Sunday, December 28, 2008

Part 3 - Relationship between Loudspeaker Measurements and Listener Preferences

Part 1 of this article presented experimental evidence from a study conducted by the author demonstrating that trained and untrained listeners prefer the same loudspeakers (see reference 1). Part 2 showed that the trained listeners performed 3 to 20 times better than untrained listeners based on their ability to give discriminating and reliable loudspeaker ratings. In part 3, we examine the relationship between the listeners' loudspeaker preferences and a set of anechoic measurements performed on the loudspeakers used in that study.

The mean loudspeaker preference ratings and 95% confidence intervals, averaged across all listeners, are plotted for each of the four loudspeakers (see the graph to the right). According to the definition of the preference scale, listeners liked loudspeakers P and I, were relatively neutral towards loudspeaker B, and they disliked loudspeaker M.

The next graph on the right shows a set of anechoic measurements for each of the four loudspeakers P, I, B, and M, shown in descending order based on their subjective preference rating. Each loudspeaker was measured at 70 different angles around its horizontal and vertical orbits in order to fully characterize the quality of its on and off-axis sounds, and allow removal of acoustical interference effects from resonances, which can cause harmful colorations to the reproduced sound. These resonances are visually presented as peaks and dips in the frequency response. In each graph, the frequency curves represent, from top to bottom, the quality of the direct sound, the average listening window, the first reflections, the sound power, and the directivity indices for the first reflections and the sound power. The reader is referred to references 2-4 for more background on how these measurements were derived and experimentally validated through controlled listening tests.

There are clear visual correlations between listeners' loudspeaker preferences and the set of frequency graphs. Both trained and untrained listeners clearly preferred the loudspeakers with the flattest, smoothest and most extended frequency response curves, as exhibited in the measurements of loudspeakers P and I. Loudspeaker B was rated lower due to its less extended, bumpy bass, and a large hole centered at 3 kHz in its sound power curve. The measurements of Loudspeaker M indicate it has a lack of low bass, and has a non-smooth frequency response in all of its measured curves. Both the direct and reflected sounds produced by this loudspeaker will contribute serious colorations to the timbre of reproduced sounds.

It is both satisfying and reassuring to know that both trained and untrained listeners recognize and prefer accurate loudspeakers, and that the accuracy can be characterized with a set of comprehensive anechoic measurements. The next logical step is to use these technical measurements as the basis for modeling and predicting listeners' preference ratings. This will be the topic of a future post in this blog.


[1] Sean E. Olive, "Differences in Performance and Preference of Trained Versus Untrained Listeners in Loudspeaker Tests: A Case Study," J. AES, Vol. 51, issue 9, pp. 806-825, September 2003. (download for free courtesy of Harman International)
[2] Floyd E. Toole, "Loudspeaker Measurements and Their Relationship to Listener Preferences: Part 1" J. AES Vol. 23, issue 4, pp. 227-235, April 1986. (download for free courtesy of Harman International).
[3] Floyd E. Toole, "Loudspeaker Measurements and Their Relationship to Listener Preferences: Part 2," J. AES, Vol. 34, Issue 5, pp. 323-248, May 1986. (download for free courtesy of Harman International)
[4] Allan Devantier, "Characterizing the Amplitude Response of Loudspeaker Systems," presented at the 113th AES Convention, October 2002.


  1. I noticed the tests were conducted mono-phonically, using a single speaker. Doesn't this ignore the fact that speakers always work in pairs, therefore testing a single speaker might not tell us how a pair of speakers would measure? Has there been an attempt to show that measuring a single speaker is statistically equal to measuring a pair of the same speakers?

  2. Sensible audio opinions for once. Why is it that people, horrified should the FDA did NOT double-blind test their medical prescriptions, airily dismiss the efficacy of double-blind testing audio equipment? An accurate aural memory lasts less than twenty seconds, yet I have read paid reviewers compare one speaker to another they hadn't heard in six months! My solution is to only audition equipment of manufacturers who use double-blind testing in the development of their products.

  3. Hi Anonymous
    I see I am preaching to the choir as far as you are concerned. Thanks for supporting the scientific method with your pocket book.


  4. Dr. Sean,

    Do speakers have measurable non-linear distortions on normal power levels, and does it affect perceived sound quality?

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    Of course, it depends on the speaker, and the extent to which the speaker is being driven into its nonlinear region. This generally happens much sooner with smaller multimedia speakers that use smaller drivers in small enclosures where driver is driven more frequently into its excursion limits. Limited amplifier power, electronics limiters are other source of distortion.

    Most larger well-designed consumer speakers have less distortion when played at comfortable levels. While the nonlinear distortion is measurable, much of it is masked by the music itself. Nonlinear distortionseldom shows up as a significant factor in our listening tests (and others) unless the speaker is driven at higher SPL's to the point where transducer mechanical, thermal or electro-acoustic limits. Turbulence from ports can be another source of distortion

  6. Wow, someone well placed in the Audio"phool" world yet not trying to phool the listeners by talking about sweetness and phatness and other propaganda stuff (for monetary benefits).

    Instead we are presented here with numbers, facts, figures, experiments and results.

    Can't believe this is happening in a capitalist world!

  7. Alpha :

    I'm glad you view this blog as a B.S.-free zone, and a refreshing departure from what you typically read in most audio propaganda. If you want to hear good B.S. just tune in to the political debates tonight on the TV :)