The throaty, melodic groans of a cello playing Bach fill the darkened space of a music hall. Each rich note reaches the audience via sound waves that radiate from the body of the instrument like ripples created by a pebble plunked into a still pond.* Some waves hit listeners' ears directly; others reflect off of the walls and ceiling, reverberating and surrounding the audience with sound. The best concert halls are built to showcase the performers' skill, but evaluating their acoustics can be a challenge, because the quality of sound is subjective.
Engineers, musicians and other experts have a checklist of factors to assess music hall acoustics, but do scores on such measures correlate with sound that pleases concertgoers best? To find out, researchers in Spain recently asked laymen to judge many aspects of the sound of 17 music halls in Valencia. They discovered several differences between the assessments of experts and nonexperts that could eventually direct architects toward music hall design that optimally satisfies both. The findings are the first to offer a systematic method for nonexpert evaluation of other halls.
Since the early 1900s experts have judged the quality of existing auditoriums by measuring the timing of when direct and reflected sound waves reach an audience. Researchers have linked arrival times to attributes such as clarity and warmth, but the data do not translate readily into guidelines for how best to design, say, the spacing between seats or stage configurations.
The new findings addressing that issue follow up on years of studies in which researchers sometimes have trouble matching expert and amateur opinions. For example, in 2010 investigators recorded acoustics in the Bolshoi Sal (Great Hall) of Moscow's P. I. Tchaikovsky Conservatory, comparing the measures with those for other venues (pdf). They found that the Russian hall had a similar reverberation time—how long it takes reflected sound waves to subside—to that in such facilities as the Boston Symphony Hall and the Sibelius Hall in Lahti, Finland (2.5 and 2.4 seconds, respectively, mid-range values that compromise between the long times preferred for choral music and the shorter times needed for speech). They also asked audience and orchestra members to evaluate the Bolshoi Sal's acoustics. Whereas both groups agreed the hall's sound quality was good, the researchers noted that answers from the audiences were varied and "in some cases ambiguous." Some nonexperts gave poor evaluations but still stressed the excellent acoustic properties of the hall.
To delve into the differences between experts and nonexperts, the Spanish team—Miguel Galiana Martinez, a professor of architecture at the European University of Madrid in Spain, and his colleagues—turned to a product-assessment method called Kansei engineering.** The technique links a customer's emotional responses and needs to aspects of a product's design. "We want to grasp the nonexpert's opinions and take them into account," Galiana Martinez says. "And then we can translate them into features that improve the sound in the venues."
Galiana Martinez and his colleagues first combed the Internet, magazines, scientific papers and books for words or phrases describing the sound and quality of music. A small group—comprising two professional musicians, two acousticians and two nonexperts—divided the descriptions by categories and chose a representative expression for each set. This method yielded 27 expressions. Next, the researcher wrote a questionnaire and asked concertgoers to evaluate the 17 auditoriums on the selected terms.
Each listener ranked their venue on a five-point scale for each of the 27 terms: totally disagree, disagree, neutral, agree and totally agree. The researchers found that assessments by nonexperts relied on five factors: "fidelity and quality," "power," "intimacy," "reverberation" and "sound defects." In contrast, experts assessed music hall acoustics using six factors: "balance and pitch quality," "intimacy and wide dynamic range," "power and brightness," "softness," "bass enhanced" and "without sound defects." The researchers published their findings in the December 2012 Building and Environment.
Some of the factors seem similar, says Galiana Martinez, but have different meanings. For example, the "power" factor for nonexperts means powerful sound—the terms grouped into this factor were not weak, distant or dull. For experts, the "power and brightness" factor included the terms resounding, treble enhanced, bright, reverberant and powerful. A second notable difference was that experts not only evaluated the presence of good qualities but also the absence of bad qualities: It was important to experts that the sound not be dull, weak or dissonant. Nonexperts were more inclined to like the music hall if the sound was harmonious and had a wide dynamic range, which means a listener can hear the range of sounds from quiet to loud. The researchers next plan to try to link these subjective evaluations to actual physical parameters in music halls.
Meanwhile, Galiana Martinez says the findings are the first step toward developing a more robust way to build the next generation of concert halls, where tuneful madrigals, seductive jazz or as-yet unwritten songs will serenade future audiences—whether they be experts or casual listeners.
*Clarification (9/11/12): This sentence has been rewritten since posting to more clearly describe how sound waves are propagated by a musical instrument.
**Correction (9/11/2): This sentence has been edited since posting. Although Galiana Martinez is a member of the research team at the Polytechnic University of Valencia, he is a professor at the European University of Madrid.