Her er et sitat fra norges ufortjent ukjente "høyttalerguru" Ragnar Lian (fra Seas og Scan-Speak)
"2: Modulation of the magnetic field. This is a neglected area. In the 50's they philosophized a great deal over why the voice coil was displaced in the magnetic field under conditions of strong drive, among other things Cunningham defined the "solenoid effect". If one takes the trouble to measure the force from the voice coil inwards and outwards respectively, at say an applied coil current of five amps, one will realize that there is a large difference. The coil pushes harder outwards than it pulls inwards. Somewhat dependent on the design, this difference will be on the order of 5-50% (!), causing both offset and compression. I have, just to tease, done calculations on three different magnet systems; my old Scanspeak system with 18 mm coil, 100 windings and a 120 mm ferrite magnet, but without SD (Symmetric Drive). Then an imagined system with a 40mmx40mm alnico magnet, and one system with a 40x10 neodymium magnet. These three systems have roughly the same magnetic field, statically speaking. The ferrite system has an asymmetry of 25%, the alnico system has 4% and the neodymium system at about 2% ! Mysterious? Not at all! If we picture the voice coil, 18 mm long, 100 turns, at 5 amps, this produces 500 amp-turns, or a field strength of 28000 A/m, this is a magnet "let loose" around the air gap. It is directed with or in opposition to the main field, depending on the direction of the current, and acts directly upon the field in the air gap, and also shifts the operating point of the magnet. The ferrite magnet's operating point is at about 2500 gauss, and has an incline such that it can easily be shifted 2-300 gauss, that's quite a few per cent! Both the alnico magnet and the neodymium magnet have operating points up around 10-11000 gauss, and an incline which makes them somewhat "stiffer", meaning that they can't be moved much. Both neodymium and alnico have the property of having a permeability close to 1, in other words the same as air, and they do not affect the inductivity of the voice coil! Then we can go back to the early 70's, when JBL spoke of "The Alnico Sound" - that was no lie! "
Henter herfra:
http://btvbtv.narod.ru/Ragnar.html
Jeg har liggende i et word dokument et helt innlegg som Lian holdt på et eller annet møte. Han snakker om mye av det samme der. Hadde jeg bare husket nøyaktig hvor på det o store internett jeg fant det...