FIR AUDIO Neon 4

Audiophile Heaven praises bass impact on the scale of basshead headphones or studio speakers, while retaining strong detail. Sub-bass extension is singled out as exceptional, with audible subsonics and extension more commonly associated with high-end full-size headphones.

The midrange is described as refined, natural, rich and full of musical texture, with an intentionally non-fatiguing character. At the same time, the reviewer identifies it as recessed within the overall V-shaped balance, so vocals will not be the dominant focus.

Treble is said to extend superbly and contribute air and detail without making the earphones sound excessively bright. The upper range is lifted rather than neutral, but the review characterizes the overall tuning as controlled and unfatiguing.

The review explicitly calls its detail flagship-grade and highlights outstanding instrument separation. This suggests the Neon 4 keeps individual lines clear while preserving the weight and excitement of its bass-forward presentation.

Audiophile Heaven describes the stage as focused rather than diffuse, but also clearly wide rather than small. Listeners should expect a coherent, organized space rather than an artificially oversized presentation.

The Neon 4 is repeatedly characterized as incredibly impactful, punchy, explosive and full of life. That energetic delivery appears to be a central strength, especially for music that benefits from strong rhythmic impact.

The reviewer reports that the supplied tips work well and that a variety of alternative tips, including Final models, also fit successfully. That flexibility should make it easier for most universal-fit users to find and maintain an effective seal.

The universal shells are described as both attractive and quite comfortable. The custom version is said to offer an even more individualized, comfortable fit, as expected from a shell made for the listener's ear.

Although vented, the Neon 4 is reported to provide good passive isolation. Audiophile Heaven estimates roughly 20 to 25 dB of attenuation depending on frequency, which is a useful result for a vented design.

The supplied specifications list machined aluminum universal shells, sapphire-glass faceplates, interchangeable ATOM XS modules and a protective leather case. The review offers little direct commentary on long-term durability, connector behavior, cable quality or accessory execution in daily use.

At $2,300, the Neon 4 is firmly positioned as a premium IEM. Audiophile Heaven explicitly considers it worth the asking price, citing its distinctive tuning, flagship-grade detail and unusually authoritative bass performance.