Appreciable Effort

Ratings

Pros

• Soft, warm, rich, lush, full, dense, homogeneous and full sound.
• Musical refinement, accentuated in the low and middle range.
• Musical, organic and very suitable for extended listening.
• Great sonic potential, more enjoyable the more time you spend with them.
• Improved ergonomics, lighter and more comfortable.
• Modular cable.
• Very good presentation.

Cons

• Energy drop in the high end, treble is smooth and controlled.
• The sound is somewhat dark, it can be difficult to get into at first.
• It may be necessary to roll tips to find the most appropriate sound.
• Although detail has improved, it still does not show more noticeable clarity. The use of different tips can help or hinder this.
• The choice of matt finish and resin colour does not offer a very distinguished or elegant look, rather the opposite.
• Sensible price jump compared to the S12.

Purchase Link

https://letshuoer.net/es/products/letshuoer-s15-third-generation-14-8mm-planar-driver-r-sonic-passive-filtering-module-hifi-wired-in-ear-monitor

Link to the Store

https://letshuoer.net

Introduction

It was not a new brand when LetShuoer launched its IEMS planar S12, but it is true that it has been one of its most famous models. It is also true that the brand itself has been going round and round about the same model, bringing out variants such as the Z12 or the Pro version, until it finally decided to bring out a new planar. And even the process has not been easy, as it has been delayed after the first demonstration units. Officially, the S15 is out this December 2023 and what it brings with it is not just a planar, but the brand has pulled out all the stops with them. The first thing that will catch your eye is the price, which has risen to $329, more than double the price of the S12. So what’s in the S15 to justify the price hike? If we look at the exterior, there are many differences. The capsule is high precision 3D printed, the outer face is precision CNC machined aluminium alloy. Yes, it is no longer a full metal capsule. Its design has changed and the surface is as if it were made of some kind of rough resin. Many might think that this new capsule is not worth the high price, compared to the finish of the S12 Pro, for example. So where are the improvements? Well, you have to look inside. The LetShuoer S15s incorporate a third-generation 14.8mm dual-chamber planar transducer. To ensure smooth transitions between octaves, the S15 employs a dual acoustic tube structure with a crossover filter scheme. But one of the most important technologies is the addition of a 6mm passive filter module outside the planar driver. This passive filter module features LetShuoer’s new R-Sonic dynamic harmonic technology. This is a positive filtering of sound energy through proprietary filters. This technology is explained in the following link:

https://letshuoer.net/es/blogs/news/letshuoer-r-sonic-dynamic-harmonics

In short LetShuoer R-Sonic PFM uses a membrane that acts as a filter that adjusts the amount of pressure inside the ear canal, allowing the headphone to be adjusted for a more comfortable listening experience, especially during long listening sessions. More details on R-Sonic technology are provided below:

1. R-Sonic is an adjustable module for ear canal pressure tuning.
2. The fundamental operating principle of R-Sonic is the adjustable characteristics of the passive membrane/transducer environment.

While the SPL is louder, the PFM membrane is activated, the pressure is transferred to the earcup chassis and thus the excursion of the active transducer piston movement is reduced. Thus, hearing fatigue is reduced.

Let’s see how all this new technology affects the sound of the S15s, as well as other aspects in this review.

Specifications

• Driver Type: Third generation 14.8mm dual chamber planar driver + 6mm passive filter module.
• Frequency Response: 20Hz – 40kHz.
• Sensitivity: 106dB.
• Impedance: 30Ω
• Capsule material: 3D printed resin.
• Outer face material: Anodised aluminium alloy.
• Jack connector: interchangeable 2.5mm/3.5mm/4.4mm 90° angled.
• Capsule Connection Type: 2Pin 0.78mm.
• Cable: 1.2m 216 strands of silver plated monocrystalline copper.

Packaging

The LetShuoer S15 comes in a relatively large grey box. On the main side there is only the brand name on the top left, the model name on the top right and the Hi-Res logo, with the design lines of the outer side of the IEMS on the left side. All in white ink. The back side has the specifications, contact details and the warranty seal. After removing the outer cardboard, only the brand name and the phrase «Sound Alive» appear. The box opens like a lid and the first thing you can see is a closed seal with a sticker just like the external design of the S15 faces. Underneath are the two capsules inside a mould lined with the same cardboard as the rest of the packaging. There is a lower level that opens like a drawer. In it is a round blue-grey box with a rubbery matte finish. It opens with a screw lid. There are also the three 2.5mm/3.5mm/4.4mm connectors angled at 90°. The envelope contains a poster with the logo on the outside. There is a warranty card, 3 pairs of vocal tips and 3 pairs of balanced tips, plus the cable.
Although there is not much variety of tips, the presentation makes for a great unboxing experience and perhaps this feeling justifies the contents.

Construction and Design

The S15 has a big difference in the design of its capsules compared to the S12. It is not metallic, it is larger, the capsules are 3D printed with a bluish-grey resin with a matte look and feel. Only the outer face is made of anodised aluminium alloy and has a relief that is repeated as if it were its seal. You could say it’s a letter C with an arrow pointing inwards, all in relief. Going back to the capsule, it is all one piece except for this outer face. It is an integral design that has a slightly more elongated mouthpiece than the S12, it is also larger and thicker. On each one you can read the make, model and channel lettering in white ink. There are two holes on the inside and one on the side, near the 2Pin 0.78mm connection. This connection is flat, the interface is embedded in the capsule. The mouthpieces have a narrower inner diameter (5.8mm) and a 6.2mm crown. They are protected by a dense metal grille. The entire capsule is very rounded and there are no sharp edges.
The cable is the classic LetShuoer two-stranded cable with mixed silver and darker wires inside. The conductor is made of 216 silver-plated monocrystalline copper wires and measures 1.2m. It has three interchangeable 90° angled 2.5mm/3.5mm/4.4mm plugs. The sleeving of these connectors is mixed, near their connection interface is silver metallic, while the elbow is white rubber. All plugs are gold-plated and have tailor-made protective sleeves for protection. The cable exits the connector protected by a small, transparent sleeve. The splitter is a matt metal cylinder. The pin is a translucent plastic ring with a pair of holes in it. The sleeves of the 2Pin 0.78mm connectors are both matt metal cylinders, in the same style as the splitter. There is a dark letter on each of them to specify the channel, there is also a red (R) and a transparent (L) disc, as a base for the two gold-plated pins. There is a velcro strip to tuck the cable away.
Anyone could criticise the new capsule design: it is larger and not metallic. The emphasis on the logo created for the outer face seems to be intended to be an iconic hallmark of the S15 model. And although the S15 is more comfortable than the S12, I like the design of the S12 better – those did have something unique.

Adjustment and Ergonomics

Well, beyond the design, talking about fit and ergonomics, you could clearly say that the S15s have improved over the S12s. Those were smaller, but the nozzles were shorter. Here they are longer, the angle is good and they allow both a shallow and an almost medium, quite occlusive fit. The capsules are light. Their surface is matt and very smooth. The fit is immediate, I didn’t have to waste a second to find the right tips, I used my big home-made tips filled with foam and nothing else. Immediate fit, the best possible sound and a great feeling of isolation. There is perhaps a higher degree of rotation than with the S12s, depending on the degree of insertion. But the capsules fit correctly in the pinna to stop the movement. In my opinion, the S15s are an ergonomic improvement which, perhaps, justifies their external design.

Sound

Profile

Let’s come to the most important issue of this new model. It is common knowledge that the tuning of planar IEMs has been criticised for the energy of their treble. It is not that it is a peaked high zone, but rather that it maintains a relatively linear extension, spreading the energy over a more extended frequency range. This could cause hearing fatigue for some sensitive ears. Well, LetShuoer has reduced the presence between 2kHz and 10kHz compared to the S12, while almost maintaining the bass and midrange up to that 2khz point. Strictly speaking, and trusting my measurements, there is only a small difference in favour at the 1.5kHz point and to the detriment of the sub-bass end. What does the profile of the S15s look like, then? Well, it keeps that w-shape but now it’s in lower case. Everything is more balanced and the result is somewhat darker and warmer. There is not so much reinforcement in the sub-bass, resulting in a more homogeneous sound throughout the frequency range. Perhaps there is some loss of punch, both in the bass and beyond the upper-mids, but the S15s are tuned for hours and hours of enjoyment, with a sound that is quite natural, restrained and free of artifice. This is the result of a more rounded and refined FR, but also with less brightness, hence the darkness and sobriety are more evident.

Bass

First of all, the impact of the passive filter module on the sound is a mystery. As the system specifications state, the R-Sonic PFM device is activated depending on the SPL level, so it releases internal pressure from the IEMS. At what SPL level does it activate? Well, it is not specified. So, in reality, the beneficial outcome of the R-Sonic PFM system cannot be assessed individually. What can be done is to evaluate the low end of the S15s as I have traditionally done so far: with my own ears in the recurring very low-frequency pure tone test. Starting with the latter, one feels that the audible low end does not possess as much energy as its smaller siblings. The response at 20Hz is audible, not very sensory, very subtly coloured and quite good in execution, but not as pure as dynamic drivers of the same price. At 30Hz and above it feels more powerful and punchy, but there is still some colouration replacing a deeper feel. The vibration at 40Hz is more energetic, complete, fuller and already possesses more sensory and physical capability, but the audible side still drags that subtle colouration. This behaviour, translated to real music, explains that certain roughness in the bass, as well as a certain lack of depth and that audible rather than deep feeling in the bass lines. The bass is not heavy, nor does it take up too much volume, but it feels more respectful of the rest of the frequencies, as it is not as invasive. Nor does it feel as predominant as in the S12s. The bass of the S15s is certainly noticeable, but it doesn’t come across as a wall of sound. There is undoubtedly a good level of energy, depth and force in their punch, but there is a sense of control, as if there is some limiter – could it be the fault of the passive filter module? I don’t know, but it is true that there is no sensation of violence in his hit, even though it is powerful. On the other hand, the rubbery or elastic sensation in the hit is light, but enough to offer a pleasant, deeper and somewhat rounded aspect, together with that subtle roughness on its surface that makes it more attractive and enjoyable. In conjunction with this behaviour, there is also a good degree of speed and low decay. Fortunately for the full development of the low end, the sum of these abilities means that the bass does not feel swamped, bloated or magmatic. The speed of the transitions allows for space between hits, facilitating control, definition and resolving ability down low. Where it shows its technical ability and skill is in the worst conditions. The S15s are capable of reproducing unfiltered bass lines without losing naturalness in performance or distortion even at high volumes. The best thing about it is that it can play such complex bass lines alongside other lines without losing its composure, managing to stratify all the layers, as well as not influencing the upper ranges. Perhaps this is typical for planar IEMS, but I insist that there is that point of control, that release valve that seems to keep the energy at bay so that the bass is executed in the best possible way. Maybe it’s a particular feeling, but it’s a welcome one, because the result elevates the range.

Mids

I must confess that the S15 didn’t impress me enough to leave me with my mouth open on first listen. Perhaps I was expecting a spectacular sound, but that’s not the case. On the contrary, it is quite natural, with a certain warmth, soft in the upper range, moderately energetic and very decisive in the lower range. But it is in the mid-range that the natural, neutral feeling is most noticeable. It is true that something that is characterised by being neutral does not seem to stand out on first impression, but rather, with the passage of time and hours of listening, it becomes an acquired taste whose value progresses as the days go by and the more time one spends with them, the harder it is to stop using them. For so are the mids of the S15s, their virtue lies in rounding out the music, in playing it in a more subdued, slightly warmer way, but retaining that gentle neutrality that makes it musical, more analogue, but undoubtedly expressive, descriptive and detailed, to the point of being emotive and beautiful. The S15s possess the ability to magnify the mids, to recreate them in a broad and expansive way, without them even being shown in the foreground. Yes, the male voices are not predominant, but they are very well represented, but also very well wrapped by the whole instrumentation. In this sense, this mix is very well achieved, there is a great respect between music and voices, keeping the distance, balancing the prominence and generating a highly musical, conjunct and euphonic sensation. The result is very pleasant, attractive and highly harmonious. There is no sensation of a wall of sound, although the perception of fullness is almost overwhelming, due to the amount of information it is able to deliver, but without becoming saturated. This is the symptom of the richness of the midrange, of its breadth, but also of its balance, its naturalness and neutrality. If there is one point to criticise, it would be the slight imbalance between the centre and the upper midrange. I would have liked this small step to be smaller, to bring the first half a little closer. It’s not the step itself, but the sinking of that first half. Because it’s small enough not to elevate the female voices too much, and it’s big enough to add clarity and transparency, but without offering a hint of excitement in the midrange. Hence the idea of balance and neutrality in exposure, in the weight of the notes and in their thickness persists. In this way, the distance between male and female voices is not too great, while the mix in the upper range continues to maintain its proportion. The result is a central range that is not particularly prominent (unless tips favouring the midrange are used), but which, without a doubt, has a very ample presential and descriptive fullness.

Treble

Planar IEMS have the advantage that they can subtract energy in their high end, without the sound becoming dull or veiled. I think LetShuoer could have stretched the S15s towards a more clean, crystalline, bright and analytical side, given the capabilities of the driver used. But it has preferred to be conservative in the high end. And due to the intrinsic virtues of this new driver, it has worked out well. The quality of the S15s allows them to be clear and transparent without the need to add energy in the midrange. But it also allows them to be very expressive and with great detail despite lowering the energy in the highs. And that’s just it, the virtue is that lowering energy doesn’t mitigate or qualify the treble, it’s just balancing it out in the mix. The sense of extension and fullness is still there but not as eloquently. Perhaps there is more depression in the air zone, but the treble of the S15s is representative for a moderate, yet rich and sufficiently extended brightness. In that way, the treble is not only smooth, because it maintains a good degree of information and expressiveness. They keep sibilance at bay and are pleasant for long listens or for short, but loud, listens. It is at this point that I realise that the S15s maintain a characterful treble but with a connotation of control taken to a higher level. The S15’s treble is not just controlled, smooth, moderate… it’s all of that but without losing the virtue of brightness when necessary, yet eliminating the pejorative and penetrating part to maintain musicality and, once again, neutrality.

Soundstage, Separation

In front of a natural, neutral sound, a realistic, well-structured scene is possible. The S15s are spacious, but not three-dimensional, ethereal or holographic. They do not surround the head, but there is a certain enveloping ability, as they are very capable of stratifying and separating music into layers, planes and elements, offering a sense of vibrancy. This ability favours the listening of live music, adding an extra sense of presential realism. The grandeur of the music also benefits from this ability, which, together with the other technical virtues of the driver, allows for a remarkable level of separation and distance between elements. Despite the somewhat dark and warm character of the sound, the S15s are quite transparent. Again, their outstanding level of resolution and definition ensure a very neat, clean, very well delimited sound, which allows a glimpse of a dark background, even space in the separation. This is enough to describe the micro detail, even if it is not faithfully represented in its entirety, perhaps because it is not sufficiently analytical, rather analogue. All in all, the image is expressed in an easy way and the location of the elements appears effortless.
The S15s have many virtues, including the ability to be suitable for long, leisurely listening as well as for more intense, critical listening. In both scenarios, these IEMS will be able to deliver what is asked of them, offering detail, resolution and definition when demanded and smoothness and musicality when listening to music for pure pleasure. This duality is not always present and this adds superior value to this new model.

Comparisons

NiceHCK F1 Filtro Silver

The NiceHCK F1s are perhaps one of the most unknown planar IEMS. However, they are one of my favourite IEMS in terms of sound. They have several characteristics that have favoured them to be so: they have 3 tuning filters, a more analytical sound than the rest of the planars and too short mouthpieces. The latter is clearly a disadvantage, but it favours that the search for suitable tips to improve ergonomics generates a sound somewhat different from what could be expected for its FR. As I say, their mouthpieces are too short and I had to resort to ultra-wide tips instead of my large foam-filled tips. The sound you get with them is not as full, the bass is not as sensory and the midrange, treble and clarity of the sound is enhanced. It loses fullness, but gains detail and resolution. Maybe it is not the most faithful sound to its signature, but it is the one I can get due to its bad ergonomics and the union with the tips suitable to my morphology. In no case the sound is bad, on the contrary, it is very good because it is different. The filter used for the comparison has been the Silver, which provides a more balanced sound.
In terms of construction, the NiceHCK F1 is a medium bore and overly thick cylinder. They are made of aluminium alloy using 5-axis CNC machining. The outer face has a micro-stepped slope to a thick C-shaped carbon fibre flat. The nozzles are short and their angle is not the best of all, the fit obtained is only superficial. With an ultra-wide silicone tip, clarity and a more technical sound is favoured and this is what I notice even though I have one of the most relaxed FRs at that time in high-mids and treble. Now, the S15’s are very similar in their FR. The low end seems to be a carbon copy and from 1kHz onwards the differences are small. It is true that the S15s are more rounded in their curve and that gives them a more distinguishable refinement.
I have used the same ultra-wide tips on both models to equalise the listening conditions as much as possible. Sensitivity in both is very even. Overall, the S15s are slightly darker and drier than the F1s, subtly more muted. In the low end, the dryness is felt, offering a tighter, smoother bass. The F1s have a rougher, slightly more textured bass, but are lighter, take up less volume and have less weight. The S15s feel denser and wider, with more energy and fullness, which gives them a greater sense of depth, but they also have more presence and impact within the sound.
There is more light and clarity in the midrange of the F1s, their sound is brighter and contrasts with the greater darkness of the S15s. There is more density in the midrange of the S15s and a sense of greater openness in the F1s. The sound is warmer in the S15s, with a perception of greater fullness and intensity in many respects. The F1s are lighter, their notes have less weight and are thinner. The density of the S15s gives them a more pronounced lushness, although the F1s’ lightness gives them more freedom and a little more openness. If you try to match the wall-of-sound feel of the S15s with the F1s, the tendency is to turn up the volume, but the result is undesirable, as the sound becomes less pleasant and gentle, losing the more appropriate control that the S15s do have. Thus, the male voices on the S15s are more physical, fuller-bodied and have a juicier, richer corpulence. The base of these male voices place the S15 among my favourite IEMS in this regard. A similar thing happens with the female vocals and also with the instrumentation. The sense of presence and closeness, as well as its physicality is higher on the S15. It is warmer and fuller, also darker, but its density gives it a very high sense of weight and immersion, which makes the listener become more integrated in the sound.
In the top end the F1s are thinner and brighter, with a little more energy, though they are also more penetrating and not as restrained, softened and controlled as the S15s.
It’s true that the thinner notes offer a little more vividness to the micro detail and a slightly more ethereal feel to the ambience, giving a sense of greater separation. The S15’s denser and somewhat darker sound is a little more complex and doesn’t seem as analytical as the F1. However, it is more refined and pleasant. The F1s can sound more strident, even less natural. Whereas the timbre of the S15s is more organic, warm and analogue. The F1s can offer a more open feel, while the S15s are wider and deeper.
In short, the F1s are finer, cooler and more analytical, have more light, clarity and appear more dispersed and ethereal. They offer good micro detail, but their timbre and note finish is somewhat more artificial, rougher, even harsher. The S15s are denser, darker, warmer, but offer more closeness in both bass and midrange, offering a higher level of lushness and richness. Their sound is fuller, with a heavier, more full-bodied base. But it is also refined at the edges, never harsh and more controlled even in the worst situations. The result is a more balanced, homogeneous, dense, thicker, complete and very musical sound. A step further in musical refinement.

Conclusion

It seems that LetShuoer has given a lot of thought to the release of its evolution of the famous IEMS planar S12. It could have followed the same path and created a more refined planar, following a continuist line. But it has not been like that, the S15 is a different model in many aspects, from its external design, with its capsules printed with 3D resin that gives them a less refined aspect, due to its matte finish and its colour. Ergonomics have been improved and weight has been reduced. In the end, these are aspects to be taken into account in favour of obtaining a better sound and pleasurable result. And it seems that pleasure has been the keynote to follow. The S15s have been softened in the midrange and the overall treble energy has been reduced, for a more balanced sound, with less noticeable sub-bass and more homogeneity in all ranges. The sound is now warm, even darker. A little more light can be obtained depending on the tips used, but it is clear that the treble is softer and more controlled, for a longer and more lasting enjoyment. The sound is richer and more lush, micro detail exists if you look for it, though it is not in the foreground. The S15s offer more than meets the eye at first glance, and that denotes a potential quality that increases with each passing hour.
On the other hand, to achieve these improvements, it is worth mentioning the effort of the brand, adding a new technology inside the IEMS. The S15s combine a new third-generation 14.8mm dual-chamber planar driver with a 6mm passive filter module. This module features LetShuoer’s new R-Sonic dynamic harmonic technology. Complex technology for a step up in sound quality in a very tight price range. It’s noticeable that when one reaches a point of excellence, every bit of quality one wants to gain costs a lot more and I think LetShuoer has done their part to achieve this.

Sources Used During the Analysis

• Aune X8 XVIII Magic DAC + EarMen ST-Amp.
• Aune M1p.
• Aune Yuki.
• Burson Audio Playmate II.
• Hidizs S9 Pro Plus Martha.