A Method and Apparatus for Precisely Determining the Direction of a Sound Signal, whether in the Air or in Water.
Year: 1897

page_text: A Method and Apparatus for Precisely Determining the Direction
of a Sound Signal, whether in the Air or in Water.
I, EDOUARD HARDY of Dreux, department of Eure and Loire France, Physicist. do
hereby declare the nature of this invention to be as follows:-
The method and the apparatus I have invented to ascertain the exact direction
from which a sound proceeds, are based on two simultaneous observations of a sound
signal which are so planned that the vibrations of the two observations meet at one
point in a curved tube, designed for this purpose, before reaching the listener's
ears.
Two acoustic-trumpets, receivers of the sound signal, are fixed one within the
extension of the other, or parallel to each other, at a certain distance. They are so
arranged that they can turn round a central axis, or any other means may be adopted
to enable one of the trumpets to be turned towards the sound while the other turns
away from it.
"
When the sound comes from any distance in a line perpendicular to the two
or "mouths" of the
trumpets and passing through their axis the two "bells
trumpets are at an equal distance from the sound-signal. Consequently they are
These half-waves
reached simultaneously by the same portions of the sound waves.
unite, as has been remarked, and, combining with one another, convey to the
listener's ear the phonetic signal in all its intensity.
One
The listener will then turn the whole apparatus round, upon its central axis.
of the trumpets is thus directed towards the signal or sound, while the other is turned
away from it. There comes a moment when the difference between the two distances
of the phonetic signal from the "bells" or "mouths" of the trumpets are equal to
half a length of the sound-wave proceeding from the signal. Then, those are half
waves of opposite designations which strike on the "bells" or "mouths" at the same
moment and which unite in the common tube. These half waves interfere with and
destroy each other mutually, so that the sound-signal is interrupted, or at all events
the merest minimum reaches the listener's ear.
The listener then turns the apparatus the opposite way, and finds another point at
which the signal is interrupted in the same way or reaches him only with very
0 minimised intensity.
Now the direction of the phonetic or sound signal will be found to be exactly on the
bissector of the two observations giving a minimum effect.
It is necessary that the hearing or acoustic trumpets and the acoustic tubes,
through which the vibrations reach the ears of the listener should be of equal length,
5 in pairs so as not to cause any disturbance or confusion of the phenomena.
1
11:.00d doy of January 1897.

page_text: A Method and Apparatus for Precisely Determining the Direction
of a Sound Signal, whether in the Air or in Water.
I, EDOUARD HARDY of Druex, department of Eure and Loire, France, Physicist
do hereby declare the nature of this invention, and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
The present invention consists of an apparatus serving to ascertain the direction of
a sound signal, thus removing one of the greatest difficulties which navigators meet
with in foggy weather and avoiding their fouling through uncertainty about the exact
direction to be attributed to a phonetic signal.
The principle of the apparatus is based on two simultaneous observations of the
sound vibrations, by making use of the interferences of the sound waves.
The annexed drawing which is given as an example, represents a form of the
apparatus. In this drawing:
Fig 1 shows a vertical section of the apparatus.
Fig 2 gives a side elevated view of the same apparatus.
This is composed of two rigid and parallel bars A, B rigidly connected by three
small crosspieces, two of which fixed at the extremities of the bars, are not visible in
the drawing and the third occupies, at X, the centre of the two bars.
This rigid
structure of the two bars is intended for two slides Y and Y¹ which slide
longitudinally between these two bars. We may also make use of one bar only upon
which two suitable slides work.
In any case, the two slides bear the ear-trumpets E, F. This slide frame allows
the ear-trumpets to be suitably separated.. The double-bar A has its middle part
fixed on a tube or hollow axle C, D dividing at its upper end into two tubes G, H
which communicate with the end of the trumpets E, F by flexible acoustic
tubes a, b which have exactly the same length.
The hollow-axle C, D can turn with the top bar to which it is fixed; for this
purpose, it is guided by the bearing I of a vertical pedestal fixed to the body of the
apparatus, and at its lower part, it forms a pivot in a fixed tube J, K of the same
interior diameter as the exterior diameter of this tube C, D. This tube J, K
possesses at K, two branchings L, M with which two flexible acoustic tubes €9 d are
connected and which are applied to the observer's ears.
The observer can turn the tube C, D on its axis by means of a hand wheel N
wedged upon it or by any other arrangement producing the rotation of the
axle-tube C, D without noise.
By means of a transmission of movement by the cog-wheels O, P, Q, or by any
other suitable arrangement, the axle C, D controls a hand R in its movement in a
horizontal plane, in such a way that each turn of the axle C, D produces a revolution
of the hand R in this horizontal plane, the rotations of the axle C, D and of this
hand being in the same direction.
The hand R marks its position upon a fixed divided and horizontal circle S placed 4
before the observer: this direction indicated by the hand is consequently, at each
moment that of the top bar A. If the distance between the trumpets E, F is equal
to half the length of the sound wave produced by the phonetic signal, which distance
we can easily obtain, as will be seen hereafter, and if the observer moves the turning
system already alluded to, he will remark, by applying the ends of the acoustic
tubes C, d to his ears, the following facts :
Each time the bar A, in its circular movement, is perpendicular to the direction of
the sound ray, the two ear-trumpets receive at the same time, the same portions of

page_text: the sound waves which, uniting in the central tube C, D, J, K get mixed together
and consequently the observer has the sound of the phonetic signal in all its intensity.
Each time the bar A is placed in the exact direction of the sound ray, the trumpets
no longer receive the same portions of sound-waves at the same time. If, for
instance, they are the condensed semi-waves which penetrate into the trumpet E, it will
incontestably be the dilated semi-waves that will penetrate at the same time into the
trumpet F these semi-waves positive and negative, meet in the central tube C, D, J, K
come into collision and destroy each other in it so that the sound of the phonetic
signal ceases to be heard by the observer, or at least is considerably weakened.
During a complele rotation of the apparatus the observer notices two maxima and
two minima of intensity: the direction of the two minima is that of the sound ray.
If the distance between the two ear trumpets were greater than the semi length of
the sound wave of the signal, more than two maxima and two minima for every
rotation would necessarily be produced. In this case, therefore, the trumpets must
be drawn nearer each other until only two maxima and two minima per rotation are
perceived: the separation between the trumpets is then suitable for observations.
To quickly determine the position of the two minima, it is well to place around
the divided circle S another circle not indicated in the drawing which is movable
around the centre of S, bearing two diameters traced perpendicular to each other one
of which is marked very broad. During the observation this movable circle is turned
the other diameter then
until the latter diameter coincides with the maxima ;
corresponds with the minima and gives the apparent direction of the phonetic signal
observed.
The observe can, if he desires, determine still more exactly the position of the
minima, by simply making the apparatus oscillate to the right and left of the minima
to be observed: he easily perceives at each side a point where the sound of the signal
weakens or changes, he notes these two points on the divided circle S and the bisector
of these two observations is the position of the minima required, that is to say, the
apparent direction of the phonetic signal with an approximation of 1 to 3 degrees.
The acoustic tubes c and d are supported by a pivoting device fixed to the body of
the apparatus, and composed of two small axles m, n turning in supports fixed to
the frame of the apparatus, and to which axles two hooked arms g, h are fixed,
turning with them; these hooked arms are also fixed to the acoustic tubes c, d at a
certain distance from the free extremities of these tubes; a spring p continually
draws the hooked arms towards each other; this arrangement keeps the ends of the
acoustic tubes to the ears, and consequently enables the observer to make use of his
hands to work the apparatus. By making the tube C, D of a certain length so that
there might be a sufficient distance between the bearing I and the slide-bar A, the
ear-trumpets E, F can be reversed in such a way that their opening will be turned
downward. (In the annexed drawing this mouth is turned upward). This new
arrangement has the advantage of preventing the rain or snow from getting into the
trumpet.
We can also arrange the ear-trumpets horizontally: their mouths are then better
placed to receive the sound waves which come almost horizontally.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is―
1. A process for determining exactly the direction of a phonetic signal which
consists in taking two simultaneous observations of the sound vibrations which are
brought to a collision to obtain two minima which will indicate the direction of the
sound.
2. An apparatus for exactly ascertaining the direction of a phonetic signal,
distinguished by a central tube which can turn around its axis receiving the sound
waves by two tubes communicating with two ear-trumpets, there waves coming into
5 collision in the central tube, according to the position of the bar, upon which the
ear-trumpets are fixed with relation to the direction of the sound waves.

page_text: 3. The pivoting device keeping the acoustic tubes to the ears of the observer
allowing him to make free use of his hands for working the apparatus.
4. In an apparatus claimed in 1, the experimental method described for ascertaining
the position of the minimum of intensity perceived by the operator by making an
operation to the right and another to the left of this minimum, the bisector of these
two observations giving exactly the position of the minimum, that is to say, the
direction of the sound-rays.
5. A method and apparatus for precisely determining the direction of a sound
signal substantially as described and shown."
This 20th day of October 1807