PH509003@brownvm.brown.edu (Jon Kjoll) (03/06/90)
>in article <2649@uwm.edu>, ST801804@brownvm.brown.edu (steve liebling) > > I was wondering if someone could possible go into the fundamentals of > the structure of electrostatic speakers and also electromagnetic > speakers that are not the conventional cone type. I neither have time to write a lot about different speaker designs but just to provide a start to a hopefully more elaborate article: "Electrostatic" speakers consists of two conducting planes that are mounted parallell and close to each other and where the two "planes" are fed a high-voltage alternating signal (transformed up) that causes the two planes to have a net electric charge on them. They will then expell/attract each other according to the laws of electric charge-charge physics and a soundwave can be generated. (Straton, Quad etc.) Of problems are max allowed amplitude, sparks, sound "beaming", diaphram suspension etc. The other planar speaker construction possible is to take saran-wrap (sp?) and glue to it carefully a long worm of conducting aluminum tape (like the one taped to the window of jewlery-stores) and thus create a planar conductor. Using the laws of how conductors behave in a magnetic field you can now arrange magnets on a steel plate (perforated!), suspend the saran wrap in front of the magnets and feed the two ends of your aluminum worm from an amplifier. This is pretty much how the bass part of Magneplaners and Apogee works. A ribbon tweeter is using the same principle but here the magnets are not mounted in a plane behind or in front of the vibrating membrane but on each side of a narrow ribbon with a conducting path on it. Below S -- N indicates a magnet, ======> indicates a magnetic fluxline between to magnets. In this magnetic field is a ribbon suspended with a conducting path that terminates into + and -. If I feed alternating current into the + and - terminals the ribbon will move towards us, i.e it generates a sound wave if the signal fed to it is withing the audible regime. Ribbon: VERTICAL | : ---- + plus : ! : ! ! S -- N ====!==> S -- N ! ! S -- N ===!==> S -- N ! ! !---- - minus Now to *my* question, I have been speculating making my own ribbons. What stopped my was the excessive price of high quality magnets. Apogee for example makes their own magnets. I have been speculating making ribbons using horse-shoe magnets. I still wonder what happens to the rear-wave that will bounce into the the horse shoe. I have the patent used by Apogee and I'll have too look it up now but I think the tweeter ribbon is 60 cm tall and 2 cm wide. After the aluminum is attached it is corrugated and suspended in the magnetic field. Anyone out there has a pile of magnets?? Jon Kjoll "Damn, I forgot where to put the smiley" Dep. of Physics Brown University Providence, RI