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This review first appeared in the June 2013 issue of hi-end hifi magazine High Fidelity of Poland. You can also read it in its original Polish version here. We publish its English translation in a mutual syndication arrangement with publisher Wojciech Pacula. As is customary for our own articles, the writer's signature at review's end shows an e-mail address should you have questions or wish to send feedback. All images contained in this review are the property of High Fidelity or Raidho. - Ed

Reviewer: Wojciech Pacula
CD player: Ancient Audio Lektor Air V-edition
Phono preamplifier: RCM Audio Sensor Prelude IC
Cartridges: Miyajima Laboratory Shilabe & Kansui
Preamplifier: Ayon Audio Polaris III Signature with Regenerator power supply
Power amplifier: Soulution 710
Integrated amplifier/headphone amplifier: Leben CS300 XS Custom
Loudspeakers: Harbeth M40.1 Domestic + Acoustic Revive custom speaker stand
Headphones: Sennheiser HD800, AKG K701, Beyerdynamic DT-990 Pro 600Ω vintage, HifiMan HE6
Interconnects: CD/preamp Acrolink Mexcel 7N-DA6300, preamp/power amp Acrolink 8N-A2080III Evo
Speaker cable: Tara Labs Omega Onyx
Power cables (all equipment): Acrolink Mexcel 7N-PC9300
Power strip: Acoustic Revive RTP-4eu Ultimate
Stand: Base IV custom under all components
Resonance control: Finite Elemente Ceraball under CD player, Audio Revive RAF-48 platform under CD player and preamplifier, Pro Audio Bono PAB SE platform under Leben CS300 XS
Review component retail in Poland: 69.950zł/pair in Walnut as reviewed

Speaker specifications as quoted by their manufacturers can be quite useful. Reading those supplied with Raidho Acoustic's D-1 one learns that they are two-way speakers, 200 x 370 x 360mm and 12.5kg each sporting a 2nd-order crossover at 3kHz, rear vent, ribbon tweeter and 115-mm 'diamond' mid/woofer. The latter's diameter is that of the cone without surround. What one doesn’t learn from these specs is that the speakers are very expensive, beautiful, very solidly built and employ a proprietary Raidho cutting edge diamond technology woofer cone coating that was used for the first time in this model.

The latter is the only difference between the D-1 and C-1. Although that difference might seem small, The Abso!ute Sound editor Jonathan Valin had no doubts about awarding them 'Best of Show' in his coverage of CES 2013. Diamond has long been known and appreciated in audio. It’s been used in turntables for styluses and bearings and in tweeter and midrange diaphragms for it unmatched rigidity and abrasion resistance. In the case of driver diaphragms key is diamond’s hardness which gives it unparalleled stiffness. According to Raidho diamond is 140 times harder than the ceramics which many manufacturers already consider to be a much better material than paper. Raidho implemented their diamond differently than most. Instead of for the entire cone, a thin layer forms a surface skin.

The amount of pure diamond applied to each cone equals 1.5 carat [that's 0.3g – Ed] to make it extremely expensive. The cone’s base is a sandwich composed of a thin aluminium core with sintered ceramic skins on either side. By adding a final diamond layer to both sides the first fundamental cone resonance is pushed up from an already very high 12.5kHz beyond 20kHz.

This may seem unimportant when the driver is crossed over at a much lower at 3kHz where even a gentle 2nd-order filter should adequately deal with a 12.5kHzresonance. In reality parasitic cone resonance is extremely difficult to suppress. I know this only too well from various driver designs. The D-1’s 3dB resonance peak—which must be stressed is quite modest—is damped by 36dB at the crossover frequency. It's still not very much but significantly more than in the case of aluminium and ceramic cones.

The Raidhos also feature a unique tweeter. The manufacturer uses a rather large FTT75-30-8 quasi ribbon in a sealed chamber to provide damping. It incorporates an array of neodymium magnets to power an ultra-thin 0.02g aluminium membrane. The mid/woofer is angled upward to ensure better phase alignment with the tweeter. Thick aluminium front and rear panels ensure proper cabinet rigidity. The D-1s also come with great looking stands (at 6.950 PLN/pr). Those are not too heavy but well thought out and tailored to these particular boxes. Special care was taken to provide maximally efficient speaker isolation. The box doesn’t sit directly on the top plate but decouples from the stand via small discs supported on metal ball bearings.

Using heavy speaker cables like my Tara Labs Omega Onyx may prove to be a problem. The decoupling in the stands has some play both beneath the speakers and in the floor footers. If we put weight at the rear of the speaker, the whole assembly moves backward lightening the front to be less than ideal. I solved this by putting a pile of heavy books on each stand’s MDF plinth.

Two men are responsible for Raidho's speaker and driver designs - president and chief designer Michael Børresen and co-designer/sales manager Lars Kristensen. Lars’ professional career is particularly interesting. He is associated with the Nordost Corporation hence all Raidho speakers use very expensive internal Nordost wiring. The D-1 goes all out with Odin Supreme Reference. Lars is also associated with the Dantax Group led by John Jensen, former Scan-Speak owner. That association resulted in the development of in-house drivers which is quite unique. Typically speaker manufacturers with a few exceptions like Dynaudio, Focal, Triangle, Cabasse, Harbeth and Spendor (save for tweeters) use drivers manufactured by big specialists like Scan-Speak or Seas. Developing advanced transducers in-house requires money and experience. In this case both were provided by the Dantax Group in addition to Raidho’s own design and creative ideas. In fact almost all the components in these speakers were made in a small Raidho factory or order by one of their Danish subcontractors. Only the wooden cabinets come from China to look better than a large proportion of those made in Europe.