Why High Output Impedance Affects Multi-Driver IEMs

If your source has an output impedance above 2.0 ohms, it can change the frequency response of multi-driver IEMs — and most computer motherboards fall into that category, which makes them unreliable for driving multi-driver sets. Single dynamic driver (1DD) IEMs are typically unaffected, so the same motherboard that muddies a multi-driver IEM may sound fine with a single-DD one.

The mechanism in plain terms

A multi-driver IEM is not one speaker. It splits the work across separate drivers — often a dynamic driver for lows and balanced armatures for mids and highs — and those drivers don't all present the same electrical load across the frequency range. Each driver's impedance varies with frequency, and the crossover network feeding them adds its own impedance behavior.

When the source's output impedance is low relative to the IEM's impedance, the voltage the IEM sees tracks the source signal closely. When output impedance is high, it forms a voltage divider with the IEM's frequency-dependent impedance. Frequencies where the IEM's impedance is low get less voltage; frequencies where it's high get relatively more. The result is a shifted frequency response — not a subtle measurement artifact, but an audible change in tonal balance.

A single dynamic driver has one motor and one impedance curve, so the same voltage-divider effect doesn't produce the same kind of response shift across separate driver sections. That's why 1DD IEMs are typically unaffected.

Why motherboards are the usual suspect

Most computer motherboards have significant output impedance. The guide's framing is blunt: they are unreliable for using multi-driver IEMs. The practical consequence is that a multi-driver IEM plugged straight into a motherboard jack may not sound the way it does on a low-impedance source — and the difference isn't a matter of "better" or "worse" in the abstract, it's a change in the tuning you thought you bought.

This matters most when you're evaluating an IEM. If your only source is a motherboard jack, you may be hearing the source's interaction with the IEM rather than the IEM's intended response.

What to do with this

• Check your source's output impedance if the spec is published. Above 2.0 ohms is the threshold the guide flags for multi-driver IEMs.
• If you can't find the spec, treat a motherboard headphone jack as a high-impedance source by default. The guide states most motherboards have significant output impedance.
• Prefer a low-impedance source for multi-driver IEMs — a dedicated DAC/amp or dongle with a published low output impedance figure.
• Don't assume a 1DD IEM needs the same care. Single dynamic driver IEMs are typically unaffected, so a motherboard jack is a more reasonable pairing there.
• When reading impressions, remember that the reviewer's source may differ from yours. A frequency response graph is a better reference point than a verbal sound description, which the guide itself calls a weak approximation.

The limits of this rule

The 2.0-ohm figure is a threshold for concern, not a guarantee of audible change. How much the response shifts depends on the specific IEM's impedance curve and how far above the threshold your source sits. And the guide's broader warning applies here too: aesthetics, wearing comfort, and perceived sound quality are subjective, and ear anatomy, hearing ability, and sound-tilt preferences vary. Take impressions and reviews with a grain of salt — including any claim about how a given source will sound to you.