C. Hinton
Lecture Hall Acoustics
MAE 496
ON LECTURE HALL ACOUSTICS
For an optimal learning environment inside of a lecture hall, sound is no small consideration. Classroom
and lecture hall acoustics have long been studied in an effort to achieve a regularly hearing-friendly class
session. Regulations have been implemented and alleviative measures have indeed been taken – resulting
in an improved modern classroom for the listening student. This classroom, fused with technology and
built with careful engineering, challenges the old wisdom that calls students to “sit in the front of the
classroom” or “get to class early if a seat in the front is desired”.
According to an excerpt on room acoustics consultation, there are three essential elements to consider
when analyzing the acoustics of a room: absorption, reverberation and sound insulation. Because the laws
of physics dictate that sound energy is absorbed, reflected and transmitted when it strikes a wall,
absorption is very significant in relation to the propagation of waves in a room. Reverberation is
described as “the sound persistence due to repeated boundary reflections after the source of sound has
stopped”. Excessive reverberation results in reduced intelligibility of speech in a room by causing overlap
of successive syllables. Likewise, reverberation tends to raise the sound-energy density in the room
undesirably. This unwanted sound, i.e. noise, becomes more audible and is cause for concern. To reduce
the sound that transmits to adjacent rooms, sound insulation is needed. 1
In another excerpt entitled “Instructional Spaces”, lecture halls are described as “audio-visual facilities”.
Present day lecture halls are out-fitted with technology aimed at enhancing the lecture presentation. With
the implementation of microphones and loudspeakers, acoustic problems that do not occur in a natural
setting arise. For example, during question and answer sessions, directional and voice-adjusted
microphones are suggested for use by the students and teacher, respectively. Because few lecturers are
able to speak sufficiently loud in enclosures of more than 50000 ft3 in volume, some limits and
recommendations are presented. In this setting, most cannot produce a sound pressure level of 60 dB or
more for comfortable hearing. When noise is generated by ventilation, cooling fans and other devices, the
un-reinforced speech of the lecturer is even less understood. To alleviate this problem, this excerpt
suggests that audio video enclosures larger than 10000 ft3 should have facilities for amplifying the
lecturer’s voice. Also, the loudspeakers should be located above and slightly in front of the lecturer’s
normal standing position. 2
These aspects considered, an article on classroom acoustics takes the discussion to the next tier of social
satisfaction. Because poor acoustics in educational settings can negatively affect the student’s opportunity
to learn and the teacher’s vocal health, classroom acoustical standards began institution in 1998 by the US
Access Board and the Acoustical Society of America (ASA). This initiative produced what we know
today as the Classroom Acoustics I and II regulation booklets 3. From testing this new use of regulation in
classroom architecture, the two parties found some persistent problems. Though the levels of background
noise and reverberation times in a poor acoustic setting do not affect adults as it does younger, less mature
listeners, all agree that a noisy classroom is an unsuitable learning environment for anyone. The
consensus is that considerations must be taken to maximize speech intelligibility. Recommendations for
architectural annotations are presented, but the article urges educators to take the lead in advocating good
acoustics for the classroom. 4
Not only students, but listeners in general, measure the quality of the particular sound heard by certain
qualitative aspects. An article discussing psycho-acoustic quantities suggests that measures of sound
C. Hinton
Lecture Hall Acoustics
MAE 496
quality such as loudness, sharpness, roughness, and fluctuation strength can be quantified. These and
other psycho-acoustic quantities are used to indicate the pleasantness of speech and music5. Focusing on
these perceived sound quality aspects, the sound quality of lecture halls can be quantitatively and
qualitatively measured. However, the qualitative measurement requires knowledge of human sound
perception. The study of audiology is concerned with the response of the human ear to auditory stimuli,
according to the audiologist’s field guide entitled Audiology. The book explains that the sensation level of
a listener is the observer’s threshold for hearing a sound sensation above 30dB, but it is highly dependent
on the individual’s ability. Because hearing is conducted by air conduction (i.e. by the air to the ear drum
and inner ear) and bone conduction (i.e. by the bone casing of the inner ear causing movement of the fluid
inside the inner ear directly) special care is taken to ensure that both mediums are addressed in speech
recognition6. People who suffer from damage to the ear or undeveloped hearing capability bring an
additional factor in providing proper intelligibility to the learner within a lecture hall setting.
To alleviate this issue for some, the development of cochlear implants provides an avenue of ability for
students with hearing loss or disability. According to an article on regeneration, repair and protection of
the inner ear due to cochlear implants, the purpose of a cochlear implant is to repair a damaged auditory
system as well as regenerate-repair and protect the auditory system. Cochlear implants also serve the
purpose of preserving and restoring the functional elements of the cochlea7. This improvement for the
hearing impaired considered, many in the field of audiology discuss the implications of cochlear implants
in an academic environment. In an article discussing such educational implications, the terms integration,
inclusive education and least restrictive environment are used to describe the growing influx of students
with disabilities into the same classrooms and lecture halls as their peers. The response of educational
institutions was to pursue awareness and development of suitable settings in which these and students
without disabilities could substantially learn. However, this caused strain on educational systems in which
teachers needed extra training or were required to make financial concessions to provide for these
students with disabilities. This paper urges educators and audiologists alike to answer the question of will
there be collaboration or conflict in the future of educational institutions and cochlear implant centers8.
This, of course, is an important issue to address because of the implications (monetary, social, and
political) associated with pursuing an optimal learning environment for as many students as can be
included.
Revisiting the discussion of using loudspeakers or other means of amplification in a lecture hall, the use
of such speech reinforcement (coupled with technological advances in the field of audio) have contributed
significantly to the development of speaker-equipped lecture halls. In an article on implementing a sound
field in large lecture halls, a noted observation is that the placement and orientation of the line of
propagation of a sound field is what determines the student’s ability to hear in a lecture hall setting with
speakers. Also, the placement of the absorption materials in the room is of great importance. This is due
to the fact that the angle at which sound is allowed to reflect from the walls and ceiling of the lecture hall
is determined by this material. The consequences are directly related to the quality of speech intelligibility
9
. In another study on the sound-to-noise ratio in common classrooms, the amplification is found to
improve the audibility of the teacher’s voice by over ten decibels above the noise floor level10. In a similar
study, the speech recognition performance of college students with normal hearing is tested in reference
to the American National Standards Institute (ANSI) acoustic standards11. The results show significant
differences in performance between classrooms with and without amplification. The article concludes that
the ANSI standards are also beneficial for young adult listeners and classroom amplification is a useful
C. Hinton
Lecture Hall Acoustics
MAE 496
tool for improving speech recognition in existing classrooms. These studies will allow for accurate
assessment of existing lecture halls in an effort to compare environments for acoustic quality.
Overall, one can see the need to address the concerns for optimal hearing environments, which is directly
related to the learning environment. The importance of this study is in the fact that it provides reasoning
behind recommendations for access to adequate lecture environments for the hearing impaired and
students in general. In other words, the more that consideration is taken in audibly optimizing the lecture
hall, the better the environment, and in turn the more welcoming is the institution.
References:
1
M. Rettinger, “Room Acoustics,” Acoustic Design and Noise control, 86 – 146, (1973).
2
M. Rettinger, “Instructional Spaces,” Acoustic Design and Noise control, 458 – 464, (1973).
3
S. Reese, “Classroom Acoustics,” Techniques: Connecting Education & Careers, Vol. 83 Issue 8, 8 – 9,
Nov/Dec (2008).
4
Classroom Acoustics Regulations: asa.aip.org/classroom/booklet.html
asa.aip.org/classroom/bookletII.pdf
5
J. Blauert (Editor), “Modeling of Psycho-Acoustic Quantities,” Communication Acoustics, 143 – 150,
(2005).
6
H. Newby, “What and How We Hear,” Audiology, 5 – 29, (1964).
7
H. Staecker and T. R. Van De Water, “Regeneration-Repair and Protection in the Inner Ear: Implications
for Cochlear Implantation,” Cochlear Implants. 17 – 28, (2000).
8
S. M. Archbold, “Educational Implications of Cochlear Implantation – Conflict or Collaboration?”,
Cochlear Implants, 257 – 264, (2000).
9
D. Kahn, “An investigation of sound pressure level predictions in large lecture halls,” J. Acoust. Soc.
Am., Volume 75 Issue S1, May (1984).
10
J. B. Larsen and J. C. Blair, “The Effect of Classroom Amplification on the Signal-to-Noise Ratio in
Classrooms While Class Is in Session,” Language, Speech, & Hearing Services in Schools, Vol. 39 Issue
4, 451 – 460, Oct (2008).
11
American National Standards Institute. “Acoustical performance criteria, design requirements, and
guidelines for schools,” ANSI S12.60-2002, (2002).
12
J. B. Larsen, A. Vega, J. E. Ribera, “The Effect of Room Acoustics and Sound-Field Amplification on
Word Recognition Performance in Young Adult Listeners in Suboptimal Listening Conditions,”
American Journal of Audiology, Vol. 17 Issue 1, 50 – 59, Jun (2008).