Raidho C2.1Earlier this year, at the Consumer Electronics Show, I had a conversation with Michael Børresen, president and chief designer of the Danish loudspeaker manufacturer Raidho Acoustics. He made one specific point about his company that, while simple in concept, struck me as alarmingly important in understanding his loudspeaker-design philosophy. Børresen said that whereas most companies buy raw drivers from third-party vendors but make their cabinets in-house, he decided early on that Raidho would do the opposite. He realized that while cabinet-making capability is readily available, designing and building drive-units from the ground up would give him the absolute technical control he needed to make Raidho speakers sound precisely as he envisioned them. Basically, he didn’t want to outsource what is arguably a loudspeaker’s most important component: its drivers. 

That conversation hit me like a ton of lead. Why don’t more speaker manufacturers actually make the things that make the sound -- the drivers -- themselves? Based on my experience, I’ve concluded that the answer is one of two things: Either they don’t know how to design drivers, or they don’t have the capital to invest in the manufacturing capability. 

One thing was certain from my conversation with Børresen: Raidho speakers are designed from the ground up and the inside out, starting with the drive-units. But then there are a number of technical elements that are important to Raidho. Read on . . .


The Raidho C2.1 ($28,000 USD per pair) is the smallest floorstanding model in the company’s C series. The new .1 designation (the previous model was the C2.0) stems from changes made in the development of Raidho’s flagship model, the C4.0. Above the C2.1 is a larger floorstander, the three-way C3.1, and below it the stand-mounted, two-way C1.1. The C2.1 (45.5”H x 20.5”D x 8”W, 110 pounds each) is a 2.5-way design, meaning that its top two drivers -- a 1” sealed-back ribbon tweeter and a 4.5” midrange-woofer -- are basically configured like a standard two-way (there is no low-cut filter on the midrange-woofer). The difference is that the C2.1’s third driver -- the bottom woofer -- augments the bass response of the midrange-woofer above it below 180Hz. This 2.5-way configuration is increasingly popular in compact floorstanders because it retains most of the simplicity of a two-way crossover while adding more bass and power handling than a single-woofer design could provide. 

Raidho C2.1 base

I exchanged a number of e-mails with Michael Børresen to learn exactly what was new in the .1 models, and he was quite forthcoming with information. That was a good thing, as nothing is different in the speakers’ appearance; it’s all under the skin, starting with the ribbon tweeter: “We have revised the tweeter by giving it a new interlocked conductive trace pattern,” Børresen said. “Where the former had a straight-line pattern, the new one has a waved interlocking pattern. The main result of this is that the tweeter membrane is driven over a much larger area and the non-driven areas have been reduced by more than 90%. The thing is that, from a measurement point of view, nothing has changed: specs remain the same, distortion unchanged; but to the ear everything has changed. I believe that the main change is in the frequency band above the hearing/measuring limit, and performance there is equally important.” 

The bass driver used in Raidho’s original C-series speakers was developed eight years ago. Some would say it was ahead of its time, due to its excellent stiffness in-band and the use of neodymium magnets. Also novel is the mounting method: the front face of each driver’s chassis, machined from aircraft-grade aluminum, also acts as a portion of the speaker’s front baffle. The new versions of the Raidho drive-units offer evolutionary improvements. Børresen: “It’s all about the dynamic nonlinearities that are present in all loudspeaker designs. There’s deflection in the surround and suspension, there is inductance in the voice coil, and hysteresis losses in the voice-coil former, just to mention a few of the items that have been refined. In real terms, it means that geometry has been optimized, that the voice-coil former material has been changed to titanium, and that the inductance in the voice coil has been reduced to one third! The titanium is free from the dynamic hysteresis damping that is so present in the aluminum material previously used.” 

Raidho C2.1 binding posts

As for the C2.1’s crossover, that, too, has been tweaked in terms of the wiring and parts quality. As for his company’s overall approach to crossover design, Børresen said, “In Raidho speakers the drivers are wired in series and the unwanted frequencies are then diverted around the driver by the crossover components. This has one profound advantage: In the crossover region, the drivers are fed the exact same current. This keeps the phase response stable under dynamic loads. It translates into speakers that don’t change character when loaded, and the acoustic image remains stable. In the C2.1 the crossover point is at 3kHz. The bottom bass driver in the 2.5-way system is rolled off at approximately 180Hz. The cabling on the Cx.1 is now a combination of Nordost Valhalla and Odin.” 

Lastly, I was impressed that Raidho can not only make a speaker that has flat frequency response, but that they have the psychoacoustic understanding and the engineering expertise to make it not flat in a very specific way. Børresen: “The crossover region becomes rather critical, and though the school books tell you to make this region straight and flat, I don’t make it flat, because flat means it stands out! Our hearing will immediately recognize the tiny differences going on in that region and thus divert our attention there. The solution is to make a deliberate suckout in the crossover region where the frequency response has a 2-3dB dip centered at the crossover point. So Raidho speakers do not deliberately measure straight, they sound straight. This was the accident of the famed BBC monitor LS3/5A; people have often seen this curve as a target curve for loudspeaker design, and even some digital-correction units have this BBC curve built-in for adjusting speaker response, which is plain wrong. The BBC curve is not universal, but fits those drivers in that exact implementation.” 

The C2.1 has a claimed sensitivity of 87dB (2.83V/1m), a nominal impedance of 4 ohms, and a frequency response of 40Hz-50kHz. There are three ports on the rear panel, and a single pair of five-way binding posts. The finish options are Walnut Burl Veneer, Black Piano, and White High Gloss. The rather narrow C2.1 has a plinth with a wider footprint than the speaker itself, for solid lateral stability. I found the overall build quality to be very good, and in keeping with what’s typically seen at the price. 

It’s fair to say that Raidho speakers are highly engineered, and specifically voiced to produce a sound that is all Raidho. The question was, what would I think of that sound? 


Although I gave the Raidho C2.1s a solid week of break-in before I began any serious listening, it was during that week that my first observations formed. I watched several movies in those first seven or eight days, and with each film there was at least one interesting moment in which my head darted to one side of the room or the other. Each time, some odd effect here or there in the soundtrack seemed to come to life, sounding both strikingly real and ultraprecisely placed to the outside of a speaker cabinet: a screeching chalkboard, metal scraped against metal, a voice off to one side -- these movie effects were the first hint that the Raidhos were quite different from other speakers that have recently visited my Music Vault. 

Raidho C2.1 set up

Once I began listening to music, the C2.1’s character took on a more definite shape. First, there was no indication that the output of the ribbon tweeter was in any way sonically disconnected from that of the midrange driver. The transition was simply seamless -- the two drivers sounded as one, as Michael Børresen had indicated they would. I repeat: You won’t hear the C2.1’s tweeter while separately hearing its midrange. The blend, as near as I could tell, was perfectly transparent. 

Looking at the C2.1’s in-room measurements, that depression centered at 3kHz that Børresen referred to is clearly obvious visually. Also, you can see the smooth rise in level out to just about 20kHz. I was somewhat concerned that the rise might make the speaker sound a bit hot in the uppermost treble over the long term, but that never happened. So much for conventional wisdom. The ribbon sounded detailed and airy when it needed to be, but never bothersome or sonically obvious in any way. The takeaway: The Raidho C2.1 could be just right for those listeners who love ribbon tweeters and for those who can’t stand them. 

Raidho C2.1 in-room responseFrequency response in Jeff Fritz's Music Vault listening room (smoothed to 1/6th octave).

Moving down into the midrange, the good news continued: I heard a substantially neutral midband with no tonal discontinuities. As you might also surmise from the frequency-response graph, the mids weren’t upfront in the soundstage, but nor did they sound distant or diminished in scale. First-rate articulation was a defining characteristic of the C2.1, which reproduced all the small shifts and nuances that make music sound exciting and lifelike. Kristy’s version of the 1944 standard “It Could Happen to You,” from her My Romance (16/44.1 AIFF, Alma), was smooth but not homogenized. Don Thompson’s bass never got boomy or indistinct, as it can sound through lesser speakers. The C2.1s could play intimately, but with finesse and speed. 

But could they rock? I played Adele’s “Rollin’ in the Deep,” which everyone in the world now owns, from her 21 (16/44.1 AIFF, XL Recordings). The sound was punchy and clear, even if the recording itself lacks the dynamic range to make the song as good as it could be. Nonetheless, the Raidhos were not so polite that they robbed the music of its energy and propulsion, as some audiophile speakers do. In short, rock rocked. 

Those invisible crossover frequencies were again not on display with acoustic piano music of all genres. I tried to listen for where and when the lower woofer in this 2.5-way design came into play and found it simply not doable. The upper bass was punchy and quick but not lean or thin. The lower bass was surprising, given the modest driver complement. I was not expecting the smallish woofers to be able to do justice to the bass-drum whacks in “Norbu,” from Bruno Coulais’s music for the film Himalaya (16/44.1, Virgin). Although the post-whack decay was cut a bit short, and the C2.1s failed to fully pressurize my room as larger speakers have, the initial stroke was clearly audible, and there was enough impact that I could feel it in my chest. Impressive, even if not fully realized. 

Raidho C2.1 footers

There were times when I knew I was reaching the limits of what the C2.1 could do in the bass. Jonas Hellborg’s The Silent Life (16/44.1, Day Eight Music), particularly “Low,” will test the limits of any speaker. His electric-bass playing on this track (and on the whole album) is pure energy, and soars in a way rarely heard from this instrument. The Raidhos were capable of getting about 90% of his virtuosic performance just right, but couldn’t quite reproduce the scale and physical propulsion of the bottommost frequencies that are required to make “Low” come fully alive. But I’ve never heard a speaker with so limited a driver complement reproduce as wide a bandwidth as the Raidho C2.1. 

And when it came to high-resolution music, the C2.1 was quite capable. In fact, here is where it shone. As I fed the Raidho better and better source material, it kept pace by giving me more and more resolution of fine detail and musical nuance. It never got hot in the top end or brittle in the midband, but just kept digging deeper and deeper into the recorded event, exposing more musical beauty at every turn. I listened to our own 2L-TWBAS 2012 Sampler (2L, in its entirety at 24-bit/176.4kHz. The Norwegian Armed Forces Staff Band’s version of Eugène Bozza’s Children’s Overture sounded outstanding. I could hear deep into this recording and marveled at the detail, particularly in the highs. The bells and brass were simply crystalline in nature, with completely delineated decays and crisply rendered transient attacks.

Raidho vs. Sonus faber

The Sonus faber Amati Futura ($36,000/pair) is a bit more expensive than the Raidho C2.1, but both are stylish, modestly sized floorstanders designed to enhance their surroundings rather than detract from or dominate them. With its engraved chrome and stringed grilles, the Amati is the visually “louder” speaker; you could say that it’s exceptionally tasteful in its bling, but understated it is not. The Raidho C2.1 is a touch more subdued. Its aluminum front baffle (actually, drive-unit faceplates) is matte black and it has a very narrow profile, but these elements are optically set off by its bright-white drivers. The body of the Raidho’s cabinet is very nicely finished, if not quite to the same glass-like glossiness as the Sonus faber’s. In terms of build quality, the speakers seem about equal: Both are solidly constructed, and all parts, seams, and fittings appear to have been sweated to the same level. The Amati is physically slightly more substantial, but that’s no surprise given its larger size, four drive-units vs. three, and wider front baffle. 

The Raidho C2.1 is a 2.5-way, the Amati Futura a 3.5-way, which means the Sonus has substantially more cone surface area for reproducing bass frequencies. In addition to that, perhaps the most obvious difference between the two -- and this proved important in the listening -- was the C2.1’s ribbon tweeter vs. the Amati’s soft dome. The ribbon, in this case, sounds more extended, and is the more high-resolution driver, plain and simple. 

The Sonus faber sounded softer and more polite up top, and therefore not able to reproduce the air and space around performers as well as the Raidho. The Amati was slightly more forgiving of bright recordings and the speaker’s overall voicing was always easy on the ears, but even with its ribbon and the detail it imparted, I didn’t find the C2.1 at all aggressive up top. The Sonus faber Amati Futura sounded, in the upper frequencies, exactly as its in-room frequency-response plot would lead you expect it to sound, but the Raidho did not -- it didn’t sound a bit tipped up, even though the graph indicates that it should. 

As different as the two speakers’ highs were, their reproduction of the low end also greatly diverged. The Sonus faber could play bigger and go deeper in the bass than the Raidho -- not surprising, given its bigger bass drivers -- but the C2.1 was more adept at following bass lines with maximum articulation and faithfulness while perfectly tracking the musical flow. Both speakers’ midbands were generally neutral, and neither exhibited any tendency to compartmentalize the various regions of the audioband, which indicates an ideal blending of driver outputs in each. Last, as mentioned, the Sonus faber could sound bigger and more authoritative, but the Raidho surprised me with its ability to pull details out of recordings and spring them on unsuspecting me. Both pairs of speakers cast a wide, deep soundstage; with either, I had nothing at all to complain about in the departments of soundstaging and imaging.


The Raidho Acoustics C2.1 is a high-resolution, maximum-articulation transducer that delivered sound in a wholly digestible way that will suit more people than not. It could wow me with its ability to resolve fine detail, but it never fatigued me over the long haul. And its great sound comes in a handsome package that will nicely suit most rooms in which the C2.1s might be placed. 

I now know exactly why Michael Børresen wanted to design the C2.1 from the inside out. He was after a particular sound, and he needed to follow his own technical path to get it. In an era of me-too products, the Raidho C2.1 stands out as unique: You won’t find its drivers in speakers made by any other company, nor will you hear this sort of sound from any other product. I recommend that you find a place to listen to a pair of C2.1s, to hear if their performance fits your vision of what high-fidelity sound should be. Me, I’m a believer. 

. . . Jeff Fritz

The World’s Best Audio System, May 2012 

  • Speakers -- Sonus faber Amati Futura
  • Amplifier -- Gryphon Audio Colosseum, McIntosh Labs MC452
  • Preamplifier -- Gryphon Audio Mirage, Ayre Acoustics KX-R
  • Sources -- Apple MacBook running OS X Snow Leopard, iTunes, Amarra 2.1, Audirvana; dCS Debussy DAC
  • Cables -- Nordost Valhalla, AudioQuest Wild Blue Yonder interconnects; Nordost Valhalla, AudioQuest Wildwood speaker cable

Raidho Acoustics C2.1 Loudspeakers
Price: $28,000 USD per pair.
Warranty: Five years parts and labor. 

Raidho Acoustics
c/o Dantax Radio A/S
Bransagervej 15
9490 Pandrup
Phone: +45 98 24 76 77