Saturday, November 7, 2015

Factors that Influence Listeners’ Preferred Bass and Treble Levels in Headphones

Most people would agree that headphone purchase decisions are heavily influenced by the brand and styling (size,  weight, color, quality of  materials).   But what is considered stylish and fashionable  by me is not shared by my 15-year old daughter (this week donning purple hair), and vice versa. In other words, the perceived visual aesthetic  of the headphone  is really in the the eyes and mind of the beholder, and this can vary with age, gender, culture, and other demographic category. 

But what about sound quality?  To what extent does the consumer's  age, gender, culture and prior listening experience influence their taste in headphone sound quality?  Is there a scientific basis for headphone manufacturers to design headphones that have different amounts of bass and treble aimed to satisfy the tastes of a targeted demographic group? 

To answer this question, we recently conducted a  study on factors that influence listeners’ preferred bass and treble balance in headphone sound reproduction. Using a method of adjustment a total of 249 listeners adjusted the relative treble and bass levels of a headphone that was first equalized at the eardrum reference point (DRP) to match the in-room steady-state response of a reference loudspeaker in a reference listening room. Listeners repeated the adjustment five times using three stereo music programs. The listeners included males and females from different age groups, listening experiences, and nationalities (Canada, USA, Germany and China).  The results provide evidence that the preferred bass and treble balances in headphones was influenced by several factors including program, and the listeners’ age, gender, and prior listening experience. The younger and less experienced listeners on average preferred more bass and treble in their headphones compared to the older, more experienced listeners. Female listeners on average preferred about 1 dB bass and 2 dB treble than their male counterparts. Listeners over 55 years preferred less bass and more treble than the younger listeners suggested that they were compensating for possible hearing loss that is associated with increased age.

We recently presented the results of this study at the 139th Audio Engineering Society Convention in New York City, October 29th-November 1, 2015. The paper is available for download in AES e-library. A PDF copy of the presentation can be found here. Or you can view an animated version of the presentation on Youtube.

Wednesday, October 22, 2014

The Influence of Listeners' Experience, Age and Culture on Headphone Sound Quality Preferences

At the recent 137th convention of the Audio Engineering Society we presented our latest research paper entitled, "The Influence of Listeners' Experience, Age and Culture on Headphone Sound Quality Preferences."

The paper describes some double-blind  headphone listening tests conducted in four different countries (Canada, USA, China and Germany) involving 238 listeners of different ages, gender and listening experiences. Listeners gave comparative preference ratings for three popular headphones and a new reference headphone that were virtually presented through a common replicator headphone equalized to match their measured frequency responses. In this way, biases related to headphone brand, price, visual appearance and comfort were removed from listeners’ judgment of sound quality. On average, listeners preferred the reference headphone that was based on the in-room frequency response of an accurate loudspeaker calibrated in a reference listening room. This was generally true regardless of the listener’s experience, age, gender and culture. This new evidence suggests a headphone standard based on this new target response would satisfy the tastes of most listeners. 

The paper is available for download from the AES e-library. You can also find a PDF of our presentation here or view the presentation on YouTube.

Wednesday, June 11, 2014

My Article on Headphone Sound Quality in 2014 LIS

The 2014 Loudspeaker Industry Sourcebook came out this week. In it, you can find an article I wrote called "Perceiving and Measuring Headphone Sound Quality: Do Listeners Agree on What Makes a Headphone Sound Good?"

The article is a summary of some recent published research we've conducted at Harman on the perception and measurement of headphone sound quality.

Together, these studies provide scientific evidence that when headphone brand, price, fashion, and celebrity endorsement are removed subjective evaluations, listeners generally agree on what makes a headphone sound good.

So far, this has been true regardless of users' listening training, age, or culture.  The more preferred headphones tend to have a smooth, extended frequency response that approximates an accurate loudspeaker's in-room response. This new target frequency response could provide the basis for a new and improved headphone target response. You can find more details on the research here.

Tuesday, January 28, 2014

Interview in Professional Sound: The Lack of Meaningful Loudspeaker & Headphone Specs

Last October,  I was in Toronto giving a presentation to the local AES section on the perception and measurement of headphones. After the talk, I sat down with Mike Raine from  Professional Sound for an interview. Some of what we discussed is summarized in this article called Sound Advice.

The theme of article is a recurring one that I've discussed before in this blog (see "The Science and Marketing of Sound Quality" and "What Loudspeaker Specifications are Relevant to Sound Quality?").  The bottom line is that the loudspeaker and headphone industry has utterly failed to provide consumers meaningful product specifications that indicate how truly good (or bad) the products sound. Read on to find out why.

Monday, January 6, 2014

Do Listeners Agree on What Makes a Headphone Sound Good?

This past weekend, I attended the ALMA 2014 Winter Symposium in Las Vegas where I gave a talk entitled, "The Perception and Measurement of Headphone Sound Quality: Do Listeners Agree on What Makes a Headphone Sound Good?" The presentation gives a summary of some key findings of our headphone research conducted over the past 18 months. It also includes some unpublished preliminary findings from a current study on headphone preferences of trained and untrained listeners both young and old from China, Canada, USA, and Germany. The focus of this study is to determine whether listeners from different cultures and age groups prefer the same headphone sound quality as trained listeners when the influence of headphone brand, fashion and celebrity endorsement are removed from the test. 

The abstract for my talk is reproduced below. A PDF of the slide presentation can be downloaded here:

The popularity of headphones has now exploded to produce annual worldwide sales of almost $10 billion. Premium headphones ($100+) now account for 90% of the annual revenue growth, as consumers’ audio experiences are becoming a primarily mobile one. Market research indicates sound quality is a driving factor in headphone purchases with brand and fashion also being important factors among younger consumers. Yet, ironically the science behind what makes a headphone sound good and how to measure it is poorly understood. This combined with the lack of perceptually meaningful headphone standards may explain why purchasing a headphone today is like playing Russian Roulette with your ears. The magic bullet to achieving more consistent headphone sound quality is science.

We recently conducted a series of controlled double-blind listening tests on popular headphones (both real and virtualized models) to better understand the relationship between their perceived sound quality and acoustic performance [1,3,5]  A second set of experiments measured listener preferences of different headphones equalized to different target curves responses including the recommended diffuse and free-field target curves [2].  A third set of experiments used a method of adjustment where listeners directly adjusted their preferred bass and treble levels of a headphone and loudspeaker equalized to the same in-room target response [4]. In this way, we could measure the variation in individual listeners’ taste in headphone spectral balance, and determine the extent to which the preferred headphone target response should simulate the response of an accurate loudspeaker in a reference listening room.

Together, the results of this research show that when the influence of brand, fashion and celebrity endorsement are removed from headphone tests, both trained and untrained listeners regardless of age and culture, generally agree on which headphones sound best and this correlates to their acoustical performance.

  1. Sean E. Olive and Todd Welti, "The Relationship between Perception and Measurement of Headphone Sound Quality", presented at the 133rd Audio Eng. Soc. Convention, San Francisco, USA, (October 2012).
  2. Sean E. Olive, Todd Welti and Elisabeth McMullin, "Listener Preferences For Different Headphone Target Response Curves",  presented at the 134th Audio Eng. Soc. Convention, Budapest, Hungary, (May 2013).
  3. Sean E. Olive, Todd Welti and Elisabeth McMullin, "A Virtual Headphone Listening Test Methodology", presented at the 51st Audio Eng. Soc. International Conference, Helsinki, Finland, (August 2013).
  4. Sean E. Olive, Todd Welti and Elisabeth McMullin, "Listener Preferences for In-Room Loudspeaker and Headphone Target Responses"  presented at the 135th Audio Eng. Soc. Convention, New York, USA, (October 2013).
  5. Sean E. Olive, "Do college students prefer the same headphone sound quality as trained listeners?", presented at the 4th ISEAT, Shenzhen, China, (November 2013).

Friday, December 20, 2013

Harman Kardon factory tour: Pure to the art of sound

Some of the Harman and competitor headphones that we've recently tested.
Giving Harman R&D lab tours and presentations to customers and audio journalists is a part of my job. Recently, we played host to some automotive journalists in town attending the Los Angeles Auto show.

Automotive audio journalist Shawn Molnar wrote this great article about his visit to our R&D labs that you can read in his popular BMWBlog.

Shawn gives an overview of  his visit to our labs where we showed the journalists our R&D facilities used for testing and evaluating Harman loudspeakers, headphones and automotive audio systems.  Most people I meet know Harman for its JBL and Harman Kardon consumer and professional products. They are surprised to lean that 75% of our sales are from Harman branded (JBL, Harman Kardon, Infinity, Lexicon, Mark Levinson) automotive audio and infotainment systems.

Research by CEA has found that consumers now spend almost as  much time listening to music in their cars as they do in their homes.  Moreover, the audio experiences in the car are increasingly more sonically satisfying than those experienced in the home. Branded audio systems in premium cars typically provide 7-channel surround sound through 16+ loudspeakers that deliver a full-range, balanced, enveloping sound stage that can reach concert sound pressure levels. Compare this to the tinny, spatially bereft stereo speakers in your MacBook Pro or flat panel TV, and you begin to understand why people are listening to music through headphones when they're not listening in their cars.

So, why don't automotive journalists spend more time writing about audio / infotainment systems in cars given that consumers tell us it's an important factor in their overall satisfaction rating of the car?  When reading reviews of new cars, wouldn't it be nice to hear more about the quality of the audio system than how many heated cup holders it has?

Wednesday, July 3, 2013

The Science and Marketing of Sound Quality

To my surprise, this morning an audio friend tweeted a link to an article I recently wrote for our company's  internal newsletter  entitled, "The Science and Marketing of Sound Quality."  My article can be found on a new Harman Innovation website  launched today that features articles on current and future disruptive technology that will impact consumers' infotainment experiences. Check it out.

My article focuses on a longstanding pet peeve of mine (first mentioned in this blog posting): The lack of  perceptually meaningful loudspeaker and headphone specifications in our industry.  While consumer surveys repeatedly report sound quality to be a driving factor in their audio equipment purchases, consumers lack the necessary tools and information to identify the good sounding products from the duds.

This is particularly true for loudspeakers and headphones where the typical throw-away "10 Hz to 40 kHz" specification provided by the manufacturer is utterly useless. This specification only guarantees that the product makes sound, with no guarantee that the sound is good.  While the science exists today to accurately quantify and predict the perceived the sound quality of  loudspeakers (and hopefully, soon headphones), the audio industry continues to drag its heels into the 21st century,  and not routinely provide this information to consumers.

A rare exception is JBL Professional who provides comprehensive detailed measurements on studio/broadcast monitors like the new JBL M2 Master Reference shown below. Inspecting the measured frequency response curves shown  below, you can easily recognize the loudspeaker sounds exceptionally neutral and accurate based on the shape (flat, smooth, and extended)  Based on this set of measurements, we can predict how a listener would rate the sound quality of the loudspeaker in a controlled listening test, with 86% accuracy. The only pertinent information not shown in this graph is how loud the loudspeaker will play before producing audible distortion (trust me, this loudspeaker will play very loud! )

Perceptually meaningful loudspeaker specifications like these have been available for almost 30 years! Yet,  these specifications are currently not part of any professional and consumer loudspeaker standard. Such a standard would go a long way towards improving the quality and consistency of recorded and reproduced sound. Audio consumers want to hear the truth. We need to provide better information and audio specifications so they can find it.

JBL M2 Master Reference Monitor provides true reference sound quality that is clearly indicated by its technical measurements shown below. 
The spatially-averaged frequency response curves of the JBL M2  (from top to bottom) for the listening window (green), the first reflections (red), and the total radiated sound power.  At the bottom are shown directivity indices of the sound power (dotted blue) and first reflections (dotted red). These measurements tell us that the quality of the direct and reflected sounds produced by the loudspeaker will be very accurate and neutral over a relatively wide listening area.