Daily Kennebec journal. [microfilm reel] (Augusta, Me.) 1870-1975, 1912-01-26
WHEN SOUND MAKES SILENCE,
Professor Sabine Gives an Interesting
Lecture on Architectural Acous-
tics"


Two paradoxes and the exemplfication
of one of them, formed the bulk of lee
ture of Professor Wallace c. Sabine In
his Lowell Institute course on "Architcc-
tufal Acoustics. One of these puzzles
is that two sounds may make h silence
and the other that rugs result in the in
crease of sound in a room. although ma
terial of that nature had in the previous
lectures been noted as absorbent.
The first phenomenon is that termed
interference, which was easily studied in
the Orient in a consideration of why at
point on the shore of the China Sea
there Were no tides. The reason for this
is that the tidal wave enters the sea by
two routes One of the ways is broad
and the other narrow and congested with
Islands, The result of the combination
is that the movement of the water is de-
layed in the narrower entrance Just six
hours, so that when it would be high tide
by the direct wave it is also low tide by
the delayed wave. The two neutrallze
and consequently there is no tide at all
In similar way the waves which pro-
duce sound may be so affected in their
progress by obstacles or reflections, that
wave length apart, in which case they
produce silence. The point was admir-
ably illustrated by means of the sensi-
tive flame. which is greatly affected by
the sound of Kisses. sibilants and
whistles. But by judicious reflection of
the sound the whole audience could see
that the flame, while normally keenly
sensitive TO the whistle, lost that sensi-
Election. although the audience conld hear
the whistle equally we'll all the time. In
reference causes local spots of deafness
that in practice are to be found in some
halls, in which it is impossible TO hear
what the speaker may be saying.
The ingenious and careful way in which
Professor Sabine has made experiments
regarding this phenomenon of interfer-
ence is interesting. 1t consisted in the
determination of the acoustic conditions
of practically every point of a rectangu-
lar room with a barrel roof. A means of
producing sound was installed centrally
in the room near the floor and a tele-
phone was arranged on an arm revolving
horizontally in the room, the tele-
phone being so arranged that there was
a continual take-up In its movement, so
that at the end of the experiment it had
described spiral extending from the
outer walls to the centre. a continuous
record was made by the telephone APP
paratus, which ingeniously, through the
magnetic currents set up in it by the
sound, agitated platinum thread in the
field of powerful magnet, the vibrations
of which caught by the sensitive photo
graphic film, presented the perfect acous-
teal picture of the room.
1t was most surprising in the way in
which adjacent places varied in the
amount Of sound reaching them, which
ranged from actual silence to well de-
fined maxima, The charting of the
points of equal intensity made interest
ing diagrams suggesting to those famil-
lar with contour maps. which they much
resemble, regular and pleasing land
scape work with symmetrical hills and
valleys. BY means of the rotating device
it was possible to determine the acous-
teal rating of all the points in the room
at any desired level.
With reference to the rugs, which usu-
ally absorb sound the explanation was
more difficult to follow. 1t involves ques-
tons of the relationships of sources of
sound to the reflections of their own
sounds. which come back to them and
under certain time relations actually re-
enforce the original sound. The tele-
phone measured the intensity of the
sound everywhere and recorded it, so
that there can be no question as TO the
validity of the observations. With few
| observations on echoes and whispering
galleries and the promise of the suSges-
| tion of the practical application of the
principles enunciated to be set forth in
the next address the lecture closed.-Bos-
ton Transcript.