KOSS ESP-950 Thread - Page 29

Quote:

Originally Posted by obobskivich 


1.7 is a "Quasi-Ribbon" according to Magnepan. They're vague on the 3.7, on one hand I see "Quasi-Ribbon" but on the other I see "True Ribbon" (both of these are Magnepan terms) like the 20.7. I don't think any of their speakers are truly analogous to what you'd find if you ripped a BG apart though.

I have a pair of Magneplanar 3.6's, and they do, indeed, have a 'true' ribbon tweeter. So do the 3.7, the 20-series, the "Mini Magneplanar" and a few other of their speakers.  In the 3.5, 3.6 and 3.7, the tweeter is a 6-foot-long (or is it 5 feet?) pleated piece of aluminum foil hung in a strong magnetic field.  Just a very thin piece of foil, through which you run your treble signal.  2.9 ohms.  There are tiny dots ( 1/64 inch or so) of silicone adhesive along the edge between the foil and the magnets along the sides, about every 8 inches.  These are apparently to keep the diaphragm from getting stretched out easily- they tie the diaphragm to the frame of the tweeter, but since the foil is pleated it is still quite free to vibrate.  These little "suspension dots" are hard to see.  I think Magnepan has a patent on this aspect of the tweeter. 

Here's a company that rebuilds Magneplanar tweeters for folks in South Africa, where I suppose it's difficult or costly to use the "exchange replacement" service that Magnepan offers. On their website you can see pictures of the tweeter as it appears on it's own, removed from the speaker "panel" http://www.celestialsounds.co.za/magnepan-ribbon-rebuild/ .  The tweeter can be damaged by WAY too much power, DC, or other failures of judgement or equipment. In my system, which is tri-amped, the tweeters are driven directly by a Nirvana Electronic Works  class-A amplifier.  If the amp's output stage ever failed and sent DC through the tweeter, I imagine the diaphragm would melt until a spot burned all the through and opened the circuit. There's a fuse, but the Semmelheinz corollary of Murphy's Law states that the expensive tweeter diaphragm will open first, saving the 50-cent fuse from damage. If that were ever to happen, one just packs the tweeters off to Magnepan in Minneapolis, and they send a new pair for something like $300.  They're very clever, those Magnepan folks. To protect the tweeter in shipping- either when installed in the speaker or when being mailed as a replacement part- they use a 5 foot long piece of steel banding tape- the stuff that is used to secure items to shipping pallets.  The magnets just hold the steel tape in place firmly, making a very good "shipping cover" for the tweeter.

Here's a picture of the tweeter as it is installed in the speaker, as viewed from the back- that's the tweeter on the right....

The midrange and woofer drivers in Magneplanar's ribbon-equipped models are actual 'planar magnetic'  drivers, which conductors bonded to a plastic film, suspended in a magnetic field. The tweeters in ribbon-equipped models are just thin aluminum foil, no plastic film "base."

Not all Magneplanars use ribbon tweeters. The Magneplanar models that use "quasi-ribbon" tweeters have conductors bonded to a plastic film for the highs just like the MG 3.6's midrange and woofer panels.  In fact, the MG 3.6's midrange panel is flat to about 18,000 Hz and only down 3 dB or so at 20,000. It would be prefectly useable as a tweeter- but the "true ribbon" has a lower moving mass, is MUCH narrower which improves horizontal dispersion, and so on.  The ribbon is a better treble driver.

Just all FYI.