January 2001

Oscar Heil Aulos Loudspeakers

by Neil Walker

Review Summary Sound "No question these are musical speakers -- easy to listen to, capable and charming as they bring out the beauty and emotion I seek from music." Features Heil AMT driver along with a 6" woofer; unique styling and cabinet with real-wood veneer. Use Ditch the grilles for serious listening as they degrade the sound noticeably. Value "For $1850 USD per pair, the Oskar Heil Aulos are candidates for the winner’s circle."

Many speakers these days look downright odd. The average consumer wants to see a 10" chromium or clear polypropylene woofer surrounded by an array of metallic-cone midranges and tweeters. But a speaker that resembles a hooded monk at prayer or Darth Vader with metal pipes for legs is not going to fulfill the average listener’s fantasy of high-tech gizmos. However, now that I am growing accustomed to the unusual and the arcane in speaker design, I was beginning to think that I had seen it all.

Just in time to reassure me that I had not seen everything in the area of unusual design, along comes the Oskar Heil Aulos. With its grille in place, it looks fairly ordinary. But once the grille is off, it really stands out.

Technical description

When you remove the speaker's grille, you have to defy the laws of physics; that is, you have to allow it to bend so that you can wiggle out the little plastic pegs that hold it in place. Imagine an L attached at both ends. There is no way you can install or remove such a structure without breaking the L or snapping one of the pegs (which had already happened to one of the speakers I received for review).

Once you have the grilles off, leave them off except for shipping or for repelling the inquisitive hands of curious two-year-olds. The Aulos's grille definitely degrades the sound. Once you have it off, you can appreciate what makes this speaker so unusual. The tweeter, also known in this configuration as an Air Motion Transformer (AMT) or Air Velocity Transformer (AVT), appears to be little more than a small rectangular plate filled with what appear to be horizontal ventilation slots, each attached vertically to the speaker enclosure just above the upward-pointing woofer. It covers the range from 1500-23000Hz. The woofer is set at a 45-degree angle to maintain correct phasing. This 6" driver is claimed to respond within +/- 3dB from 40Hz to the crossover point of 1500Hz.

This tweeter is the product of genius. It is the design of Dr. Oskar Heil, a physicist who invented the field-effect transistor. We learn from Précide S.A., the Swiss manufacturer of the driver, that Dr. Heil began his research into loudspeaker design by studying "…how nature designed and constructed the human ear. Then his studies concentrated on animals of a small proportion, which can produce a loud sound, especially compared to their size. These studies led to Dr. Heil’s formulation of his basic diaphragm design theory and the subsequent development of the Oskar AVT (AMT) Air Velocity Transformer."

The unique design feature of the OSKAR AVT, which distinguishes it from all other speakers, is an extremely lightweight diaphragm, folded into a number of accordion-like pleats to which aluminum foil strips are bonded. The diaphragm is mounted in an intense magnetic field and a music signal is applied to the aluminum strips. This causes the pleats to alternately expand and contract in a bellows-like manner in conformance with the music signal, forcing air out of the pleats and sucking in on the other side. The air movement is five times greater than the movement of the membrane; therefore the velocity must also be five times greater. The total moving mass is approximately 1 gram, and we have therefore an almost perfect transducer system. The AVT multiplies (transforms) the air motion by a factor of 5.3 (with a total mass of less than 1 gram) and is, therefore, appropriately called an Air Velocity Transformer.

The cabinet of the speaker is constructed of MDF, and a high-quality wood veneer covers it on all sides. While the wood veneer is attractive and quite conventional, the bass ports (yes, ports, as in two of them) on the front of the speaker are unique. Instead of the usual big hole, there are two round ports 1" in diameter.

This moderately sensitive speaker earns a manufacturer’s claim of 89dB/W/m sensitivity. Its impedance of 4 ohms and sensitivity presented no problems whatsoever for the Audiomat Arpège integrated amplifier’s push-pull EL34s at 30Wpc. At all volume levels, the sound remained clear and undistorted, and at low volume it still presented a reasonable soundstage and low-frequency response.

At 19 pounds, with dimensions of 9"W by 11.8 "D x 20"H, this speaker, as odd as it may look to some, is easy to place, attractive with its real-wood finish (oiled walnut, cherry or black maple veneer are the choices) and is family-room friendly.

Sound

With such unique design and appearance, does this speaker work? Absolutely. And let’s start at the beginning. At first, the Aulos sound did not seem especially rewarding, but once I had the speakers set up in the correct position and on solid stands, they provided a fine listening experience.

When I first heard the speakers, I was not overly impressed with their presence, bass, or upper registers. The speakers sounded OK, but not great. On the other hand, I knew that they could be much better -- I had often heard, and liked, them at my local audio dealer’s shop. For several months, they were the speaker in use whenever I visited, and every time I entered the shop, their fine sound made me look to see what was making the music. No matter what the owner used to drive them with, they always excited my curiosity.

After some repositioning, the Aulos speakers took my breath away with the first piece I played. The bass was clear, powerful, and well articulated, but never overbearing. The mids and treble were well defined. I could hear the orchestra as an ensemble of musical instruments, not an undifferentiated wall of sound. No question these are musical speakers -- easy to listen to, capable and charming as they bring out the beauty and emotion I seek from music.

For example, Simon Rattle’s 1987 recording of Gustav Mahler’s Symphony No.2, "Resurrection" [Angel 48796] demands that a speaker have several apparently conflicting qualities such as subtlety, detail, speed, forcefulness in the bass, and outstanding midrange clarity. The Heil speakers deliver all of these. Listen to the strings in the second movement -- the plucked bass viols, the violins skimming along on the cellists’ silken ensemble playing. Then the snapping of the three ominous beats on the tympani at the beginning of the third movement rivets you to your chair. Janet Baker’s vocal entrance at the beginning of the fourth movement and the chorale, the outright thunder of the fff tutti passages -- horns, drums, tympani -- were enough to satisfy the worst of the classical music lease-breakers. Throughout all of these demands, the Aulos speakers kept their composure and coherence. They produced all the emotional power of Mahler's moving work.

After the workout which Mahler and Rattle’s superb CBSO forces gave the speakers, I felt tempted to say, "So what else was it you want a speaker to do? This review is complete." But I know that our editor would not let me off that easily. So, I think, let’s listen to one of my drum-and-bass favorites, the vinyl of Modus Operandi by Photek, aka Richard Parkes [Virgin Records QEDLP1 LC3098]. The Heils brought out every ripple of Parkes’s evocative layering of electronic sounds in "The Hidden Camera." With "Modus Operandi" and "Minotaur," I had never previously heard quite the same presence and depth in this record as with these speakers. Part of my enjoyment of Photek’s work is the tactile quality of his music. The bass and midbass of any music derives most of its qualities from its upper harmonics, so that much of the accuracy and musicality in the bass of this speaker comes from the "super tweeter." In the case of Photek, this quality adds a dimensional quality I had not previously noticed in this album.

With a good system to drive these speakers, you seem to be able to hear not just the ting and bang audiophile record addicts treasure, but the actual wood and metal of the sound source. One of my favorite jazz albums is Joe Henderson’s Lush Life [Verve 314-511-779-2], and another is James Carter's Real Quiet Storm [Atlantic 82742]. Henderson’s "Take the A Train" takes on a new life with the Heils, as the brushes and drums fill the room, and Henderson’s tenor sax sits squarely in front of you. On the Carter CD, you can feel the wood in the reed that makes Carter’s baritone sax so moving on "Round Midnight."

When I turned to TLC’s CrazySexyCool [LaFace 26009], "Kick Your Game" came pounding through. The Heils roll-off of the bass at about 50Hz does nothing to diminish enjoyment because what the speakers lack in bass extension, they make up for in clarity and harmonic detail.

All of the Beethoven violin concerto’s orchestral parts emerged intact and in phase (Hilary Hahn, violin; Baltimore Symphony Orchestra, David Zinman conducting Concerto for Violin and Orchestra in D Major, Op. 61; Beethoven Violin Concerto, Bernstein Serenade [Sony Classical, SK 60584]). Hahn’s violin, remarkable for its pure, singing tone, kept all its grace, and every note of hers and the orchestra were distinguishable. Similarly, my LP of Strauss waltzes (Fritz Reiner and the Chicago Symphony Orchestra, Strauss Waltzes [RCA Victor Red Seal LSC-2500]) kept all the fire and grace of the orchestra, with very musical, easy strings and stirring drum claps on "Vienna Blood," "Thunder and Lightning Polka," and "Roses from the South."

By now, I was beginning to plot and scheme: "They’ll have to fight me for it. This speaker is staying put. Maybe I can change my telephone number. Maybe I’ll just hole up and make them come and get me." Then I played Mozart’s clarinet concerto and clarinet quintet recording (English Chamber Orchestra; Jeffrey Tate, conductor [Hyperion CDA66199]), which features Thea King playing basset clarinet. The timbre of the basset clarinet’s deep notes, the woody, roundness of sound I treasure in the clarinet, the way in which the ECO leapt to life, all added to my appreciation of these speakers. I began building a fortification around the door to the cold cellar. "Let them just try to get their speakers back," I grunted to myself as I started to stockpile provisions.

Leaving the world of my militia-inspired fantasies, I would sum up the sound of these speakers as detailed, but not overly so, with an overall musicality. The pleasure you derive from these speakers grows the longer you listen to them because they do what a good speaker should do: involve you in the music they reproduce. For $1850 USD per pair, the Oskar Heil Aulos are candidates for the winner’s circle.

Comparison

When I began reviewing the Heil speakers, I had just finished my review of the Athena S2/P2 combo. By comparison, the Heils are much more refined. While they do not have the punch in the bass that the Athena subs deliver, they have a very well-defined, forceful bass -- as far as it goes. In terms of the midrange and treble performance, these speakers are more laid-back, more natural-sounding. They possess coherence -- you hear the music more than you hear the speakers, a big consideration when evaluating speakers for a long-term engagement.

One very biggest differences was in how the Heil and Athena speakers presented orchestral music. Where the Athena S2/P2s were quite adequate for small-group music, the symphony orchestra came across as an undifferentiated wall of sound. For the additional $700, the Heils offer imaging and resolution that allow you to hear the individual instruments. This comparison in no way detracts from the Athenas. After all, $700 ought to buy something.

Conclusion

I liked the Heil Aulos speakers -- a lot. Their biggest obstacle will likely be the fact that they look a little odd. But they deliver the goods: a rich, detailed musical experience at a reasonable price. Only when the distributor pried them out of my clutches did I let them go -- I had finally run out of excuses to postpone the review, postpone the test, whatever.

Are they for everyone? Yes, if everyone wants accurate, enjoyable sound of which they will never get tired. And if you want a genuine high-tech conversation piece bearing the name of a certified electronic genius gracing your listening room, these are definitely your babies.

...Neil Walker
neil@soundstage.com

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