Evening star., 1923-10-20
Study PROBLEMS
OF SOUNDPROOF|NG.
Experimenters at University
of Illinois Discover New
Principles.

A study of the problem of making
partitions sOundproof has been made
by the engineering experiment sta
ton of the University of Illinois at
.Urbana.
Because certain principles of sound
ttons that would ordinarily be an eff
fectivs barrier to sound occasionally y
fail to function.
:. Sound may be transmitted from
one side of a partition to the other in
three ways. 1t may progress through
continuous air passages, 1T may pass
as an elastic wave through the solid
structure of the partition or by set
ting the partition in vibration 1t may
originate sound waves on the further
side" says q bulletin reviewing the
study of the subject of soundproof
partitions at the experiment station.
Composition Of Sound.
These actions are quite readily
understood, continues the bulletin.
ny remembering that sound consists
or series of ComprcsSionS and rare
factions that progress rapidly through
a medium without interruption un-
less they meet new medium with a
dIferent elasticity or density. For
instance, sound waves in air proceed
without hindrance through air pas
saSes, such as ventilation openings in
partitions. If, however. the passages
case OF porous material, the progress
IS hindered and certain amount of
absorption of the energy takes place.
due to the friction set up between
the vibrating air column and the
sides of the pores.
In case the partition is impervious
TO air the direct progress of the air
waves is interrupted. A third partition
Is set In vibration and thus originating
new waves on the side opposite the in
cldent sound. For thicker, more rigid
partition the vibrations are smaller and
a very considerable part of the energy
Is reflected. The transmission in this
case takes place by congressional
waves communicated to the solid mate
rial of the partition. The amount of
small.
Effective SOundprooffng.
I'm view of these considerations a
soundproof partition should be as rigid
and tree from air passages as possible.
For effective Soundproofing of a group
of rooms, the partitions. foors and CELL
ingS between adjacent rooms should be
made continuous and rigid. Any nee
essary openings for pipes. doors, win
dows and ventilators should be placed
in outside or corridor walls where a
leakage OF sound will be less OBJ
jectionable.
SIN case the sound Is generated in
set up by a motor bolted to the floor
the congressional waves proceed
through the continuity of solid ma
tertals. In order to stop them it is
necessary to make a break in the
structure, so as to interpose a new
medium, differing in elasticity and
density. For instance. the vibrations
of motor may be minimized by
placing layer of hair felt or SINH
lar air-filled material between the
supporting base and the floor Where
the machine is quite heavy. footings
may be made of alternate layers of
asbestos. lead and leather. Boiling
through this material will reduce
the Insulation, because the vibrations
in this case will pass easily through
the bolts to the floor. The Insulation
should thus be left without any
bridging over of the discontinuities.
Air gaps in masonry will be effective
if the air space is not bridged over
at any point. a floor fioated on
sand. sawdust or hairfelt would ap-
proXimate this condition. The edges
OF the floor should be insulated from
the walls by felt or similar material.