March 2001

The Second Réthm Loudspeaker
Review by Dick Olsher
Click here to e-mail reviewer

  Let me first dispense with the first obvious question. No, it's not pronounced like in "I've got rhythm." Rather, Réthm is Sanskrit for harmony, and its intended design objective is to communicate the music's body and soul. The Réthm Loudspeaker is the brainchild of Jacob George, an architect with a practice in both California and India. As the story goes, Jacob bought a 5-watt amplifier in 1998 and started a frustrating search for a suitable high-efficiency speaker. I think that most of us who've been there and done that can sympathize with Jacob. Eventually, his search led him to the Lowther driver. The second Réthm - the top of the line - uses a single Lowther driver. That's it! There are no additional woofers and tweeters. The cost of the system depends on the Lowther driver model selected by the customer: the DX3, PM2A, and DX4 being available. My review samples were outfitted with the DX4, which I consider to be the best of the current Lowther driver catalog.

There's a fair amount of controversy that surrounds the Lowther full range driver. On its best behavior, the midrange magic is absolutely stunning, and true believers would argue that it surpasses even the famed QUAD-57 electrostatic in terms of transparency and dynamics. On the other hand, one has to contend with some nasty cone breakup modes, the most annoying ones being centered between 2 and 3 kHz. This so-called "Lowther quack" has driven many listeners off the deep end. And, of course, there is still the practical problem of matching the midrange sensitivity of the Lowther in the bass. The hackneyed rear horns of the 50s and 60s (e.g., the Acousta 115) just didn't get the job done in the bass. As a consequence, Lowther-based loudspeakers had been stereotyped as severely bass shy. I certainly could not live with the Acousta 115's lack of bass response, and I don't think that many mainstream audiophiles out there would put up with a 90 Hz bass response. But the bass problem has never been Lowther's fault. It's merely a question of application.

I find it ironic that the Lowther paper twin-cone driver, originally patented by Paul Voigt in England in the 1930s, and considered state-of-the-art some 60 years ago, has once again surfaced as a candidate for supreme musical transducer. The techies look at its cartridge paper main and funky whizzer cones with derision. The implication here being that a light twin-cone design just can't compete with ribbons, electrostatics, and multi-way electrodynamic speakers using a flock of sophisticated drivers. Read my lips: oh yes, it can!

If one were to dissect the current loudspeaker population, I imagine that it would be possible to define a normal distribution. The "bell shaped" curve would be dominated at its center by the vast majority of modern designs, namely multi-way box speakers. The tails of the distribution would be taken up by more exotic designs. For example, ionic tweeters, electrostatics, and good sounding planars would fall to the right of center, and stuff that attempts to defy the laws of physics (i.e., just doesn't work) to the left of center. The vast speaker middle ground follows established engineering principles and yields predictable sound quality as well as an extended frequency range. It's canned sound at its best, and most of us take it for granted that this is what hi-fidelity is all about. And how can you judge any differently, having grown up in a multi-way speaker world.

So what's wrong with multi-way speakers? In a single word, they lack coherency. Exactly what is coherency? It's a difficult sensation to put into words, but I certainly know it when I hear it. It reminds me of the story about a dog who chased cars all his life. When he finally caught one, he was asked about it: I don't know exactly, but it kind of tasted like chicken. Imagine drivers spread out on a front baffle; woofer on the bottom, a midrange a foot away, and a dome tweeter near the top. Such conventional designs are based on the premise that it is permissible to divide up the frequency range and assign portions of it to a dedicated driver. A tweeter, being physically small, excels in the treble range, while a woofer performs the grunt work of moving air in the bass and midrange. Thus is born the ubiquitous two-way speaker. Furthermore, the availability of good inexpensive $10 dome tweeters allows for an economical design. Unfortunately, what you end up with is a speaker where the music's fundamentals and some harmonics are reproduced by one driver, and most upper partials by another. In other words, each instrument is reproduced by two voices (in the case of a two-way) or multiple voices in the case of three or four-way designs. This is the crux of the matter. It has nothing to do with the electrical crossover network, which is often pointed to as a sonic culprit. The few caps and coils of such a network pale in comparison to the part count of the preceding electronics. The lack of coincidence is more serious. Since the drivers are spread out of the front baffle, interference effects are unavoidable. It's possible to find a microphone location which yields a well-behaved response, but move the mic a few inches one way or another and serious response dip and peaks result. Guess which frequency response measurement makes it into the speaker's promotional brochure!

The most serious problem, however, is the mere fact that two or more voices are reproducing each instrument - each voice with its own set of colorations and harmonic distortion spectra. This creates a big problem for the auditory system, as it tries to sift through the auditory stream and fuse related harmonics into a perceptual whole. The post processing within the brain attempts to untangle the jumbled harmonic tapestry arriving at the ear into distinct perceptual streams. Related harmonics are fused together on the basis of synchronicity and common pitch and volume modulations. The brain has to work harder to form an external picture of the soundfield when the harmonic spectrum of each instrument is reproduced and modified by disparate drivers. This is an issue with even $50K multi-way system, because the midrange driver is typically crossed over at 3 kHz, right smack in the upper midrange. The proof is in the listening. A good full-range driver produces a far more believable, life-like image of a musical instrument than a multi-way is inherently capable of. Before you start those nasty letters and e-mails coming my way, note that I freely admit that multi-way designs are capable of exquisite focus. It's just that they never transcend the line between a copy and the real thing. Voigt firmly believed that the audio spectrum should be covered by a single speech coil source, and Donald Chave, the founder of Lowther, continued that design philosophy. To date, Lowther has never deviated from that principle. Another pioneer of full-range driver technology, H. A. Hartley, experimented with a two-way design as early as 1930. He displayed that speaker at the National Radio Exhibition in London in 1931 and many people thought it was wonderful. Ultimately, he withdrew it because he thought it sounded terrible. There was that woofer resonance he hated, but also because he "disliked the sound coming from two separate and distinct sources."

The Réthm Technology

The unique cabinet design never fails to elicit a quizzical double take. I can see the wheels turning: why the Swiss cheese "holes" in the side panel? These are actually vents or ports for the rear line. The cabinet is not really a box at all. It basically consists of a long folded fiberglass shell, which terminates in two ports. The shell slopes toward the rear, then makes a loop and comes up toward the driver.

The most popular solution for matching the midrange sensitivity of the Lowther in the bass range has been to use a rear horn. Not only are all of these rear horns folded to save space, but they are also of constant width. That is, the width dimension remains constant along the length of the horn - the flare taking shape only along the height dimension. Thus, well-known rear horns such as the Acousta 115 and the Medallion-II bear little physical relationship to straight circular cross-section horns that they attempt to emulate, and the entire design process becomes an art form. Jack Dinsdale, in his classic series of horn articles for Wireless World (1974) puts it as follows: "As soon as one departs from the straight horn of circular cross-section, the scientific design principles described cease to be relevant and become more of an approximate value…" This follows on the heels of Wilson's admonition (1972) about the performance of folded horns: "It cannot legitimately be assumed that a horn incorporated in a cabinet has the precise characteristics of any particular type of straight horn, whether exponential, hyperbolic, catenary or tractrix, even though their dimensions have been used as guides in its construction. The multiple changes of direction, coupled with reflections and absorptions and internal resonances, are always such as to destroy any legitimate comparison. Every internal (horn) enclosure construction must be judged on its own merits as revealed by measurement and by listening tests." No wonder then that so many competing rear horn designs have surfaced over the years, with each designer claiming to have finally seen the Promised Land. An even bigger practical problem is that all current designs known to me are not long enough and therefore lack sufficient mouth size to support deep and uniform bass.

Réthm Impedance

Having said all that, you might expect that the Réthm breaks new ground in rear horn design. Despite the claims, the surprising finding is that it is not a horn at all. Jacob George initially experimented with rear horns without any satisfaction, and finally decided to throw the book out. After many iterations, he came up with the present configuration, which legitimately can be described as an acoustic labyrinth. Horns come in many shapes, but they have one feature in common: they expand from a narrow opening called a throat to a larger opening called a mouth. Here the rear line does not flare at a specific flare rate required by a true horn; it is basically a pipe coupled to the back of the driver. A damped pipe would be acoustically equivalent to a transmission line, while an acoustic labyrinth features little or no damping. Hence, one would expect such a line to generate multiple organ pipe resonances.

These resonances are evident in the impedance magnitude plot, each peak denoting an odd harmonic of a fundamental pipe resonance. Overall, this is a very easy amplifier load, with the minimum impedance not dipping below about 9 ohms.

The peak at 3 kHz indicates a strong cone breakup mode, which brings me to the business of taming the Lowther quack or shout. Lowther claims to treat the cones in order to eliminate "uncontrolled" cone breakup. But considering how thin these cones are, any treatment should be considered as no more than a band aid. A thicker cone would of course be better damped, but the mass gain negates efficiency. For example, the Fostex full range drivers are considerably thicker, and thus better damped internally. Based on my experience with the Fostex FE208 Sigma, it is also better behaved.

Out of the box, the Lowther drives me crazy with its upper midrange and treble excess. The first impression for many naïve listeners is: wow, I've never heard anything so clear and lively! Yeah, a 10 dB peak at 2-3 kHz will definitely rattle your ear wax. But anyone who in the long run can embrace the raw, untamed, Lowther sound is either a masochist or totally clueless about natural musical timbres. Clearly, the Lowther benefits from a significant break-in period. The factory recommends a period of some 60 hours, although several hundred hours is probably more optimum, during which time the cone breakup becomes a bit better behaved. But continued play time will never eliminate the quack. More radical means are required. Various acoustic means have been attempted to control the midrange peak. These include placing wool or foam behind the whizzer cone. The usual result is to suck the life completely from the driver. I have experimented with passive electrical means of equalizing the midrange and upper range of the Lowther with excellent results. Instead, Jacob George opted to use a novel acoustical filter. He suspended a tertiary cone just outside the whizzer cone. This cone does not actually touch the whizzer, but provides some damping and attenuation for the whizzer cone output. As you will see in a moment, this solution is not entirely successful.

The Sound

Réthm MLS

Careful room placement is essential in order to elicit the Réthm's full sonic potential. Allow about five feet of breathing space from the rear wall. In addition, toe the speakers either straight out or at the most slightly in toward the listening seat - depending on the distance of your listening seat from the speakers. Feel free to experiment in this regard, but I think you will agree with me that this is not a speaker that is meant to be listened to on axis. As you can see from the above frequency response plot, the speaker does not gel in the near field (1 meter), and the lower treble is quite excessive, being peaked by about 6 dB. However, once you move off axis, at least 3 meters away into the room, the response smoothes out considerably. The following plot shows the measured response at my listening seat.

The intent here is to illustrate the tonal balance I experienced. The deep bass is clearly deficient in level. But the midbass, while uneven, sounded tight and punchy - a far more convincing bass performance than I was able to elicit from the Lowther Club of America Medallion II rear horns (a variant of the Acousta 115). The overall balance worked much better for a Jazz ensemble than it did with symphonic music, being too thin to properly support an orchestral foundation. A few more dB of sound level in the upper bass would have helped in fleshing out the power range of the orchestra as well as preserving the full majesty of a cello's timbre. Neither are the highs state-of-the-art. The treble lacks the ultimate in finesse and resolution, but I can tell you that it integrates nicely with the midrange, which is where the Réthm clearly blooms.

Réthm MLS

The Lowther's large magnetic flux and lightweight cone guarantee a huge acceleration factor. In fact, the complete diaphragm assembly weighs a mere 11 grams - including air load. This is yet another example of Newton's law in action: a large force acting on a small mass, giving high acceleration. Here, unimpeded by disruptive early reflections from the compression chamber (a major issue with the Acousta 115 rear horn), musical transients are launched with remarkable speed and clarity. But there's a lot more to the Réthm's magic than that. If you're even remotely a music lover, its startling sense of coherency will take you breath away. After a lifetime of exposure to the safe and plodding sound of multi-way speakers, there's bound to be an instinctive reaction to the music's believable immediacy, natural ebb and flow, and dramatic urgency. The Réthm is exceptional in communicating the music's emotional content. Listen to familiar music and discover what you've been missing all these years. This was especially true of female voice. For example, a studio recording by Nana Mouskouri (Quand Tu Chantes, Philips 818-175-2), which I've always thought to be totally and hopelessly insipid, came to life unexpectedly. Although it's tempting to dismiss Nana as the Greek Linda Ronstadt, she is in fact a chanteuse of the highest order. New layers of emotional nuances emerged and catalyzed the music like never before, and instantly this album shoots from the bottom of the pile straight to the top. It is interesting to note that the "singer's formant," a prominent spectral peak near 3 kHz, found in voice sounds produced by classical operatic singers and which allows them to cut through the power of a full orchestra, coincides with the upper midrange response emphasis produced by the Lowther.

This same emphasis, however, did not always serve the music. It's a narrow peak, but when it's excited the driver rings, and I'm not talking about the telephone here. Michala Petri's recorder (The Ultimate Recorder Collection, BMG74321-59112-2) took a direct hit, sounding far too shrill. With this speaker, you'll have to choose your music carefully. Some albums will sound divine, and others pretty wretched. This brings me to the business of matching amplifiers. Power is normally not an issue, as I've used the Diva Seduction series 2.5 wpc 2A3 amp quite successfully. If you plan to drive these speaker hard in large rooms, 10 to 15 wpc is good idea. What is more critical, however, than raw power, is the amplifier's tonal perspective. Avoid bright sounding amps that would merely aggravate the Réthm's forward upper mids.

Soundstaging is spectacular. Spatial dimensions expand to the side and back of the listening room, seamlessly filling in all of the gaps. The sound is definitely very much out of the box. The Second Réthm makes it impossible to ignore the music. Forget about reading the newspaper while listening to music. It draws you in, slowly warms the heart and satisfies the soul. If this is what Réthm is all about, then I'm a true believer.

Conclusion

The analogy that comes to mind is a 400-pound tiger. I'm being careful here. I avoided the oft-used imagery of a 400-pound gorilla because they take change in bananas while tigers demand a pound of flesh. The Second Réthm is far from being a perfect speaker. Its shortcomings can be infuriating. Still, on balance, I find the Second Réthm to be the most accomplished commercial implementation of full-range Lowther driver technology. Careful room siting is necessary to elicit its full bass potential - but don't expect any real deep bass. Its midbass, however, sounds far tighter and more detailed than my previous experience with rear-horn loaded Lowthers. If you listen to a lot of symphonic music, then this is probably not the speaker for you. Careful control of internal reflections, nudges the already legendary Lowther midrange clarity to new heights, but care with ancillary equipment and music selection is essential so as to not aggravate its midrange peaks. When everything clicked, I enjoyed the Second Réthm immensely - far more than any of the typical $10K to $20K audiophile multi-way wonder boxes I've reviewed in the past. The bottom line is that there is no substitute for coherency. And the Second Réthm has it in spades. If you're a music lover, be sure to treat yourself to an audition. You'll be glad you did.

Specifications

Pricing for the Second Réthm:
· Enclosure only - US$ 4,000/pr.
· with DX3 driver - US$ 5,000/pr.
· with PM2A driver - US$ 5,500/pr. 
· with DX4 driver - US$ 6,000/pr.

Dimensions: 1056 x 900 x 320 (HxDxW in mm)
Weight: 40 kg ea.

Manufacturer

Réthm
444 South Flower Street, Suite 1688
Los Angeles, CA 90071
Tel.: (213) 624-6908
Fax: (213)-624-1188
E-mail: anilverma@earthlink.net
Web site: http://www.rethm.com