pathy@omssw1.UUCP (Mohan Venkatachalapathy) (09/10/86)
In article <3300014@datacube> john@datacube.UUCP writes: > >>Anybody want to buy a pair of obsolete tri-amped techno monsters? > >That does bring up a good point I have been wondering about for some >time. > Does anyone have HOMEMADE electrostatics?
bill@videovax.UUCP (William K. McFadden) (09/11/86)
In article <161@omssw1.UUCP> pathy@omssw1.UUCP (Mohan Venkatachalapathy) writes: >In article <3300014@datacube> john@datacube.UUCP writes: >> >>>Anybody want to buy a pair of obsolete tri-amped techno monsters? >> >>That does bring up a good point I have been wondering about for some >>time. >> > > > Does anyone have HOMEMADE electrostatics? Yes. A friend and I made our own electrostatic speakers several years ago as an experiment (just to see if we could do it). The first one was made from a large piece of 1/8" thick sheet metal and a window screen. Between the sheet metal (a large road sign-- don't ask me where we got it) and the window screen we placed a sheet of aluminum foil inside a pillow case. Then we connected it as follows: TRANSFORMER 1 2 3 >-------- -------------| | | 1= SHEET METAL ) || ( | | | 2= ALUM FOIL ) || ( | | | 3= WINDOW SCREEN ) || ( | | | AUDIO ) || ( | | | AMP ) || ------+ | | | 8 OHMS ) || ( | | |-+ |-----+ ) || ( | | | ) || ( | | | ) || ( | | | >-------- ------+--------------+---------+ | | | | | | +--- + HV - ---+ HIGH VOLTAGE DC POWER SUPPLY We used about 475 volts for the supply. (Current drain was very small- less than 1 mA.) The transformer was a push-pull audio output transformer taken from an old vacuum tube amplifier. The speaker worked, but was very inefficient, even for an electrostatic. The main reason for this was the large spacing between the elements. Since the speaker was a big capacitor, its response was essentially that of a high-pass filter, making it a very good tweeter. We improved on our initial design by using three sheets of aluminum foil for the elements and layers of waxed paper as insulating material. This was sandwiched together and ironed (the heat melted the wax) so the whole thing would hold together. (We got a lot of funny looks from our friends as they saw us ironing this thing.) The result was a flat sheet one foot wide and five feet long, which we hanged from the ceiling. The effeciency was much better than before, but still not as good we were hoping for. Nevertheless, we had a very good sounding tweeter. Experimentation led to a final configuration of three layers of waxed paper between the aluminum foil sheets. Fewer layers caused arcing; more layers reduced efficiency. On the outside we put layers of waxed paper to insulate it. Here's how the layers were arranged: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | P F P P P F P P P F P P = WAXED PAPER F = ALUMINUM FOIL The best feature of this speaker is that it is very inexpensive. It isn't a really practical speaker, but it was a lot of fun. -- Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-594 Beaverton, OR 97077 UUCP: ...{ucbvax,ihnp4,uw-beaver,decvax}!tektronix!videovax!bill GTE: (503) 627-6920 "How can I prove I am not crazy to people who are?"