Headphone specification sheets are filled with numbers and technical terms that can seem meaningless without context. What does a 40mm driver actually tell you? Is 20Hz-20kHz frequency response actually important? Does higher impedance mean better quality? This guide demystifies common headphone specifications, explaining what each measurement means and—crucially—how much it actually matters for your listening experience.
Driver Size and Type
The driver is the component that converts electrical signals into sound—essentially, a tiny speaker inside each ear cup or earbud. Driver size is typically specified in millimetres.
What the Numbers Mean
Over-ear headphones: Typically 40-50mm drivers
On-ear headphones: Typically 30-40mm drivers
Earbuds: Typically 6-14mm drivers
Does Bigger Mean Better?
Not necessarily. Larger drivers can move more air, which theoretically helps with bass response and overall volume. However, driver quality matters far more than size. A well-engineered 40mm driver will outperform a poorly designed 50mm driver. Additionally, driver size must be appropriate for the headphone type—you wouldn't want a 50mm driver in an earbud, even if it were physically possible.
đź’ˇ Driver Types
Dynamic: Most common; uses a diaphragm and voice coil—good all-round performance
Balanced Armature: Common in IEMs; excellent detail but limited bass
Planar Magnetic: Premium option; exceptional clarity and detail
Hybrid: Combines multiple driver types for full-range performance
Frequency Response
Frequency response indicates the range of audio frequencies the headphones can reproduce, measured in Hertz (Hz).
Understanding the Numbers
Human hearing typically ranges from 20Hz (very low bass) to 20,000Hz (very high treble). You'll often see headphones specified as "20Hz-20kHz" or similar ranges. Some headphones claim extended ranges like "5Hz-40kHz"—frequencies that humans can't actually hear directly.
Why Extended Ranges Exist
Frequencies beyond human hearing aren't completely irrelevant. Ultra-low frequencies can be felt as physical vibration, and some argue that high-frequency harmonics interact with audible frequencies in ways that affect perceived sound quality. However, these effects are subtle and debated among audio engineers.
âś… Key Takeaway
Frequency response range is largely meaningless without context. A headphone claiming 5Hz-40kHz isn't necessarily better than one claiming 20Hz-20kHz. What matters is how flat and accurate the response is within the audible range—information not conveyed by the spec alone.
The Missing Information
Raw frequency response numbers don't tell you how evenly the headphones reproduce those frequencies. A headphone might technically reach 20Hz but produce bass at significantly lower volume than mids. Frequency response graphs (if available) are far more informative than the numerical range alone.
Impedance
Impedance, measured in Ohms (Ω), describes the electrical resistance of the headphones. It affects how much power is needed to drive them and how they interact with audio sources.
Typical Ranges
Low impedance (under 25Ω): Easy to drive; works well with phones and portable devices
Medium impedance (25-100Ω): Still portable-friendly but may benefit from amplification
High impedance (over 100Ω): Typically requires a dedicated headphone amplifier
Why Impedance Matters
Bluetooth headphones have built-in amplification, so impedance is largely handled internally—you don't need to worry about matching impedance to your phone. However, for headphones with wired options or audiophile over-ear models, impedance becomes relevant.
Higher impedance headphones can actually sound better when properly amplified—they're less susceptible to electromagnetic interference and may offer more controlled bass. But driven by an inadequate source, they'll sound quiet and lifeless.
Sensitivity
Sensitivity (sometimes called efficiency) measures how loud headphones play at a given power input. It's typically expressed as decibels per milliwatt (dB/mW) or decibels per volt (dB/V).
What the Numbers Mean
Higher sensitivity means the headphones produce more volume from the same power input. Most headphones range from 90-110 dB/mW. A difference of 3dB represents roughly a doubling of acoustic power (though our perception of "twice as loud" requires about 10dB increase).
Practical Implications
Combined with impedance, sensitivity determines how well headphones work with your devices:
- High sensitivity + low impedance = very easy to drive (ideal for phones)
- Low sensitivity + high impedance = requires powerful amplification
For Bluetooth headphones, sensitivity still matters because it affects how the internal amplifier needs to work—and consequently, battery life.
Total Harmonic Distortion (THD)
THD measures how accurately headphones reproduce audio without adding unwanted artefacts. It's expressed as a percentage—lower is better.
Understanding THD Values
- Below 0.1%: Excellent; distortion is essentially inaudible
- 0.1-1%: Good; unlikely to notice distortion in normal listening
- Above 1%: Distortion may become audible, especially at high volumes
Most quality headphones have THD below 1%, and many specify less than 0.5%. At these levels, distortion is unlikely to affect your listening experience noticeably.
⚠️ Spec Sheet Caution
THD is often measured under ideal conditions at moderate volumes. Distortion typically increases at higher volumes and lower frequencies, so the specified THD may not represent real-world performance at loud listening levels.
Bluetooth Specifications
For wireless headphones, Bluetooth-related specifications matter for connection quality and features.
Bluetooth Version
Bluetooth 5.0 and newer: Current standard; offers improved range, stability, and power efficiency over older versions. Bluetooth 5.2 adds LE Audio support for newer audio features. Bluetooth 5.3 and 5.4 bring incremental improvements.
Note that Bluetooth version primarily affects connection characteristics, not audio quality—that's determined by codecs.
Supported Codecs
As covered in our codec guide, supported codecs (SBC, AAC, aptX, LDAC, etc.) determine potential audio quality and latency. This is often more important than Bluetooth version for audio performance.
Connection Range
Manufacturers often specify range in metres (typically 10-30m). Real-world range depends heavily on obstacles, interference, and environmental factors—actual performance is usually less than specified.
Noise Cancellation Specifications
Some manufacturers specify noise cancellation effectiveness in decibels (e.g., "up to 30dB noise reduction"). Be cautious with these claims—there's no standardised testing methodology, and results vary dramatically by frequency. ANC is most effective against low-frequency sounds and much less effective against mid and high frequencies.
How to Use Specifications Wisely
Specifications provide useful context but shouldn't be the primary basis for purchasing decisions. Here's a practical approach:
- Use specs for compatibility checking: Ensure impedance works with your source devices; verify codec support matches your phone
- Treat specs as minimum thresholds: Avoid headphones with clearly inadequate specs (very high THD, limited frequency response), but don't assume higher numbers are always better
- Prioritise listening impressions: Where possible, try headphones yourself or consult detailed reviews that describe actual sound characteristics rather than just repeating specifications
- Consider the complete package: Comfort, build quality, features, and real-world usability often matter more than marginal specification differences
Remember that two headphones with identical specifications can sound remarkably different. Specs describe measurable characteristics but don't capture the full audio experience—the art of headphone tuning goes beyond what numbers can express.
For more on specific technologies, explore our guides on noise cancellation and Bluetooth codecs.