Description
The RD-75 planar ribbon is extremely rare, no longer in production. It is the late David Graebener’s “ultimate transducer” magnum opus. Ultrawideband 100Hz-17KHz response; they combine incredibly low moving mass with the surface area of a 12” woofer and 200 watts power handling. 88dB sensitivity, they play very loud with no visible excursion, and have a fast, light, transparent character with large presentation and big stereo image. 7.5 octaves bandwidth from a single driver. For 12 years this pair of Bohlender-Graebener RD-75 ribbons were the centerpiece of my “Ultimate 2 Way System.” These RD-75s are mounted in a closed-back box (monopole, not dipole). The speakers are in excellent condition, built in 2005. Well cared-for. The cabinets were custom made for me by 3DZ audio in Colorado Springs. Matte black finish has no significant scratches or blemishes. Baby grand piano not included :^> They need no crossover in the ultra-sensitive 2-5K region where the ear is most sensitive. This is why the sound is so top-to-bottom coherent. These line-source handcrafted ribbon drivers deliver transparency, resolution, and transient ability. The proprietary RD-75 ribbon driver uses an ultra-lightweight aluminum foil diaphragm suspended between powerful neodymium magnets. Properly integrated, the response is smooth and level everywhere throughout the room. You can stand up, sit down, or even lay on the floor, and sound is consistent everywhere. This design minimizes floor and ceiling reflections. As soon as your ear rises above 6 feet elevation, the high frequencies vanish. That’s because the ribbon emits a cylindrical wave that does not reach the ceiling. You clearly hear every layer of detail in the recording. Vocals are lush and full and transparent. Percussion has clarity and drive. Plucked strings are almost visceral, when they need to be. One of the most remarkable aspects of the RD-75 is its ability to capture the attack and decay of musical notes with startling realism. The ribbon drivers lightning-fast response, combined with their exceptional linearity, ensures that even the most dynamic passages are reproduced with effortless precision and authority. Measurements and photos were taken this morning, which you see in the photos: Frequency response, several distances, on axis, left and right channels averaged together.Step response. Extremely clean with no phase reversals.Spectacular impulse response2nd and 3rd harmonic distortion below 1% above 150Hz Phase response, which is +/-30 degrees from 200Hz-15Khz. Unheard of.Notice the graph of Left/Right responses overlaid in real room. Im 95% sure the differences below 500Hz are because of the different position of the speaker in the room, not differences between the drivers; which match to within 1dB for great imaging.Because the ribbon is a line source (and not a point source), SPL drops 3dB each time you double distance, compared to almost all other speakers which drop 6dB each time you double distance. Greater projection for large rooms, and wider stereo image sweet spot for small rooms. Impedance is 6 ohms, resistive and almost straight-line flat. Super easy to drive. I used these in biamp configuration with active DSP crossovers. You can also use these with passive crossovers. If so, they need a notch filter to pad down the area around 5K. The schematic is available for that, just message me. I recommend using them above 200Hz with 12dB/octave crossovers. If you have a couple of woofers or subs with accurate low-midrange response and a DSP, its pretty easy to put together a fantastic sounding system that rivals commercial designs costing 10-20X the price. If you wish to use these dipole, you can take the backs off of the enclosures or take the RD-75’s out of the enclosures. Any mods are up to you. In my application, I was easily able to attain near perfect frequency, impulse, step and phase response with a 2-way system - at listener position in a real room with zero crossover voodoo (no exotic FIR filters, just standard 12dB slopes). Almost impossible to pull off with any other driver. Guaranteed to work as described. No other warranty, and I do not accept returns. The speakers MUST be crossed over at 150Hz or above, either passive or active. Match to suitable woofers. DIMENSIONS: Main enclosure: 76.75H x 14W x 5.5D Base: 18W x 14D Pick up from my home in Chicago. Shipping and packaging in continental USA only, will take time to arrange.
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