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2014 Loudspeaker Industry Sourcebook 20 INDUSTRY REPORTS C onsumers are experiencing more of their audio content through headphones. In 2013, headphone sales were $8.2 billion worldwide with premium headphones ($100 or more) accounting for 90% of the growth.  While consumers clearly want better quality sound from their headphones, the science behind what makes a headphone sound good and how to measure it is not well understood. This article summarizes some of the recent scientific research, which we conducted at HARMAN International to improve our knowledge about the perception and measurement of headphone sound quality. The research focused on four questions: • Do trained listeners agree on what makes a headphone sound good? • Do listeners' headphone sound quality preferences vary according to their listening experience, age, or nationality? • What is the preferred headphone target response? • Can listeners' subjective ratings of headphone sound quality be predicted based on the headphones' acoustical performance? What Makes a Headphone Sound Good? To answer this question, we conducted a series of controlled listening tests where 11 trained listeners evaluated six popular circumaural (over- the-ear) headphones from different manufacturers and dif ferent price points based on overall preference, spectral balance, and comfort (see Resources). The blind listening test was conducted to ensure that non-auditory biases (e.g., brand, price, fashion, and celebrity endorsement) would not influence listeners' judgment of the sound. However, the headphones' tactile feel and weight remained part of the test. Figure 1 summarizes the average preference ratings of the headphones. Listeners preferred the models that sounded neutral and spectrally well balanced. This data corresponded to a measured response that was both smooth and extended in frequency. In cases where the headphone's perceived spectral balance did not agree with its measured response (e.g., the HP4, a closed- back design), the headphone's fit and seal on the listeners' ear was the culprit. Headphone Perceiving and Measuring Headphone Sound Quality By Dr. Sean Olive Director of Acoustic Research, HARMAN International, and President, Audio Engineering Society (AES) Do Listeners Agree on What Makes a Headphone Sound Good?