Device for Measuring Sound in Airplane Engines Page: 2 of 6
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS.
TECHNICAL MEMORANDUM NO. 266.
DEVICE FOR MEASURING SOUND IN AIRPLANE ENGINES.*
By T..Rob ovsk .'
Nearly all airplane and engine constructors have experimented
with devices for diminishing the noise of engines. Various types
of silencers (Schneebeli, Ad Astra, Skribechk, etc.) have been
tried with fairly satisfactory results.
Since, however, this problem has not yet been perfectly
solved and endeavors to invent good silencers are being continued,
I will here call attention to a device, constructed according to
the system of Gati, with which it is possible to measure the
sound of an engine and test the effect of a silencer.
Fig. 1 gives the sound diagram for an automobile engine.
It shows large oscillations, because the engine had been much used.
Fig. 2 gives the diagram for an ai-rplane engine. It may be
seen that the sound of the la-ter is rather musical, its frequency
being about 1800. In this figure, the upper curve is the sinu-
soidal curve corresponding to an alternating current with a fre-
quency of 42 per second. The diagram was obtained as follows:
A microphone was placed on an elastic mass near the engine.
The primary current was transformed with an ordinary telephone
induction coil. The secondary current was conducted through an
oscillograph which rendered it possible to photograph the record
shown in Fig. 2.
* From "L'Ala d'Italia," March, 1924, p.70.
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Robrovsky, T. Device for Measuring Sound in Airplane Engines, report, June 1924; (https://digital.library.unt.edu/ark:/67531/metadc277468/m1/2/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.