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Positive Feedback ISSUE 37
may/june 2008


sleek audio

SA6 In-Ear headphones

as reviewed by Adam Goldfine






Wilson-Benesch A.C.T. loudspeakers.

Music Reference RM-4+ phono stage, Primare Pre30 line level preamplifier, Reference Line Preeminence One Series II (passive) preamplifier, Music Reference RM-200 amplifier, Dynaco ST-70 (with Welborne Labs mod) amplifier.

DIGITAL: Vacuum State Level 6 modified Sony DVP-S9000ES DVD/CD/SACD Player, Musical Fidelity CR324 up sampling DAC.
ANALOG: Music Hall MMF-7 turntable, Pro-ject 9 tonearm, Pro-Ject Speed Box Mk. II, Benz Micro ACE H cartridge, Magnum Dynalab FT-101A Tuner.

Music Reference Pegasus and Majestic interconnects, Hovland interconnects, Sonic Purity interconnects, Apogee Wyde-Eye interconnects (balanced), Kimber D-60 digital cable, Audioquest VDM-3 digital cable, Coincident Speaker Technology speaker cable, homebrew speaker cable.

JPS Labs Aluminata power cord, World Power Power Wing power conditioner, Ringmat 330 MKII XLR Anniversary, Radio Shack FM antenna, Sanus SF6 component rack filled with lead shot, VPI 16.5 record cleaning machine, Record Research Labs Power Cleaner, Record Research Labs Everyday Cleaner, various LAST record cleaning products, Hunt E.D.A. Mark6 brush, miscellaneous wet cleaning brushes, Zero Dust Stylus Cleaner, DB Systems alignment protractor, Tone Cones, Tip Toes, Echo Busters, HiFi News & Record Review Test LP, Cardas Test LP, XLO Test CD, Stereophile Test CD, Chesky Test CD vols. I & II, Craftsman True RMS Multi-Meter, Philips PM3211 Oscilloscope, Panamax Max 5100 Power Center, Caig ProGold contact enhancer.


Prior to venturing into the melee of this year's CES I decided to peruse the vendor listings, looking for anything new and unusual that might have otherwise escaped my notice. I came across Sleek Audio, a company claiming to manufacture in-ear earphones that could be tuned to the inherent resonance of the individual listener's ear cavity. Intrigued by the idea, I set out to find them; finally locating a group of gentlemen crammed around a conference table in a small meeting room located on the outskirts of one of the show's many main floors.

Sleek Audio was founded by Mark and Jason Krywko in Bradenton, FL. The company was born from over 40 years of experience in the hearing aid industry with the goal of creating personal audio devices that take a different look at audio technology, based upon the science behind how people hear sound and music. CEO Mark Krywko got into the hearing aid industry out of his love for music and has over 30 years of experience as the owner and operator of a hearing aid manufacturing company. He is Board Certified in Hearing Instrument Sciences and a certified Audioprosthologist (maybe we'll see that word in the next Scripps National Spelling Bee). Mark is also an active member of both the Florida Society of Hearing Health Care Professionals and the International Hearing Society.

Mark's son, Jason, is the COO of Sleek Audio and has 10 years of experience in the hearing aid industry. He is also Board Certified in Hearing Instrument Sciences and a member of the Florida Society of Hearing Health Care Professionals and the International Hearing Society. Having fit over 10,000 hearing instruments and examined countless ears, the Krywkos formed Sleek Audio. After three years of development they have created unique in-ear earphones that combine loudspeaker technology with hearing aid science, the SA6, which are said to give music lovers the opportunity to find the sound that works best for their unique ears and choice of music.

In designing the SA6s the Krywkos examined both the earphones' fidelity to the music as well as clarity of speech, taking into account what happens acoustically when you insert something into the ear canal. Mark told me there is a natural, in ear resonance between 1000 and 3000Hz which varies from individual to individual. That resonance is completely lost when something, such as an in-ear earphone is inserted into the ear canal.

This acoustic phenomenon coupled with the fact that there is no standard in testing in-ear earphones and nothing that can test accurately beyond 12000Hz. makes it especially important to be able to customize the sound to the user's taste. The SA6 is designed to compensate for this loss of resonance in such a way that it can be tailored to each user and mate optimally with the acoustics of each individual's ear. With a pedigree unique in the world of high end audio, it seems like Mark and Jason are the right guys for the job.


The VQ or Variable Equalization System is Sleek Audio's tuning system that allows the user to vary the bass and or treble response of the SA6s thereby customizing the sound to his or her ear. It consists of a series of bass ports and treble tips that can be interchanged and either cut or boost the level within a particular frequency range. (see chart)

The treble tips consist of hollow tubes that snap firmly into the drive unit. A tapered end holds one of three included sizes of silicone ear tips. To change the tips you pull them from the drive unit, then peel off the silicone ear tips which can be somewhat difficult to remove, especially the first few times. The new tip is then snapped into the drive unit, the silicone ear tip replaced and voila.

The SA6 includes a neutral tip, a plus tip, a plus-plus tip, and a minus tip. The tubes themselves each seem to contain a slightly different density screen or grill with a different color surround, yellow for minus, green for neutral and gray for plus. The plus-plus tip contains no screen and thus no surround. The tips appear to alter the treble response by changing the density of screen the sound waves must pass through before entering the ear, similar to adding or removing speaker grills which definitely affects treble response.

The tips themselves are black with a small +, =, or molded into them, indicating the value. The plus and plus-plus tips both have a single + making it necessary to look inside the tip to check the screen should you mix them up. Color coding the entire tip would make it much easier to keep track of which tip is which since the indicators are quite small and black on a black background. But since you probably won't be switching tips after the initial set up, it shouldn't present a problem during long term usage.

Three bass ports are included with the SA6, labeled +, =, and for plus, neutral, and minus respectively. The neutral and minus ports appear to create a sealed bass alignment for the driver. The minus port is completely solid; both sealing the bass "cabinet" and providing the least internal volume, while the neutral plug, though also sealed, provides greater "cabinet" volume and therefore deeper bass response. The plus port is actually ported, changing the system from a sealed system to a bass reflex alignment.

The bass ports are also all black but are easier to distinguish from each other due to the obvious porting of the plus port, and the different chamber sizes of the neutral and minus ports. The bass ports were easier to change than the treble tips since they are slightly larger and don't require removing the silicone ear tips to get to them.

The system includes, unusually, a black detachable cable, available in either 4 or 5 foot lengths. The cable includes the ubiquitous 3.5mm jack for connecting to almost all portable electronics and a pair of detachable coaxial jacks on the other end that plug into the drive units making the cable replaceable by simply unplugging it and replacing it with a new one. The cable also includes a bolo tie-like slider for taking up the slack while wearing the earphones. A plug in receiver will soon be available to replace the cable allowing the drive units to be used wirelessly.

Since the cable is detachable, the connectors themselves indicate which side is left and which is right with L and R molded into the small jacks that plug into the drive units. The black on black lettering is again a little hard to read and impossible in low light; color coding would be better.

Three sizes of silicone ear tips are included in the package. They are designed to slide deep into the ear canal with the drive units almost disappearing. The smallest sized ear tips created a nice tight fit in my ears, sealing out almost all background noise. Looking at the largest tips leads me to believe that there are those among us with freakishly huge ear canals.

The kit also includes a carrying case for the drives units and the cable and a small tool with a wire hook on one end and a brush on the other, apparently for keeping your system free of unsightly and performance degrading ear wax build up.


With 12 possible combinations of treble and bass loading, the options could drive you crazy. With the exception of the plus bass port the differences were commendably subtle making the process more of a fine tuning than a radical change. Straight out of the box with the neutral bass and treble tips installed I found the sound exceptionally clean if a bit laid back, a bit dull and lacking in air. The plus treble tip added just the right amount of bite and sparkle to the sound without sending the highs over the top or making them sound artificially etched or detailed. The plus-plus tip was a bit too much of a good thing to my ears, making the piano sound a bit too clangy and cymbals more splashy than metallic.

Using the plus bass port and thereby changing the whole design from a sealed alignment to bass reflex predictably changed not only the bass quantity but the bass quality. Though the plus port added greater weight and punch, the bass resolution suffered a bit as well, with the sound becoming a touch soft and ill-defined. I found the neutral bass port to have plenty of impact with greater resolution and a nice balance of attack and bloom. With the minus port installed the sound became a bit thin.


I initially connected the SA6s to the headphone jack of my laptop and while the sound was decent, the hardness of the op amps from the internal sound card made it hard to tell what the earphones were really doing. So I connected a Rega Ear headphone amplifier to the tape outs of my Primare Pre 30 preamp and fed them some digital playback from the VSE Level 6 Sony DVP-S9000ES. The 50-ohm input impedance of the SA6s should be an easy load for most amplifiers causing little if any modification of the frequency response as a result of Ohm's law. I did all of my listening with the plus treble tips and neutral bass ports installed.

Since first hearing a pair of KEF speakers in the mid 80s I have always thought they did an exemplary job in the bass registers, among other things. At a recent demo of the Reference 205/2 loudspeakers KEF's Richard Colburn turned me on to Marcus Miller's M2, (CD, Telarc CD-83534) an album long bass torture test. First heard on the KEFs, the very deep bass synthesizer used on "Nikki's Groove" was mind blowing in its power and articulation. Though not to the same degree as the KEFs (which cost 40 times more and are probably 1000s of times larger and heavier) the SA6s delivered tight, deep bass with the kind of thick growl that gets under your skin. They also provided a satisfying and convincing sense of weight.

Only a handful of speakers I have heard can equal the Wilson Benesch A.C.T.'s ability to deliver tight, focused bass, without some muddying of the midrange. It came as no surprise that at 1/72nd the cost, the SA6s couldn't either. On "Nikki's Groove" through the SA6s I heard a very slight thickening of the alto sax and synthesized oboe and a sense that the extreme dynamic demands were taxing the rest of the earphone system, though no more than what I've heard on many high end speakers. An unfair comparison to be sure, but still useful in determining the SA6s place on the scale between average and excellent sound. The SA6s placed commendably high on that scale.

Played at a realistic volume, the first chord of the first movement of Vaclav Nelhybel's "Trittico" (Dallas Wind Symphony with Frederick Fennell conducting, Reference Recordings HDCD Sampler, (CD, Reference Recordings RR-S3CD)), will make the unsuspecting listener jump out of his or her seat. (Literally. I've done this to several of my friends to my great amusement.) Listening to this track through the SA6s, the bass drum didn't have the visceral wallop and resolution of the A.C.T.s but both the attack and bloom were very well resolved with just a bit of overhang. The horns were crisp, blatty and brassy though missing that last bit of harmonic resolution that gives each horn its own distinct sound, the timbre of the Trombones blending with the Trumpets a bit. The dynamics were quite good though I could hear a bit of flattening, with a slight loss of ambience and drama, the final crescendo compressing in the same way that it does on all but the most dynamic high end speakers. But overall the SA6s were clean, clear and tight. They did an excellent job on a very dynamic and complex piece.

The SA6s did extremely well with Dick Hyman's solo piano performance of Duke Ellington's "The Gal from Joes", also from the HDCD Sampler. They produced a convincing piano sound with a great balance of attack and bloom, something many earphones and speakers just don't get right. The piano had the kind of weight and growl in the lower registers you usually only get in more expensive speakers.

On "Love is Here to Stay", When Harry Met Sally (CD, Columbia CK-45319), Harry Connick, Jr.'s vocals were rich and grain free. The bass had a nice woody bloom and overall the SA6s delivered great high end sound. And though the soundstage was limited to the space between my ears, I heard excellent lateral separation of instruments. "Stompin' at the Savoy" from the same disc had a well resolved and full metallic cymbal sound without the kind of splashiness or flattening heard even on more expensive speakers and headphones. Once again, the piano weight was excellent.


If the goal of high end audio is to sound like the real thing, very few recordings allow a system to come as close to reaching that ideal as Bucky Pizarelli's Swing Live (SACD, Chesky Records SACD223). Recorded live with a single pair of stereo microphones, the sound has an immediate, dynamic and tonally right quality that will tell you instantly if a piece of gear has the right stuff. On "Lime House Blues" the vibe sound was convincing. The somewhat mellow sounding attack of the mallet hitting the bars was well balanced with the resonance of the aluminum. The kick drum had the kind of skin sound you hear live. No one note bass here, (though using the ported plus bass port did push things in that direction). The clarinet and bass were each woody in their own way and overall the sound was very convincing. Even the sound, mid way through the track, of a beer bottle being tossed into a garbage can full of empties (a sound with which anyone that has spent any amount of time in a bar is intimately familiar) was startlingly real.


All in all Mark, Jason, and company have created a true pair of high-end in-ear earphones. The ability to tailor their frequency response to the individual listener makes them unique in the market and the thoughtful touches, such as the detachable cable, make them a pleasure to own. The small and difficult to see markings on the interchangeable treble tips shouldn't prove to be much of a problem since setting them up should be a one time deal though I would have liked easier to see L and R markings on the cable.

You might think comparing the SA6s to reference quality loudspeakers is a bit unfair or is designed to point out their shortcomings but that isn't the point. The point is to determine where they fall on the scale between poor and reference quality sound. And the fact that they performed so well is a testament to the engineering and concern for fidelity that went into these earphones. All in all I consider them to be a true high end product, delivering the kind of reproduction demanded by music lovers. I estimate you would have to spend at least $3000 or more on loudspeakers to get this kind of sound quality. And though the SA6s will most likely be used with lower quality electronics, (iPods, laptops, airplanes, etc.) they really need to be used in the context of a high-end system to hear what they are truly capable of. Adam Goldfine


  • Standard Cable: 60 inches

  • Impedance: 50-ohm

  • DC Resistance: 24-ohm

  • Speaker Type: Ultra Wide Band Balanced Armature Driver with Custom Porting

  • Sensitivity: 110 dB SPL/mW

Retail: $249.99 Factory Direct

Sleek Audio
3904 9th Avenue West
Bradenton, FL 34205
TEL: 800.777.7937
web address: