Raidho Acoustics D-5 Loudspeaker

Diamonds Are Forever

Equipment report
Raidho D-5
Raidho Acoustics D-5 Loudspeaker

If you’d like to hear all that is right about my current reference loudspeakers, the majestic, seven-driver, three-way Raidho D-5s, put on the Feria from Ravel’s Rhapsodie espagnol [RCA LSC-2183]. If you want to hear the very little that is wrong with them, play the same thing.

This is a recording with gorgeous string and wind tone— among the best on any RCA (and now even better on the Analogue Productions 200-gram LP reissue). But even the most silken strings and winds can turn a little rough-sounding when dynamics go way up—and part of what makes the Feria so delightful is that, after three languid movements, Ravel does dial dynamics up in his festive finale, starting with those dancing, dotted rhythms on piccolo and flute, proceeding to leaping mezzofortes on clarinets and bass clarinet with colorful harp and string glissandos, ebbing into swirling orchestral decrescendos that are like a great gathering of breath before the culminating exhalation of the crescendos, in which everything (winds, horns, trumpets, trombones, timpani, castanets, gong, celesta, strings, even a sarrusophone) sounds its glorious, floor-shaking note.

The trick with any stereo system is to reproduce all this—the individual voices, the murmurous decrescendos, and the explosive tuttis—while maintaining a concert-hall balance, i.e., without tipping into harshness or excess brightness on piccolos, flutes, strings, horns, and trumpets on fortissimos, or into muddiness on cellos, doublebasses, and timpani on pianissimos.

The D-5s can do this essential trick with even more sensational clarity, beauty, power, and realism than the Overall Product of the Year Award-winning Raidho C-4.1s I reviewed in Issue 236.

But, as was also the case with the C-4.1, you do have to pay an occasional price in midbass definition and control for all this musical largesse. In a little patch between about 60Hz and 80Hz—precisely where the doublebasses in the Feria occasionally play ostinatos—the D-5s can (can, mind you) sound plumper and somewhat less well defined than they do everywhere else. (Such excess midbass is common in ported loudspeakers, and I’ll have more to say about how to deal with it in my sidebar on setup.)

Raidho’s new flagships, the D-5s don’t so much replace my previous references, the C-4.1s, which are still in the C Series line, as exceed them in technological sophistication, performance, and cost. Though the two pairs of speakers look nearly identical— tall, svelte, ported, D’Appolito floorstanders with four mid/ woofers (two on top, two on bottom), two midrange drivers (one on top, one on bottom), and a single quasi-ribbon tweeter midway between—they are, in fact, substantially different. For one thing, the C-4.1s use aluminum-oxide ceramic diaphragms for their mid/woofs and midranges; the D-5s use extremely costly diamond/carbonite ones, made for Raidho at the Physical Vapor Deposition (PVD) Laboratory of the Tribology Center of the Danish Technological Institute in Aarhus. (The Tribology Center is dedicated to finding practical commercial applications for the ideas developed at the Technological Institute. Its PVD Lab is equipped with advanced machinery capable of depositing a layer of diamond on the membranes of Raidho’s drivers. Obviously, this kind of science and the equipment needed to execute it is well beyond the means of hi-fi companies, save in Denmark, where the government and the universities work in concert with small manufacturing firms. Of course, use of the Tribology Center doesn’t come for free. Companies like Raidho have to pay a sizable fee for the services of the PVD Lab. Nonetheless, the fact that a small company can access such a state-of-the-art facility is remarkable.)

What are the advantages of diamond/carbonite diaphragms? They are harder and stiffer than diaphragms made from any other material, which means, at least in theory, that they will remain linear and distortion-free up to a much higher frequency than ceramic cones (the second hardest, stiffest material). Where Raidho’s C Series midrange drivers have a peak breakup of 3-4dB at 12.5kHz, its D Series midrange driver doesn’t peak at the same amplitude until well above 20kHz, a full octave higher.

Why does this improved pistonic behavior matter? Because the higher in frequency a midrange’s breakup modes fall, the less likely those modes will add distortion to the sound of the tweeter. In the case of Raidho speakers, this is especially critical, since the tweeter is an extremely low-mass sealed-ribbon, whose own distortion levels are minimal.

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