You know what? I kinda get what Ikko was going for with those oval-shaped silicone tips. Now, I do have averagely sized ears, so the ear mold just about perfectly represents my own experiences. Size M silicone tips are my go-to for testing since foam tips are not included by some, and seen above are how the ear tips contour around the entrance of the ear canal. This makes for a nice fit, and the provided six sizes, although realistically more like three separate sizes, should make a good fit possible for most people. The memory foam tips are not as conducive here, and you see how the ear buds jut out of the ear more than with the silicone tips. These are relatively tiny IEMs thus, having a lot of space around them when in the ear. There is no outward pressure to worry about, or any fatigue since these just weigh ~7 g each. The only thing to consider is the MMCX connector with its 360° rotation, so you may have to fiddle around with it slightly to make sure the cable is oriented correctly for it to go over the back of the ear, following which the Ikko OH1S is just going to look like a small piece of bling depending on whether you go with the blue or gray set.
Ikko uses a hybrid dual-driver system for the OH1S, which means these IEMs have a Knowles 33518 balanced armature driver for the midrange and high frequencies, which is paired with a new flagship IEM driver from the brand in the form of a 10 mm deposited carbon nano dynamic coil driver for the lows and bass. This type of hybrid driver system is by no means unique to Ikko and indeed something fairly common in IEMs that cost far less, too. The use of a dual-driver system is more excusable with the smaller shells compared to the OH10, but it ultimately comes down to the entire setup and how well they are tuned. The aluminium alloy and resin layers in the shell are chosen with this in mind, especially with the resin for sound damping as part of what Ikko calls the SVAS acoustic cavity technology used to minimize resonances and internal reflections.
Driving the hardware is harder than with the average IEM but still easy enough with a rated impedance of 32 Ω; no aftermarket amplifiers are required. DACs will always go a decent way in the audio experience, however, and a portable DAC/amp might well be part of your collection if you are considering IEMs and other audio solutions in the $150+ price range. Also, the lack of a 3.5 mm audio jack for most phones these days is another reason to consider a DAC/amp that takes digital input and provides a 3.5 mm jack on the other end, since you will have to use an adapter anyway, or even a dedicated DAP. If not on the go, space is less of an issue, but the 1.2 m cable might be a potential handicap if connecting to a PC as the audio source. Ikko also rates the signal sensitivity at 106 dB and a frequency response of 20 Hz to 40 kHz, but good luck making use of that range!
Frequency Measurement and Listening
Before we proceed, I will mention that I have a general preference for a V-shaped sound signature emphasizing elevated bass and treble with recessed mids. I also generally prefer instrumental music over vocals, which complements the V-shaped profile.
Our reproducible testing methodology begins with an IEC711 audio coupler/artificial ear ear buds can feed into to where you have decent isolation similar to real ears. The audio coupler feeds into a USB sound card, which in turn goes to a laptop that has ARTA and REW running and the earphones connected to the laptop through the sound card. I begin with an impulse measurement to test for signal fidelity, calibrate the sound card and channel output, account for floor noise, and finally test the frequency response of each channel separately. Octave smoothing is at the 1/6th setting, which nets a good balance of detail and noise not being identified as useful data. Also, the default tuning was used for testing, and no app-based settings were chosen unless specifically mentioned. Each sample of interest is tested thrice with separate mounts to account for any fit issues, and an average of the three individual measurements is taken for statistical accuracy. For IEMs, I am also using the ear mold that fits the audio coupler for a separate test to compare how the IEMs fare when installed in an ear geometry, not just the audio coupler itself. The raw data is then exported from REW and plotted in OriginPro for easier comparison.
Now, after calibrating the sound card and accounting for the base floor noise levels, I am a touch more confident about the SPL label, but there is likely still a significant offset across the board owing to the overall resistance and impedance in the system. I should really also normalize the curves to a set frequency, but the IEC711 is such that you can't really compare these results with most other test setups anyway, just across our own library of measurements. What is really useful information is how the left and right channels work across the rated frequency response in the Ikko OH1S earphones, or at least the useful part of it. The left earbud was separately tested from the right one, and colored differently for contrast. I did my best to ensure an identical fit for both inside the IEC711 orifice, so note how the right channel ends up having a slightly boosted sub-bass response followed by a dip before rising again at the higher frequencies. Both generally have the same profile shape across the 20 Hz to 20 kHz test range, which is good to see. I will also mention that there was no discernible break-in period or effect. Ikko says that the company tests each individual unit separately and pairs the left and right channels based on how close they test to each other.
So yes, there is not much to differentiate the two channels of the gray set here. But I then tested the left channel of the blue set out of curiosity, and there obviously are some sample-to-sample variations. The left channel of the blue set tested more like the right channel of the gray set, but even more so with a further boost in the lows that was also felt when listening. If anything, I personally would have preferred all the OH1S sets to be like the blue L-channel here since the gray set does not have an appreciable bass response. Sub-bass is non-existent, but things get better past 100 Hz to where there is added warmth. The blue set, on the other hand, is more punchy without being overpowering. The best way to describe the Ikko OH1S is to say it has a warm neutral sound signature, and I suppose the gray set fits the bill more in that regard.
There is a tiny dip with the transition into the upper mids, where the new Ikko 10 mm dynamic driver still holds sway clearly. Based on my listening, the crossover to the Knowles balanced armature driver happens around 1 kHz, but there is tuning leeway for Ikko to customize. What the company has done is prioritize the mids, with vocals emphasized for separation and detail. Male vocals especially sound amazing, with just the right amount of added energy to want to listen to more. Female vocals are more subdued, but there is even more clarity as you head towards the highs. Treble is laid back, to say the least, which does help in listening to classical music for long periods of time without any fatigue. It's an interesting tuning, and I still don't know which set is more representative, but regardless of the bass response, you are going to have to choose whether the neutral-with-a-kick profile is for you.
With the artificial ear mold of the test setup, I used an orange color to show that it is still the right channel in red (also there as a control), but different from it. For those wondering, this is with the gray set since I tested it fully before testing the blue set on a whim. We see a near-identical bass response and slight dip past 200 Hz, which continues until the crossover with the BA drivers is complete, which is where things move slightly above. This is also where I noticed the transparent character and more laid-back approach, while still sounding really good with female singers and tenors in opera music.
Comparison to other IEMs
The Ikko OH1S is supposed to be an update to the company's budget-friendly OH1, which seems to be EOL. I do not have those here, and there has been a significant bump in the pricing from the OH1 to the OH1S to where the OH10 actually comes in at the same price as the the OH1S. As such, this was the natural first comparison to make. Seen above is the left channel of the gray OH1S next to the left channel of my OH10 set, which finally gets a frequency response measurement after all! The two could not be further apart, with the OH10 being a bass monster that loses clarity in the mids in a trade-off before getting really punchy in the highs. It's also far less comfortable to wear and listen to, so I suppose you could consider the OH10 a sprinter compared to the marathon runner that is the OH1S. The soundstage on the OH1S is deeper, but not as wide as on the OH10.
I currently do not have any other wired IEMs at the same price point as the OH1S, although there is one that just landed and will get tested soon enough. The Thieaudio Legacy 5 is technically superior with active crossover involving a total of 5 drivers, and I personally think it does a better job in appealing to those who prefer the popular V-shaped profile, too. It costs 25% more, however, and the tuning is deliberately different enough not to be a fair comparison. Some TWS earphones I have tested before are also priced similarly, including the Audio-Technica ATH-ANC300TW and EVA2020 x final, but both have the massive power bottleneck with pure output and compromise with Bluetooth bandwidth restrictions to where the Ikko OH1S beats the pants off them easily just about everywhere for the pure listening experience.