The RD-75 is extremely rare, no longer in production. It is the late David Graebener’s “ultimate transducer” magnum opus. 88dB sensitivity, 100Hz-17KHz response; they combine incredibly low moving mass with the surface area of a 12” woofer and 200 watts power handling. They play very loud with no visible excursion, and have a light, transparent, fast sound with large presentation and big stereo image.
For 12 years these 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 cabinet was custom made for me, matte black finish and 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 I took this morning:
Above: Frequency response, several distances, on axis, left and right channels averaged together.
Above: Step response. Extremely clean with no phase reversals.
Above: Impulse response.
Above: 2nd and 3rd harmonic distortion.
Above: Phase response, which is +/-30 degrees from 200Hz-15Khz. Unheard of.
Above: left/right responses overlaid in real room. I'm 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.
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 online https://techtalk.parts-express.com/filedata/fetch?id=1317741
I recommend using them above 200Hz with 12dB/octave crossovers. I wrote up the system I used these with, you can read all about it here:
https://www.perrymarshall.com/articles/ultimate2way/
If you have a couple of subwoofers with good midrange response and a DSP, it's 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.
As you can see from the article, 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 no crossover voodoo (no exotic FIR filters, just standard 12dB slopes). Not easy to pull off with almost any other driver.
DIMENSIONS:
Main part of enclosure: 76.75H x 14"W x 5.5"D
Base: 18"W x 14"D
Price: $1950 OBO for the pair. Pick up from my home in Chicago. Estimated shipping (continental USA via truck, will take time to arrange): $1000.
For 12 years these 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 cabinet was custom made for me, matte black finish and 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 I took this morning:
Above: Frequency response, several distances, on axis, left and right channels averaged together.
Above: Step response. Extremely clean with no phase reversals.
Above: Impulse response.
Above: 2nd and 3rd harmonic distortion.
Above: Phase response, which is +/-30 degrees from 200Hz-15Khz. Unheard of.
Above: left/right responses overlaid in real room. I'm 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.
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 online https://techtalk.parts-express.com/filedata/fetch?id=1317741
I recommend using them above 200Hz with 12dB/octave crossovers. I wrote up the system I used these with, you can read all about it here:
https://www.perrymarshall.com/articles/ultimate2way/
If you have a couple of subwoofers with good midrange response and a DSP, it's 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.
As you can see from the article, 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 no crossover voodoo (no exotic FIR filters, just standard 12dB slopes). Not easy to pull off with almost any other driver.
DIMENSIONS:
Main part of enclosure: 76.75H x 14"W x 5.5"D
Base: 18"W x 14"D
Price: $1950 OBO for the pair. Pick up from my home in Chicago. Estimated shipping (continental USA via truck, will take time to arrange): $1000.
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I would have been all over these if I hadn't bought the Acoustat 6600's a few weeks ago! Very rare and hard to find, the RD-75! I have a pair if RD-50's for the TV and they sound fantastic....Good luck with your sale!