Much concern has arisen in late years in the minds of architects
because of the faulty acoustics that exist in many auditoriums. The
prevalence of echoes and reverberations with the consequent difficulty
in hearing and understanding on the part of the auditor defeats the
purpose of the auditorium and diminishes its value.
The Auditorium at the University of Illinois presents such a case. The
building is shaped nearly like a hemisphere, with several large arches
and recesses to break up the regularity of its inner surface. The
original plans of the architect were curtailed because of insufficient
money appropriated for the construction. The interior of the hall,
therefore, was built absolutely plain with almost no breaking up of the
large, smooth wall surfaces; and, at first, there were no furnishings
except the seats and the cocoa matting in the aisles. The acoustical
properties proved to be very unsatisfactory. A reverberation or undue
prolongation of the sound existed, and in addition, because of the
large size of the room and the form and position of the walls, echoes
were set up.
If an observer stood on the platform and clapped his hands, a veritable
chaos of sound resulted. Echoes were heard from every direction and
reverberations continued for a number of seconds before all was still
again. Speakers found their utterances thrown back at them, and
auditors all over the house experienced difficulty in understanding
what was said. On one occasion the University band played a piece which
featured a xylophone solo with accompaniment by the other instruments.
It so happened that the leader heard the echo more strongly than the
direct sound and beat time with it. Players near the xylophone kept
time to the direct sound, while those farther away followed the echo.
The confusion may well be imagined.
Thus it seemed that the Auditorium was doomed to be an acoustical
horror; that speakers and singers would avoid it, and that auditors
would attend entertainments in it only under protest. But the apparent
misfortune was in one way a benefit since it provided an opportunity
to study defective acoustics under exceptionally good conditions
and led to conclusions that not only allowed the Auditorium to be
improved but also indicate some of the pitfalls to be avoided in future
construction of other halls.
[Illustration: FIG. 2. PHOTOGRAPH OF INTERIOR. VIEW OF STAGE.]
[Illustration: FIG. 3. PHOTOGRAPH OF INTERIOR. VIEW TOWARD BALCONY.]
An investigation of the acoustical properties of the Auditorium was
begun in 1908 and has continued for six years. It was decided at the
outset not to use “cut and try” methods of cure, but to attack the
problem systematically so that general principles could be found, if
possible, that would apply not only to the case being investigated but
to auditoriums in general. This plan of procedure delayed the solution
of the problem, since it became necessary to study the theory of sound
and carry out laboratory investigations at the same time that the
complex conditions in the Auditorium were being considered. The author
spent one year of the six abroad studying the theory of acoustics and
inspecting various auditoriums.
The main echoes in the Auditorium were located by means of a new method
for tracing the path of sound, the time of reverberation was determined
by Sabine’s method, and a general diagnosis of the acoustical defects
was made. Hangings and curtains were installed in accordance with the
results of the study so that finally the acoustical properties were
improved.
_Acknowledgment._--The author desires to express his great appreciation
of the advice and encouragement given by President E. J. James,
Supervising Architect J. M. White, and Professor A. P. Carman of
the Physics Department. He desires also to acknowledge the material
assistance cheerfully rendered by the workmen at the University, which
contributed in no small degree to the successful solution of the
problem.