An Electric "Hooter" or Loud Sound Producing Apparatus.
Year: 1891

page_text: Date of Application, 7th Apr., 1891-Accepted, 4th July, 1891
An Electric "Hooter" or Loud Sound Producing Apparatus.
We HENRY ALFRED CHARLES SAUNDERS, and ALFRED CHARLES BROWN,
both of No. 50 Old Broad Street, in the City of London, Electricians, 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:
This invention has reference to apparatus for producing, by means of the
electromagnetic vibration of a diaphragm, a very loud sound capable of use for
various signalling and other purposes, for instance, in those places where a steam
whistle, bell, horn, siren or detonating signal is at present employed.
Various instruments, known as electric "buzzers" or vibrators, have heretofore
been made, but in practice it has been found that where the diaphragm of such
instrument has been made beyond a certain small size it has not given any sub-
stantial increase of sound in proportion thereto.
To remedy this defect, and to effect other improvements, and to produce an
apparatus capable of emitting a very powerful, intense and piercing sound, are the
objects of our invention.
In the instruments for producing sound by the electromagnetic vibration of a
diaphragm heretofore made, the diaphragm has been clamped or held in a simple
ring with bridge to carry the electromagnet, or clamped over a chamber which is
not airtight thus allowing access to the outer air on both sides of the diaphragm.
Our improvement in this direction consists in causing such diaphragm to form one
side or wall of an airtight or nearly airtight chamber over which it can vibrate.
By this means the sound is greatly increased and we find that the diameter of the
diaphragm may be considerably enlarged without preventing its effective vibration.
Consequently an increase in the diameter of the diaphragm is accompanied by a
proportionate increase in its sound-producing power.
We will proceed to describe our invention by reference to the annexed drawings
in which,
Figure 1 shows a front elevation,
Figure 2 a transverse section through the line c, y, and,
Figure 3 a back elevation, of an apparatus made according to our invention.
Figures 4 and 5 are diagrams showing the electrical connections of such
apparatus.
We construct a frame, preferably of metal, in two portions, A, and, B Sheet 1.
The front portion, A, has preferably a trumpet-shaped opening, b, and may be
provided with a bridge, c, rigidly affixed to it, or forming part of it, for the
purpose hereinafter mentioned. The rear portion, B, is preferably shaped out in
the centre as at, d. To the inner side of this latter portion is attached an electro-
magnet, C, to which a diaphragm, D, is opposed. We prefer to make this
diaphragm of thin sheet iron but it may be made of other suitable metal, or mica
or other similar substance in which latter case an iron armature is attached to it
opposite the poles of the electromagnet. If the diaphragm is not made of metal
a thin metallic strip, wire spiral, or other means (not shown in the drawing) must
be used to electrically connect a platinum contact carried by the diaphragm with
the frame of the instrument. The two portions, A, and, B, of the frame are
fastened together by means of screws, e, securing the diaphragm, D, by its
periphery, It is necessary that this joint should be practically airtight and
quite flat and to this end, therefore, a suitable packing may be employed, if
requisite, but we prefer to slide-rest or turn up truly the faces of the frame. The
DQJ1

page_text: electrical connecting wires are carried through cement sealed ´insulated holes, g.
It will thus be seen that an airtight chamber is formed between one side of the
diaphragm and the rear portion, B, of the frame. On the front portion, A, of the
frame, in a position, preferably at or about halfway between the centre and
circumference of the diaphragm, D, is a contact-screw, E, (preferably with a
platinum or carbon contact point) arranged to act on a contact surface also of
platinum or carbon carried by the diaphragm and to provide electrical contact
therewith when the diaphragm is in its normal position but to break the circuit
when the diaphragm is drawn towards the electromagnet. This contact-screw, E,
threads into the block. F, rigidly attached to the frame by screws, i, but insulated
therefrom by means of an insulating block, G, and plugs round the screws.
This make-and-break contact being included in the circuit of the electromagnet
generates a rapid vibration of the diaphragm immediately an electric current is
passed through the system. Figure 4 represents the apparatus joined up in the
ordinary way without other instruments in the same circuit. Upon the circuit
being completed by the key, 1, current passes through the terminal, M, coils of
electromagnet, C, connecting-wire, 2, contact-screw, E, to diaphragm contact, D,
(whilst the diaphragm is in its normal backward position) to terminal, N. 3 repre-
sents earth or return line. Immediately after the magnet begins to pull the diaphragm
forward, however, the circuit is broken at contact, E and the magnet becomes
demagnetised and the diaphragm flies back to repeat its cycle of operations in the
ordinary well-understood way, the backward movement of the whole diaphragm
in our case being expedited by the elastic action of the air in the closed chamber
acting on its whole front surface.
The sharp, piercing character of the sound for a given current can be further
considerably increased by employing a mechanical stop-screw, H, Figures 1 and 2,
threading through the bridge, c, and adjusted to touch the diaphragm at or near
its centre on the opposite side to the electromagnet.
Where the apparatus is required to be used in series with other electromagnets
in the same circuit, as may frequently be the case, we find it very advantageons
to employ a second contact-screw, K, similar to the one, E, hereinbefore described,
fixed immediately opposite the latter, and intended to act on the under side of the
diaphragm or same side as the electromagnet. This second contact-screw is so
joined up as to pass the current direct without its going through the coils of the
electromagnet on the movement of the diaphragm towards the electromagnet
immediately after the contact at, E, breaks, the space between the screws being
made as small as possible, but it is not advantageous to dispense with the contact, E,
and allow the diaphragm to act by short circuiting the electromagnet coils as by
so doing the vibration is very considerably damped in consequence of the electro-
mechanical work then taken out of the diaphragm. The electrical connections
when this second. contact-screw is used are shown in Figure 5. Upon the circuit
being completed by the key, 5, current passes through the line-wire, 6, terminal, M,
coils of electromagnet, C, connecting wire, 7, contact-screw, E, to diaphragm
contact, D, (whilst the diaphragm is in its normal backward position) to terminal, N.
Immediately after contact is broken at, E, another path is opened through wire, 8,
contact-screw, K, and diaphragm contact to terminal, N. Other electromagnets
(which may be those of any form of polarized signal or other apparatus) in the
circuit are represented at, 9. 10 represents earth or return line. By the above
means it will be seen that current is passed directly across from the terminals, M,
to, N, of the apparatus during the greater part of the time that the circuit through
the coils of the apparatus is broken at each vibration although the coils are at no
time short-circuited, consequently the motion of the diaphragm is not damped by
reason of its having to perform electro-mechanical work. By this arrangement also
the other electromagnets in circuit are kept more equally charged with magnetism
during the operation of the apparatus and, being thus subjected to less variations
of current, do not oppose so much electromagnetic inertia as they would do without
the contact, K, and the note produced by our apparatus when so joined up is

page_text: therefore considerably louder for a given current and more energy is available to
actuate the other instruments in circuit.
The reversing switches for other transmitting apparatus for operating the
additional electromagnetic appliances included in the same circuit are not shown
in the diagram as they have no relation to the construction of our apparatus and
vary with the particular form of telegraph system or signal used.
*:
A spark-trap" or shunt coil, L, of high resistance, but unmagnetic, may be
placed across the electromagnet, C, to reduce the self-induction and consequent
sparking, thereby preserving the contact surfaces.
M and N are respectively the "line" and "earth" or return line terminals.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. In an apparatus for producing sound by the electromagnetic vibration of a
diaphragm, and in which the vibration is produced by make-and-break contacts
actuated by the diaphragm itself, a closed airtight or nearly airtight chamber of
which the vibrating diaphragm forms one side or wall substantially as and for the
purposes herein set forth.
2. In an apparatus for producing sound by the electromagnetic vibration of a
diaphragm, a mechanical stop-screw at or near the centre of the diaphragm for the
purpose of increasing the sharpness of the sound produced substantially as herein
set forth.
3. In connection with an apparatus for producing sound by the electromagnetic
vibration of a diaphragm, the second contact-screw, K, and electrical connections
substantially as and for the purpose herein set forth.
4. The combination and arrangement of parts constituting our improved
apparatus substantially as herein set forth and shown in Sheet 1 of the annexed
drawings.
Tech on day 1 xp 001.
A. F. SPOONER,
9, Warwick Court, High Holborn, W.C., Agent for the Applicants.