Sleek Audio CT6 Custom IEM in Review – Perfection


Sleek Audio: Company
Sleek Audio is a father and son partnership. Since their release of the SA6 Inner Ear monitor, they have been making waves in audio circles for uniquely designed phones that excel in audio performance despite their lower cost. The Sleek Audio Custom IEM is their finest work to date and a truly audiophile product despite costing hundreds less than many of its competitors.

Sleek Audio was started by Mark and Jason Krywko, father and son respectively. It began when Mark found himself dissatisfied with the sound signature of the dozens of different earphones he had tried over the years, so as a 30 year veteran of the audio and custom hearing aid industries, he decided to build his own.

What started as a fun project turned into a three year endeavor developing a product with his son that would revolutionize the audio industry; the SA6 acoustically customizable earphone.

Mark and Jason took their extensive experience in the audio industry and vast knowledge of the ear to create a new ideology in personal audio. Rather than focus on adding multiple, larger speakers to earphones, go back to the starting point and focus on the acoustics of the ear canal and how best to  get sound from a music player to the listener’s ear in a form recording artists intended.

Sleek Audio pride themselves on offering a tailored experience to the consumer:

All of our products are designed with the individuality of every ear in mind.
Sleek Audio allows you, for the first time, to find “your audio fingerprint” without having to sacrifice anything when it comes to your music. Sharp, precise sound can come out of a small, comfortable earphone. We’ve looked at what music lovers want out of their audio experience and designed our products accordingly……incredible sound quality, comfort, and flexibility.

Sleek Audio CT6
In my life, I have been silly enough to own many 300$ plus earphones, all of which have been benchmarks in some area or another. My Westone UM2 was incredibly comfortable and came tethered to a nearly noiseless cable and perfectly designed headphone jack. The Shure E500 model presented me with to-die-for mids and a sleek design while Audio Technica’s CK10 provided both looks, great sound and superior construction.

Sleek’s Custom earphone, embodies nearly every plus that the aforementioned companies have brought to portable audio, but are better in many regards. Firstly, their removable coaxial cable is both soft and noise-free and features above-average strain relief. Secondly, they provide thick, deep bass and smooth treble that edges out my hitherto favourite: the tiny CK10. But above all, their custom fit ensures comfortable, fatigue-free wear. In fact, a custom earphone is so natural feeling, that it is possible to forget that they are in the ear.


Not available at your local Futureshop
Because Sleek’s custom earphones are tailored to your ear’s size, shape and sound preferences, they cannot be purchased directly from anywhere, unless you live in Sleek Audio’s neighbourhood. You will first need to have impressions of your ears taken which is normally done by a visit to an audiologist. Sleek will also recommend an audiologist in your area if you are in the United States in case you need recommendations. My impressions were taken locally by Brad Davidson of Hearsafe Canada.

The process of taking impressions is short and consists a couple of steps. Firstly, a bit of biologically safe putty must be injected into your ear behind a safety stopper. Then, after a few minutes, the putty hardens creating a virtual mould of your inner-ear. The final step in the process takes the longest. The moulds must then be sent to Sleek and after a few emails and a good, long telephone conversation about sound preferences, your Sleek Custom earphones will be lovingly created.

Note: custom earphones take a long time to create. Be prepared to wait. Also, have your impressions professionally done. DO NOT use a home impression kit as you can damage your ears.

Why Customs?
This is not an easy question to answer. Originally, customs were made exclusively for stage musicians who needed hearing protection from the crowd and from loud floor-standing monitors. They have been in construction for many years by different companies such as Futuresonics, Sensaphonics, Westone and Ultimate Ears – all of whom make products that start from 600$!

Recently, smaller custom manufacturers with emerging designs and markets have taken on the more established companies and created affordable alternatives for musicians and music lovers alike. Among these are Sleek, Livewires, Alien Ears, Hear Yourself and SoundCage. I have used inner earphones since 2002 and after seven years of changing flanges, losing ear pieces and the general discomfort that I sometimes experience, decided that it was worth the switch to custom monitors.

If for no other reason, the decision to purchase custom earphones can be made solely to ensure superior comfort. Because they perfectly fit your individual ear shape, custom monitors feel almost as if nothing is in the ear. That said, the hard shell does not remould as do foamies, flanges or silicon, so if you listen whilst eating or other activities when your ears may flex and move, custom phones may intermittently lose their seal.

Fit and Packaging
Because Sleek’s Custom is not a typical in-ear earphone, it does not come with a typical fit-kit. Rather, the earphones, a cleaning tool, detachable coaxial cable and box are the only accessories to the shipping box. To protect your investment, Sleek provide a crush and dust proof water resistant Pelican case. They take care to ensure that your investment will not suffer from either tough couriers or your own negligence as long as it stays within the Pelican case.

Unfortunately, Sleek neglected to ship a toss-pouch or hard-sided case for more portable use, however their packaging is not wasteful. There are no throwaway plastics or hard edges on which the customer may hurt herself – it is well thought-through with every effort aimed at simplicity and utility.


Specifications – Single Wide-range Balanced Armature Design

• Frequency Response: 10Hz-20KHz
• Noise Attenuation: -35 dB
• 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

What that means is of little importance if you are not really into your audio. If so, then just skip over this bit. Sleek’s cable is longer even than Zagg’s 1,37 cable which is a great length for portable use. Since it is light and soft, it does not impede movement.

If you care about how easy the Sleek Customs are to drive and how much hiss they will exhibit, then the above spec will help you. An impedance of 50 ohms is nearing a gold standard at which most portable audio players are let loose and able to produce deep bass and open sound stages. Even the iPhone and iPod Touch 1G will be able to sustain good, detailed bass at 50 ohms, but will still benefit from external amping.

As for soundstage, iPod and iPhone users – you are in luck. The iDevice remains to this day on top in terms of left-to-right separation even when under load. Lastly, with a sensitivity of 110b, the Sleek Customs can be driven loudly from nearly any portable and will not hiss too much with dirty sources. Phonak’s PFE are the kings when regarding the effortless rendering of a black background even with rather hissy soruces, but Sleek’s earphones are not too sensitive as to hiss with every source.

Unique Coaxial cables
Firstly, Sleek’s cable is an interchangeable creation that works on all of Sleek Audio’s high end earphones including the SA6 universal IEMs. The connection is extremely robust with no play that could damage the internal connector. I had doubts as to the reliability of this system but after owning and listening to the custom in a variety of conditions for over a month, my fears are assuaged.


Cables can be purchased in a variety of colours as well as a pioneering new wireless technology called Kleer. The Kleer option is available for 120$ and is as testified by the following reviews, lossless and definitely peerless in wireless technology and besting BlueTooth.

Sleek’s cable material is similar to Phonak’s cable – it is soft and non-microphonic but is less pourous and probably less susceptible to hardening and cracking. Strain relief is a mixed bag: though well thought out on the headphone plug, the terminal jacks which connect to the earphone are prone to splitting – a problem which Sleek are working on. The Y-Split is also missing strain relief. The headphone jack is a right-angle construction, which protects both the iDevice and the headphone jack.


Aside from those strong points, Sleek’s cable is ‘blingy’ with shiny plastic bits around the headphone jack and the lower portion of the Y-split. Personally, I find this design to be gaudy and unfitting for a high-end earphone – rather more in tune with cheaper looking mass-market alternatives. Adding to this image, the plastic bit from the headphone jack sometimes pops off. If you have read my reviews, you will understand that I am not a fan of weak, all plastic construction – a fact which lowered my ratings for the Audeo PFE.


Acrylic Housing Quality
Sleek’s Custom housing material, is made of layered acrylic which surrounds each driver unit. Since the acrylic material is hard, it is very sturdy and despite being solid and compact, when in the ear, it is incredibly comfortable.

As a true custom product much like my Marinoni Fango steel bicycle, the Sleek earphone can be chosen in a variety of colours and you can even design a custom logo for printing on the outside shell. Mine obviously, is adorned with the letters ‘tma’ in Bahaus93 font denoting TouchMyApps. I also chose differently coloured earpieces for added personality and wuffie from the audiophile crowd. Bill from Sleek Audio was very kind in walking me through colour schemes, sound preferences and any questions I had in the process of making my earphones.

It might seem strange that I mention fit as custom monitors are made to fit perfectly to you ear, but problems occur even with custom monitors. This can stem from the initial moulding process, from packaging, from the manufacturing step or from a multitude of other reasons. Have patience – this process may take longer than you expected, but in the end, it is worthwhile. Misfits occur with every custom monitor on the market, including the ultra expensive models from Ultimate Ears, ACS, Sensaphonics, Futresonics and Westone.

I had to apply a little nail polish to the under side of my ear pieces to get a snug fit and when I finish this review, will send my customs back to Sleek for a UV hardening process to finalise the fit.

Test Music
For my listening tests, I spent most of my time with these staples of my collection:
Armin van Buuren – Trance
Paul Oakenfold – Trance
DJ Tiësto – Trance
Ice Cube – Rap
MC Solaar – Rap
Kent – Rock/Alternative
Ultima Thule – Rock/Punk
Madeleine Peyroux – Vocal
Aphex Twin – I care Because You Do – Ambient, Space

Sleek will cater to your listening preferences when making your custom monitor. You can choose from nuetral, plus or minus for both bass and treble – I chose plus on both frequencies. Thus, my Sleek customs render more treble sparkle and slightly greater bass presence than the standard Sleek house sound.

At 50 ohms, Sleek’s product is relatively easy to drive – a side effect is that bass definition is superbly deep and defined even from a first generation Apple iPod Nano. However, Sleek’s products utilise balanced armature type transducers – this sort of driver tends to react quickly to variations in music and appears incredibly accurate. Part of the reason for this is that the drivers do not move as much air so bass is less tactile and apt to ‘bleed’ into other parts of the music.

On that note, bass presence is nothing like the astounding dynamic-driven Turbine or NE7M, however it has much better positioning within the rest of the audible spectrum. This is due to the very hard acrylic sound tube and the fact that the driver unit itself is further out from the ear. Since custom’s sound must travel further and achieve a tighter, less giving fit with the ear, slight rumbles are more noticeable to outer portions of the ear than with units that use flanges or foamies that dampen vibrations. There is less overall bass impact, but sound vibrations which rumble along the outer ear canal help in creating a more organic and fluid bass presentation. Saying all of that, the Sleek CT6 isn’t going to wow any bass heads, and even for the more meagre bass lovers, has a softer bass presentation than many other customs. While nothing is wrong with it, it is the weakest link in the CT6.

If you love thick bass, be sure to tell Sleek’s team so they can tailor-make the best custom for you.

Mids and Treble
Many people praise Sleek’s other model, the SA6 for its forward, lush mids and smooth highs. Their custom model is no less beautiful. I cannot say whether or not the actual sound frequency extends from 10HZ to 20 KHZ as I am not a bat, but I can say that treble reaches far on these earphones. It is smooth, non-fatiguing and simply, beautiful.

For those who love vocals, the Sleek customs will impress but not to the extent that extremely mid-oriented earphones such as the UM2 or SE530 do. Instead, the mids presentation of the Sleek customs is atmospheric and lively but does not invade into genre where overly warm mids are unneeded.In particular, Madeliene Peyroux’s voice is lovely with the Sleek on any source, but not as lusty as with a warmer sounding earphone. For this reason, the setup that I have chosen is excellent for electronic and rock music and even with rap. Again, be sure to discuss with Sleek Audio’s team about how to tailor your custom to your preferences.

Where dynamic driver based inner earphones far extend to the side and back, Sleek’s custom creates a tight but extremely well-defined sound space around your the head. If you have not noticed 3D positioning in your music before, you will with customs. They best the incredibly well placed CK10 stage and violently thrash the delicate PFE amped or unamped. Again, this likely is aided by the perfect fit that customs provide as well as from the sound vibrations that interact with your ear canal through the acrylic case rather than being absorbed into rubber or foam ear tips of universal inner earphones.

In simple terms, Sleek Audio’s Custom earphones sing an eerily accurate soundstage that dances above, below and around your head-space. They are tightly defined yet awesome in spacial presentation – unlike anything I have heard in an inner earphone.

On the Go
Because of their high-quality cable which is low on microphonic noises, Sleek’s Custom monitors are divine for out-and-about listening. They are comfortable, secure and with a good fit, unperturbed by wind noises that howl on lesser designs. However, no matter how good the sound is from an acrylic case, customs probably will not provide the same amount of isolation as a dense foamy ear tip on another deep-insertion universal earphone. This can either be a boon or a point of contention for you. Personally, I find the level of noise attenuation similar to the Turbine but lower than the PFE which nearly shut out background noises when worn with foamy ear pieces.


Since I am working on finishing a short but pithy review on the Nuforce Icon Mobile headphone amplifier, I have been religiously using my various earphones with and without dedicated amplifcation. I prefer not to amp earphones as my tastes rest in portability at the sacrifice of some sound quality. However, the Sleek Audio Custom earphone amps beautifully. The most noticeable change is their sound staging which pushes out vertically and horizontally even further and depending on the amp, treble and bass nature also change. The Nuforce adds some clarity to treble and greater authority to the bass.

Rather than a dedicated amplifier, I prefer to use an impedence cable that adds resistance to the line. This option is more elegant, requiring less baggage but also renders less stellar results. For its part, my 75 ohm resistor cable eliminated any hiss from my Rockboxxed iPod Nano and went a long way to quieting my extremely noisy Sony 828 walkman.

For the almost reasonable price of 300$ plus the dosh for an audiologist exam, you can experience unrivalled sound and comfort. The Sleek Custom audio experience is far above any inner ear phone I have yet tried – accurate, deep, expressive and smooth whilst engaging the outer parts of my ear canal for phenomenal soundstaging. Are they worth the fairly high price of admission and long wait? Undoubtedly. The cable is well constructed if gaudy with cheap plastic bits, but overall, Sleek’s presentation and packaging including strength of design is top-notch.

Finally, Sleek do not engage in marketing in the same way that many custom balanced armature companies do. Their single balanced armature provides incredible extension and body. Most companies use multiple drivers and passive crossovers or frequency limiters to ensure that an accurate sound image is still presented to the listener. Since this is likely a marketing decision more than anything else, there is no right or wrong for the consumer.

Sleek Audio’s CT6 monitor gets kissed by TouchMyApps. Please take a look at our other Headphone reviews.

App Summary
Title: Sleek Audio Custom earphones Developer: Sleek Audio
Price: $300 plus impressions and custom artwok
  • Usable and environmentally sound packaging
  • Wonderful customer service
  • Excellent sound
  • Realist sound stage
  • Detachable cables with excellently anchored contacts and wireless options
  • ‘Reasonable’ pricing compared to many competitors
  • Gaudy cable
  • Not cheap

Can’t get enough of headphones? We got loads more here in our headphone section with many upcoming custom monitors.

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