Wired headphones: how to compare impedance, sensitivity and power

When choosing wired headphones, two figures commonly appear: impedance, expressed in ohms (Ω), and sensitivity, often given in decibels (dB). They offer clues about the relationship between the headphones and the source that drives them, but they are not a quality score or a guarantee that a model will play loudly enough with any phone, laptop or amplifier. A useful comparison also requires knowing how the figures were measured and what reference was used.

Impedance describes, in simplified terms, the opposition that an electrical load presents to an audio signal. Sensitivity relates an electrical input to the acoustic level produced, but specifications may express it relative to power—for example, dB per mW—or voltage—for example, dB per volt. Those references are not interchangeable without conversion and without knowing the relevant impedance. A sensitivity figure without a complete unit or a stated method provides less information than it may seem to.

The IEC 60268-7 family of standards covers methods and definitions related to headphones. This matters because measurement conditions make more rigorous comparisons possible; it does not mean that every brand publishes figures under identical conditions or that a product sheet explains every detail. The first step is to read the complete unit and reference, not to rank products by the highest or lowest number.

A high nominal impedance does not automatically mean that headphones are better, harder to drive or incompatible with a portable source. It describes an electrical characteristic of the headphones, but the output voltage available, its current capability and the circuit design also play a role. Conversely, low impedance does not let you conclude that every device will deliver an optimal result: sensitivity and the output’s limitations still matter.

To decide whether a source can drive a pair of headphones, it is not enough to compare the headphones’ ohm figure with some supposed “limit” for a phone or computer. Look for headphone-output data in the source’s official documentation: available power or voltage under a stated load, along with any conditions or restrictions attached to that figure. If the manufacturer does not publish those details, it is not sound practice to fill the gap with a universal rule based on impedance alone.

Apple, for example, documents support for high-impedance headphones on certain Mac models and provides specific instructions for using the feature. That information should not be extrapolated to every Mac, every connector or other computers: compatibility applies to the particular model and its documentation. With a phone and an adapter, the relevant output may also be the adapter’s, rather than the phone’s on its own.

Sensitivity is particularly useful for understanding how much electrical output is needed to produce a given acoustic level, but only when you understand how it is expressed. Two specifications may both give values in dB and still not be directly comparable if one is based on power and the other on voltage. This is not a cosmetic difference: the measurement reference changes, as does its relationship to the headphone load.

Before comparing, note for each model the value, complete unit, electrical reference and, if available, the stated standard or method. IEC 60268-7 is a relevant reference for headphone measurements; IEC lists the 2025 edition alongside earlier editions. However, the existence of a standard, or its mention in a specification sheet, does not by itself prove that every published figure was obtained under identical conditions.

Do not turn a sensitivity difference into a more detailed listening prediction than the data supports. The final level also depends on the material being played, the volume setting, the signal, the output circuit and the transducer’s actual behaviour. Sensitivity helps estimate electrical requirements; by itself, it does not describe tonal balance, resolution or personal preference.

Start by identifying the complete connection path: built-in analogue output, USB-C or Lightning adapter, external DAC or amplifier. Find documentation for the exact model of every component and look for output figures under a specified load. A power figure without a load resistance, or a maximum figure without context, may not represent the conditions that matter in use.

Next, check the headphones’ sensitivity and make sure its unit and reference are comparable with the output data. If the source publishes a maximum voltage, impedance and sensitivity expressed per volt can help with an estimate; if it publishes power under a specific load, check that the condition is relevant. When units or conditions do not match, do not pretend to have precision you lack: look for the complete technical specification or ask the manufacturer.

Apple’s documentation for certain Mac models illustrates why identifying the exact product matters: its recommendation concerns a specific capability on particular computers, not a universal power standard for computers. For any brand, record the model name and generation. Similar product names can conceal different circuits; documentation for a product family does not replace the specification for the device you own.

A document-based assessment can classify the case as well documented, uncertain or in need of more information. “Well documented” means that compatible specifications were found for the source and headphones under comparable conditions; it does not guarantee a particular volume. “Uncertain” is the appropriate conclusion if sensitivity, the test load or output data is missing. An isolated figure does not turn uncertainty into a recommendation.

Some manufacturers publish ranges or explicit instructions for using high-impedance headphones with particular equipment. Treat them as guidance limited to the product described. Do not assume that an external amplifier is essential just because you see a high impedance figure, or that one is unnecessary simply because the impedance is low. The decision depends on the particular source-and-headphone pairing and on the information available.

This method also cannot establish whether the level will be comfortable, whether there will be enough headroom for quiet recordings or whether you will like the sound. Those questions depend on use and cannot be answered by ohms and sensitivity alone. If the documentation leaves an important unknown, the responsible conclusion is to leave it unknown, not turn an estimate into a performance promise.

Impedance and sensitivity alone cannot reveal tonal response, isolation, comfort, distortion across the full operating range, build quality or durability. Nor are they an overall ranking of “better” and “worse”. IEC 60268-7 covers headphone methods, while IEC 60268-4 concerns microphones; the name of a standards family does not mean that each document measures every property a buyer might care about.

A source’s output figures do not automatically describe how it behaves in every situation, either. Documentation may specify a particular condition rather than every use case. Without physical testing, you cannot claim that a particular combination reaches a given level, retains a certain quality at that level or behaves the same with every recording. This guide is therefore a document-based assessment, not a listening test.

A sensible comparison keeps three things separate: published facts, such as the impedance value stated by the manufacturer; inferences, such as the possibility that a documented output is suitable under matching conditions; and limitations, such as the absence of a comparable measurement. Keeping them distinct prevents a specification sheet from appearing more conclusive than it really is.

Gather the specifications for the exact headphones and source. If there is an adapter, identify its manufacturer and model and consult its own data. For each sensitivity figure, retain the complete unit and reference; for each output power or voltage figure, retain the load and any conditions stated in the document. If a retailer omits those details, look for the official product page or original technical sheet.

A practical check can be made in this order:

• Identify the headphones, source and adapters by model, not by generic category.
• Record nominal impedance and sensitivity with their complete units and references.
• Look for headphone output in official documentation under a specified load.
• Compare only figures whose conditions are reasonably compatible.
• Mark as unknown anything not published; do not replace it with a universal rule.
• Separate indicative electrical compatibility from sound quality, comfort and perceived volume.