Keep the units attached to the number
Headphone sensitivity relates acoustic output to a stated electrical input. A specification expressed in dB SPL per milliwatt is not directly comparable with one expressed per volt. Shure’s specification guide explains sensitivity using a power reference and treats impedance as a separate characteristic. If a listing says only a decibel number without the reference, find the manufacturer’s complete specification before using it in a comparison.
A nominal impedance figure describes an electrical load, not a sound-quality grade. Two headphones with the same impedance can have different sensitivity and therefore different output needs. Similarly, a high impedance does not by itself establish that a headphone is better or that your source cannot operate it. Avoid shopping rules based on a single cutoff number.
Read the output under a relevant load
An amplifier may quote output power into several headphone impedances. Compare the specification closest to the intended load and note the stated conditions. A headline power figure into one load should not be assumed available into every other load. If the manufacturer supplies a supported headphone range, treat it as a starting compatibility check and ask about the exact combination when information is incomplete.
For sensitive earphones, control at low listening levels can matter more than maximum power. Consider available gain settings, whether small volume adjustments are manageable, and whether the maker discusses suitability for sensitive in-ear models. More output capacity is not a requirement to use more volume.
Separate insufficient level from another problem
Before replacing an amplifier, check the source’s volume limits, application settings, cable seating, and any unusually quiet recording. A single low-level album does not prove a hardware mismatch. Start any comparison at a low volume because a different gain setting or output can be substantially louder than the previous one.
Evaluate the normal listening range with several familiar recordings. You want useful adjustment and clean reproduction at comfortable levels, not proof that the system can become painfully loud. If the current source already meets the need, a more powerful amplifier may solve no practical problem. If it does not, use the headphone’s full specification to narrow the replacement rather than choosing the largest wattage number.
A useful question for the manufacturer
When specifications are incomplete, send the headphone’s exact model, impedance, sensitivity with units, and the proposed source model to the manufacturer. Ask whether the combination provides an appropriate operating range and which gain mode is recommended. Do not ask only whether the amplifier can drive a certain impedance, because that omits the headphone’s sensitivity and the intended use.
Also describe a practical constraint. For example, you may use sensitive in-ear headphones at a quiet desk and want gradual volume adjustment near the bottom of the control. Another listener may use a less-sensitive full-size pair with recordings that have wide level variation. These are different matching questions even if both people listen at moderate levels. The answer should address the combination, not simply repeat the amplifier’s maximum output figure.
