Design solutions that pursue the sound quality and experience you need
Buying headphones means reading specs; building them means understanding how those specs are measured. This article breaks down the three core headphone test parameters — frequency response, total harmonic distortion (THD), and sensitivity — including measurement conditions, pass criteria, and common pitfalls, as a practical reference for brand owners and buyers.
Frequency response describes a headphone's output level at each frequency and directly reflects tuning quality. The headphone is mounted on an IEC 60318-4 ear simulator, driven with a sweep, and the resulting curve is recorded. Many products only claim "20 Hz–20 kHz," but what matters is the curve shape and effective bandwidth: low-frequency roll-off, midrange dips, and treble peaks are all exposed by the curve. Always request measured curves rather than relying on claimed ranges, and check left/right consistency — a difference above 3 dB produces audible image shift in production units.
Total harmonic distortion (THD) quantifies harmonic content produced during playback. The standard method drives the headphone with a 1 kHz sine at rated input level; full-band THD curves are also common. Below 1% is a typical pass criterion. Pay special attention to the low end — small drivers show sharply rising distortion at high low-frequency excursion, which is why some budget headphones with impressive claimed specs sound muddy. Distinguish THD from THD+N, which includes noise and better reflects overall cleanliness. Bluetooth models measure slightly higher due to codec losses, which is normal.
Sensitivity expresses output SPL for a standard input (typically 1 mW or the 94 dB SPL condition) and determines how easy a headphone is to drive. Above 100 dB/mW, most phones suffice; below 95 dB, clear source power requirements emerge. Sensitivity must always be quoted with the impedance condition: the same headphone can measure several dB differently from high-impedance versus low-impedance outputs. When evaluating system pairing, combine sensitivity, impedance, and source output power — never a single number — or you risk units that "pass specs but won't play loud."
Q: Is a flatter frequency response always better?
A: Flat is the target for monitoring headphones, but consumer models typically boost bass slightly and soften treble to suit mainstream preferences. When reviewing curves, focus on obvious dips and sharp resonant peaks — these are design defects regardless of tuning style.
Q: What THD level counts as acceptable?
A: Below 1% at 1 kHz is a common threshold; good drivers can reach below 0.5%. The full-band curve matters more, especially below 100 Hz: many headphones pass at high frequencies but exceed 3% in the bass, which is heard as muddiness and boominess.
Q: Does higher sensitivity mean better sound or longer battery life?
A: Higher sensitivity means the headphone plays louder from the same power — it says nothing about sound quality. Very sensitive headphones also expose the source's noise floor more easily, raising SNR requirements for the front end; designers must balance both.
Shenzhen Liwei Electronic Technology Co., Ltd. has over 10 years of experience in audio headset electronic solution design, providing complete services from electroacoustic tuning and parameter testing to PCBA development for 15+ well-known brands and 300+ customers. Contact Liwei Electronic for custom audio solutions and test support.
Shenzhen Liwei Electronic Technology Co., Ltd. has over 10 years of experience in audio headset electronic solution design. Contact us for custom audio solutions.
Keywords: headphone testing,frequency response,THD,headphone sensitivity
