Absorption. The loss of energy by a sound
wave when it strikes an obstacle which
does not reflect it completely.
Alternating current (A C). Electric current
which flows first in one direction and then
in the other.
Amplifier. A device which builds up a weak
electric current into a stronger one.
Amplitude. The maximum extent of a vibrating movement. With sound, the greater
the amplitude, the louder the sound.
Attenuation. The weakening of a sound
wave as it travels, caused by losses due to
friction, absorption, and scattering.
Audio frequency. Another-term for sonic
frequency; that is, below 15,000 cycles per
second. Compare Radio frequency.
Audio-frequency-amplifier. An amplifier
for use with alternating currents of frequencies less than 15,000 cycles per second.
Background noise. Noise that tends to mask
the sounds you want to hear. Chiefly water
noise and noise from the receiver itself.
Band filter. An audio filter which suppresses all frequencies except those between a given high and low limit. For
example, the band filter on the WCA gear
suppresses all frequencies below 600 cycles
and above 1,000 cycles.
Beam. A cone of sound waves, such as is
used in echo-ranging. Normally, a beam
can be obtained only by using supersonic
Beat frequency. The frequency obtained
by mixing two different frequencies. For
example, by mixing 60,800 and 60,000 cycles,
we obtain a beat frequency equal to their
difference of 800 cycles. This is called
Cavitation. The formation of a series of
vacuums when propellers are turning so
rapidly that the water does not flow in
immediately as the blade passes through.
Propeller noise is greatly increased when
Compression. The part of a sound wave
where the particles are packed together
more closely than normal.
Cycle. A complete sound wave compression-plus-rarefaction.
Decibel. A unit of measurement of intensity of sounds.
Detector. Generally, anything that enables
sound to be heard; e.g. the ear. Specifically,
in the receiver-amplifier, the detector mixes
two supersonic frequencies to give a frequency that can be heard. Also called a
Diffraction. The tendency of sound waves
to bend around an obstacle in their path
and meet somewhere beyond. This accounts
for your being able to hear sounds around a
corner. (Do not confuse with "refraction.")
Direct current (DC). Electric current that
flows continuously in the same direction.
A storage battery gives direct current.
Driver. An electrical device used to send
a burst of supersonic sound (ping) into
the water by means of the projector. In
the WCA gear, there are a QB and a QC
Frequency. Number of cycles per second.
Gyrocompass repeater. A device which repeats the movement of the master gyrocompass. The inner dial on the bearing
indicator is a gyrocompass repeater dial.
The main gyrocompass on a submarine is
in the control room.
Heterodyning. The mixing of two frequencies to obtain the beat frequency, which is
the difference between them.
Homogeneous water. Water in which the
temperature does not change with depth.
Hydrophone. Any device for picking up
sound waves from water. It is called a projector only when it also sends sounds out
into the water.
Intermediate frequency (IF). The frequency into which the energy entering the
superheterodyne receiver is converted in
the intermediate stage. In WCA gear, this
is 60 kilocycles.
Isothermal. Uniform in temperature. Homogeneous water is isothermal.
Kilocycle (kc). One thousand cycles.
Magnetostriction. Change in size of a metal
tube when subjected to an electric current.
This principle is used in the JP hydrophone and in the QC and NM projectors.
Modulator. A device which causes a sound
to change in pitch continuously. Sometimes
used by surface ships in echo-ranging,
when an echo is difficult to distinguish.
Negative thermal gradient. Decrease in
temperature of water with depth.
Noise level. The volume of background
noise heard in the headphones or on the
Oscillator. A device that produces an alternating current at a particular frequency.
Piezoelectric effect. The development of
an electric current when a Rochelle salt
crystal changes in size. This principle is
used in JK and QB projectors. Compare
Positive thermal gradient. Increase in
temperature of water with depth.
Projector. The hydrophone portion of QC,
QB, and NM gear. Although called a "projector," in submarines it is principally used
to pick up sounds. In echo-ranging, it projects the ping into the water.
Quick beating. Bearing of the maximum
loudness in sweeping across the target.
Also called "Maximum bearing."
Radio frequency. Frequency above 15,000
cycles per second, Compare Audio frequency.
Radio-frequency amplifier. An amplifier
for use with alternating currents of frequencies higher than 15,000 per second.
Range rate. The rate in knots at which a
target's range is changing. Useful in determining the speed of the target.
Rarefaction. The part of a sound wave
where the particles are thinned out to less
than normal density.
Resonance. The tendency of an object or
an electrical circuit to respond well to a
particular frequency, but poorly to other
Reverberations. The multiple echoes reflected from the surface, bottom, and many
small irregularities in the water. In echo
ranging, distinguished from the echo, which
comes from the target.
Salinity. The saltiness of water. Normal
salinity of sea water is 35 parts of salt
Scattering. The loss of energy by a sound
wave caused by its striking such irregularities in the water as seaweed, fish, and en
trapped air bubbles.
Screen. The antisubmarine escort craft
which are protecting a convoy.
Sonic frequencies. Frequencies less than
15,000 cycles per second.
Sound shadow. The region beyond an obstruction where a sound is not heard. See
Split bearing. A bearing obtained by computing the middle point between where the
signal comes in and where it goes out in
sweeping across the target. Split bearings
are used only when quick bearing cannot
Sweeping. Turning the projector or hydrophone so that it goes through the entire
arc of the target's propeller sounds.
TDC. The Torpedo Data Computer-a
device in the conning tower which figures
out the correct firing data, using the facts
of bearings, ranges, course, and speed.
Transducer. The technical term for what
is generally called a "projector." A transducer operates both as a hydrophone (picking up sound vibrations and converting
them into electric current pulses) - and as
a projector (transforming electric current
pulses into sound vibrations and projecting them into the water).
Vibration. A continuous back - and - forth
movement, producing sound waves in the
Wake. The ribbon of churned-up water
astern of a moving ship or submarine. It
consists of small currents, eddies and entrapped air bubbles.
Wave length. The distance from a given
point on one compression to the corresponding point of the next compression
of a sound wave.