IEM Specs Explained: Impedance, Sensitivity & Frequency Response

Every IEM spec sheet lists the same three numbers — impedance, sensitivity, frequency response — and almost nobody explains what they mean for you. Here’s the plain-English decoder, including which numbers matter and which are mostly marketing.

Impedance (Ω): How Much Power It Wants

Impedance, measured in ohms (Ω), describes how much electrical resistance the IEM presents. The practical translation: how hard your device has to work to drive it.

• Under ~25Ω: Easy to drive. Any phone, laptop, or console controller powers it fully.
• 25–50Ω: Still phone-friendly, but this range starts rewarding a stronger source. A set like the KBEAR KB02 at 40Ω runs fine from a phone — and audibly wakes up with a powered dongle behind it.
• Over 50Ω (and most planars): Wants real amplification to deliver full dynamics.

Higher impedance isn’t better or worse — it’s a compatibility note. It tells you whether a USB-C dongle DAC is optional or strongly recommended.

Sensitivity (dB): How Loud Per Unit of Power

Sensitivity measures how loud an IEM gets from a given signal — typically 95–115dB for IEMs. Two practical effects:

• High sensitivity (105dB+): Gets loud from anything. The flip side: it also amplifies your source’s flaws — high-sensitivity sets reveal the faint hiss that noisy phone and PC audio circuits produce. If you hear hissing in quiet passages, your device is the culprit; a clean dongle DAC silences it.
• Lower sensitivity: Needs more volume from the source but tends to be forgiving of noisy outputs.

Read impedance and sensitivity together. Low impedance + high sensitivity = runs loud anywhere (and may hiss on bad sources). Higher impedance + lower sensitivity = benefits most from a proper DAC/amp.

Frequency Response (Hz): The Range — and the Marketing Trap

Frequency response states the range of tones the IEM reproduces, like “20Hz–20,000Hz” — roughly the limits of human hearing. Here’s the honesty most spec sheets skip: the range tells you almost nothing about sound quality. Two IEMs with identical “20Hz–20kHz” specs can sound wildly different, because the spec doesn’t say how much of each frequency you get — that’s the tuning, and it’s why sound-signature descriptions matter infinitely more than this number. Treat extreme claims (“5Hz–50,000Hz!”) as decoration.

Driver Size (mm): Bigger Isn’t Better

A 10mm driver isn’t automatically superior to an 8mm one. Diaphragm material, magnet design, and tuning dominate. The ultra-thin 3.8μ diaphragm in the CCA CRA outresolves plenty of larger, thicker drivers — speed and control beat surface area.

The Cheat Sheet

When you read a spec table, ask just three questions:

1. Impedance: Will my phone drive this fully, or should I budget for a dongle?
2. Sensitivity: Is this sensitive enough to expose a noisy source? (Plan accordingly.)
3. Everything else: Skim it — then go read how the set is actually tuned, because that’s what you’ll hear.

Specs describe compatibility. Tuning describes sound. Every listing in The Vault Collection gives you both — the full spec table and the honest description of what it means for your ears.