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BA Maker Knowles Revisits The Harman Curve With “The Knowles Curve” For Headphones

Knowles Curve

This morning balanced armature maker Knowles unveiled a white paper outlining a new frequency curve as a response to the longstanding “Harman Curve” that serves as a guide for headphone design. The idea is one of the more complicated but important concepts that audiophiles wrestle with in their pursuit for good sound. In a nutshell, the Harman Curve stood for the average of the data collected when it comes to the populations’ preferences in frequency response.

The thinking is that if you produce a headphone with a sound signature close enough to this average, the most people out there will enjoy your headphone. This of course, weighs frequency response very heavily in terms of the overall sonic influence of any given device. As with all things in audio, one could argue that many factors make up the overall sound (or the reason why someone prefers a sound to another) but FR does seem to be a large part of the final delivery. In any case, the takeaway from the new Knowles curve is basically more treble is needed for in ears. The news also coincidentally falls with an announcement of a new True Wireless design from the company coming in Q3. You can find the full white paper on the Knowles Curve here.

More info from the press release:

Knowles Unveils the Formula for Best Earphone Music Listening Experience
New Preferred Listening Response Curve from Knowles defines the next standard in high-resolution earphones
ITASCA, Ill., May 18, 2022 — Knowles Corporation (NYSE: KN), a market leader and global provider of advanced micro-acoustic microphones and speakers, audio solutions, and high-performance capacitors and RF products, today releases research demonstrating a new Preferred Listening Response Curve for earphone design, reflecting findings to ensure the best and most satisfying music listening experience for consumers.
Sound quality continues to be at the top of the list for consumer audio demand, yet many True Wireless Stereo (TWS) earphone manufacturers have been slow to take advantage of the developing hi-res audio ecosystem. With the proliferation of lossless music streaming subscription services like Tidal, Amazon Music HD and Apple Lossless, together with availability of high data rate Bluetooth codecs, the industry is able to deliver hi-res audio wirelessly with the right hardware and tuning. Knowles’ latest research provides valuable insight into how to satisfy consumer demand for the best-sounding audio in either wired or wireless earphones.
Knowles analyzed more than 200 recordings, chosen from the last 20 years of the Billboard Hot 100 to represent much of the music that headphone wearers are likely to be streaming. This revealed significant high frequency content above 10 kHz in popular music that many earphones fail to reproduce well. From here, the team conducted controlled blind testing of a wide variety of listeners – with a range of demographics and hearing abilities – to determine what makes the best sound quality, as preferred by listeners.
Optimum high frequency response is key when designing hi-res earphones. Using technology only recently available, Knowles was able, for the first time, to extend an understanding of user preference beyond 10 kHz to create the new Knowles Preferred Listening Response Curve. By focusing on the high frequency response, the new curve is uniquely suited to give manufacturers the insight needed to deliver the best hi-res listening experience.
Key findings from the Knowles research shows that earphones tuned to earlier concepts of what sounds good severely understate the amount of high frequency energy that listeners prefer. According to the Knowles Preferred Listening Response Curve, listeners consistently preferred between 12 and 21 decibels (dB) of boost at frequencies beyond 10 kHz, depending on age and hearing ability. Designing and tuning an earphone that matches the high frequency boost identified using the Knowles Preferred Listening Response Curve is expected to consistently provide a highly satisfactory end user experience and receive high ratings from consumers.
The Knowles Curve is an especially powerful tool when used with hearing personalization algorithms. Knowles included subjects with various levels of reduced high frequency hearing response and determined their preferred amount of boost. With this data, designers of TWS earphones with hearing personalization can configure their algorithm to produce the optimum sound quality across the range of hearing abilities commonly experienced by consumers.
“Consumers want hi-res, premium sound through their TWS earphones. This has been a challenge for OEMs who have had no clear guideline for what consumers prefer across the full spectrum. Now we know exactly how to design and tune a TWS earphone to create the best sounding audio available,” said Shehab Albahri, Sr. Director of Knowles Hearing Health Technologies R&D. “Brands that design with hi-res capable hardware and tune their earphones to the Knowles Curve will unlock the true potential of lossless streaming audio.”
A Knowles Preferred Listening Response Curve whitepaper with suggestions on hardware to meet the new curve can be downloaded from This research was first presented at AES Chicago Chapter Meeting on May 17, 2022. Knowles will also release a new TWS reference design tuned to the Knowles Curve, available in Q3 2022.

More info: Knowles

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