Yinyoo D2B4 Hybrid IEM Review – Mammoth

D2B4 featured
Tested at $111

Greetings fam and welcome to another review. Today we’re looking at the Yinyoo D2B4 earphone. The D2B4 has 2 dynamic drivers and 4 balanced armature drivers per side. It also boasts some classy and very solid metal housings along with a warm, detailed sound. If you like the sound of that, let’s dig deeper.

Yinyoo D2B4 Review

  • Good build quality
  • Comfortable
  • Mature design
  • Thick, muddy bass

This sample was provided for the purpose of an honest review. All observations and opinions here are my own based on my experience with the product.

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Package and Accessories

D2B4 unboxing

This time around we see once again the larger, blue variant of the Yinyoo box. It has a subtle texture on the exterior as well as the Yinyoo logo on the top. Inside the box is a reasonably large semi-hard zipper case and we see the brand logo again here as well.

The earphones and accessories are all found inside the zipper case, so let’s break it down and check out what you get in total.

  • Yinyoo D2B4 earphones
  • Detachable MMCX cable
  • 3 pairs of narrow bore silicone eartips (S, M, L)
  • 3 pairs of wide bore silicone eartips (S, M, L)
D2B4 accessories

Build Quality and Design

The Yinyoo D2B4 is made of Aerospace-grade 7050 Aluminium and is CNC-machined to achieve that great finish. On the faceplate, there are a couple of ridges that form a kind of T-shape to create some interesting shapes and make it look more interesting.

D2B4 faceplates

Then there is a thin line of bare metal that makes an interesting silver coloured contour around the edge of the faceplate. By the way, there are two layers of anti-oxidation coating applied to the housings and the end result is very smooth and polished.

D2B4 inner shells with vents

On the inner side of the shells, there are 2 pinhole-sized vents and some dips and curves that make the earpieces fit naturally in your ears. Along the top edge is some Yinyoo branding and an L or R marking. The nozzle length is just right, neither too short nor too long and there is a solid ridge in place to securely hold on eartips. Also present of course is the usual metal mesh covering the mouth of the nozzle to prevent ear wax and other debris from getting inside.

D2B4 nozzle with mesh cover

Overall the design, while simple is quite interesting and I personally find it to be quite handsome. The quality of the earpieces feels very robust indeed like they were built to last.

Comfort and Noise Isolation

I’m sure many of you reading this will be familiar with this type of shape by now and should have some idea of what to expect in terms of comfort. But it’s not always that clear-cut right? Just this past weekend I was at a portable audio event here in Thailand and came across a similarly designed IEM that just was so awkward and uncomfortable even though on the surface it looked similar to the D2B4.

I’m pretty sure that was a result of the nozzles being too long for my ears but I digress. Let’s get back on track! In short, the D2B4 is an extremely comfortable earphone for me. All of the sides and edges are smooth and rounded, plus the outer coating makes for a comfortable experience. I can wear this IEM for hours on end easily.

Noise isolation is about average for this semi custom style design, which is to say it’s better than a lot of bullet type shells. It should be fine for most everyday situations, such as on public transport or walking about town etc. Noise leak is almost non-existent so there’s no need to worry about that.

D2B4 inner shells with box and zipper case


Gear used for testing includes the iBasso DX120 and FiiO M6 as my portable sources. Once again at the desktop was the FiiO K3 being fed FLAC files via USB from MusicBee on my PC.

The D2B4 has a warm sound signature with a mild V-shape. It does have an enhanced bass but it’s not a basshead IEM. It has good resolution with plenty of detail and a full-bodied approach, topped off by a crisp treble.

Yinyoo D2B4 frequency response

The D2B4’s bass is one of the main features in its presentation. It’s rather thick with a medium paced attack and medium-slow decay. This gives bass notes body and creates warm overtones throughout the sound signature.

While the bass feels big, it’s not too bold or excessive but it’s not for the bass shy either. Mid-bass is a little woolly and lacking speed. Sub-bass has a strong, deep rumble that is kept under control by the solidity of the aluminum housings.


There is some bass bleed present in the midrange adding colour and attenuating clarity. It lends warmth to it which makes the mids feel smoother without adversely affecting the resolution but tonal accuracy is affected. Male vocals are a little soft and lack articulation while female voices sound more vibrant. The midrange, in general, is recessed and sits behind the bass and treble.


Treble is elevated which keeps it in line with the bass with the midrange sitting behind both. It doesn’t become fatiguing and plays a fairly low-key role overall. It’s a fairly dry treble that doesn’t possess much airiness or sparkle. What it does is prevent the D2B4 from being dominated by the bass and acts as a counterbalance which is essential with such a weighted low end. Peaks at 6kHz-7kHz can lean towards edgy on occasion.


Considering the bass-oriented signature the soundstage is really quite good. It has sufficient width and depth to let the music breathe and gives midrange instruments and vocals enough distance to avoid feeling uncomfortably intimate. Imaging is fairly accurate but will become less defined on bass-heavy tracks. Instrument separation is also quite good which is a benefit of the multi-driver configuration.


TFZ Series 4 ($99)
D2B4 vs Series 4

Series 4 (review here) has a clearer and more vibrant signature. It has some killer sub-bass that has so much authority you might start calling it master. Mid-bass is well textured, punchy and fairly quick making the D2B4 sound sluggish in comparison.

The midrange on the Series 4 is less recessed, less coloured and vocals have better articulation. The upper midrange is harsher on the Series 4 while the D2B4 peaks instead in the lower-mid treble. Neither has a standout treble but the timbre of the Series 4 is more pleasing and airier. The soundstage on the Series 4 is more expansive and open while the separation and positioning are stronger on the D2B4 so long as there isn’t a large amount of bass in the track.

Each of these earphones is built to a very high standard. Both of them are comfortable too but the D2B4 feels more natural in my ears because of the contoured inner shells. The Series 4 has metal faceplates and plastic shells and the D2B4 is entirely metal.

FiiO FA1 ($99)
D2B4 vs FA1

This single-BA FA1 (review here) has a lighter and more nimble sound signature. Although the quantity of bass looks close in my measurements it does not sound like that at all. The FA1 has a light, punchy bass and a very tame amount of sub-bass that can reproduce the notes but doesn’t create any physical rumble. Its mid-bass is fast and well-defined while the D2B4 is woolly and thick.

Midrange on the FA1 is more forward, more even and boasts better clarity. During complex passages the FA1’s single balanced armature driver can get flustered resulting in a loss of separation but this doesn’t occur often.

Treble on the FiiO is very smooth and sits further back in the mix compared to the more V-shaped D2B4. Build quality and comfort are exceptional on both IEMs. The FA1 has resin shells where the Yinyoo is aluminium.


I’ve enjoyed my time with the Yinyoo D2B4 so far. The build quality, styling and comfort are great. When it comes to sound it has some admirable qualities, such as good instrument separation and solid resolution which is impressive considering the focus on bass but it doesn’t excel in any particular area either. It’s not the best all-rounder but if your music tastes fall into the bass-driven type then this could be a good IEM to consider.

  • Impedance: 19Ω
  • Earphone sensitivity: 102dB/mW
  • Frequency range: 20-40000Hz
  • Interface: 3.5mm Gilded
  • Plug Type: Straight
  • Cable Length: 1.2m±3cm
  • Color: Blue/Black
  • Earphone interface: MMCX
  • Cable Material:4 Core silver plated
  • Driver unit: 10mm Graphene Diaphragm Dynamic Driver; 2 combination balanced armature midrange drivers; 2combination balanced armature high frequency drivers

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