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Old 19th October 2008, 02:19 PM   #1
tiki is offline tiki  Germany
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Default Low Frequency Magnetostat - Introduction

Hello,

some time ago I built a LF magnetostat.
Click the image to open in full size.
The poster, presented at the DAGA 2008 in Dresden,
Some presentation slides, shown at the Hifi-Music-World at Gelsenkirchen 2007,
Some measurements.
Unfortunately the magnetic gap does not allow for large membrane excursions, approximately 3mm at maximum. The efficiency is rather low due to the low flux density inside the large gap.
Although some of the used principles are known already, that combination seemed to be new, sufficient for a patent application: DE000010056176C1.

Best regards,
Timo
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Old 23rd October 2008, 08:21 PM   #2
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Interesting... obviously a lot of work went into the design... not sure I see anything that is not simply a re-orientation and re-application of existing technology? Can you explain which aspect of the design represents something unique or new?

I do see that patents are regularly issued for things that at least imho ought not to be patentable, but they seem to do it anyhow...

Guess the main question is "how does it sound"?

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Old 24th October 2008, 08:21 AM   #3
tiki is offline tiki  Germany
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Hello,

thank you for your interest. Of course it took a long time to realise, because I'm not well experienced in electroacoustics.
I went through 50 relevant patent applications approximatly, some of the most interesting seem to be EP000001489881A1 (and US020050152577A1, the US version). I discussed already with these Japanese guys during the Pro Light fair in Frankfurt.
In my opinion the spiral coil was already known, as well as the sandwich "cone" and the double surround. The combination of all the details to build such a flat (25mm!) low frequency speaker driver could not be found. So the main idea is the woofer application of a magnetostatic assembly. Do you know any prior?

Sound? I'd like to hear no sound, but flawless audio signal reproduction.
The driver was built into an active 3-way compact box, presented here.

With the help of the DCX2496 it was relatively easy to "flatten" the frequency response. The beaming seemed to be very strong, so the off axis sound was dull. This may be an issue of the relatively plane movement of the sandwich, except the breakups, which can be of different shape and behaviour in comparison to cone drivers. The low frequency reproduction seemed to be unusually clear, although the drivers SPL capability was not that high. The Qts (Qtc not measured) is much too high, so the built-in-frequency response remained flat down to 40/50Hz.
In fact it was possible to use it as the woofer in that application for moderate SPLs.

Driven by a sine around the 750Hz-artifact (which moved down after some power), the tone was not clear. This was probably due to imperfct glueing of the sandwich and the first eigenmode.

A lot more power while observing the breakups using a stroboscope, killed the driver due to delamination.

Best regards,
Timo
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Old 27th October 2008, 07:44 AM   #4
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What drivers are those on page 25 of the presentation slides? I have some very similar in design that I have never been able to find specs or anything on really. I think Sony manufactured (or rebranded) the ones I have.
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Old 27th October 2008, 02:12 PM   #5
tiki is offline tiki  Germany
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Hello,
Alcons QR36
They look nice ... but radiate a bit asymmetrically and show some lobing. Not the drivers themselves, of course.
Regards, Timo
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Old 30th October 2008, 11:25 AM   #6
BHTX is offline BHTX  United States
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Default Re: Low Frequency Magnetostat - Introduction

Quote:
Originally posted by tiki
The poster, presented at the DAGA 2008 in Dresden.
Click the image to open in full size.

..25mm dick?? Sorry, couldn't resist.
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Old 30th October 2008, 05:50 PM   #7
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Tiki,

I wish you luck in your quest!

Not sure I can add anything to your efforts by way of comments other than to say that clearly there are some practical engineering and materials questions to be resolved in this sort of design.

One of the problems to be overcome or considered is how does this sort of design offer a performance benefit over standard technologies, and if not performance then price/cost/manufacturing benefit?

Modern cone woofers are offering pretty darn good performance today with FEM designed motors and FEM designed cones.

But don't let my comments dissuade you (prevent you) from working on your designs!

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Old 30th October 2008, 07:00 PM   #8
tiki is offline tiki  Germany
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Hello bear,

you're completely right. The main issue may be, it's not the right size for such a kind of driver. One may remember the similar headphones.
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Old 16th March 2011, 01:17 PM   #9
oyvine is offline oyvine  Norway
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Hi,
I found your paper about the TIMAG after browsing your web-site. Has there been any developments on this driver after your last posting here? I find the idea fascinating.

Quote:
Originally Posted by tiki View Post
Driven by a sine around the 750Hz-artifact (which moved down after some power), the tone was not clear. This was probably due to imperfct glueing of the sandwich and the first eigenmode.
Could you elaborate on that? Do you have a clear idea about what causes this artifact or how to move it further up in frequency?

best regards,
yvin Eikeland
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