12.000Hz, below 50 it drops like a rock; it is minus 6dB at 45Hz, minus 16 at 40. Above 12k it slowly rolls of, but I do not hear it anyway.

I made the horns and all their parts at home using simple tools and inexpensive lathe. Total cost of materials and drivers was (7 years ago) about $2,000.

How does it sound? The horns, the system and room they are in are tuned for my ears and taste. I listen to classical, mostly chamber music. And to my ears the sound is lavish and detailed; the soundstage is big and deep. The voices sound natural, strings sound vibrant and brass sounds dynamic and real. My horns are not suitable for recordings mastered to compliment sound of less sensitive speakers. So a lot of pop music sounds too detailed, too edgy, with over contrasted artificial soundstage. I also use the room as my home theatre and movies sound really good.

The rest of the system:
DIY TT plinth with modified VPI platter and bearing and Teres drive
DIY Stojek Natrix 13 tonearm; Shelter 501 II; Cary PH-302
Philips SACD1000 or Marantz BD 7004
Moth s2A3
Room is DIY trapezoid with complex acoustic treatment.

Thanks for your attention,
Marek Stojek

[rjbond3rd]

Hi Marek, absolutely stunning! I can imagine they have a fantastic image, with the very small baffle (and with the baffle a nice distance away from walls).

I agree that Lowthers (and AER's) are just fantastic on chamber music, especially with something like the right 2A3 or similar. They have a "palpable" almost 3D quality that I've never heard from any other driver. (The field coil Lowthers sound very different from the regular Lowthers.)

That's a very unusual phase plug. So did you make a "cut" to free the horn from the mold? It looks like it would be challenging given the twisty one-piece nature of the horn.

I'd love to hear more about how you fabricated the mold.

[ra7]

That is quite phenomenal, Sir. Congratulations.

[marekst]

Thanks,
The only part of the mold I have kept is the compression chamber – first picture. I have described the mold here:
Why not MDF?

[Rullknufs]

Wow, what a room! And cool speakers too, I guess they sound really good!

[adason]

The frequency response is excellent from 50 to 12.000Hz, below 50 it drops like a rock; it is minus 6dB at 45Hz, minus 16 at 40. Above 12k it slowly rolls of, but I do not hear it anyway.

could you post a fr response graph?

[marekst]

Sorry the graphs you asked for are raw measurements and not fit for publication. Quoted measurements were taken in finished room with RS meter 1m in front of one horn with two horns playing Sine signals. The level was set 90dB at 1kHz.

If you like graphs I can show you room response where mike was in listening position. After I took that graph I added more absorbing panels. The front panels are behind the screen. Picture shows room before I changed it into a dark home theatre.

[adason]

thanks for the graph, is 50 Hz enough? for most music it might be, but some will be missing lowest octaves, don't you agree? and especially movies require serious bass to be realistic

I admire your effort btw

[Rullknufs]

Originally Posted by adason

thanks for the graph, is 50 Hz enough? for most music it might be, but some will be missing lowest octaves, don't you agree? and especially movies require serious bass to be realistic

I admire your effort btw

I don't know how deep my Mar-Kel70 goes but I think they work well for pretty much any music I play on them. Might sound a little thin to some kinds of rock but hey, it's a 4" full-range driver...

[jimbro]

That's a serious set-up. Seriously cool too. Where's the tv or screen or whatever you use for movies?