True wireless Bluetooth module (maze acoustic Bluetooth earphones)
A new level of bass
Precise damping adjustment.
Adjust the ratio of bass and treble, deep bass, clear treble (marked in red).
Newly designed 3D structure, low frequency the resonance channel is longer than before (marked in blue).
Sound quality wonderful indescribable
Newly designed sport car wheel, the sculpted face cover brings a powerful transparent sound.
The second generation dome LCP diaphragm drive rich, detailed sound no matter the deep bass or clear and pure highs every note is great.
Original design process
Innovative hub cover structure
This is a completely reimagined earphone unit modules have complete acoustic vents, the refined design of Smabat M4 embodies our pursuit of sound quality and design.
Secondary anodized aluminum metal, gorgeous and exquisite drive module.
Pros: + Modular earphone concept
+ Great clarity across the frequency range
+ Clean and decently deep bass
Cons: - Potential defects in some batches of the drivers
- Lack of variety in the tuning options
Do you want to build and tune your own earphones to create your unique sound? Do you like to share that unique sound with others?
This ability has been limited to handy DIYers and influential audiophile reviewers. However, Smabat has been trying to change this situation with modular IEMs and earphones. The idea is that you can buy the main body unit and a couple of different drivers and filters to put together a unique pair of IEMs or earphones. The assembly process can be done without soldering.
I love the idea. However, can the idea stand up to the cruelty of reality?
Let’s talk about M4, the latest generation of modular earphones from Smabat.
tl;dr: the modular idea works, but more refinement is still necessary. The complexity of a modular design brings about defects and inconsistencies. The selection of drivers needs more variety as they centre around Smabat’s house sound. If you are searching for a warm and relaxing sound signature, keep searching. These are not the buds you are looking for.
Forewords
I purchase M4 and all drivers at a discount to facilitate this review. Smabat also replaced the M4 body and all of the dynamic drivers once to address a potential defect. I have no financial interest in Smabat or the success of M4.
I rate IEMs by A/B testing them against a few benchmark IEMs, regardless of price point. If a $1000 IEM scores the same as a $100 IEM, then either the more expensive one underperforms or the budget one is a gem.
I believe that great IEMs are the ones that can achieve multiple difficult things simultaneously: (1) high resolution (meaning lines of music are crisp, clear, easy to follow and full of texture), (2) 3D soundstage with a strong sense of depth, (3) bold and natural bass with a physical rumble, (4) natural timbre, (5) relaxing and comfortable tonality. IEMs achieving those criteria are rated highly in my ranking list
I use frequency response measurements to double-check my subjective impressions.
Ranking list and measurement database can be found on my IEM review blog.
What is Smabat M4
M4 is a flathead earbud with interchangeable drivers and replaceable cable (MMCX connector). Each earpiece comprises a main body unit and a screw-on driver unit. The body unit contains a “3D structure, “ essentially a bass tube connected to a vent. This structure enhances M4’s bass response and allows you to fine-tune the level of the “V-shape” of M4’s sound.
Most driver units contain a 15.4mm dynamic driver. The driver is attached to a metal structure with two circular connection pads, a pair of vents, and the threads for screwing onto the main body unit.
Hidden in the drivers are o-rings that ensure the seal between the main body unit and the drivers. This seal is critical for getting the right sound out of M4. Earlier batches of M4 drivers come with white o-rings that tend to pop out from the drivers and prevent them from screwing onto the main body unit correctly. Some of my replacement M4 drivers come with black o-rings that fit better.
Smabat also sells a set of balanced armature (BA) drivers. These drivers belong to the Bellsing Hornet series. The BA driver units are not influenced by the bass tubes on the main body unit, so they are not sensitive to manufacturing variations in the screw thread.
How to buy M4
The simplest way to buy Smabat M4 is to get a “starter kit” that gives you everything you need to create a functional M4. This kit includes the main body units, 1 pair of easy-to-drive drivers, an MMCX cable, a carrying case, and six pairs of foam. This starter kit was my option when I purchased my M4.
Alternatively, you can buy the main body units and drivers individually. This option is good when you know the drivers you want and already have spare cables and foams. This option was how Smabat sent me a replacement unit.
You should also grab the tuning filter kit even if you already have some DIY IEM filters because the filters used by M4 are pretty small.
How to tune M4
The first way of tuning M4 is by replacing the filter on the main body unit. There are four types of filters, labelled as 1, 2, 3, and 2.5 (the default filters on the main body units). A higher number indicates a higher resistance (thicker).
How do the filters work? The same as when you tune bell-shaped flathead earbuds with a big opening at the back. If you want a lot of upper-midrange and a lot of midbass with a big dip around 1kHz, use thinner filters. If you want a less contrasty presentation, use thicker filters. You can see measurements with my IEC 711 coupler below.
The second way of tuning M4 is by replacing the drivers. The drivers have a slight difference in true resolution and the amount of bass. However, their tuning is consistent with the Smabat house sound. In other words, if you want a pair of warm and dark buds, you can’t achieve that with M4.
A note on channel imbalance and manufacturing defectsPermalink
As I have alluded to a couple times in this review, I have received a new set of main body units and dynamic drivers as a replacement for the first set.
So, what happened? One driver in every pair cannot screw onto the main body unit. The screw thread on both sides refuses to connect unless I press them together tightly. Even when they were screwed in, there was still a 1mm gap. As a result, the frequency response of both channels differed significantly. Moreover, tuning filters did not work on the defective side.
After a discussion via email, Smabat reacted promptly and sent over a replacement set of main bodies and drivers. Some drivers have new black o-rings, which fit better and negate all the connection problems.
It should be noted that the channel difference still appears in measurement, particularly around the ear-gain region. However, the problem is not very noticeable in real-world listening, especially with the Type 3 filters.
How it sounds
Casual listening sessions were done with Fiio KA3, Fiio BTR5, Hidizs AP80 Pro X, Hidizs S9 Pro, Hidizs XO, and Topping G5.
All A/B tests were done using Topping G5.
Local FLAC files ripped from CDs or bought from Qobuz were used for most casual listening and A/B tests.
Tonality and Timbre: 3/5 - Average
Frequency response of all configurations. Measurements were done with an IEC-711-compliant coupler and might only be compared with other measurements from this same coupler. Visit my graph database for more comparisons.
Tonality: Crisp, clear, and forward, but can be fatiguing and not the most natural. All drivers exhibit a similar tuning with reduced lower-midrange and forward upper-midrange (ear gain). If you are used to a warm and rich tuning, M4 can sound unbearably thin and strident.
In fact, harsher vocals like Bon Jovi in Wanted Dead or Alive can sound harsh and shouty (to put it simply: too loud comparing to the rest of the mix). However, I’m still determining whether this harshness is due to the tuning choice of Smabat or the defective drivers that do not seal properly.
For me, the type 3 filter and a bit of brain burn-in (a.k.a., getting used to the sound) bring the tuning down within my tolerance level. I would say the Smabat house sound is more suitable for higher-pitched vocals and instruments. For instance, Can’t help falling in love by Kacey Musgraves sounds fantastic with M4: clear, intimate, detailed, and emotive. Meanwhile, Bach suites for cello solo by Mischa Maisky sounds a little thin and a bit off, especially when he plays the lower strings.
Despite the forward and strident upper midrange, the treble of M4 is smooth but not weak. I did not hear any “treble glare” (i.e., that random bright sound stabbing in the ears when musicians strike cymbals or pluck a guitar string). Cymbals, hi-hats, and chimes in Wanted Dead or Alive sound controlled and detailed rather than splashy.
The bass of M4 is generally “tight” and clean, focusing on the punch (“boom boom” sound) rather than the deep rumble that makes up the physical body of bass notes. Note that the bass feels even more weightless in some configurations because you must turn down the volume to reduce the stabbing ear gain.
Different drivers balance low and upper midrange differently, but the tonality and timbre never venture far from the house sound. You can tame the house sound somewhat by using a warmer driver and a type 3 filter. In the most optimal configuration, I rate the tonality of M4 3/5 - Adequate, if and only if the drivers seal against the main body unit properly.
All M4 drivers have a high degree of perceived resolution in the midrange due to how they are tuned. It means that note attacks are emphasized and crisp. The whole stereo image is clear and sharp, just like looking at a vibrant and contrasty TV. In A/B tests, the difference in clarity between M4 and Aria, my standard for acceptable resolution (3/5), is noticeable and appreciated.
However, the true resolution of M4 is only average to slightly above average. By true resolution, I mean the ability of a driver (and its enclosure design) to finely distinguish similar sounds placed closely within the soundstage or in a fast passage. If we continue with the TV analogy, M4 is more like an overly sharpened full HD screen than a proper 4k screen. It is only sharp and clear when not too much is going on.
Another indicator of the true resolution is in the texture or “micro-detail” of vocal lines such as Andrea Bocelli’s in Besame Mucho, Bon Jovi in Wanted Dead or Alive, or violin solos performed by James Ehnes. M4 fails to dig into a deeper level of micro details and texture that I hear with my Blessing 2, my standard for “good” resolution (4/5). However, it does not feel overly smoothened like some worse performers in my collection.
Based on the A/B tests, I rate the resolution of M4 3.5/5 - above average.
Percussion Rendering: 3/5 - Adequate
Percussion rendering reflects how well the tuning and technical performance of an IEM work together to recreate realistic sound of a drum set. Good drum hits have a crisp attack (controlled by frequencies from 4kHz to 6kHz), full body (midbass frequencies around 200Hz), and physical sensation (sub-bass frequencies around 50Hz). Good technical performance (“fast” driver) ensures that bass notes can be loud yet detailed. IEMs that cannot control bass very well tend to reduce the bass’ loudness to prevent muddiness.
Across all configurations, the M4 have a punchy but focused bass. This is achieved by focusing the energy to 150Hz and below and cutting back the frequencies around 250Hz. As a result, drums feel tight and clean but maintain a good presence in the mix. Drum attacks sound “quick” and snappy. The pillowy bass, like punching a pillow, common among overly-dampened IEMs do not exist with M4.
However, besides the cleanness, the drums on M4 do not sound particularly interesting. M4 still outdoes many flathead earbuds in percussion rendering. Still, the clean and focused bass prevents M4 from sounding big, bold, and engaging.
Based on A/B tests and casual listening sessions, I rate the percussion rendering of M4 3/5 - Adequate.
Stereo Imaging (Soundstage): 4/5 - Good
Stereo imaging or “soundstage” is a psychoacoustic illusion that different recording elements appear at various locations inside and around your head. Your brain creates based on the cues such as the loudness and phase differences between the left a nd right channels. Most IEMs do not differ significantly, nor can they compete with headphones or loudspeakers. However, some IEMs offer a more spacious soundstage than others. Best IEMs can create multiple layers of sound from closer to further away and make some instruments float slightly above your head.
Flathead earbuds are great performers in soundstage imaging by design. Some earbuds can sound like a pair of open or semi-open headphones. Some can be modified and tuned to produce a forward projection of the centre image, like a pair of desktop speakers.
M4 is not one of those unique earbuds. It sounds like a spacious-sounding IEM than a pair of headphones or speakers.
Because of the Smabat house sound, M4 has a very focused and forward centre image. It means that the lead vocals or instruments almost always appear in your head. The up-front centre image also reduces the illusion of depth. It’s infrequent (but possible if you listen to some classical recordings) to hear the centre image appear in front of you.
Due to the strong contrast between the upper and lower midrange, the soundstage feels large and open but also empty when you shift your attention away from the centre image. You can imagine a mix where the singer stands very close to you, but the band sounds distant in the background. That’s the M4’s soundstage.
M4’s stereo imaging, meaning the ability to pinpoint the direction and distance of sound on the stage, is nothing special to highlight. M4 does not create the illusion of sound jumping around you or the intricate layering of closer and further away sound.
Despite a slightly disappointing performance against other flathead earbuds, the soundstage projected by M4 is still quite impressive in the world of portable head-fi gear. Coming from IEMs, this soundstage performance would impress you. I rate M4’s soundstage 4/5 - Good.
Comparisons between drivers
Stock M4 driver (40ohm, 110db, LCP composite)
What Smabat says: “Drive rich, detailed sound no matter the deep bass or clear and pure highs every note is great”
What I say:
My stock drivers are likely defective, as one driver cannot be screwed smoothly onto any of the main body units that I have.
I hear a tinny, glary sound. For example, I cringe whenever a note on the E string is hit in the Bach violin solo.
I hear a shouty and strident upper midrange.
The treble is surprisingly not harsh.
Bass is more potent than what I expected.
The resolution is adequate.
BA driver (22ohm)
What Smabat says: “Enjoy the shock of high frequencies”
What I say:
What high frequencies?
The upper midrange is more tolerable than the stock drivers. The midrange is still quite forward but not strident.
The BA driver has surprisingly potent bass. Not outstanding, but surprising for a single BA driver. However, it is still BA bass that lacks texture and resolution.
Slightly boxy and bloomy sound, likely due to excess energy around 500Hz. Cello could sound better.
Micro-detail is average at most. Air is lacking.
Soundstage is small but has an okay level of layering, making it enjoyable.
ST20 driver (40ohm, LCP)
What Smabat says: “The large-size LCP diaphragm drive unit has a huge liquid crystal diagram in the moving coil unit. The treble is still clear and natural, and the volume of the bass is enhanced”
What I say:
These drivers have the most enjoyable variation of the Smabat house sound to my ears. They are my preferred units in terms of tonality.
Acceptable bass: “Fast” with a sharp punch, decent body, and rumble. Better than BA bass and even some lower-quality DD bass (e.g., Moondrop Aria)
Claps are natural and decently detailed in Synchro (Bom-ba-ye) by Tokyo Kosei Wind Orchestra, meaning the true treble range is tuned relatively correctly.
Super One driver (100ohm, fibre)
What Smabat says: “The bio-fibre driver unit has a huge bass output in a large-sized driver unit, allowing high-power audio signals to pass through, and still have a strong bass”
What I say:
Somewhat similar to the ST20 driver in tonality, but with slightly better resolution.
ST20 Pro driver (100ohm, Fiber)
What Smabat says: “Use a black-coated bio-diaphragm drive unit. Based on the composite bio-diaphragm, it mainly improves the distortion of its bass and treble, which is very low and restores better.”
What I say:
If you want a bit extra treble sparkle to the Super One drivers, these are the drivers for you.
ST10S driver (150ohm, Dome)
What Smabat says: “The bass performance is strong, the treble is very clear and accurate, good sound quality can be obtained on a player with high thrust.”
What I say:
I am not sure, both of my ST10S sets are likely defective, as one side cannot be screwed smoothly onto any of the main body units I have.
The resolution is slightly better than the Super One and the ST20 Pro drivers.
Conclusion
Smabat has a great idea with M4. However, this great idea needs more refinement. The tuning could be less aggressive. The bass could extend further. However, they need to refine the manufacturing process to eliminate the fitting problem between the drivers and the main body units. I also wish for more variety amongst the available drivers rather than slight variations of Smabat house sound.
In the current state of M4, I can only recommend these earphones to adventurous listeners who like forward vocals and want to support the modular earphones concept. For DIY-inclined folks, I recommend picking up a soldering iron, some drill bits, and some standard MX500 drivers.
Nice review, bro! You pretty much nailed it. I too found the concept to be cool and the execution to be lacking. My M4s have already been resold, but I assume they'll try an improved version of this modular earbud idea at some point in the future and if they do I'll likely give it another shot then. If they get it right by following some of your advice here they would have a unique and very versatile product on their hands. This attempt mostly ended up being a frustrating disappointment for me.
Cheers to the awesome review! Keep up the good work.
Pros: The new level of modularity is much simpler and more efficient.
- Great mid-range, ultra-clear, transparent and very well defined.
- Very good treble, well expressed, excited and tastefully tuned, as well as extended.
- Remarkable level of separation, detail, amount of air, resolution and definition.
- The sound can be tuned with dampers which can be purchased separately.
Cons: The bass does not support a normal LFO load, it vibrates and ruins the sound when its presence is a little high.
- The standard Type-2.5 damper cannot be purchased separately.
- The screw thread could be deeper, some drivers don't seem to fit quite right.
- I think they could consider using a 2PIN 0.78mm connection, instead of the problematic MMCX.
Introduction
Smabat is well known to fans of earbuds. I myself have reviewed quite a few products from this brand. What started out as a model that had achieved a very impressive bass for earbuds, has now become the reigning innovator when it comes to modularity. The current product is called M4 and is the fourth generation of modular design. As you all know, Smabat has had a fixation for separating its earbuds into parts, with the intention of providing different flavours to users. Starting with a rudimentary system that required soldering, followed by simpler connectors, to the current system whose assembly system is the most advanced, simplest and most appropriate. There is no other brand that offers a model with 5 more drivers to assemble, plus a set of dampers that allow to modify the sound even more. An extensive and very juicy review is presented. Let's see what the new Smabat M4 and all its accessories have in store for us.
Specifications
Driver Type: Original: 15.4mm dynamic driver with LCP composite diaphragm.
ST20 Driver: large 15.4mm LCP diaphragm. Impedance: 40Ω. Frequency Response: 10Hz-22 kHz.
Super One Driver: 15.4mm fibre diaphragm. Impedance: 100Ω. Frequency Response: 10Hz-22 kHz.
ST10S Driver: 15.4mm dome. Impedance: 150Ω. Frequency Response: 10Hz-22 kHz.
Balanced Armature Driver: Impedance: 22Ω. Frequency Response: 10Hz-22 kHz.
Packaging
The Smabat M4s come in a rectangular box of size 160x112x56mm. The cardboard covering is white on the main side and in the centre is a realistic photo of the two capsules, without cable. At the bottom left, there is a sticker with the technology used by Smabat. On the back is the brand logo, in black, in the centre. At the bottom, on a grey background, are the specifications and the brand's contact details, in English and Chinese.
Once the cardboard is removed, a glossy black box with a textured surface is presented, which opens like a book. Inside, at the top, in a foam mould lined with black cardboard, are the capsules, protected by a transparent plastic sheet. There are three black parts/boxes containing the whole product, one containing the capsules, as I have already mentioned, another containing the foams and a third larger box containing a zippered case and an instruction manual. The full contents are as follows:
The two M4 capsules.
The two-strand silver-plated cable.
3 pairs of complete foams.
3 pairs of donut foams.
1 zipped case.
1 instruction manual.
The zippered case is one of the best I've seen for the price, it's rectangular and tall, with plenty of room inside, even fitting two sets of earbuds without any problems. The silver-plated cable seems of a quality commensurate with the product and price. The foam sets, although there are three pairs, are the cheapest of the set, they could be more numerous, although other models come with even less. Quite good.
Construction and Design
Being the fourth generation of the modular system it has to be the best. And I think it's pretty definitive. Although there is always room for improvement. As with the use of dampers, I'm not at all skilled at changing these filters and I suppose this system can be given a twist, using some kind of screw thread.
The main module is made of aluminium alloy and contains the 3D acoustic labyrinth structure. In it the filter dampers can be changed. It has a screw thread onto which the drivers are fitted. The channel side is represented by a white mole with the lettering inside. It has two slots on the upper side. On the outer side there is a silver ring with the brand name inside. The shape is circular, but with a corner at the bottom, in the area where the MMCX connection is located. The inner side has two retractable gold-plated pins which are the connection to the drivers. These drivers have a central disc and a gold-plated ring, which are part of the connection on the other side. As the drivers are threaded, the pins rotate on the disc and the ring. Thanks to the retractable pins, a firmer connection is ensured. It is clear that the system is bold, but the connection surface is small. Large cross-section cables are used to improve the sound and both the cables and the inner connections of the drivers are of a much smaller cross-section. And this is not just a criticism of this module. Again, the system works and is effective, although the screwing process is not perfect for all drivers, which prevents complete satisfaction.
The dark gold colour is prevalent throughout the capsule and on most of the drivers. The drivers have a rounded conical shape. The front finish and the grilles are very striking. The standard driver looks like a 5-spoke car wheel rim, with triangular openings protected by a black grille with visible holes through which the inside of the driver can be seen. Around the rim of the driver, on the inside of the cone, there is a silver part on which the size and model can be read, although the legend is the same for all drivers except the BA. All dynamic drivers are the same size 15.4mm and have the same bandwidth. Each has its own outer grille. Three of them are shaped like car rims, changing the shape of the openings. The ST20Pro driver has regular pentagonal apertures. The ST20 driver also has pentagonal apertures, but with an irregular shape. The Super One driver has a full black and perforated grille, as for the ST20S, but in gold colour. The BA driver is cylindrical and dark. It consists of a thick disc in the centre of which is a larger base cylinder and a narrower one mounted on top of it, which is strictly the mouthpiece. It is protected by a dense metal grille.
Finally, the cable consists of classic cylindrical and metal connectors. It has two silver-plated strands, the MMCX connectors are not ear-shaped and have a white letter to indicate their channel. The splitter piece is a single cylinder. There is no adjustment pin.
The performance of the system has advanced and is the best. There is still room for improvement, such as enlarging the contact surfaces or improving the damping system. Maybe a 2Pin 0.78mm connection could be used, I don't like the MMCX connection. I think there is enough room for it.
Adjustment and Ergonomics
The design is closely related to the tapered crescent shape of the M0, whose shape is one of the best I have tried. There is a slight change in the thickness of the rim that forms the driver part, which is thicker than the M0 and this may be the negative point compared to that model. On the plus side is the external shape of the capsule, which has a circular shape, but has a corner under which the MMCX connection fits. This feature means that the cable is not centred, allowing for a deeper lateral insertion, which is very well thought out. The whole thing feels a bit heavier than the M0, even the standard cable and its connector seem to increase this feeling. All in all, the fit is quite good, very free, it allows rotation and the fixation is good, although the insertion is not as deep as the M0.
Sound
Profile
Smabat has been characterised by a powerful low end. But I have always had the feeling that their tunings are like a short blanket, there is always a part that is exposed. Going back to one of my previous favourite models, the M0 was not characterised by a big bass, it was much more controlled. There was more balance in the other areas. I think the base driver of this M4 is going in that direction, but with a bit more bass, which I welcome, as a bass lover. There is a clear expressiveness in the early treble, sounding very natural and splashy. The mids are not completely forward, perhaps mid-range, but well presented. The lows are not prominent, though they do have a flaw, not bearing a powerful load.
The sound is described as it comes as standard, without changing dampers and using donut foams.
Bass
It repeats the feeling I had with the M0s and their bass. Vibration-like sonority, less natural tone, unrealistic and more coloured. It has a tendency to generate a BA driver sensation. There is a sense of depth, the impact is fast, dry, restrained, quick recovery and little aftertaste. But the tone is displaced. The strokes do not move much air. At a slightly high volume, there is a vibration that affects the rest of the sound, in certain higher frequencies. I don't think the driver is broken, but it clearly doesn't support music with powerful bass and continuous bass lines. I have the feeling that the assembly is weak to control high sound pressure and that the driver is more delicate. As I say, very similar to the M0 but with a bit more presence.
Mids
I must emphasise the enormous clarity of the midrange. Once again, Smabat has done it again: achieved a luminous, very clear and crisp midrange, which sounds natural, fresh, yet with a clear bright tendency. I think it's another step up from the M0s. The low end has no impact and the first half is thin, although there is some gain and a bit more physicality. The percussions have more body, as do the male vocals. But, overall, this first half is on the simple and light side. The best thing is that there is no trace of nasal sound and the tone, though bright, is realistic, as is the timbre. The rendering is not close-up, but its brilliance brings the details closer, although the texture is also expressed in a more accentuated way. It is not fully descriptive, it has no roughness, but it does have a descriptive level that improves with the quality of the source. As the frequencies increase, the sense of proximity is greater. It seems that the tuning has an enhancement in the high-mids. But the consequence in the earbuds is more accurate and does not become fatiguing because there is a better coherence and balance with the first half. It is clear that there is not a hint of darkness, the sound is not dense or warm, on the contrary, there is an inclination towards a more analytical side of the sound. In this sense, the details are splashy, but they are homogeneous with their fundamental. It is not a profile that only exalts details and small nuances. True, these are evident, but the base does not suffer, so the sound, though thin and excited, is quite full.
The female voices are once again the star of the show. The definition, the separation, the level of resolution are high and are the best exponents of the range.
There is more balance, although the range is excited and very bright, there is a slight improvement in the first half which increases the overall quality of the range. I have to try changing the damper to see if the bass improves and thus gain body and physicality.
Treble
Really sharp, the initial sparkle is very high and the feel is very crisp. Again, there is a control on the edge that avoids a strident sonority, but those who are sensitive to treble will notice the brightness instantly. The notes are very thin and the thinness is felt like a razor's edge, producing a penetrating, very defined, high-resolution sensation. There is a sense that the treble is glassy and can cut through. Its edge is high, again it has an explosive character, with some control at the top, but it's a very high mountain. The extension seems to be good and the sense of air is clear, something that favours stretching the treble and generating lots of harmonics in both voices and instruments.
The timbre is clearly bright here, not unnatural, but not completely realistic either. The dazzling edge is perhaps a bit too much and a little more nuance would have been appropriate. Let's see if the dampers help in this regard.
Soundstage, Separation
The scene is wide, but with a medium-low depth. The splashy sound brings the sonic presentation closer together again, bringing detail and nuance to the fore. To the detriment, the body of the instruments and voices is not elevated, which accentuates a greater sense of flatness. Laterality is good and height is normal. The predominance of the scene is frontal, without many layers. There is a certain gauzy level due to the vaporousness of the nuances and the expanse of air. But the high resolution fixes the elements to their thin base.
Resolution, definition and separation are high. There is no overlapping, no congestion, but the background is not very dark.
Comparisons
ST20Pro (Fibre driver 15.4mm 100Ω)
The ST20Pro has a more V-shaped profile. There is more control in the low end, the M4 sounds more congested in this range and carries less bass load. The ST20Pro doesn't suffer when bass is prominent and handles it much better. They have a punchier, more realistic and deeper punch. They have superior low-end responsiveness, being able to recreate the low end with more body, layering, layering and depth. The M4 falls short in this regard.
In the mid-range, the M4 has a fuller, but also brighter, tuning. There is more homogeneity in its representation of the midrange, although it lacks physicality in the first part. On the ST20Pro there is more initial body, but I perceive a hollowness right in the middle, something that causes a distancing of the range, a strange sensation, a kind of emptiness that pushes away certain musical parts. My feeling is the same as I had when I reviewed the M0 body with the Super Point driver. There is more density but less clarity. The sound is muddier, the bass has more presence, but the vocals are not accurately placed.
Treble is clearer, crisper and brighter on the M4s, I prefer that response with more extension to the more nuanced, if initially punchy, representation of the ST20Pro. Their range is not as full and if you want to enjoy the treble, the M4s are better.
The detail is more beautiful in the M4s, their resolution, ability to recreate detail and their accuracy make them recommended for more critical listening. The ST20Pro also has a good level of detail, but its unevenness and a more present low end penalise it when it comes to representing the full range of details. Although it is true that it has a better soundstage, with more depth, width and height.
ST20 (Big LCP driver 15.4mm 40Ω)
The ST20 improves on the bass response of the M4 and does not suffer from the same amount of LFO presence, handling it with greater authority and naturalness. There is more realism and naturalness in the bass timbre. Noticeably responsive and dry in its execution, the punch feels tight, restrained, but more exuberant.
In the midrange the response is more balanced, it is not as crystalline as the M4, but its timbre is less bright, I would say more in line with reality. There is more density, but I don't find the hollowness of the ST20Pro, which is a clear improvement across the range. There is body and a certain level of brightness, sparkle and excitement. A good midrange.
The treble is sparkling, not as dense, not as thin, not as thin as the M4s, but very much in keeping with the more homogeneous and fuller profile that these ST20s offer. They have a good initial sparkle, not as bright, but with good extension and overall representation. Again, quite good.
Good detail at the macro level, suffers a little in some micro details, but has a good level of resolution overall. Its scene is more coherent and normal, with more depth, although the separation is not as clear as in the M4s. Overall, its sound is more mature, fuller, balanced and homogeneous. It's not stellar at some points, but it's a more all-rounder driver that you can get more out of, even get a good level of detail with a good break-in and better sources. I like it.
Super One (Fibre driver 15.4mm 100Ω)
Back to darkness, warmth and congestion. The bass is back, but with great control and depth. The punch is precise, concise, terse and very well drawn. It holds dirty bases without difficulty and handles the low end with authority. They have a darkness that makes them special for this range. Although it also makes them a bit murky.
The mids are more muted, lacking sparkle and clarity, possessing a comparative veil to the M4s and ST20. The unevenness in the midrange doesn't seem as pronounced as in the ST20Pro, but there is a good density and uneven representation in terms of closeness/farness of the elements across the range. Enjoyable for those who like a darker sound, with a hint of nuance.
The treble is presented in the same way as the rest: there is a good initial sparkle that is damped by a final clipping. It is as if the extension is limited, filed down, muted. This prevents the range from being extended and one feels a lack of air, greater density, less separation and a more compact, blended scene. Good sense of depth, oval scene, but with little projection of the notes.
ST20S (Dome driver 15.4mm 150Ω)
Back to a more balanced driver with a little more light. Its low end is not as impressive in quantity, but remarkable in quality. There is a good representation of bass, with very good control and dryness in exposure and response. However, it is not very suitable for complex bass reproduction either, and it suffers when power and punch are demanded beyond its capabilities. It doesn't suffer as much as the M4s, but it suffers when the volume is high. Despite their quality, they would not be suitable for electronic music sessions.
The good bass response gives it a slight warmth and body in the first part of the mids. It has a clean but not as crystal-clear representation as the M4s. Although, in turn, the balance is superior, lacking an extra point of clarity to give it a sense of superior transparency that it lacks, comparatively speaking, compared to the M4s. But, it is possible that in terms of timbre and naturalness they are in a sweet spot, along with the ST20. Again, a great all-rounder, with a more audiophile point due to its lighter low end. Its quality also increases with powerful sources and scales with a richer, more overwhelming sonic fullness.
Perhaps the most coherent, balanced and tight upper range of all the drivers. The best treble blend and presentation. It has sparkle, extension, a good finish, a realistic sonority, all without being obtrusive, retaining control and a good crisp feel. It is on the natural side, fair but effective. It responds when needed, but without overdoing it.
I thought it was going to have more micro detail, but it does not. In this respect, I was a little disappointed. It is more focused on normal sized detail and, in the background, the separation is not as obvious, being less transparent than expected. It's hard to find darkness in the separation and its scene is more cohesive, albeit broad. It has good height, good depth, good laterality, an oval recreation, but the layers don't feel very well defined or distinct, there is a bit of a mix in them.
The ST20S are good at many things, but in bass, separation and micro-detail they are not the best of the bunch. Their overall balance makes them a good all-rounder, though, more geared towards quality mids and highs.
Balanced Armature (22Ω)
Does this pretend to be a full-range IEM BA? The bass representation is awful, any resemblance to the real thing is purely coincidental. Unless the driver is aimed at enthusiasts with a very fine ear who enjoy listening to music very quietly. As soon as the volume is turned up to a normal level, the bass is distorted like never before. The low end response is deplorable.
The mids are more "natural". Although it is not an easy BA to move, the power is bad for it, any bass is painful. As such, the representation of the mids, while not entirely bad, lacks realism and sounds incomplete. Nor are the IEMS crisp or clear. The highs are not fully represented, beyond the high-mids and the initial sparkle.
Overall, they sound like defective IEMS and I would never recommend this driver to anyone. It's as if it's broken or, really, it's defective.
Finally, I did a frequency response measurement and it showed a crosstalk of almost 5dB at the low end, plus some lighter crosstalk in the high-mids. Does this fact justify its poor bass response? I don't know. But they are definitely flawed, so judge for yourselves.
After some research on how the dampers affect, I decided to switch to Type-2. It seems that the M4 has a Type-2.5 damper fitted as standard, which can't be bought separately. It's a pity, because that means that once removed, unless you are a real handyman, you won't be able to get the original sound back. Thus, the comparison will be by memory. According to the frequency response graph, the dampers alter, above all, the central range. And it can change it significantly. So I decided to go for what I was really looking for: to increase the first half of the midrange and lower the upper midrange a bit. And that seems to have been the case. Now the mids have more body, the extra clarity and brightness that this model possessed has been lost, but the midrange has been compensated. There is more physicality in that first half, a little more density, getting just what I wanted. Of course, the bass is not fixed, it still suffers from thick bass swells. For that reason, they are still not suitable for electronic music, although I can't deny that the sound is now more all-round, even more mature. For many, it may be a change for the better, it usually is, at the cost of losing the distinguishing feature that made it superior.
Conclusion
Smabat has once again taken a very positive step towards modularity. Everything is much easier now, except for the positioning of the dampers, which requires the use of a magnifying glass and calm hands. But if even I have been able to do it, I don't think the rest of the users can't do it. After creating deeper threads and a system of retractable pins and gold-ring contacts, Smabat's DIY has moved up to a much simpler and more effective level. In terms of sound, the M4s sound like an evolution of my beloved M0s. I thought the brand was going back to a more bass-heavy sound, but they have maintained a brilliant tuning, with extra-clear mids and present and extended treble. It's clear that its sound may not be for everyone, but that's what the various drivers, including the dampers, are for, to tune the sound to our final taste. On the negative side, the bass is not up to the level of the whole, because it does not support a normal LFO load. The threads don't seem to be the most durable points of the main body either, some more thread would have given more consistency.
Sources Used During the Analysis
Earmen Angel.
TempoTec Variations V6.
Hidizs AP80 PRO-X Red Copper Limited Edition.
ACMEE MF02s.
xDuoo XD05 BAL.
S.M.S.L Sanskrit 10th MKII + iFi ZEN CAN.
Ratings
Construction and Design: 88
Adjustment/Ergonomics: 88
Accessories: 80
Bass: 62
Mids: 89
Treble: 85
Separation: 90
Soundstage: 85
Quality/Price: 89
Penon Audio Store, offered me this model, in exchange for writing an honest review. I want to make it clear that all my opinions written in this review have not been conditioned by this fact, nor will I ever write anything that I do not really think or feel here. I will only write about my personal opinion in relation to the revised product.
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Cheers to the awesome review!