Harrisburg telegraph. [volume] (Harrisburg, Pa.) 1879-1948, 1916-04-10
BY a Member of Engineers Society
PENNSYLVANIA.


Pennsylvania.
Do you remember when you were
youngster how you shouted down the
cistern and how your voice came back
as IL from fairy with pair of lungs
stronger than your own?
Perhaps you have gone into a great
empty hall and accidentally allowed
ber how the place became filled inn
mediately with n roar of sound, how
doors seemed TO slam from all direc-
tions at once until the noise was deaf
ening? You had to wait until the
noise quieted down.
What actually happened was that
the sound waves from the slamming
door, travelling at the prodigious speed
of $50 miles an hour, struck the walls
and roof of the enclosure, rebounded,
and were reflected again and again
until they were finally lost; scientists
say hcanged into heat.
Sound Control a Science
It is popularly supposed that audi
bility in an auditorium is beyond the
ken of science-a matter of mere
chance. However, 1t has been demon
strated by laborious scientific expert
ments during the past Is years that
the action of sound in enclosed spaces
conforms to definite laws which de-
pend solely on the form of enclosure
and the materials used in its construc-
ton. According to Dayton c. Miller,
professor of physics, Case School of
Applied Science, and a recognized au-
thority on sound. the acoustic proper
ties of any structure may be definitely
ascertafned before a single building
stone is laid. He advises expert advice
in planning all such structures.
Failures and Successes.
y striking example of defective
acoustics in a civic building is the new
San Francisco convention hall, which
has a capacity of $4,000. 1t is a con-
crete building of imposing appearance,
but on account of reverberations due
to defective interior design, it is i'm
possible to listen with enjoyment to a
discourse held in it.
Most HarrisburgerS know how easy
it is to hear the speaker in the House
of Representatives in our own Capitol.
though it is said that the speaker on
the roStrum cannot hear quite as well
n person speaking from the floor.
An amusing incident caused by de-
fectiNe acoustics took place at con-
cert held in the Convention Hall of the
University of Illinois, during a xylo-
phone solo. The orchestra leader
heard the echo more strongly than the
instrument itself, and beat time with
1t; the resulting confusion may be
A1AAoclAAtbs k1lllNt lIOll. Tue tCllO6S III
this building have been reduced by
use of wall hangings.
Notable among those structures
which have fine acoustics is the Hill
Auditorium of the University of AIichi-
gan, seating over 5000. The Boston
Opera House, built after consultation
with experts. is an equally fine exam
pie of the application of the laws of
sound to architecture. The Mormon
To harm pla af al
5000. has long been famed as the
place one may hear the pin drop"
at a distance of 200 feet.
How Sound Acts
In order to understand how sound
acts, we must first know what sound
is. Simple experiments show that
sound is merely air set in motion by Il
vibrating object. Not only do these
air movements radiate from the source
as ripplos, on the Surface of pond
spread outward when a stone is
thrown in, but the form of the air
waves themselves is very similar to
those in the water. 1t is these sue
cesSive condensations and rarefactions
in the atmosphere, analogous to the
crests and troughs of water waves,
which produce on the ear the effect we
call sound. The ear is not tuned to
receive all sounds; hence those deep
sounds which have less than 80 waves
or vibrations per second, or those very
high-pitched sounds having more than
10000 cannot be distinguished.
y legion of factors enter into consid-
erations of building design by the
acoustic engineer. In order that hear
ing be good in any room, the sound
must first of all be loud enough This
is commonly obtained by elevating the
speaker, and at the same time, rails
ing the rear seats which gives tha air
vibrations an opportunity to radiate
to those in back instead of being en-
tirely absorbed by the audience close
at hand.
The walls must be so placed that
successive waves of sound rejecting
from them do not interfere" with