IMPROVEMENTS IN ACOUSTIC AND STENTOROPHONIC INSTRUMENTS
Year: 1882

page_text: LETTERS PATENT to Frank Wirth of the firm of Wirth and Company
Patent Solicitors, at Frankfort on the Main, in the Empire of Germany
for an Invention of "IMPROVEMENTS IN ACOUSTIC AND STENTOROPHONIC
INSTRUMENTS A communication from Adolph Rettig, Barrister, à person
resident at Saarbrücken in the Empire of Germany
"
PROVISIONAL SPECIFICATION left by the said Frank Wirth at the Office of
the Commissioners of Patents on the 21st July 1882.
FRANK WIRTH, of the firm of Wirth and Company Patent Solicitors, at Frankfort
on the Main, in the Empire of Germany, "IMPROVEMENTS IN ACOUSTIC AND
STENTOROPHONIC INSTRUMENTS," a communication from Adolph Rettig, Barrister,
a person resident at Saarbrücken in the Empire of Germany,
This invention relates first to speaking and hearing tubes, applicable alone or in
combination with telephones.
The improved instrument consists of two paraboloids cut off near their apex and
connected by a short intermediate tube, so that they have the same axis (of
rotation) and the same focus, but are placed in opposite directions. The plane
cutting off the apex of a paraboloid is perpendicular to its axis and passes between
the apex
and the focus which is thus situated within the cylindrical connecting
tube. The two paraboloids are preferably of unequal size, the larger one being the
speaking tube proper, while the smaller one serves as its mouthpiece. A soft india-
rubber ring encloses the mouth of the tube so as to fit the tube tightly to the mouth
and ear.
Instead of using the smaller paraboloid as a mouthpiece, an ordinary mouth-
piece may be applied to the india-rubber ring. The distance of the focus from the
apex being very small, the paraboloid resembles somewhat a truncated cone and
may be made telescopic. A ring of rigid material may be used in addition to the
india-rubber ring, and if used with telephones the short intermediate tube is made
detachable.
The invention further relates to the acoustic apparatus previously constructed
by the same inventor and consists in connecting the ring which holds the conducting
tube with the needle or pin by means of a movable joint. The invention further
consists in surrounding or coating acoustic apparatus by soft elastic rings with or
without the addition of rigid rings, for the purpose of rendering the sound softer
and more intelligible.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Frank Wirth in the Great Seal Patent Office on the 20th January
1883.
FRANK WIRTH of the firm of Wirth and Company, Patent Solicitors, at Frankfort
on the Main in the Empire of Germany "IMPROVEMENTS IN ACOUSTIC AND
STENTOROPHONIC INSTRUMENTS," a communication from Adolph Rettig, Barrister,
a person resident at Saarbrücken in the Empire of Germany.
A paraboloid (that is to say: a curved surface which may be produced by the
rotation of a parabola around its axis) of considerable axial length, and having its
focus near the apex, is cut perpendicularly to the axis of-rotation so that the focus
is situated between the apex and the plane of section. With this paraboloid is
connected a smaller paraboloid, cut in a similar way and having also a small focal
length, in such a manner, that the foci of the two paraboloids coincide, and their
axes form one straight line. To avoid loss, it is commendable to use a smaller
paraboloid of equal or smaller focal length, than that of the larger paraboloid.
The two paraboloids are connected to each other by means of a short cylindrical
tube.
The common focus of the two paraboloids is therefore situated inside of this
connecting tube, and the larger paraboloid forms the speaking tube proper, while
.the smaller paraboloid forms the mouth piece of the same.
The front-opening of the smaller paraboloid is usually made of such a size as to
be capable of completely enclosing the open mouth or the ear. When used for
speaking the said opening is pressed firmly against the mouth, when used for
hearing it is pressed firmly against the head and over the ear. The front opening
or mouth of this paraboloid is enclosed with a soft india-rubber ring by means of
which the tube is tightly fitted to the mouth and ear, while preventing any pain
which might be caused by pressure.
The apparatus represents at the same time a powerful speaking tube as well as
an effectual hearing-tube and may be used for both purposes in immediate
succession and without alteration.
The concentrated pressure of the sound-waves proceeding from the mouth, upon
a quantity of air enclosed in a long and narrow tube (which sound waves, being
unable to escape at the rear, can only act in a forward direction) and the effect
depending on these conditions, are the same in the present apparatus as in ordinary
conical speaking tubes.
As
Owing to its peculiar construction the present apparatus, however, produces such
a strong sound and forcing power in a straight direction towards the place of
destination which is not to be obtained by the usual conical speaking tubes.
'the mouthpiece in this case forms a paraboloid, the sound-waves arrive from this
parabolic mouth piece with increased power at the focus which it has in common
with the speaking tube proper, and where they are concentrated into extraordinary
strength. From this focus they are thrown out towards the place of destination,
without dispersion, in a straight line and parallel to the axis, while this is only
partly the case in the conical speaking tubes according to the law of reflection of
the cone.
For ordinary portable speaking tubes a parabolic mouth piece of medium
axial length is to be recommended owing to its handiness. If manual use is not to
be taken into consideration, for instance in the case of a speaking tube mounted on
a fixed stand, the size of the parabolic mouthpiece may be increased at will and the
acoustic effects of the speaking tube increased in proportion. If in this case the
front aperture of the parabolic mouthpiece is larger than required to cover the
mouth and ear a truncated hollow cone of suitable form or a second paraboloid cut

page_text: off near its apex and the focus of which lies between the apex and the plane of
section, is joined by its front aperture to the said parabolic mouth piece.
The opposite aperture of such joint or prolongation is made of the required size
and enclosed with a projecting soft indiarubber ring in the manner already
described. For the purpose of speaking a mouthpiece of the ordinary kind may be
applied to the parabolic mouthpiece or to its prolongations. Such a mouth piece
may be easily and rapidly joined to the indiarubber ring for the purpose of
speaking while it may easily and rapidly be removed when the apparatus is to
serve as a hearing tube, the usual mouthpiece not being adapted for the purpose of
hearing owing to its shape. An ordinary mouth piece only, such as generally
used, may evidently be joined to the speaking-tube proper which, however, is less
advantageous because in this case the strengthening of the sound by the parabolic
mouthpiece is omitted, the sound-waves do. not all pass through the focus, and
consequently they do not all issue from the tube parallel to the axis.
Paraboloids of small focal length are specially adapted for speaking tubes. For
instance a paraboloid having a focal length of 1 millimetre and an axial length of
2.5 metres has a front aperture of only 0.20 metres diameter.
2 Metres is usually
a sufficient length for a speaking tube. If the apparatus is made of steel, which
allows of a thickness of the walls of 0.5 to 075 millimetres, the apparatus may be
made very light which is desirable for portable speaking tubes. Both paraboloids,
namely the speaking tube proper and the parabolic mouthpiece, may be made of
several joints similar to telescopes. If the apparatus is to be used only as a
speaking tube, the short cylindrical connecting-tube between the speaking tube
proper and the parabolic mouthpiece is screwed off and a conical conducting-pipe is
joined to the speaking tube proper. To this conducting pipe is fitted an india-
rubber pipe provided, with a terminal or ear-piece, as generally used in my acoustic
apparatus. Or a conical conducting tube may be joined to the front-opening of the
parabolic mouth piece of its (parabolic or cylindrical) prolongation, and the
arrangement otherwise completed in the same manner.
In a similar manner the parabolic mouth piece may be used alone as a hearing
tube. Each end of a telophonic line may also be provided with a complete apparatus
or only with a speaking-tube proper, or with a parabolic mouth piece, and all special
devices herein before described and serving either for hearing or for speaking may
be applied to the telephone in a suitable manner, by which means the effect of the
telephone may be considerably increased. If only the speaking-tube proper is to
be applied to the telephone transmitter, the short connecting-tube between the two
paraboloids is made moveable, or detachable.
The accompanying drawing illustrates the construction of the apparatus. The
invention also consists in an improvement in the appliance for holding the terminal
or ear piece of the conducting tube of acoustic apparatus in the desired place,
which appliance is described in the specification of an earlier British Patent
(No 1972, dated 6th of May A.D. 1881).
The ring holding the conducting-tube is connected with the needle by means of
a link, whereby the facility of placing and holding the terminal of the conducting
pipe in any desired position is increased. The invention further consists in a
method of avoiding or removing disturbing sounds (resonance) in acoustic apparatus.
For this purpose the said apparatus are enclosed or lined with soft elastic rings; for
instance of india-rubber.
By this means the sound becomes more smooth and less irritating, without losing
strength, and what is still more important, the words spoken into the apparatus
become thereby more intelligible. The proportion of the surface to be thus enclosed,
depends on individual requirements.
Soft india-rubber rings with walls about millimetres thick are very useful.
It is advantageous to lay around the soft elastic rings auxiliary rings of more solid
material, for instance leather or metal.
These rings are made capable of being tightened more or less as occasion may
require

page_text: described.
2. The improvements in the appliance for maintaining the terminal of the
conducting-tube of acoustic apparatus, at the desired place, substantially as
described.
3. The method of removing the disturbing sounds (resonance) of acoustic
apparatus, by lining or enclosing them with soft elastic rings, with or without the
application of auxiliary rings of more solid material, substantially as described.
In Witness whereof I, the said Frank Wirth have hereunto set my hand and
seal this sixteenth day of January A.D. 1883.
TO