Fosi IM4 IEM Review - $99 Open-Back Choose-Your-Own-Adventure IEM

Fozzy Audio IM4 Review: Are They Worth $99?

Introduction to the Fozzy Audio IM4

• The speaker introduces the Fozzy Audio IM4, a $99 open-back in-ear monitor (IEM) featuring a single dynamic driver.

• The review unit was acquired at Canjam SoCal 2025, where the company offered it for an honest evaluation without any conditions.

Kickstarter Campaign and Affiliate Link

• The product is being launched through a Kickstarter campaign, with an affiliate link provided for potential buyers.

• The speaker emphasizes their commitment to providing an honest and thorough review of the product.

Design Features and Accessories

• The IM4 features interchangeable nozzles (brass and black), allowing users to customize sound profiles.

• A blue carrying case is included along with a basic 3.5 mm single-ended cable; however, the lack of a 4.4 mm pentacon connector is noted as a downside.

Comfort and Fit

• The IEM is described as comfortable for extended listening sessions, particularly for users with narrow ear canals.

• While they provide decent isolation, they are still open-back designs that allow some ambient noise in during use.

Sound Quality Considerations

Sound Test Insights and Gear Overview

Plane Noise Impact on Sound Quality

• The interference from plane noise affected the mid-range sound quality, making it harsh. This issue was not replicable at home with different nozzles.

Equipment Used for Testing

• Two digital audio players (DAPs) were utilized: FIO M21 and IBSO DX180, primarily using a 4.4 mm two-pin cable. Local files in lossless or high-res FLAC formats were played during testing.

• The FIO M21 also functioned as a Rune endpoint, allowing streaming of high-resolution files from Kobas or DSD files while maintaining sound quality.

Sonic Preferences and Observations

• The black nozzle and black bore ear tips provided a preferred listening experience characterized by full bass and good treble tonality, contrasting with the brass nozzles which exhibited tonal unevenness.

• Frequency response graphs indicated that brass nozzles had peaks in mids and treble that led to listener fatigue, whereas the black nozzles offered a more balanced sound profile.

Overall Sound Characteristics

• The overall presentation is mostly neutral with good bass extension; however, variations in tip types can modify bass presence significantly. Despite some peaky characteristics in mids and treble with brass nozzles, they remain enjoyable across various music genres without being overly fatiguing.

• While the tonality lacks naturalness compared to other transducers, the open-back design contributes to an expansive soundstage but sacrifices some isolation from ambient noise during use. Users may hear surrounding sounds even in quiet environments like homes or gyms.

Comparisons with Other Audio Devices

Audio Comparison: FT1 vs IM4

Overview of Sound Characteristics

• The FT1 in-ear monitors (IEMs) are noted for their warmer sound profile, featuring enhanced mid-bass and lower mid-range presence, which adds weight and body to the tone.

• The FT1 offers a smoother mid-range and treble presentation compared to the IM4, resulting in a more realistic and natural tonal quality.

• Both IEMs exhibit similar performance in terms of resolution, staging, imaging, separation, three-dimensionality, and holography; however, the FT1 is preferred for its tonal qualities.

Isolation and Design Considerations

• Despite the IM4's open-back design leading to less isolation than typical IEMs, it still provides better isolation than closed-back headphones like the FT1.

• The choice between IEMs and closed-back headphones involves nuanced considerations that will be explored further in an upcoming podcast episode titled "Making Waves with Wave Theory."

Performance Insights on IM4

• The IM4 is recognized for its solid dynamics and bass extension but has uneven tonality that can vary based on nozzle color (brass vs. black).

• Users have options to modify sound characteristics through different ear tips included with the IM4 package.

Connectivity Concerns

• A notable downside is the absence of a 4.4 mm Pentacon connector on the stock cable; users may need to purchase an aftermarket cable for optimal compatibility with various devices.

General Recommendations

• While not class-leading in tonality or organic sound reproduction, both models remain highly listenable; they serve as good entry points for those new to high-end audio equipment.

• The review suggests these products are suitable for exploring personal audio preferences regarding bass and treble levels.

Additional Content

• A sound leak test was conducted at a reference listening level using specific tracks; results were recorded but not detailed in this summary.