HI-END ribbon high-frequency loudspeaker NdRL 81 MKII

    Direct radiating ribbon loudspeakers are used very often in the modern HI-END audio systems  for reproduction of the high frequencies. The reason is due to the method of transducing the electrical energy into acoustic one, which ensures high electro-acoustical properties.
    *  The Frequency Response is very smooth in the reproduction range, as the applied electrodynamic force is equally distributed across the whole area of the ribbon. Thus regardless of the high compliance of the ribbon (it's thickness  is very small - 3...10 micrometers),  it  vibrates like a piston. So, there is no way local vibating systems to be developed, which are the primary reason for irregularities in the frequency response of the speakers.
    *  The nonlinear distortion of the ribbon drivers is very small. It is based on the reason, that the vibrating of the whole ribbon is controlled by the synchronous and equally distributed electrodynamic force. This does not allow additional parasitic vibrations.
    *  The Impulse response is very correctly reproduced by ribbon drivers. In the reproduction frequency range the mechanical impedance of the moving system is determinated mostly by the radiating resistance, which is active, and therefore the ribbon vibration is aperiodic. This determines the best achievable "waterfall" characteristic, as the vibration stops almost immediately after the end of the electrical signal at the input. This is why the ribbon drivers are the least colorating speakers.
    *  The polar response is omnidirectional in horizontal plane (with ribbon oriented verticaly!) because the width of the ribbon is less than the wavelength of the highest reproducible frequency. There is some narrowing of the radiation in vertical plane, due to the length of the ribbon.
    *  The electrical input impedance is easy to be made active and almost constant, wftich is very Important for the correct work of the filter and the power amplifier, driving the loudspeaker.
    *  The power handling capacity of the ribbon driver depends on the thermal capacity of the ribbon itself. Essentially it is small, as the mass of the ribbon is very small. The thermal capacity can be expanded with appropriate heatsinking in the form of two, acousticaly transparent metal lattices, placed at small distance at front and back of the ribbon. The power capacity depends also from the crossover frequency and the slope of the highpass filter feeding the driver.

    The last modification of direct radiating ribbon high frequency loudspeaker, which is produced in Audio Research Laboratory is NdRL 81 MkII. Much of its electroacoustic parameters are published in the journal Hobby 6 / 2005. This modification is using neodymium-iron-boron permanent magnets. Magnetic induction in the area of the ribbon is 0.42 T. The ribbon is mounted on a stable framework of doublesided copper clad plate, 1.5 millimeters thick, and is elastically glued throughout its periphery. It is further cooled by two acoustically transparent aluminum lattices, placed at front and back of the ribbon.
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