Hej Igen,
Ja det verkar efter lite googling att Ni har rätt. Impedansen håller sig strax under 4 Ohm...
Jag måste ha förväxlat med gamla Infinity eller liknande.
Hittade en intressant text på nätetwww.nutshellhifi.com
Magnetic Planars and RibbonsMost of these types are made in the USA, represented by Magneplanar (the pioneer), Apogee, Eminent Technology, and others. These fall in two classes:
• Magnetic-planars, which are sheets of stretched Mylar or Kapton film with an aluminum "voice coil" either printed or glued on the film.
• True ribbons, which use a very thin corrugated aluminum "voice coil" hanging freely like a streamer in a side-by-side magnetic field.
Magnetic-planars use arrays of magnets on the back side of the film (not too good for IM distortion) or on both sides (much lower distortion, but also creating a small resonant cavity between front and rear magnet pairs). The arrays of magnets provide a somewhat uneven drive field, so the uniformity of diaphragm motion is not in the same class as an electrostat. Then again, HV arcing is not problem, so the magnetic-planars can play much louder than their electrostatic cousins.
Magnetic-planars have a lower BL product than conventional direct-radiators as a result of the much wider pole-to-pole magnet spacing and the shorter length of wire immersed in the magnetic field. Diaphragm damping is mostly provided by the air load, and very little comes from the amplifier. In electrical terms, it is very loosely coupled the amplifier, which is why the impedance curve is resistive (if the BL-product were any higher, you'd see the typical reactive up-and-down impedance curve exhibited by conventional drivers).
Although a resistive load is great for the amplifier, it’s not too great for the driver. Drivers are naturally reactive, since all of them are bandpass filters with a bandpass much narrower than the full-range amplifier that drives it. Since the amplifier is driving the band-reject region, a tightly-coupled driver will present a load that looks like a filter ... this is the starting point of Theile/Small theory. The only way to have the amplifier see a resistive load is: design complex pseudo-crossovers that are the inverse (conjugate) of the total speaker load, or use drivers that have very loose magnetic coupling.
The idea that a perfect loudspeaker would present an amplifier with a resistive load is a marketing myth. This myth would only come true if some genius could design a single driver with a working bandwidth of, say, 10Hz to 100kHz. If such a wonder driver were available, who would care about the amplifier load?
Returning to magnetic-planars, the only ways to improve the coupling and raise the efficiency are:
1) Decrease the magnet spacing. This limits the excursion and adds to the requirements for a precise and rigid frame that holds the opposing magnets apart.
2) Increase the number of "turns" by lengthening the path of the wire or aluminum plating on the plastic film. The limit to this approach is adding excessive mass to the diaphragm, which degrades both efficiency and the transient response. Doubling the diaphragm mass cuts the efficiency to one quarter of the original value, so most designers go out of their way to prevent adding mass to the radiating surface.
3) Use magnets with higher coercivity. The newest magnets using exotic rare earths may offer significant improvements here. As the magnets get stronger, though, the requirements for a stronger frame also increase.
Magnetic-planars designers confront a series of design challenges that are not too different from the ones presented by electrostats. One has to wrestle with powerful magnet arrays that want to twist on the mounting frame, the other with high-voltage arc-over punching holes in the diaphragm.
Let’s move on to a technology that looks superficially similar, but actually is quite different than the preceding magnetic-planars. The freely hanging true ribbon is free of the stretched film resonances and obstructing magnets of the planar-magnetic, so it offers outstanding pulse response, uniform drive, and a good approximation of a line source. On the other hand, the impedance is extremely low (a fraction of an ohm) and ribbons are not suitable as a woofers or midrange drivers due to the small radiating area. Most practical ribbons require a matching transformer in order to successfully couple to the amplifier.
Planar speakers, being free of any kind of enclosure, have resonance-free reproduction in the important 100Hz to 1kHz region, resulting in sound quality is usually midway between a good dynamic and an electrostatic, with a genuine freedom from cabinet colorations. (Flexing modes in the supporting frames can be a problem, though.) The large surface area of the panels, their ability to operate at sound levels approaching horns, and the lack of lower-midrange coloration makes the planars a good match for music with a really big sound, such as large-scale symphonies or choral groups.
Like their electrostatic cousins, resonances appear in the 40 to 200Hz region as a result of drum modes on the panels coupling with room modes, so careful room placement is no casual matter. In addition, though, the side-by-side arrangement of the bass, mid, and treble drivers provides a very complex and "lobey" radiation pattern at the crossover frequencies, so the requirements for the best stereo imaging may well conflict with the location that provides the smoothest bass. In short, these speakers work best in a large, symmetric room, with a very powerful amplifier to compensate for the low efficiency and low BL product.
These kinds of speakers aren’t my cup of tea, but I know many people who really enjoy the neutral, relaxed type of sound they offer. In addition, a true ribbon offers some of the best treble around, surpassed only by the plasma driver.