Dunu DK-4001 – Thunderstruck!

If you’re looking for a hybrid with superb build and cable, class leading bass that is both fun and technically faultless, natural mids with slightly forward vocals and lead instruments and exciting treble then you’d be hard pressed to find a better alternative than DK-4001 for the price!

Price : 899$
Product page : https://www.dunu-topsound.com/dk-4001

​The Dunu DK-4001 packaging is quite premium, with a nice and compact leather carrying case. You can also find Spinfits CP145 and Comply tips, airline adapter and cleaning tools.

Worth mentioning is a « stock » cable that is more up to par with a very good upgrade cable as reflected in the price of the Dunu Noble cable (389$) that is provided with the DK-4001. A cable worthy of a flagship.

It’s a high-purity Furukawa Single crystal copper and pure silver braided cable. The cable features the fantastic interchangeable plug system that was found with the DK-3001 and continued with the Dunu Hulk. It come with 2.5, 3.5 single ended (and 3.5 pro balanced) and 4.4 termination. Note that Dunu added an additional interference-killing OCC copper sheath around the wires – a construction rarely ever seen in earphone cables. Interestingly, when I tested the Dun Lyre of the DK-3001 Pro, I noticeably picked up interference when running the N6ii with wifi on.

On top of this Dunu opted for their own patented catch-hold type connectors, « lowering connection instability and pin breakages, and effectively prolonging the service life of MMCX connector interfaces ». Catch-Hold® MMCX connectors are universally compatible with all standard spec MMCX seats which means upgrade cable are of course possible.

Fit, Build & Isolation

The DK-4001 fit is one of the best I have had with an universal IEM, it small, lightweight and ergonomic. The DK-4001 is one of a short list of IEM with a Zirconium shell, like Sony IER-Z1R. The use of Zirconium « effectively suppress harmonic resonance » according to Dunu.

Design wise, I like that the nozzle has a small ridge line to allow for deeper tip insertion, I didn’t need it but it can come in handy and reflects the ergonomic focus in the DK-4001 design. Included spinfits are really good and I didn’t need to do any tip rolling with my own tips. The over the ear cable configuration with preformed hook makes wearing the DK-4001 very secure. Isolation is good thanks to deep insertion and as usual for best results comply tips provide additional isolation.

Introduction

Dunu is now a well established brand in the audiophile world, which started as an OEM for famous brands. Since 2014, Dunu built its own IEM and now has a fairly complete lineup of dynamic and hybrid IEMs (Titan series, DN and the top DK series). After launching the DK hybrid series in 2015, Dunu set out to design the most compact, optimal shell fit that would define our flagship series. The DK-4001 says it has taken their head engineer Andy Zhao three years refining the acoustic formula, going through several redesigns before settling on its current form.

Dunu states : « We used two Knowles in tandem for four drivers in total, giving the DK-4001 the ultimate in treble headroom, and allowing its bandwidth to extend all the way beyond 40 kHz. To dial in the ideal balance between detail and harshness, we spent two months alone adjusting the tubing diameters, lengths, and damping materials, as well as the ideal crossover point for these tweeters. The result is a rich, luxuriating treble response pegged right where we want it to be. » About the dynamic driver, they state : « This 13mm speaker retains the speed and rigidity of a pure Beryllium cone, reproducing the kind of realistic timbre and wide staging that audio lovers crave. We allow it to sing freely by letting it take over the entire audio spectrum all the way to the low treble, reproducing music truly the way it was meant to be heard. »

The product page on Dunu’s website doesn’t expand too much on the DK-4001 tuning except from exceptional bass control deriving from Zirconium properties and the acoustic design through their patented ACIS which is a spiral design pathway : « To take full advantage of the speed and dynamics of the Beryllium driver, we wanted to take on the challenge of integrating a bass reflex system normally found only in home speakers. After long hours and endless trials tweaking its length and size, the resultant, labyrinthine Air Control Impedance System (ACIS), was born from an obsession that nearly spiraled out of control. The end result is a spectacular bolstering of frequencies under 80 Hz while still retaining depth and agility. »

Clearly, Dunu invested a lot into the design of the DK-4001 : materials with the zirconium, acoustic design with ACIS and tubing and damping of the Knowles drivers, coating of the beryllium driver. How does that translate in terms of sound quality? Let’s see !

Sound

The very first minutes into auditioning the DK-4001, the first thing that came to mind was how good the bass was, as in definitely top tier good : Dunu certainly has found a superb balance between engagement and technicality there. The second thing that came to mind was that detail retrieval : very very good, but maybe a tad over accentuated upper treble for my taste reaching the edge at times on some recordings. Not unforgiving, just a tad to present upper treble peaks for my taste and limiting the naturalness of the DK-4001. This was even more apparent with the T01 motherboard for the N6ii so I kept the A01 on for the rest of the review

I began suspecting the silver in the Dunu Noble cable was maybe not in the line with my personal preferences and despite its stunning build and fantastic form factor I should try something different. Unfortunately my Dunu Hulk is 2pin so I couldn’t test that. I swapped the Dunu Lyre which is also a full copper and… the result was much more in line with my personal preferences. I found the DK-4001 gained musicality and didn’t have any peaks in the upper register as well. Sure, the Noble provides greater detail retrieval but to me at the cost of too much upper register emphasis, taking the attention away from a beautiful midrange. I then tried on a Hansound Zen full copper 8 wire cable and… the DK-4001 soundstage expanded to holographic territory with better imaging and layering. Obviously your mileage may vary and not everyone has the same preferences. This speaks to the scalability of the DK-4001 as well, which shows that it has great potential to fit your personal preferences.

The soundstage is not massive like say Campfire Solaris but it’s pretty good nonetheless, quite wide and fairly deep but not very tall. The image is not congested and remains articulate but separation is not accentuated, the image is more of a continuum while not falling into the wall of sound category. Vocals and lead instrument are clear and distinct, but not significantly forward either. Note attack is snappy and decay is very natural.

I didn’t find the DK-4001 hard to drive and the N6ii was set on low gain at fairly moderate level (35-50/100). I suspect though that the DK-4001 could reach yet another level with an amp, I see the DK-4001 having good scaling potential with its 32ohms impedance and dynamic drivers usually like power.

Bass

Note : The DK-4001 bass was great right out of the box but got even better with burn in with things settling in nicely after 40 hours or so. The main benefit is tighter bass with better control as the beryllium driver settles in.

The DK-4001 bass shows that Dunu’s R&D and work on acoustics of the shell (ACIS), optimized resonance with Zirconium and driver coating certainly paid off as advertised on their product page. The bass extends deep and exhibit fantastic control with very low resonance indeed. This is especially stunning on sub bass : there is plenty of subs but close to no distorsion whatsoever the subs are as clean as I have heard them.

This results in one of the best if not the best portraying of bass I have heard to date. This is an experience not unlike the legendary Sony EX-1000 with bigger than life bass that sure rarely belong in an IEM but rather in good closed back full sized headphones and not often with that level of control. Impressive if you factor in that it’s faster than the EX1000. Mid bass have great slam factor and remain clean and controlled whatever I threw at them. Despite its relatively big size (13mm) the beryllium dynamic driver is quite fast with quick decay and recovery time, providing a very good sense of pace.

The DK-4001 bass make the DK-4001 a very engaging listen, bass guitar have good weight, kick drums have such a satisfying, toe tapping punch and there is a physicality from the subs that make the DK-4001 a very powerful IEM that almost sounds like a full sized headphones.

This is class leading bass performance with a touch of basshead pleasure, although I don’t think pure bassheads will find the quantity to be enough. Dunu strived to keep the DK-4001 in the flagship category meaning it shows proper restraint and does not overdo it. But you can feel that given the right source, right EQ and right cable the driver probably has basshead potential for those who would want to go down that route.

Mids

The DK-4001 mids are not as warm as those featured on the DK-3001 Pro and more in line with what you would expect from a flagship : natural sounding with good tonal balance and articulate image.

Given the strong bass presence Dunu wisely kept the lower mids on the leaner side gently rising from 600Hz and topping a little before 2kHz. For the same reason given the treble presence, Dunu rolled off the upper mids from 2kHz to 4kHz where it reaches its lower point and then a rise to plateau at 6kHz up into the treble section. Clearly, the mids presence is derived from the 1-2kHz range. This results in mids that give instruments a slightly forward placement but avoiding too much excitement, attack on percussive and rhythm instruments is on the softer side.

The DK-4001 excitement is focused on its bass and treble but the fairly neutral mids are placed a bit forward to balance the overall frequency range and avoid a U shaped signature. A wise choice as too much lower mids would have resulted in a warmer signature (aka DK-3001 Pro as we will see in an upcoming review) and too much upper mids would have made the DK-4001 a very fatiguing IEM. On the flip side, this affect the bass guitar snap, the saxophone bite or energetic cymbals « clang » for example.

Treble

It’s very clear with the DK-4001 that Dunu aimed at a different goal than the more « mainstream » (this is in a good sense) DK-3001 Pro. Flagship often equates to resolution and definition, by way of more upper treble presence among other things. I believe this also explains the choice of a copper-silver mix in the Dunu Noble cable that comes stock with the DK-4001. As I hinted before, this clearly boost the upper treble section and make the DK-4001 detail retrieval greater but it also was a source of frustration to me as it kind of broke the naturalness of the upper register. For the rest of the review, I alternated between the full copper Dunu Lyre and the Hansound Zen 8 wire that both brought a more natural tone and smoother treble presentation.

The DK-4001 has good lower treble energy with a 6 to 8kHz plateau, snare drums have a satisfying snap and Piano, hi hats and cymbals have nice overtones that contribute to the musical engagement the DK-4001 provides. Despite the energetic lower treble, the DK-4001 manages to remain smooth and never harsh. Treble tone is accurate, and the note weight is quite balanced it’s neither a full bodied nor a feather like treble but rather very natural sounding notes.

Upper treble roll off steeply between 8 and 10kHz with a steep rise past 12kHz up to a 20kHz peak. The DK-4001 has good resolution and air and never feels congested but to me it’s not up there with the best here in terms of sheer resolution and refinement.

Verdict

The first contact with a brand is usually a good way to measure the quality of their product and upon my contact with the Dunu Hulk I was very impressed that a 300$ cable was built better than some products 3x as expensive not even taking into account the fantastic interchangeable plug system. It was just as impressed with the DK-4001 from the unboxing to the superb build and cable and the great fit.

In the very competitive hybrid universal landscape, the DK-4001 stands proud as a proper flagship product the Dunu brand packed a lot of R&D into : zirconium shells are notably hard and costly to produce (and featured in much pricier IEMs), driver coating process, and acoustic research (ACIS, tubing, damping…) clearly paid off especially in the bass department. The effort was furthered by packing the best build on a stock cable I have ever seen in a product and a very rare instance on the market (aside from LCD-i4, I don’t know of other examples of such premium stock cables).

All in all, you’d be hard pressed to find a competitively priced hybrid that packs as much R&D and premiums materials and cable, bar the Sony IER-Z1R priced over twice the DK-4001. This tells you something about Dunu’s commitment to grow their product range.

If you’re looking for a hybrid with superb build and cable, class leading bass (I am thunderstruck!) that is both fun and technically faultless, natural mids with slightly forward vocals and lead instruments and exciting treble then you’d be hard pressed to find a better alternative than DK-4001 for the price!

If you’re willing to sacrifice a bit of bass control, overall technicalities and like a warmer tone and smother presentation then its little brother the DK-3001 pro is definitely an alternative worth looking at. If you’re willing to spend a bit more, the Rai Penta will be airier with greater soundstage and imaging but you won’t get the satisfying bass experience or the body and weight you’ll get from the DK-4001. You could also satisfy your inner basshead and go to Campfire Solaris to enjoy massive soundstage, subwoofer like sub bass and sparkly lower treble but you won’t get the same control and balance as the DK-4001. In the technically proficient category, you could get a look at StealhSonics U9 to get further refinement in the upper treble section and more detailed mids but you would miss out on the incredible DK-4001 bass experience and you wouldn’t get the same bodied presentation.

I must say I am very eager to see what Dunu will come up next with the DK-4001 Pro and any other product for that matter!

This review was originally published on head-fi.org :
https://www.head-fi.org/showcase/dunu-topsound-dk-4001.23687/reviews#item-review-22845