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Old 21st August 2012, 03:54 PM   #61
Hentai is offline Hentai  Romania
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Old 22nd August 2012, 09:32 AM   #62
Magura is offline Magura  Denmark
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Quote:
Originally Posted by Hentai View Post
Email sent
And replied as well



Magura
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Old 14th October 2012, 07:46 PM   #63
Hentai is offline Hentai  Romania
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An update on the works,

I'm still considering the carbon fiber cones, i guess until i tested things wont be clear for me. I love the sound of paper on cones tho so i'm a little stubborn but i will test the carbon in the future as well.

I have modified the magnetic structure meanwhile (i will post about it soon) The new structure will allow for a more precise assembly and mounting of the copper shorting rings.

This weekend i made a test reflex enclosure from fiberboard. 110L tuned around 40Hz. I wanted to see the impedance curves with different current through the field coil.
I used a 32 ohm ECCAW voicecoil from tests i did before ( i will post on these as well as soon as i arrange the data) so the lowest Qts value (3Amps through VC) is aprox 0.4.

Here are some pics:

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As you can see pretty much a typical behaviour at low frequencies. At high frequencies we see that the impedance drops with increasing current through voice coils. Permeability of plates changes with the changing flux density. We can see some little glitches appearing gradually in the linearity of the curves with increasing current.
I could not associate these glitches with any dips or peaks in freq response, could be resonances too subtle, and with weak current through field coil there is not enough energy to excite them.

Using it in reflex is a waste though of efficiency. The high-mid region would need notch filtering. Horns are the way and that will be done pretty soon.

Some videos playing with it: Ryu DIY Field Coild Loudspeaker - YouTube
Attached Images
File Type: jpg DSC03168.JPG (80.9 KB, 22 views)
File Type: jpg DSC03169.JPG (91.6 KB, 18 views)
File Type: jpg DSC03170.JPG (68.6 KB, 18 views)
File Type: jpg DSC03172.JPG (68.6 KB, 93 views)
File Type: jpg impedance measurement in vented box.jpg (131.9 KB, 89 views)
File Type: png phase measurement of vented box.png (146.9 KB, 21 views)
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Old 14th October 2012, 10:52 PM   #64
Hentai is offline Hentai  Romania
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Here is my idea of the frame, will take shape soon.

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Attached Images
File Type: png FrameAl01.png (70.3 KB, 16 views)
File Type: png FrameAl02.png (68.2 KB, 15 views)
File Type: png FrameAl03.png (68.5 KB, 16 views)
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File Type: png FrameAl06.png (121.0 KB, 14 views)
File Type: png FrameAl07.png (140.5 KB, 18 views)

Last edited by Hentai; 14th October 2012 at 11:02 PM. Reason: added pictures
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Old 16th October 2012, 09:55 AM   #65
Pnotus is offline Pnotus  Sweden
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I know this is OT but I must ask you - what program du you use for 3D modeling?

/Pontus
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Old 3rd November 2012, 03:33 PM   #66
Hentai is offline Hentai  Romania
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*Pnotus got his reply on pm

I have been listening for a little while now and i am pretty much please with where i am now. There is, of course, room for improvement and this is what occupied my time lately.

The magnetic structure suffered a few tiny but important changes as well as the voice coil. I have underestimated the battle against inductance in an underhung design. The relationship between electrical parameters makes it difficult to make a choice and i still have a couple more options to test and evaluate.

So attached you will find plans for the first version, if there are builders going this path i can provide more info, sketches etc.

Also some pics with the new motor structure, allows for a more precise assembly, central pole and bottom plate are from a single chunk of metal, a nice change on the gap geometry.

Click the image to open in full size.
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With the new structure i hope i will finally defeat inductance.
As sound goes, high dynamics, impact and so sweet midrange.
Attached Images
File Type: jpg ryuv201.jpg (129.2 KB, 49 views)
File Type: jpg ryuv202.jpg (125.3 KB, 62 views)
File Type: jpg ryuv203.jpg (119.7 KB, 60 views)
File Type: jpg Fieldcoil sketch 2.jpg (799.1 KB, 165 views)
File Type: jpg Fieldcoil sketch.jpg (701.1 KB, 133 views)
File Type: jpg Mag Assembly 1201 pg1.jpg (663.7 KB, 164 views)
File Type: jpg Mag Assembly 1201 pg2.jpg (646.6 KB, 124 views)
File Type: jpg Mag Assembly 1201 pg3.jpg (648.0 KB, 82 views)
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Old 3rd November 2012, 04:46 PM   #67
Allar88 is offline Allar88  Estonia
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Am i right thinking that the drawings do not match the new motor... ?
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Old 3rd November 2012, 05:57 PM   #68
Hentai is offline Hentai  Romania
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Yes, the sketches are for the first version tested. The new version has some improvements that i will need to put to the test.
There is still some polishing to be done and i will upload more detailed pics and rest assured the sketches as well .
Also in page one the view is the central pole piece and the bottom plate. Top plate is on page 3.
I believe the sketches of the first version represent a good foundation for anyone who wants to explore sound with a field coil speaker.
There are a few people that manifested an interest in this design and i hope by the end of the year there will be reviews in some of the audio zines. Much work to do...
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Old 3rd November 2012, 06:41 PM   #69
hispls is offline hispls  United States
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Incredible fabrication skills!

A couple questions:

Besides the "because I can" answer, why use an electromagnet VS. fixed magnet in loudspeaker design? Roughly what size ceramic magnet does this replace at your intended current through the field?

Has anyone experimented using a huge electromagnet motor with fixed magnets (say an array of small neo slugs) attatched to the cone (in place of a coil)? For low frequency applications you have the benefit of high mms and potentially unlimited thermal power handling with a big enough coil?
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Old 3rd November 2012, 08:20 PM   #70
Hentai is offline Hentai  Romania
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Thank you hispls,

The main advantages of a field coil design are:
- control over the units' parameters. with a pm driver you can not change any of it's parameters so there is little flexibility in designing a box. with a field coil you can make it suitable for any kind of loudspeaker.
- lasts forever, no demagnetization
- from a DIY point of view, it is a lot easier to assemble than with permanent magnets unless you can magnetize them after assembly (expensive machinery and dangerous to build)

To reach 1.5T in that gap would require a ceramic 5 magnet ring of 220-240mm outer diameter and 70 mm inner diameter. (20mm thick)

Im not sure about unlimited thermal power, even if you make your electromagnet to withstand tons of power, neo magnets don't like high temperatures.
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