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Old 15th November 2008, 03:33 PM   #1
Helmuth is offline Helmuth  Netherlands
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Default isodynamic? whats that.

Hi music lovers,

I have bin very long interested in magnetostatic loudspeakers. And did order once one from visaton. But that one was not to new so they couldn't deliver so I bought a Visaton DSM25FFL then in 2000. And I tried a morel horn loaded soft dome in 2005.

Now it is so far, I bought the hivi researche (swans) RT1C-A

swans rt1

Click the image to open in full size.

It is a isodynamic tweeter. But what means isodynamic?

They explain it on their site, see the link. But I do not see it what isodynamic is, when I read it.
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Old 15th November 2008, 04:16 PM   #2
Pano is online now Pano  United States
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I would say this pretty much sums it up:

"The key element of the RT1C-A is the membrane, which consists of Kapton Film with a pattern of Aluminum conductors. The conductors cover about 90% of the whole vibrating area."

So it's not a ribbon, which would be made from a conductor, it's more like the Magnapan type of diaphram, only with aluminum film instead of wire.

I've heard the Hi-Vi planars, they're pretty darn good (and big). Isodynamic might be a silly name, but the drivers are good.
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Old 15th November 2008, 04:22 PM   #3
GM is offline GM  United States
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Just what the paper defines: "......has a driving force distributed evenly over the whole area of the vibrating element.", i.e. is a true point source.

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Old 17th November 2008, 06:07 PM   #4
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the root of the prefix "iso-" means "equal"

so perhaps the name isodynamic is meant to imply that the whole vibrating area moves as a plane--equally.
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Old 17th November 2008, 06:20 PM   #5
Dr_EM is offline Dr_EM  United Kingdom
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Thats what I took it to mean. I own the Hi-Vi RT2-EA tweeters. Theres some distortion tests out there that show relatively high distortion but mainly 2nd harmonic which isn't very audible. The imaging is great with them, thats the most noticeable feature for me. Also very fast, resolves the impact of a drum (sticking on a cymbal for instance) really well.

They don't use a transformer as a real ribbon would as far (as I can tell?); can't really be a bad thing. Element is comparitively durable too I believe (still definately use capacitor if bi/tri amplifying).

They are quite big as someone mentioned. The one you link to is a smaller one than the "2" series ones and needs to be crossed quite high.

To add on a question here, when using a tweeter like these, does one count driver spacing (ie from the mid) as from the top (furthest) part of the element, the middle or the bottom (closest)? I heard it was just from the closest part since it has this "iso-dynamic" behaviour. Would be nice if this was certain but am still unsure.
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Old 17th November 2008, 06:49 PM   #6
Helmuth is offline Helmuth  Netherlands
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Hi just got the drivers to day and mounted the direct.

Just like many times before the sound is different as I aspect. I thought it would have more brilliance then the Visaton dsm25ffl.

Wrong my first impression the sound is more natural and not harsh. I though the source of some harshness was the titanium dome of the visaton TI100. This isnt the case for what I hear with the swans rt1.

Click the image to open in full size.

The sound stage is more has some more stable behaviour I would say voices don't move. I think this is thanks the nice resistor behaviour of the driver.

But the differences are very small fist I only modified one and it was almost not noticeable when you didn't know it.

The new set up. Visaton BGS25NG bandpass 45-170Hz Visaton TI100 150-5000Hz and Swans Hivi research RT1 5000-40kHz.

The front plate is out of aluminium not of plastic very nice driver.

Click the image to open in full size.
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Old 17th November 2008, 07:05 PM   #7
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Isodymanic speakers are a "planar" technology a bit like an electrostatic. Instead of a coated plastic membrane between two charged plates they imbed a fine wire into the membrane and that vibrates between two magnets. At least that is what I understood the principle to be. (They are NOT the same as Heil's airmotion transformer although my description might sound like it. ) There have been several examples sold over the years. In the UK about 40 yrs ago Wharfedale produce a pair of headphones ,which were called Isodymanic, using this sort of thing as did Peerless (I have a pair). Also from the 1970's there was a range of tweeters from Foster/Fostex in Japan that worked on the same idea. I suspect that is what is behind the local Jaycar product sold here in Australia lately and marketed as "ribbons" but you would have to check that out to be sure. From memory I think people regarded them as an economy version of an electrostatic which was not quite as fast due to the heavier membrane............but at this point the debate will probably start and could become pasionate as I know one or two who have very strong opinions on this so I'll leave it there....okay?

Hope that helps but with marketing hype you can't be sure that people mean the same thing for a particular term over a 40 yrs period........wait until Planet 10 comes on line as he's sure to have sold some 35 yrs ago......

Looking at you photos again makes me think that I would like to hear from someone who has taken one apart!!! They do LOOK more like Heil technology although what I said about the earlier products is correct.

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Old 17th November 2008, 07:37 PM   #8
Ron E is offline Ron E  United States
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These are just a membrane of film with a printed voice coil - the attempt being to drive the diaphragm over its entire surface. Infinity/ Genesis did these in the 70's and 80's, IIRC. These have a flatter impedance because of fewer winds, but they have excursion limitations. 2nd harmonic means the mag field is asymmetric WRT the plane of the diaphragm.

It would be relatively difficult to get rid of the asymmetry and still have an open diaphragm, IMO. I wonder if you tensioned a piece of film with a hole in the middle and used a traditional motor arrangement with the diaphragm sandwiched between a split top plate, shaping the pole piece to be a phase plug sticking through the open center of the diaphragm. Might make an interesting experiment.
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