Headphones that measure well can sound wrong on the wrong amplifier. The cause is usually an impedance mismatch, and unlike most audio disagreements it is arithmetic rather than opinion.
The eighth rule
Aim for a source output impedance no higher than one-eighth of the headphone's nominal impedance. A 32-ohm headphone wants a source under about 4 ohms; a 300-ohm headphone tolerates up to roughly 37 ohms.
Break the rule and the headphone's impedance curve starts shaping the frequency response. Dynamic drivers have an impedance peak at their resonant frequency, usually in the bass. Feed them from a high-impedance source and that peak becomes a bass bump -- audible, unintended, and different on every model.
Sensitivity decides how much power you need
Sensitivity is quoted in dB per milliwatt or dB per volt. A headphone rated 100 dB/mW reaches comfortable listening levels on almost anything. One rated 90 dB/mW needs ten times the power for the same output. Combine low sensitivity with high impedance and a laptop jack simply cannot deliver enough voltage swing -- the result is thin, dynamically flat sound that people mistake for the headphone's character.
Do you need a separate DAC?
Modern integrated DACs are good. The audible failures in a signal chain are almost never converter resolution -- they are noise from a shared power rail, a hissy amplifier stage, or an impedance mismatch. A combined DAC/amp unit with a clean, low-impedance output solves more real problems than separates chosen on converter spec.
Separates start earning their keep when you need specific I/O, balanced outputs, or the ability to upgrade one half of the chain independently.
Practical pairings
- High-impedance open-back (250-600 ohm): needs voltage. Look for a desktop amp quoting output into 300 ohms, not just into 32.
- Low-impedance planar (below 50 ohm, low sensitivity): needs current. Check the milliwatt figure at the actual impedance.
- Sensitive IEMs: need a low noise floor above all. Many powerful desktop amps hiss audibly into IEMs; a dedicated low-gain setting matters more than raw output.
Frequently asked questions
Will a headphone amp make quiet headphones louder only?
Loudness is the visible part. Adequate power also preserves transient dynamics and keeps the low end controlled at volume.
Does a more expensive DAC chip sound better?
Implementation dominates. Power supply design and analogue output stage matter far more than the chip part number.
Is balanced output better for headphones?
It typically doubles available voltage swing and can lower crosstalk. Useful for demanding headphones, largely irrelevant for efficient ones.