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my ribbons full range in CB
my ribbons full range in CB
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Old 26th September 2017, 05:51 AM   #61
WrineX is offline WrineX  Netherlands
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Join Date: Mar 2004
Location: Den Haag
Quote:
Originally Posted by lupi View Post
Hi WrineX
I tried moving away the microphones, both the Umik and the Technics, to have a SPL 10 dB less, but oddly the THD seems a little higher. I've been trying to find out if there's something around responsible for the phenomenon, but I have not found anything. As I said in the post above I will come back to the topic when I get the new ribbons
I was trying to tell that I had a umik that was 10 dB of I the high freq. So if you got any other mic to check if it is working correct ? I should.
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Old 27th September 2017, 12:15 AM   #62
lupi is offline lupi  Italy
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Quote:
Originally Posted by WrineX View Post
I was trying to tell that I had a umik that was 10 dB of I the high freq. So if you got any other mic to check if it is working correct ? I should.
Sorry wrineX, some phrases google translate it very badly. If now I understand you had a UMIK wrong 10 dB in high frequency. My umik seems OK: Compared to both the Tecnics (on which I mounted the kecg2742 capsule) and the electret capsules KECG2742 and MCE4000 on my assemblies the differences on the shape of the SPL are contained within a couple of dB, and the same is for the THD. Of course, the absolute value of the SPL is different for the different microphones, since only the umik is calibrated but the frequency-dependent trend is very similar. When I connected the umik I immediately loaded the calibration file.
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Old 27th September 2017, 09:51 AM   #63
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by lupi View Post
Sorry wrineX, some phrases google translate it very badly. If now I understand you had a UMIK wrong 10 dB in high frequency. My umik seems OK: Compared to both the Tecnics (on which I mounted the kecg2742 capsule) and the electret capsules KECG2742 and MCE4000 on my assemblies the differences on the shape of the SPL are contained within a couple of dB, and the same is for the THD. Of course, the absolute value of the SPL is different for the different microphones, since only the umik is calibrated but the frequency-dependent trend is very similar. When I connected the umik I immediately loaded the calibration file.
Aaah ok then forget what i said
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Old 14th November 2017, 12:09 AM   #64
lupi is offline lupi  Italy
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Join Date: Mar 2011
It's been a long time since my last post, but I've been busy building the engine:
First I realized the structure of the back magnetic field closure. As with the short ribbon, I do not make a continuous structure, to avoid resonances, but use 10x15mm section bars, spaced by a 26mm pitch, with the 10mm side welded to the 6x25x112mm bar behind the magnets. In total to have a section equivalent to that of the simulation I have to cut 180 short pieces (vertical) + 90 long (horizontal) pieces. The hard part is to weld them in the right position, because the retraction of the cooling metal always deforms the structure. I built a mask to keep the pieces in place during the welding, but anyway I even found some errors of 1 mm. I also underestimated the deformation of the metal caused by welds. The bars have curved much more than expected, and, worse, the overall curvature is given by the sum of many small local curvatures, so I've had a lot to work to straighten out.
after welding.JPG


After a first straightening of the bars, in order to remove the local deformations I have skinned the surface facing the magnets by grinding with diamond paste and after much work I was satisfied with a good result.
iron bars straightened.JPG


I planned to stick the transverse bars on one side with welding, and on the other with M4 screws.
First I made threaded holes (88!) And through holes, then assembled the structure by holding it together with thicknesses and clamps, so that the short welded bars can be leveled, then I fastened the transverse bars with the screws, and finally I weld them on the other side.
To avoid deformation of the structure under the action of the magnetic field I put 3 cylinders of aluminum spaced about 30 cm.
To support the clamps for electrical connections, I welded 2 mm thick stainless steel angular sections at the ends of the long bars. On these are attached, with screws, aluminum bars of section 5x15 mm, which are the bases for clamps.
iron structure.JPG
Attached Images
File Type: jpg after welding.JPG (373.0 KB, 90 views)
File Type: jpg iron bars straightened.JPG (366.5 KB, 85 views)
File Type: jpg iron structure.JPG (418.6 KB, 83 views)
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Old 14th November 2017, 10:59 PM   #65
lupi is offline lupi  Italy
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At this point I disassembled the structures and on each bar I put magnets, NdFeB N38 25x25x5mm, and polar pieces, which are held only by friction without glue. It was pretty simple.
The assembly of the structure with the magnets, on the other hand, was by no means simple, and I regretted not having followed the same type of prototype construction, that is with the transverse bars fixed with screws on both sides. In fact, with that type of construction, the two parts with the magnets could be approached, first placing a thickness in the middle, without problems, and then they could fix the transverse bars by screws one by one, so the magnetic field was closed step by step. Instead, having soldered all the transverse bars on one side to halve the thread count, as soon as I approached the two sides they were drawn violently with my hand in the middle. It was not pleasant, but fortunately I only brought a couple of small holes. Then I improved the technique and went all smooth.
motors finished.JPG
The wooden blocks that are seen below the polar expansions are used to keep them in place during the work. In fact, as the structure weighs 17 Kg, by dropping it on the table, magnet down, the polar pieces may slip out of place.The other wooden blocks that are seen on the sides of the clamps for connections are used to close the air passages at the ends of the ribbon. A job as a chaser! Now the 2 engines are over and "only" ribbons and return wires remain
Attached Images
File Type: jpg motors finished.JPG (422.3 KB, 69 views)
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