Page 17 - Fall_DTF

Using an amplification system for teachers voices can so that listeners can understand how different rooms affect
dramatically improve the signal-to-noise ratio, leading that listening experience. Auralization has been particularly
to better speech intelligibility (Rosenberg et al., 1999). useful for subjective testing because it allows researchers to
Although amplified solutions remain viable, most test the effects of different acoustic environments in a more
consultants in architectural acoustics will shy away from controlled laboratory environment.
an_ unphlied _so1Imon lo mmgate _madeq“ate s‘gnal_t_0- Some of these laboratory studies on classroom acoustics
noise ratios in classrooms. Amplified systems require _ .

_ _ _ _ _ have been shifting toward the measurement of speech
more substantial partition construction to ensure suflicient _ . . . .
_ _ _ _ _ comprehension that involves higher levels of cognition
isolation between classrooms. I.ricreasirig the signal-to-noise _ . .

‘_ b d th h_ bl _th m I '1 rather than simply recognizing words, phrases, or sentences
” ‘° 2”“ °" “C _‘°‘”_ ° W‘ “_ ”‘_ '°‘_’"‘ “_°'“ :5 (Klatte et al., 2010; Valente et al., 2012; Lewis et al., 2014).
can be Coumerpmducuve wnhout considering lsolauom Results from those studies indicate that background noise
Other studies have focused on how the interaction between and room reverberation have more detrimental effects
a classroom’s volume, geometry, and materials can result on comprehension than on speech recognition. Work has
in overly reverberant conditions that negatively affect the also branched into characterizing how classroom acoustic
speech intelligibility. Sounds produced inamore reverberant conditions influence occupant listening effort or listening
environment will linger longer than in less reverberant difliculty (Howard et al., 2010). Building on this concept,
environments, increasing the overall average noise level Prodi’s research group has focused further on quantifying
within the space. Researchers have investigated the impact “listening efliciency” as a measure of both the accuracy of
of reverberation time on speech intelligibility, often in speech intelligibility and listening effort (Prodi et al., 2010,
combination with varying background noise levels (Bistafa 2013; Prodi and Visentin, 2015).
and Bradley, 2000; Hodgson and Nosal, 2002; Wroblewski
et al., 2012). For a constant signal-to-noise ratio, higher The Arnarican Natinnalstandarda
reverberation times do result in poorer speech intelligibility. Inst'.i1'.uba/ Acoustical Society of Arnarica
Though limiting excessive reverberation is important for S‘l 2.50 Classroom Acoustic Standard
optimal speech intelligibility, Yang and Bradley (2009) I.n 2002, the American National Standards Institute (ANSI)
caution that reverberation should not be eliminated because published the first classroom acoustics standard in the United
early arriving reflections from room boundaries are found States, ANSI S12.60 (ANSI, 2002): Acoustical Performance
to improve intelligibility by supporting the sound energy Criteria, Design Requirements, and Guidelines for Schools.
that arrives directly from the source to listeners. The current standard recommends that the A-weighted

_ _ _ sound level measured in an unoccupied classroom with
Starting in the late 1990s, a growing number of measurement . . .

_ d ‘ k t ‘h t ‘ f I ventilation (mechanical) systems on should not exceed 35
Cunpalgns were “n_ er a m_ _o gauge E S a E 0 C assmofn dB(A) (ANSI/Acoustical Society of America [ASA], 2010).
acoustics. Acoustic conditions were documented in . . .

_ _ 1 h H H d 1999 h 15 Y This standard also states that the maximum reverberation
university “mm a s( 0 gson’ _ )‘ Presc 00 (_ mg time averagedoverthe 500,1,000,and2,000 Hzoctavebands
and Hodgson, 2005), elementary or primary schools (Picard . .

_ should be less than or equal to 0.6 second in classrooms with
and Bradley, 2001; Shield and Dockrell, 2004; Nelson et al., 3 3
an enclosed volume less than 10,000 feet (283 meters ) or
2008), and secondary schools (Astolfi and Pellerey, 2008;

h_ Id 1 fth _ _ _ f d th less than or equal to 0.7 second for classrooms larger than
S _‘e_ et a “d2_0_15)‘ 0 ex:_sbe_mves“gat_‘°ns °_Iml 2]: 10,000 feet’ but smaller than 20,000 feet‘. The first edition
“mung Con mom 1 not 1 1t appropriate Home eve of this standard provided the perceptual, educational, and
and,” reverberation times for Optimal speech intelligibility‘ developmental rationale for the recommended criteria
Recent computational developments in software and as well as the empirical evidence from which the criteria
hardware have led to studies aimed at understanding were derived (ANSI, 2002). The rationale was that verbal
classroom acoustic effects using auralization techniques communication is essential to learning, developing
(Yang and Hodgson, 2006; Hodgson et al., 2008; Neuman et language proficiency, and developing cognitive skills. Verbal
al.,2010;Valente etal.,2012).Auralizationreferstorendering communication can only successfully occur when there
the sound field of a built environment through modeling is a high degree of speech intelligibility. Minimizing the
and simulation. For example, a recording of a teacher’s background noise level and controlling room reverberation
voice can be auralized in different classroom environments helps to create a clear communication channel between

Fall 2013 | Annuslzlcl Tnduy | 15