Before starting this review, I would like to share technical aspects and package details.
Here is the link of ISN Audio CU4: https://penonaudio.com/isn-audio-cu4.html
Material: High purity single crystal copper
Number of cores: 4 strands, single strand is 115 cores
Sheath: environmental protection transparent PVC
Aluminum alloy CNC cutting integrated slider
Secondary oxidation gold foil gold ring
The solder joint is silver–contained tin
Connector: MMCX/2pin 0.78mm
Plug: 3.5mm audio/2.5mm balanced/4.4mm balanced Rhodium-plated plug
Cable length: 1.2M
THX AAA 789 & D50s
Penon Audio Sphere
ISN CU4 comes with their standard rectangular small cardboard box and inside the box, there is nylon rectangular case. There is a cleaning tool and carabiner as well as cable inside of the case. First thing that I realised how thick is CU4. I believe it is 22-gauge size which is almost a headphone cable, but boy, it looks so beautiful. It screams quality and those strands looks gorgeous. Each braid has 115 strands which is impressive. Cable is a bit bulky, heavy and thick but it is comfy to use anyway. My cable terminated 2pin with 2.5mm balanced but you can terminate MMCX, 3.5mm, 4.5mm. Jacks, pin connectors, y-splitter and chin slider are all black and has gold painted rings. Cable looks really beautiful. I know sound is the most important thing but c’mon, visual design is also so important for all gear-freaks and CU4 put your earphones look another level.
As expected from the CU4 copper cable, it is warm sounding cable that touches mid and bass area more than high. The sound character is warm, lush, organic and highly detailed. Some copper cables I tried made the overall presentation slightly dark, but CU4 certainly does not dim the sound and makes extremely positive improvements.
It does not contribute much in the extension of the upper frequencies, but I can easily say that it improves the overall resolution and detail. It gives the upper frequencies softer and textured air that reduces sharp edges. I noticed that the upper frequencies are a bit laid back with the Nocturnal Atlantis, and the treble in general has a softer presentation. Overall detail and resolution are slightly better than the stock cable but this is not the best magic of CU4.
The mid region of CU4 has a meaty and fuller presentation as expected due to the characteristic of the copper cable. With Atlantis, it has a more bodied and accentuated presentation in general, and also lower mids have gained body. Vocals are relatively forward, bold and I especially like male vocals. The lightly warm mids of Atlantis have become noticeably smoother and bodied with the CU4. It will be the right choice especially for users who wants to tune lower mids.
The bass are quite distinctive and bodied. With Atlantis, I felt more quantity and strokes than I have ever heard before. For better understanding, I listened to the same track with the stock cable and listened to A / B several times, and the difference is definitely obvious. Sub bass goes deeper and increase in quantity, it hits harder and more in quantity. The CU4 will definitely shine when combined with the right earphone.
CU4 vs Effect Audio Ares:
I mention this on my all cable comparison but Effect Audio Ares is one of my favorite cable in this price range. It is a great copper cable and it makes pretty good improvement on the sound. I did my comparison with Nocturnal Atlantis IEM. Both cables are great in terms of build quality. Ares is 26 gauge while CU4 is 22 if I am correct. It is thicker, heavier, less ergonomic but looks better. Ares and ISN CU4 are sharing the same material, copper but they are differing in sound type. Ares is overall more linear, slightly bright and neutral while CU4 is more bodied, lush, warm and thick in presentation. CU4 touches bass notes more than Ares does, and it adds more quantity and body on low frequencies. Bass has overall more impact and power on CU4. Ares also adds body and thickness but not as much as CU4 does. Mids are warmer and lush with CU4. Its natural organic sounds add some body on Atlantis’ mid frequencies. Ares is slightly less thicker and more recessed. Actually, Ares’ performance is almost same with Atlantis’ stock cable, of course it adds more details but overall sound doesn’t change drastically. Trebles are where the difference is more obvious. Ares is slightly more extended and prominent on trebles area and it adds more quantity. CU4 also add some extra quantity but it aims more in presentation. It’s lush and detailed sound continues on Trebles. Resolution and details are the same but it all depends how you combine it. Soundstage is very similar but Ares feels just a bit wider but difference is not that obvious.
CU4 vs PW Audio No:5:
Like Ares, No5 is also great and I have x2 No:5 in my collection. Both cables build and material quality are great, there is not much thing to say about it. CU4 is thicker, heavier and a good-looking cable. Their sound is very similar than I expected. Both cables have similar quantity on low frequencies, maybe CU4 adds slightly more quantity and impact but it is hard to define. CU4 has great impact and affect on bass frequencies which improves bass frequency a lot. No:5 also improves sound in a similar way but bass is less thicker. I also tried both cables with Penon Sphere IEM. CU4 adds more rumble and bass notes on sound. No:5 has similar effect on sound but bass notes are slightly lighter and impacts are not as noticeable as CU4. Mids are very similar again but I felt more air on No:5 here. Normally I wouldn’t say No:5 is bright but it is slightly bright and open than the CU4. CU4 adds more organic, natural tone and makes sound thicker. Both cables’ treble sounds are similar again but tonality are lusher and warmer on CU4 while No:5 is slightly less warmer and open. Both cables great on details and resolution but it is all about synergy. CU4 is a great cable with bright earphones which improves some specific areas like bass and mid notes.
CU4 vs Rhapsodio Dwarf:
Dwarf is Rhapsodio’s copper cable and I use it with many earphones in my collection. Dwarf is thinner, lighter and less attractive looking cable when I compare side by side but it provides better usability with its slim profile. Sound of Dwarf is similar with Ares but bass notes are more prominent and emphasised. CU4 has more bass quantity and impact while Dwarf has lesser on quantitiy but still has good impact and rumble. Mids are slightly recessed and thinner on Dwarf while CU4 provides thicker and bolder tonality. Vocals sound is more organic and smoother on CU4 while Dwarf is slightly recessed and laid back. Trebles are similar in quantity but tonality is different. CU4 has smoother, rounded easy listening and it provides fatigue free experience. Dwarf is brighter and more open which is slightly airy. Soundstage is similar but Dwarf is better on wideness but CU4 provides deeper soundstage.
This is my first cable review of ISN Audio and definitely I’m impressed by its sound. It is really good copper cable for its price and as I said before, it will be shine with the right earphones when you combine. Also, material and build quality is top notch. It looks and feels gorgeous and makes your earphone looks much more beautiful. You might think thickness of the cable is disadvantage for ergonomics and you might be right, but soft design makes it easy to use and it is not bulky when you wear it. Overall, CU4 is great copper cable and if you are on the market you can consider it to try.