The Sennheiser HD 650 headphones are widely regarded as some of the most neutral-sounding headphones on the market. The graph below shows the frequency response of these headphones, measured using six different measurement tools available on the market. All curves are normalized based on the 100 – 1000 Hz range. While most of these devices capture lower frequencies somewhat similarly, the consistency above 1kHz is abysmal, as the spread soars up to +/-15dB.
Keep this graph in mind the next time you see some frequency response chart on the internet—the usefulness of such data is limited at best. It’s evident that there’s a lack of standardization in the measurement equipment industry as all of these tools are designed to capture the same thing, yet results are so vastly different. We have done a lot of testing of measurement tools for headphones, however, our primary use case is to use the measurement to create a calibration filter that would cancel the measured acoustic flaws. Yet our tests revealed that none of these measurements directly translate to human perception. Sonarworks has developed speaker and headphone calibration software that delivers the same sound targets on speakers and headphones. To achieve this we had to develop a new headphone measurement technology from the ground up. You can read about it in our latest whitepaper.
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