Isodynamic (aka orthodynamic)
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Isodynamic (aka orthodynamic) driver principle
Isodynamic drive headphones have drivers with flexible plastic film diaphragms into which a flat voice coil (spiral or serpentine in shape-- see photos below) is embedded or glued on for even distribution of the drive force. That is, the diaphragm is driven more or less equally over its entire surface at once, obviating the need to make the diaphragm rigid so that it can therefore be as lightweight and agile and nonresonant as possible. Isodynamic diaphragms are either lightly tensioned or corrugated to supply restoring force.
Magnetic assemblies (bar magnets or perforated disc magnets) on both sides of the diaphragm supply the magnetic field against which the voice coil's varying magnetic field reacts, which makes the diaphragm vibrate.
Isodynamic diaphragms are more massive than electrostatic diaphragms, but the equal-force drive principle allows them to move very quickly and in a coherent, uniform way, so provided there is sufficient mechanical damping, an isodynamic headphone gives excellent transient response and a sound quality not unlike that of an electrostatic.
Below you can find several brochures and pictures of various isodynamic drivers:
Brochures
 Yamaha YH-5M and HP series brochure (in Japanese) |
 Yamaha 19985 YHD series brochure (in German) |
 Yamaha YHD-1/2/3 Brochure - front |
 Yamaha YHD-1/2/3 Brochure - back |
 Yamaha YHD series brochure (in Japanese) |
 YH-1, YH-2 and YH-3 brochure front cover |
 YH-1, YH-2 and YH-3 brochure page 1 |
 YH-1, YH-2 and YH-3 brochure page 2 |
 YH-1, YH-2 and YH-3 brochure back cover |
 Yamaha Orthodynamic Brochure |
 Yamaha YHD-1 Manual |
 Yamaha YH/HP series brochure (in German) |
 Yamaha Orthodynamic brochure cover, with HP-1000, YH-5M and YH-100 |
 Aiwa 1978 headphone brochure |
 Fostex 1986 RP lineup, front |
 Fostex 1986 RP lineup, back |
 Fostex 1980 RP lineup Page 1 |
 Fostex 1980 RP lineup Page 2 |
 Fostex 1980 RP lineup Page 3 |
 Fostex 1980 RP lineup Page 4 |
 Fostex 1978 RP lineup Page 1 |
 Fostex 1978 RP lineup Page 2 |
 Fostex 1978 RP lineup Page 3 |
 Fostex 1978 RP lineup Page 4 |
 Sansui SS-100 Page 1 |
 Sansui SS-100 Page 2 |
 Aiwa 1977 headphone brochure |
 Tandy / Realistic headphone brochure |
 Realistic Pro 30 ad |
 Heco PHI 300 |
 Wharfedale Isodynamic headphones article |
 PMB Orthodynamic Lineup Brochure (in German) |
 Saba headphone brochure (PMB OEM?) |
 Telefunken 1978 headphone brochure (PMB OEM?) |
 Tandberg brochure(PMB OEM?) |
 Dual 1977 headphone brochure (PMB OEM?) |
 Dual headphone brochure (PMB OEM?) |
 Peerless Brochure p1 |
 Peerless Brochure p2 |
 Peerless Brochure p3 |
 Peerless Brochure p4 |
 Peerless Brochure p5 |
 Peerless Brochure p6 |
 Peerless Brochure p7 |
 Peerless Brochure p8 |
Pictures of drivers
 Yamaha HP-1 driver |
 YH-1000 Driver. Photo by Tomek |
 HP-50a Driver, Photo by ludoo |
 HP-50S Driver, Photo by DAC |
 Yamaha YHD-2 driver, photo by Góras |
 PMB 100 Driver Diaphragm (55mm dia.), showing corrugations |
 PMB 100 Driver Diaphragm, showing spiral voice coil traces |
 Technics EAH-830 Driver disassembled |
 Technics EAH-820 Driver Diaphragm |
 Sansui SS-100 Driver in housing |
 Amfiton TDS-15 Driver with bar magnets |
 Fostex T10 Driver removed from housing |
 Fostex T20V1 Driver |
 Fostex T50RP Driver - current model |
 Fostex T50RP driver with damper off |
 Maior RPT-50 Diaphragm And Magnet Structure |
 Realistic Pro 30 Drivers, Showing Damping Layer |
 Akai_ASE-50 driver, photo by ericj |
 Akai_ASE-50 driver, photo by ericj #2 |
 Grundig GDHS224 driver (55mm), photo by DAC |
 HOK80 v2 driver (44m), photo by DAC |
 Dual DK 830 driver, photo by M. Sieg. |
 Dual DK 720 driver, photo by DAC |
 SFI 120ohm, Scan by Ericj |
Links to Articles of Interest
