The Passive Bass

Ratings

Pros

• Balanced tuning, nice and smooth treble.
• Good sub-bass level.
• Natural, open and separate sound.
• Present mid-range.
• Ergonomics, feel and construction.
• Good transport box, good cable and good accessories for the price.
• Very good value for money.

Cons

• The mids are somewhat thin and lean.
• Treble is too soft and not very well represented.
• I expected a higher level of bass presence due to the passive radiator. Overall, the bass is a bit lacking.
• The design of the outer side contrasts negatively with the inner side.
• Although I like the rubbery material on the inner side very much, it is susceptible to staining and could even degrade.

Purchase Link

https://letshuoer.net/products/letshuoer-dz4-triple-dynamic-drivers-single-passive-radiator-edc-hifi-in-ear-monitor

Link to the Store

https://letshuoer.net

Introduction

LetShuoer became famous for its planar IEMS, but it was already an established brand with several models under its belt. After introducing a PRO version of its famous S12, the brand released an impressive top-of-the-line model called Cadenza, an IEMS with 12 drivers, titanium chassis, six-way electronic crossover, five acoustic holes and 204-strand 6N monocrystalline copper and silver hybrid cable. This model is priced at $2299. A little later the brand has put its feet back on the ground and surprised with a triple 6mm dynamic driver in conjunction with a passive radiator, also 6mm. This is the model that concerns us in this review. It has a semi-open front design and its body is a fusion of metal and resin. Inside, it uses four-way acoustic tubes and a two-way crossover circuit. The transducers are connected to the 2-pin receptacle via a flexible printed circuit (FPC) crossover board.
The model was released before its price was discovered. During this period the DZ4s have passed through the hands of a few reviewers, myself included, and it has elicited various opinions about the use of its passive radiator in a semi-open environment. Be that as it may, after their $89 price tag was revealed, it is time for me to write my opinion about these great IEMS.

Specifications

• Driver Type: 3 x 6mm titanium dome dynamic drivers + 6mm passive radiator.
• Frequency Response: 20Hz-40kHz.
• Sensitivity: 104dB.
• Impedance: 12Ω.
• Chassis material: 3D printed resin.
• Jack Connector: 3.5mm SE gold plated.
• Capsule Connection Type: 2Pin 0.78mm.
• Cable: 1.2 0.05m*216 silver-plated monocrystalline copper wire.

Packaging

The LetShuoer DZ4 comes in a white, elongated box with dimensions 157x105x51mm. On the main side there are four circles nested by a kind of chains. They are partly orange. They give the impression that they are the three dynamic drivers plus the passive radiator. At the top left is the brand name and slogan. Bottom right is the model name. On the back are the specifications, in several languages. At the bottom are the brand’s logos, as well as the logos of the certifications that the product complies with. With the outer cardboard removed, the box is completely white with the brand name in the centre and its slogan underneath in silver ink. After lifting the lid, there is an orange instruction manual on one side, white on the other. There is an enlargement of the external image, focusing on the circle with a tunnel in it. Then there are several cards, a product certificate, a card with QR links to the various social networks and a warranty card. Finally, you come to the foam layer containing the capsules and a rubbery, circular, black box containing the silicone cable and tips, along with a sachet of silica gel. In summary, the contents are as follows:

• The two DZ4 capsules.
• The cable.
• Three pairs of black silicone tips, sizes SxMxL, «Vocal ear tips».
• Three pairs of translucent white silicone tips with black core, sizes SxMxL, «Balanced ear tips».
• Social media card.
• Product certificate card.
• Warranty card.

The round case is rubbery on the outside and has a black rubber coating on the inside. It has a screw top closure and looks like a cream jar, if not for its completely black colour. I think it is a great box for storing and protecting IEMS, although I think it is not completely suitable. Firstly, because the thread is long, it is not quick to open or close the box. Secondly, because of the size and shape of the box, it is not very practical for transport. However, it is possibly a very suitable storage for IEMS.
On the other hand, it is not clear to me which are the vocal tips or the balanced tips. The text «Vocal ear tips» is above the small black tips, but the text «Balanced ear tips» is in between the large black tips and the small white tips, being ambiguous. For the clearest reference, I would say that the black tips are the «Vocal ear tips».

Construction and Design

As mentioned in the introduction, the capsules are made of metal and resin. The outer face is metal and has the N pattern that is on the outer face of the case. At each junction and termination of the N is a circle that grows in one direction. Underneath this pattern is a perforated orange grid, which is the open part of the IEMS. The shape of this face has the form of an equilateral triangle with an extra side on the hypotenuse. On the other hand, the three vertices are rounded. The body is covered with a very light brown rubbery resin. It has been 3D printed. On the edge of the capsules you can read the model, below it the brand name and on another line the channel letter inside a circle, all in black ink. The 2PIN 0.78mm connection is embedded in a rectangular transparent plastic plate with rounded corners. This plate is completely integrated into the capsule and does not protrude at all. The nozzles are projected and regular. It is a double cylinder, narrower at the base, with a diameter of 6 mm. The crown is 6.3mm in diameter and the total length is approximately 5mm. The nozzle has three orifices, one is narrower and does not appear to be protected, the other two have a kind of metal cup inside, at the bottom of which there is a grid attached to the walls.
I have to say that the design doesn’t leave me indifferent. While the external N-shape doesn’t quite convince me, the body of the capsule and its rubbery look (which is also repeated in the round case) are irresistible to me. It’s a pity that the light colour and matt surface can be a magnet for dirt.
As for the cable, LetShuoer is used to creating good cables. On this occasion, the cable is made up of four twisted strands, equal in pairs, some lighter and some darker. It is specified as consisting of 216 0.05m strands of silver-plated monocrystalline copper. The sleeve of the plug is a faint champagne-gold coloured microtextured metal cylinder. The brand name is written on it lengthwise. The splitter piece is the same, but smaller, the past is a hollow translucent plastic cylinder. The 2PIN 0.78mm connector sleeves are both cylinders of the same type, with a ring at the end closest to the cable. The 2Pin base is coloured plastic, red for the right side, transparent for the left side. There is a grey Velcro strap to tuck the cable in, with the brand lettering in white.
On this occasion, the cable is unbalanced and the 3.5mm SE connector has a plastic protector.

Adjustment and Ergonomics

A construction is not excellent if the ergonomics fail. Luckily, LetShuoer knows what it is doing and the ergonomics are outstanding. The weight is low, the feel is very soft, the fit is superior, the insertion is completely adequate, somewhere between shallow and slightly deeper, for use with narrower tips. I can comment that my ear canals are like underground tunnels and that’s why the diameter of the nozzles doesn’t seem big to me, but it’s possible that, together with the length, it could be a problem for some people. In my case, with my large tips filled with homemade foam, the DZ4s fit spectacularly in my ears. The fit is immediate, the seal is high, there is no rotation and none of the capsule parts rub annoyingly against my ears. The experience is very pleasant even for several hours. What makes it not so suitable is that being open, they can disturb people around more obviously than the other closed IEMS.

Sound

Profile

Its profile is close to a neutral curve, but with an emphasised sub-bass nuance, something that adds a point of colour and fun. On the other hand, the treble is smooth, beyond neutral. Despite what you might think, I don’t consider the DZ4s to have a midcentric profile, nor a dark one, although they are pleasant, musical and balanced.

Bass

The first thing you might think coming from LetShuoer and being an IEMS with 3 dynamic drivers and a passive radiator, is that the bass should be the star of the show. What’s wrong? They are not. The bass is not thunderous, this is not a Bass-Heads set. But neither are they neutral in this respect. It is clear that the size of the drivers can have an impact on the power in the lower range. But there is one element that should add that missing bonus. This is the passive radiator. You can look up information about this element, for example, on Wikipedia. As a quick summary, it is a dynamic driver with no coil, no magnet, «it is simply a cone and a suspension, so it does not need any electrical energy to work. The energy that makes this bass radiator work comes from the driver that accompanies it in the loudspeaker itself, from the air that it displaces with each movement. Its purpose, like the bass reflex, is to add a reinforcement of the lower frequencies by entering into resonance with the frequencies radiated by the driver that accompanies it in the same loudspeaker».
I found it very eloquent to include this description taken entirely from Wikipedia because it puts the finger right on the problem. The idea for the passive radiator to work accordingly is that it must be in the same enclosure as the bass driver and that the enclosure must be closed. In the manufacturer’s pictures you can see that the passive radiator is in the same enclosure as the three drivers, but it is not a closed enclosure. So, to what extent does the passive radiator influence the bass development? This could be a clear question, but I am sure there are many others. On the other hand, the discussion of this element is beyond my knowledge and is something that has been commented on in the networks by some famous reviewer we all know. You only have to google it to find out. As a humble reviewer, I will leave aside the actual performance of the passive radiator and proceed to the description of each range, as usual in my reviews.
While it is true that the bass of the DZ4s is not powerful, I repeat that it is not neutral. There is its elevation at the sub-bass end and also the cleanliness of its sudden drop towards the mids. Such tuning generates a bass of fast consumption and very low persistence. Its body mass is low and its energy feels limited by this effect. The volume occupied is small, hence its influence on the sound is quickly diluted. It is also true that the presence of the bass is not superimposed on any other frequency, something that could attest to its neutrality. But the tilt of the sub-bass adds a little more bite to the bass drums, a different sonority, a sensory and subtly visceral motif that brings a bass emphasis beyond innocuousness. It’s not big enough to move a newsworthy amount of air, capable of flooding our ears, nor does it possess the power to deliver a punchy kick. But in the very low frequency pure tone test, the DZ4s perform very well, offering a quite sensory and natural low-end, but with limited power. You can clearly feel the power drop from 40Hz to 75Hz, hence the bass feels so clean, albeit with a subtle vibration that becomes more noticeable above 40Hz. Such an effect is very small and not noticeable in real music, but some may wonder where it comes from and why this is so. I don’t think in that sense, there are many other IEMS with a similar effect, let alone what happens when the bass driver is a BA.
The result is a relatively dry bass, low in roughness, relatively fast in its punch, faster in its decay and evaporation. Its impact on the sound is low even though the music is loaded with bass. There is a clear presence and energy to it, but so focused on the low end that its impact is minor. Again, that is its cleanliness and the reason for the neutrality in the sound. It is able to follow complex, unfiltered bass lines because its reproduction does not generate an unmanageable mass of air. Being a more low end focused bass its volume is much more limited and that allows for continuous, glued and overlapping bass lines to not pose a difficulty or problem in its reproduction. It is true that its presentation feels reduced and minimised, but it enjoys a realism in its timbre and more controlled execution. In addition, such a differential cut makes the mids be totally decoupled from the bass. As they say: every cloud has a silver lining.

Mids

It is clear that a neutral tuning in the centre favours female voices. In addition, the cleanness of the bass does not generate warmth in the first mids. Although the sound may seem to be slightly warm, it is more because of the softness of the treble than anything else. I must stress that this tuning generates a very analogue, even euphonic, representation of the female voices. They are not sparkling, but their musicality, tone and timbre is extremely pleasant, silky, melodious and musical, highly enjoyable. The mid-highs are controlled in a sweet spot, free of sibilance, with a calibrated and homogeneous amount of brightness, enough to bring clarity, but not brightness. There is no glare, there is adequate lucidity to avoid ambiguity and help discern the elements to gain in freedom, neatness and separation.
The male voices don’t have as much of a base, they are a little leaner and less corporeal. But they do have presence and impact in the sound. They feel near and close, but they lack the physicality that the female voices possess, better balanced and more fully composed. There is also a lack of texture in the male voices, a deeper rumour, a broader base. On the other hand, the details are more evident and the balance leans towards this side more ornamental than fundamental. Something similar happens in the instruments of this initial part, the sound is thinner and lacks a certain density to lift the weight of the notes. There is not much forcefulness, the representation is soft, lighter, it may lack punch in certain aspects and in musical genres such as rock, it will lack a certain bite that makes the music more vibrant, realistic and effective. On the other hand, the timbre is not penalised and the sound is really pleasant in this area, although I still think it lacks some brute force to enhance the music.
The upper midrange is sufficiently emphasised to detract from warmth in music that is so, as well as alleviating density in music that is overdone in this regard. Arguably, the DZ4s are able to thin out the music in some respects, but without adding extra or detrimental brightness. Clarity is still very appropriate and calibrated to add detail and widen separation within the density, but without sibilance. The DZ4s are never overdone in negative respects, never sounding piercing, hurtful, grating or out of place. They are, however, delicate, though not overly inclined towards micro detail. The execution is neat, the low density helps in this respect, but the technical skill is not superior in exposing micro nuances to the foreground. In that respect, the DZ4s are not analytical and their level of resolution is good, but it is not an ultra-detailed set. That affects the mids not to feel as exposed in their level of detail.

Treble

The treble is relatively nuanced and smoothed. The DZ4s belong to a set of IEMS that have a more analogue cut, in which the treble is softened and rounded in its representation. They are not sparkling, not crisp, not piercing, not sharp. It is a controlled, respectful, even warm high end. There is an initial sparkle, restrained, but apparent, based more on the gain of the bell than on the treble zone itself. The extension also feels clipped and I don’t understand why if, in theory, there is a driver for the high end. A more excited result would have broken the balance of the tuning, perhaps it could have thinned the notes more, but a little more brightness could have raised the technical aspects, at least, in an apparent way. Possibly, the upper zone is too safe and is the least represented band of the ensemble. And this may lead one to think that the DZ4 is more midcentric than homogeneous, but because of the sub-bass elevation I don’t think so. This is not a strange range, I have reviewed IEMS with similar tuning in this respect. But it is clear that those looking for more finesse, more incisive, delicate, sharp and refined high notes will have to look elsewhere. The DZ4s are just the opposite, the treble is meant to complement the sound and not for its own showcasing. In this sense, it is a complementary range, which works well for the midrange and adds relative richness. But more was expected.

Soundstage, Separation

The scene is open but not too big. There is a good level of separation and the sound does not feel congested. Its low density helps in this respect, as does its thinness. The sound is wide, especially in width, and is able to offer a good ethereal, vaporous, even three-dimensional feeling. But it is not a very deep sound, nor is it very high. On the other hand, the mids are presented in a close manner, which gives the sound an intimate, close aspect, but combined with a volatile character that helps it to spread out. It seems somewhat contradictory, on the one hand the DZ4 are able to offer a somewhat holographic staging, where the elements enjoy an enveloping provenance. However, the elements are close to the listener. It is not a claustrophobic scene, nor is it concentrated, it is just that the stage is not so big, but a smaller environment, a smaller room. But that does not detract from the fact that there is a three-dimensional projection within it. Perhaps this aspect is what makes the DZ4 unique in this price range.
In terms of detail it is good, bordering on a B. But it lacks the level of resolution to describe fine details with superior descriptive ability. There is some finesse, more for the leanness of its sound than for any technical or analytical skill. However, in some phases of the sound it can be surprising in its exposition of detail, while in others it will remain a mere exposition of it, especially those at deeper levels.

Comparisons

KiiBOOM Allure

Surprising as it may seem, there are a few IEMS that I have reviewed this year that have a similar profile to the LetShuoer DZ4. Perhaps not with as much emphasis on sub-bass, perhaps not as shaded in treble. But, for example, TinHifi has several current models that have similarities, as can be seen in the comparative frequency response graph. Even, the TKZK Ouranos also moves in those parameters, but even with more air (you have to take into account that the IEC60318-4 01 microphones are not very reliable in the high end).
But I’m going to go for another model that is particularly soft in the treble, but with a more powerful sound in the mid-range. This is my beloved KiiBOOM Allure. Anyone could say that this model is also a niche model and looking at the graph there are clear similarities. In principle, the Allure is more expensive, $99 compared to $89 for the DZ4. In terms of construction, the Allure are metallic, except for the external face, with that stabilised wood panel in shades of green and black. Although I like the internal surface of the DZ4s a lot, because of the smaller size, thinner and design, I prefer the Allure. Although the cable is better on the DZ4s, as well as in terms of accessories. The huge zippered case of the KiiBOOM is hilarious, for so few accessories. In this respect, LetShuoer could be a good example in terms of quality/price/packaging. In terms of ergonomics, the DZ4s have a good fit due to the projection of their nozzles. But the integration is superior in the Allure, they are tighter and better inserted in the pinna.
In terms of sound level the first impression is in the sensitivity, at the same volume the Allure sound louder. Another aspect is the density of the sound, while the DZ4s are lighter, the Allure is characterised by a much denser and somewhat darker sound. The emphasised sub-bass of the DZ4s is not present in the Allure. In contrast, the bass-midrange and the first bars of the mid-range are more bodacious in the KiiBOOMs. This is the source of the sensation of density and wall of sound that the Allure offers, perhaps the big difference between the two: the level of power, energy and punch in that area from the lows to the initial mids. In the low end, the behaviour is key. The cleanliness, the restraint, the greater dissipation in the DZ4 contrasts with the more extensive, forceful, voluminous and physical bass offered by the Allure. Both are fast, but the decay is slower in the Allure, because of the differential characteristics it possesses. In favour, the texture is more pronounced, pleasant and enjoyable. Yes, the fun factor falls on the side of the Allure, but they are also deep, weighted, more gummy, but they also enjoy a good level of technical, resolution and agility. They are also capable of carrying heavy loads, generating a good level of layering and drawing bass lines with clarity and crispness. Comparatively speaking, they are darker than the DZ4s. All this is simpler in the DZ4. Due to their tuning, they do not tend to go into difficult terrain, as they have a lower level of presence in these areas. Thus, by avoiding the complex range, certain problems are avoided, although a certain comparative hollowness is also evident, in favour of the Allure.
The battle is very complex between two mid-ranges that I like. The DZ4s are thinner, leaner, with no contamination from the bass. The Allure have a denser, more physical and corporeal first half, also darker and somewhat more nuanced, not so much in the foreground, despite the wall-of-sound feeling they offer. The cleaner DZ4s make the mids brighter and better separated. However, the male voices have a deeper and more fundamental base, they are thicker and that makes them fuller and more complex. That feeling carries over to the strings, guitars, even pianos. With a more succulent base, the descriptive capacity is juicier, other nuances are appreciated that in the DZ4 are more relegated and missed after a quick switch to the Allure. When the music is warmer, the Allure adds more meat, while the DZ4 thins the mix.
In the upper-mids there is a little more light and clarity in the DZ4s. They seem to have more definition, more proximity, sharper edges and that characteristic cleanliness. The Allure is still more grounded, but a little more diffuse and fuzzy. The timbre of both is a very combative point, but for the greater weight, base and fundamental capability I’ll take the Allure.
There are also many similarities in the treble area of both models, but I think there is more extension in the Allure and a subtly brighter sound. In terms of definition, cleanliness and separation, the DZ4s are above them, albeit with less airy feel.
The level of separation is more evident in the DZ4s, but the amount of detail is very even. Looking for differences in tracks with hidden detail in the mid-range, the level of resolution of the two is very similar. They are not able to highlight these minute nuances, but they manage to intuit them. The analytical level of both is at that point, neither of them reaches that level of definition. But in more obvious aspects, in terms of better separation, thinness, delicacy and neatness, the DZ4s are a little above.
The soundstage is more open in the DZ4s, with that more pronounced three-dimensional feel. The Allure presents a wall of sound that is louder, wider and deeper, but also more frontal, with more volume, but without that surrounding, gauzy or ethereal feel that the DZ4s possess.

Conclusion

It is clear that this new LetShuoer release has had a certain impact due to its triple dynamic driver, its passive radiator and its open design. At first glance, such a configuration might make some people think that the DZ4s would be a bass cannon. But this is not the case. If you look at the concept closely, these are 6mm drivers, which are relatively small to deliver a powerful bass. But that’s where the passive radiator should come in, to positively influence the area it shares with the driver it’s attached to. And, well, maybe that’s the reason, is it really attached to any driver in the same enclosure? That could be a question. And speculation is just another game in this hobby. But, if one takes away all this theoretical stuff related to the construction of the DZ4, one finds oneself in front of some remarkable IEMS.
When they arrived I didn’t know their price and I liked them for their open, clean, smooth and clear sound. The feel of the capsules, their cream box for men, conveniently rubberised both on the outside and, above all, on the inside, their cable and their set of tips led me to expect a price of over 100$. But, to my surprise, they have stayed at $89. And I must say that, for this price, they are very good. Then we have to talk about their profile and performance. These are IEMS that follow a line that is being usual in many IEMS that I have tested lately, but with a clear emphasis on the sub-bass and more smoothness in the treble. Some label this profile as midcentric, but I don’t completely agree. The drop from the sub-bass is obvious and that makes the lower range and the transition to the mids very clean and quick, without any aftertaste. Consequently, the mids are clear, but somewhat lean and light in this initial part. Even so, they are present enough to bring out that midcentric aspect that other reviewers talk about. This is coupled with a controlled emphasis on the mid-highs, which favours luminosity, more prominent and vivid female voices. Possessing a relatively light, but natural, smooth, organic and analogue timbre, as a result of the conjunction of nuanced, controlled and not overly extended trebles, which are coupled as a support band, rather than as a single band in its own right. Another big plus is the separation and sense of openness of the sound. Without being too wide in volume, like a small sphere, the sound is remarkably enveloping, ethereal, even gaseous, allowing detail to come from many different directions, yet without giving off a close, close intimacy, driven by a subtle lack of depth. The DZ4s are not analytical, they are pleasant, smooth and musical, made for hours of enjoyment, supported by their great ergonomics and feel.
The LetShuoer DZ4s are a great set, but perhaps, the expectations of their configuration made us ask for something more, even something different. And maybe this is the problem that prevents us from better understanding the sound of these remarkable IEMS.

Sources Used During the Analysis

• Aune X8 XVIII Magic DAC + EarMen ST-Amp.
• Tempotec MARCH III.
• Burson Audio Playmate II.
• Aune M1p.
• Tempotec V6.