In the fall of 2004 I declared my commitment to study the development, if any, of Yamaha's old line of Orthodynamic headphones, which used a driver type known generically as isodynamic, small-O orthodynamic, planar-magnetic, or magnetostatic. Why? 1) they'd been virtually extinct for 20 years, and 2) despite their age (they were made from 1975 to about 1990), they can still, at their best, give even an electrostatic a run for its money, and the simplicity of the drive principle makes it easy to tinker with them until they are at their best. This, plus the fact that examples can be had fairly easily on eBay for as little as $35 (and sometimes much less) makes them something of a bargain [UPDATE: No surprise, this situation couldn't last once the secret was out, but online-auction prices at least seem to have stabilized]. I believe that a good example of this type of headphone, given a little DIY TLC, can stand sonic comparison to today's popular enthusiast, even audiophile, moving-coil dynamics. Yes, "orthos" partake of some the best of both the dynamic and electrostatic worlds. They won't be everyone's cup of darjeeling, but they have unique virtues that should put them on headphone enthusiasts' shopping lists and in manufacturer's catalogs. But until very recently (see the note below), they haven't been, and I wanted to know why. Even though during the late '70s and into the '80s a buyer in the US could choose from examples of isodynamic 'phones sold by Audio-Technica, Radio Shack, Pacific Stereo, Lafayette, Bang & Olufsen and Burwen, I picked Yamaha's Orthodynamics to study because Yamaha stayed with the idea of marketing this type of headphone to the mainstream longer than anyone else, long enough to produce three distinct lines before the death of what we might call the isodynamic dream in the late '80s. Fostex is the exception, the company having kept the type in production from 1975 to the present, but Fostex is primarily in the business of supplying the professional and semi-pro audio markets, and, outside of the odd OEM here and there, its products rarely pop up in the mainstream, especially since its current production is not "audiophile" quality-- by design-- until extensive modifications are done. What I propose here is simply to describe the pros and cons of living with examples of Yamaha's three Orthodynamic strains, since I now have an example of each. Under roof now are, in chrono order, models HP-1, YH-1, YH-100 and YHD-1. These were the most expensive models of their respective lines. You will have counted four examples, though I mentioned three distinct strains. To explain: An unexpected discovery was that the highly-regarded founding model, the HP-1, and the later, much lower-priced YH-1 are very nearly identical; they look the same both inside and out and sound very similar. It's as if Yamaha were having another pass at the market with the same models at a much lower price point. Ergo, only 3 distinct lines, though there were four different model lineups. The YH-100 and its predecessor, the frighteningly rare/expensive YH-1000, were flagship or statement models and not really part of a line as such; rather they represented a summation of everything Yamaha had learned up to that point, including how to hit the maximum on the cost/benefit curve, as you'll see. If a budding Orthodynamicist wants to get his feet wet, he should start with an inexpensive and relatively common model like the YH-1, which should still go for about $60 on a good day, depending on the whim of the market and whether the item comes in its original box, et cetera. There are other possibilities as well, including a Fostex model or two. Next I'll go into detail on the individual models, taking them in chronological order, and try to explain why these old dinophones still merit close attention. So welcome to our little corner of the madness and our chronic fixation on a headphone type that with the exception noted went out of production more than 20 years ago. Our operating motto is whatever works. NOTE TO ORTHOPHILES, 2011: You'll notice this thread is now very long. It threatened to die young, but then came back to life, and has been thriving ever since thanks to a group of dedicated Ortho enthusiasts worldwide whose tenacity and ambition and ninja procurement skills continue to amaze me. It's become a group (not to say cult) global effort. We've tackled many practical problems of headphone design over the last seven years, mostly because we had to learn how headphones work as a system, with their cups, pads, vents and baffles, in order to get the sound we wanted, the sound we knew was built into the vintage ortho phones from the beginning but never realized in the marketplace. Long threads means finding what you want to know can seem impossible, but put down that guitar of discouragement and fret not-- one of the thread's stalwart friends, Ludovico Magnocavallo, made for us a dedicated SEARCH ENGINE, which I commend to you. Or use Google by adding the term <site:head-fi.org "orthodynamic roundup"> to your search terms in a URL field to restrict your search to this thread. The good news is that "orthos" are now back in the marketplace from two small companies, one in the US, the other in China, and with that, can orthos from the major brands be far behind? Hope is in the air.