>>I am brazilian and I speak portuguese, so forgive my english, I’ll use translation tools to help<<
INTRO:
After reviewing the FOSI DS3 DAC/AMP dongle, it’s now time for the in-ear earphones, the FOSI IM4. These IEM stand out for their minimalist aesthetic and high-quality construction. So far, this is the first in-ear earphone I’ve seen FOSI manufacture… I may be mistaken if they’ve made others in the past.
Price: $99.99 USD
Color: Black (Obsidian) or Silver (Galaxy)
Cable: 3.5mm with Mic.
FOSI review: DS3.
FOSI LINKS:
https://s.click.aliexpress.com/e/_c3xxoN1F (PC)
https://s.click.aliexpress.com/e/_c3wlHQ5J (APP)
SPECIFICATIONS:
Single DD:
- (1) 10mm beryllium coated Dynamic Driver per side
– Effective frequency: 20Hz – 20kHz
– Impedance: 21Ω
– Sensitivity: 109dB
– THD: <1%
– Connectors: 2pin 0.78mm (detachable)
– Cable Plug: 3.5mm SE (straight design)
– Cable size: 1.20m
– Cable material: 5N OFC Silver-plated Copper Cable
– Shell: 6063 CNC Aluminum Alloy
– IEM weight: 6.4g (one side)(without eartips)
– Cable weight: 23.6g
– Total weight (packaging, iems, etc): 280g
– Packaging size: 17.5cm [H] x 12.7cm [W] x 5.7cm [D]
UNBOXING:
PHYSICAL ASPECTS:
Construction:
- Excellent build quality.
- Quality that’s worth more than the price (subjective).
- Made of aviation-grade aluminum.
- Minimalist aesthetic (I really like it).
- Open-back design.
- Removable nozzles.
- Features 2 vents.
- Good carrying case, although basic.
- Interesting unboxing, it’s a good kit for the price.
Eartips:
- 3 types of eartips: Balanced, Bass, Deep Bass.
- 3 pairs in sizes S/M/L.
- The Balanced eartip is wide bore.
- I found the variety of tips good.
- I confess they are generic tips, but functional.
- Standard size, if you wear M, then it’s M.
- It’s possible to find the ideal sound with the stock eartips (subjective).
- I don’t see the need to acquire other eartips (subjective).
- I did the review with the Deep Bass eartip (size M).
Cable:
- High-quality cable.
- Very light and thin, and also beautiful.
- Great malleability.
- Doesn’t tangle.
- Doesn’t develop “memory” (creases).
- The earhooks are thin and comfortable.
- No microphonics.
- The chin slider works very well.
- 2-pin 0.78mm connectors.
- I see no need for replacement (subjective).
Fit and comfort:
- Vertical fit. Great stability.
- Very comfortable. Great ergonomics.
- The skin contact is very soft.
- Good shape for all ears.
- Medium insertion.
- Good isolation.
- 6.4g is still a good weight for an IEM.
Earphone kit (accessories):
- IM4 earphones.
- 3 types of ear tips (9 pairs).
- 3.5mm cable.
- 1 extra pair of filters.
- Carrying case.
- Manual and guide.



















SOUND ASPECTS:
Sound:
- Forward, fun, and lively sound.
- V-shaped tuning with a slight emphasis on the upper-mids.
- Somewhat reminiscent of the Harman Target.
- More prominent bass and upper-mids, linear treble.
- The definition is good.
- The detail is also good.
- It can be considered an IEM with a certain balance.
- Rock and Hard Rock were two genres that sounded very good.
- If you listen to music very loudly, be aware that the pinna gain can be tiring (subjective).
- The open-back design didn’t alter the sound (in my opinion).
- There is indeed sound output through the opening, but for me it only created “leakage”.
Bass:
– Quantitative:
- Moderate to high bass frequencies.
- Not for bassheads.
- Although the bass here doesn’t disappoint.
- I like bass and I really enjoyed the IM4 bass.
- Sub-bass and mid-bass with great presence.
- Both regions stand out linearly.
- Great balance between sub-bass and mid-bass.
– Qualitative:
- Full, strong, authoritative, fast, and warm bass.
- Great texture and physicality.
- The extension is very good. There’s no roll-off.
- Bass that brings a dose of fun and versatility.
- The definition is very good.
- The impact is very audible and “tight”.
- They don’t invade the mids.
- Bass that combines well with various musical genres.
- They aren’t boomy, not bloated, not muddy.
- Not for Bassheads but it’s good to EDM, Reggae, Rock, Hip-Hop, etc.
- For me, the bass is the best part of the IEM.
Mids:
– Quantitative and qualitative:
- The mid/upper-mids are “forward.”
- These frequencies are closer to you.
- Pinna gain with a certain emphasis.
- Although “forward,” I didn’t feel harshness or aggressiveness.
- I’m not a big fan of “forward” upper-mids, but I could hear them.
- I listen to music at lower volumes.
- If you listen at very high volumes, be aware of fatigue (subjective).
- The definition is very good.
- Great clarity and transparency.
- Good airiness and detail.
- This upper-mids region has a cold touch.
- Guitars and vocals stand out well.
- Wind instruments have great energy, the sound is more “frontal.”
Voices:
- Good for both types of voices (low or high).
- High/female voices performed slightly better.
- “Forward” IEM deliver more clarity and vitality for high-pitched tones.
- “Rolling in the Deep – Adele” has great clarity and projection.
- Fortunately, lower voices also performed well.
- IEM that render various voice types very well.
Treble:
– Quantitative:
- Moderate treble frequencies.
- To me, they sounded neutral.
- It was the least prominent frequency in the IEM.
- I didn’t experience fatigue because of the treble.
- Not for trebleheads.
- Suitable even for those with sensitivity in that region.
- Discreet treble because the upper-mids are more prominent.
– Qualitative:
- Linear, controlled, comfortable and of good extension.
- Natural/normal sparkle.
- Good detail and airiness.
- Good level of definition.
- Not shrill, not sharp, not harsh.
- I didn’t experience sibilance, coloration, or peaks.
- Hi-hats have good resolution, without harshness.
- Ride cymbals sound natural.
Soundstage:
- I found the soundstage to be good.
- Good spatiality, but nothing beyond the standard.
- Good width and height. Average depth.
- V-shaped IEMs generally have a good soundstage.
Imaging:
- I found the instrumental separation to be good.
- The stereo image is also good.
- Hybrid IEMs have an advantage (this isn’t a rule).
- The Hexa and EM6L are better in this regard.
Detachable filters:
- I tested the IEM with the black filter.
- I only felt a slight emphasis on the upper-mids (with the golden nozzle).
- In my opinion, the black filter is the best.
- I think changing the eartips has more influence on the sound.
Driver flex test:
- The IM4 didn’t have Driver Flex characteristics.
Amplification:
- Easy to push.
- Doesn’t need a powerful amplifier.
- A DAC/AMP dongle is sufficient.
- I review the IM4 with the FOSI DS3.
- I only used the 3.5mm output.
- DS3 at Max (60 steps) and 20-30% (100 available on the W10).
PROS AND CONS:
– Good value for money
– Aesthetically pleasing (subjective)
– Excellent build quality
– Forward sound
– V-Shape tuning
– Good resolution level
– Good soundstage
– Good imaging
– Easy to push
– Comfortable to use
– Great fit
– Good for all ear types
– Good for long listening sessions
– Great cable
– Variety of eartips
– Good carrying case
– Upper-mids beyond I like (subjective)
– Filters don’t alter the sound as much as eartips
– Open-back didn’t make difference in sound
– Sound leakage to the outside
GRAPHS BY SUPER*REVIEWS:




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