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Full drive orthodynamic headphones created through the fusion of the developers' spirit of inquiry and high manufacturing technology.
These headphones were called sensational right from their release thanks to two distinct features. One was the introduction of the "orthodynamic" full drive dynamic sounding body. This features a voice coil printed directly on the diaphragm, sandwiched in front and behind between thin perforated magnets through which sound passes, meaning that because the drive source directly becomes the sound source, divided vibration and transmission loss will in principle not occur.
This line of thought had been around for a long time, but although there were commercial products making use of the concept prior to the HP-1, none had been successful. The reason was simple. Basically, such products were difficult to manufacture, and not much benefit was found to offset the difficulty.
Looking at the HP-1 sounding body again, its diaphragm was composed of 12μ thick polyester, exactly the same as the thickness of a C90 cassette tape. That is, it could be described as an ultra-thin film. On this surface, the voice coil was densely photo-etched in a 250μ interval spiral. The voice coil was further divided into five concentric rings, the winding directions alternating for each section and the magnet likewise divided into five corresponding sections with alternating N and S poles. This meant that through a combination of the curiosity of developers and advanced manufacturing technology, this method could be successfully realized for the first time.
The other feature lies in the simple and practical form commissioned from renowned Italian industrial designer Mario Bellini. Even more than simply the beauty of its appearance, the contact of the ear pads with the ear, twin headbands sharing in supporting the entire headset on the head, and its light, airy fit thanks to a universal joint connection that allowed the ear pad section and headband to move freely must have strongly impressed the meaning of the concept of industrial design upon the audiophiles of the time.
The mid-1970's were a period of exploration seeking the next generation technology to replace the traditional round dynamic speaker. With attention in the high-end scene focused on full drive (planar) speakers, several leading makers introduced condenser (electrostatic) headphones into the market in quick succession. Considering the magnet plate as being replaced by electrodes, in operating principle the HP-1 orthodynamic headphone was very close to condenser models, an ideal method for combining the characteristics of the condenser and the ease of use of the dynamic model, no doubt serving as a demonstration of its own principles. From the catalog of the time, you can see the development team's enthusiasm to try to create something from zero that had never previously been seen anywhere in the world.
