Improvements in or relating to Telephones and Microphones.
Year: 1891

page_text: Date of Application, 18th Dec., 1891
Complete Specification Left, 16th Sept., 1892-Accepted, 5th Nov., 1892
PROVISIONAL SPECIFICATION.
Improvements in or relating to Telephones and Microphones.
I, ADOLF RETTIG of Saarbrücken, in the Empire of Germany, Lawyer, do
hereby declare the nature of this invention to be as follows:-
This invention relates to telephones and microphones and consists in the improve-
ments in and connected with the arrangement of the diaphragms and vibratory
parts of the receivers and transmitters by which the effective power of these
instruments is increased and the speech is transmitted with greater sound and
distinctness.
The invention consists principally in combining in each instrument whether
microphonic or telephonic transmitter or receiver several diaphragms of various
sizes and of the same material or of different materials in such a way that the
larger but weaker vibrations of the first diaphragm, the receiving diaphragm of
the instrument, are converted into stronger vibrations of less amplitude upon the
last diaphragm by which the ultimate result of the particular instrument is effected.
Thus in a telephonic transmitter the vibrations caused by the speech are received
upon the larger diaphragm and carried from there to the smaller diaphragm by
which the field of the electro magnet is affected whereas in the telephonic trans-
mitter the vibrations are given by the electro magnetic or other receiving apparatus
to the larger diaphragm and imparted from the larger to the smaller by which the
audible sounds are diffused in the atmosphere and thus reach the hearer.
It is also the purpose of the invention to utilize the capacity of the wooden
casing for conducting vibrations so as to increase the effect, and to arrange a correct
system of damping to regulate the resonance.
In the telephonic transmitting instrument the smaller diaphragm may be of oval
form with radial extensions fixed by screws on the lugs projecting on the inner
surface of a tube screw threaded for adjustment to and from the electro-magnet.
These lugs carry pins against which the diaphragm rests so that the pins divide
the diaphragm into a number of short vibrating parts which makes the quality of
sound better, clearer, and more distinct. This diaphragm should be of metal or of
some substance such as rubber armed with metal.
Above this diaphragm is another diaphragm at a distance therefrom, this second
diaphragm may be of metal or of rubber or any other suitable material supported
and fixed as the nature of the material of which it is made best permits. Over
this diaphragm is a third diaphragm generally of metal with a screw-threaded
socket tube in the middle to receive a sound collector such as a parabolic reflector
of the Rettig system as patented in Great Britain under numbers 1014, 1972*1,
3467, 12058. This diaphragm is fixed firmly by means of the aforesaid socket
in the wooden cover of the casing, but outside the flange of the socket it extends
out of contact with the wood.
Each of the two upper diaphragms is connected with the wooden floor and cover
of the casing, through the intervention of metallic posts fixed in the floor, extending
up through the diaphragms and fixed by nuts over the cover plate. The middle
diaphragm rests upon a nut on each post and light spiral springs surrounding the
posts bear on each diaphragm.
The floor and cover of the wooden casing are for strength cut with the grain of
the wood.
The vibrations of the larger diaphragms are carried to the smaller or lowest
diaphragm by means of a suitable lever like construction connected to the centre
diaphragm near its edge bearing on a spring cushion on the small diaphragm.
When the centre diaphragm is of metal this lever may be a spring bearing on a

page_text: screw fixed in a spring which is fixed near the edge of the small diaphragm and
having its free end resting on the free end of another spring similarly fixed to and
also resting on the small diaphragm.
At the point of contact of the lever spring and the screw head of the cushion
spring the lever spring may be provided with a small membrane to avoid the
disturbing sound of metal striking on metal.
Where the middle diaphragm is of rubber or other stretched material it is carried
in a suitable frame or stretcher preferably attached to the upper diaphragm. The
lever spring is then fixed to the latter or to the frame.
To prevent disturbing sounds from being transmitted when speaking into the
telephone, a flexible shield may be attached to the latter to surround the mouth of
the speaker and so prevent disturbing sounds in the room from being reproduced
in the telephone.
The receiver is of the same general construction as the transmitter but reversed
that is to say a large diaphragm is placed near the electro-magnet, being movable
for adjustment as described with reference to the small diaphragm in the trans-
mitter and having similar means for damping.
In transferring the vibrations from this larger diaphragm to the smaller one,
which is provided with the same springs as described with reference to the trans-
mitter, the lower diaphragm carries a spring with a pin with round head pressing
lightly against the middle rubber diaphragm and the latter is touched on the
opposite side by the round headed pin on the smaller diaphragm springs, or one
pressing direct against the small diaphragm when the springs thereon are not
. employed. The latter may then be made of rubber.
Dated this 18th day of December 1891.
HERBERT & CO.,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in or relating to Telephones and Microphones.
I, ADOLF RETTIG, of Saarbrücken, in the Empire of Germany, Lawyer, 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 relates to telephones and microphones and consists in the improve-
ments in and connected with the arrangement of the diaphragms and vibratory
parts of the receivers and transmitters by which the effective power of these
instruments is increased and the speech is transmitted with greater sound and
distinctness.
The invention consists principally in combining in each instrument whether
microphonic or telephonic transmitter or receiver several diaphragms of various
sizes and of the same material or of different materials in such a way that the
larger but weaker vibrations of the first diaphragm, the receiving diaphragm of
the instrument, are converted into stronger vibrations of less amplitude upon the
last diaphragm by which the ultimate result of the particular instrument is
effected. Thus in a telephonic transmitter the vibrations caused by the speech are
received upon the larger diaphragm and carried from there to the smaller
diaphragm by which the field of the electro-magnet is affected whereas in the
telephonic receiver the vibrations are given by the clectro magnetic or other
receiving apparatus to the larger diaphragm and imparted from the larger to the
smaller by which the audible sounds are diffused in the atmosphere and thus reach
the hearer.
It is also the purpose of the invention to utilize the capacity of the wooden
casing for conducting vibrations so as to increase the effect, and to arrange a correct.
system of damping to regulate the resonance,

page_text: In the telephonic transmitting instrument the smaller diaphragm may be of oval
form with radial extensions fixed by screws on the lugs projecting on the inner
surface of a tube screw threadel for adjustment to and from the electro-magnet.
These lugs carry pins against which the diaphragm rests so that the pins divide the
diaphragm into a number of short vibrating parts which makes the quality of
sound better, clearer and more distinct. This diaphragm should be of metal or of
some substance such as rubber armed with metal.
Above this diaphragm is another diaphragm at a distance therefrom, this second
diaphragm may be of metal or of rubber or any other suitable material supported
and fixed as the nature of the material of which it is made best permits. Over
this diaphragm is a third diaphragm generally of metal with a screw threaded
socket tube in the middle to receive a sound collector such as a parabolic reflector
of the Rettig system as patented in Great Britain under numbers 1014 of 1880,
1972 of 1881, 3467 of 1882 and 12058 of 1884. This diaphragm is fixed firmly by
means of the aforesaid socket in the wooden cover of the casing, but outside the
flange of the socket it extends out of contact with the wood.
Each of the two upper diaphragms is connected with the wooden floor and cover
of the casing, through the intervention of metallic posts fixed in the floor,
extending up through the diaphragms and fixed by nuts over the cover plate. The
middle diaphragm rests upon a nut on each post and light spiral springs surrounding
the posts bear on each diaphragm.
The floor and cover of the wooden casing are for strength cut with the grain of
the wood.
The vibrations of the larger diaphragms are carried to the smaller or lowest
diaphragm by means of a suitable lever like construction connected to the centre
diaphragm near its edge bearing on a spring cushion on the small diaphragm..
When the centre diaphragm is of metal this lever may be a spring bearing on a
screw fixed in a spring which is fixed near the edge of the small diaphragm and
having its free end resting on the free end of another spring similarly fixed to and
also resting on the small diaphragm.
At the point of contact of the lever spring and the screw head of the cushion
spring the lever spring may be provided with a small membrane to avoid the
disturbing sound of metal striking on metal.
Where the middle diaphragm is of rubber or other stretched material it is
carried in a suitable frame or stretcher preferably attached to the upper diaphragm.
The lever spring is then fixed to the latter or to the frame.
To prevent disturbing sounds from being transmitted when speaking into the
telephone, a flexible shield may be attached to the latter to surround the mouth of
the speaker and so prevent disturbing sounds in the room from being reproduced in
the telephone.
The receiver is of the same general construction as the transmitter but reversed
that is to say a large diaphragm is placed near the electro-magnet, being movable
for adjustment as described with reference to the small diaphragm in the trans-
mitter and having similar means for damping.
In transferring the vibrations from this larger diaphragm to the smaller one,
which is provided with the same springs as described with reference to the trans-
mitter, the lower diaphragm carries a spring with a pin with round head pressing
lightly against the middle rubber diaphragm and the latter is touched on the
opposite side by the round headed pin on the smaller diaphragm springs or one
pressing direct against the small diaphragm when the springs thereon are not
employed. The latter may then be made of rubber.
This invention is illustrated in the annexed drawings in which
Fig. 1 is a section of a transmitter in which nietallic diaphragms only are
employed.
Fig. 2 an under plan view of the same with floor plate removed.
Fig. 3 a section of a transmitter in which metal and rubber diaphragms are

page_text: Fig. 4 a section through the same between the lower and middle diaphragms.
Fig. 5 a receiver in which metal and rubber diaphragms are used, in section.
Fig. 6 a plan view of the lower diaphragm thereof.
Fig. 7 a receiver in which only metallic diaphragms are used.
Fig. 8 a plan view thereof.
Fig. 9 is a receiver in which both the middle and lower diaphragms are of
rubber.
Fig. 10 a plan of the middle diaphragın thereof.
In the transmitters shown in Figs. 1 to 4 three diaphragms are used namely a b
and c or a band -the diaphragm is of rubber, the diaphragms a band cof
metal. The lower diaphragm a which may be of oval form as shown in Fig. 2 is
adjustable to or from the end of the magnet M by screwing in or out the tubular
socket to lugs on which the extended tongues of the diaphragm are fixed. The
small pins or projections on the under side of the lugs rest with their rounded
ends against the diaphragm and serve as dampers for regulation of the resonance.
These pins divide the diaphragm into smaller vibrating parts so that the reduction
of the amplitude of vibration so obtained produces a clearer and more distinct
tone. This metallic diaphragm a is placed in all transmitters of this kind whether
rubber or metal diaphragms are used therewith.
In Fig. 1 a metallic diaphragm and in Fig. 3 a rubber diaphragm is arranged
over the diaphragm a, either of these being considerably larger than the metallic
diaphragm a so that the larger but less powerful vibrations communicated to the
larger diaphragm are converted into smaller but more powerful vibrations of the
diaphragm a.
Over the middle diaphragm bor is a third diaphragm c always made of metal
with a short outstanding metal tube for receiving a mouth piece such as a
paraboloid tube of the Rettig system before mentioned. This diaphragm c lies
firmly against the wooden cover of the casing of the instrument so far as the
flange at the base of the tube is concerned but outside of this flange it extends
clear of the wood. All three diaphragms are in connection with the wood of the
casing.
The posts are firmly fixed in the base plate A of the casing; they may be of
brass or bronze and serve to connect the upper diaphragms to the wooden plate A
and thus through the intervention of the wood to the metal diaphragm a.
The
vibrations of the upper diaphragms are thus carried to the lower diaphragm,
strengthened by passage through the wood. For this purpose and to provide for
vibration generally the posts wherever they lie free in the interior of the casing
are surrounded by very light spiral metal springs . The posts pass up through
the upper plate of the casing and are fixed by nuts 4 when the whole is assembled
after the interior mechanism has been put together on the plate A. The trans-
mitter head so formed is afterwards secured on the casing containing the electro
magnet.
The floor plate A is for the sake of strength cut parallel with the fibre of the
wood, but the metal arrangement in its centre allows of the vibrations along the
fibres being brought into use, these being three times as powerful as those received
square to the fibres.
The vibrations of the larger diaphragm or are carried to the smaller
diaphragm a direct by a lever construction in combination with a spring device
as shown in Figs. 1 and 3. If the middle diaphragm bis of metal, the spring k
is fixed at the edge of the diaphragm and extends at an incline downwards to
under the middle of the diaphragmn where it is bent to extend horizontally.
The diaphragm 6 rests on the collars or nuts 2 on the posts so that it main-
tains its position and does not affect the adjustment of the lever k. The
diaphragm is held pressed on these collars by the spiral springs above the
diaphragm. If the diaphragm b vibrates towards the diaphragm a its centre sinks
and its rim rises thus depressing the lever k, when the centre of the diaphragm
rises its rim sinks and the lever is lifted. This motion of the lever is transferred

page_text: to the diaphragm a by the springs a¹ a², the former of which fixed at one ed; e;
of the diaphragm a is bowed upwards and extends over the diaphragm aga n
descending to rest on the diaphragm with its end which is turned spirally upwards
and backwards. The spring a fixed near the first is curved upwards and its outer
end rests on the spirally turned face of the spring a without being fixed thereto.
The spring a carries an adjustable screw or pin a³ arranged vertically above the
centre of the diaphragm a and having a rounded head which touches the under de
of the end of the lever very lightly. The movement of the lever is thus
transferred to the springs a a² and thus to the diaphragm a. To avoid the
disturbing sound of metal striking on metal the under face of the lever is
covered with a piece of very fine membrane. The special manner of fixing the
one end of the spring a to the diaphragm a and allowing the other end to rest
lightly on the latter causes powerful vibrations to be set up in the diaphragm a.
On the under side of the upper metal diaphragm c are fixed plates with pins
with rounded points intended to regulate the resonance of this diaphragm. The
vibrations of this diaphragm are very strong especially if a paraboloid mouth
piece is fixed in the connecting tube, or even an ordinary single sound collector,
also if the mouth of the person speaking is pressed against the cover plate. The
vibrations are carried from the diaphragm c to the middle diaphragm b by means
of the spiral springs which surround the posts and through the posts themselves
to the wooden casing and thence also to the diaphragm a. The proportions and
disposition of the pieces is throughout such that the vibrations set up are all
usefully conveyed to the membrane a and thus influence the magnet.
So far as concerns the wooden part of the telephone head, this is made so that
the vibrations whether direct or indirect as for instance through the floor plate act.
along the fibres of the wood. The side walls of the telephone head are made
with the fibres standing vertically. To fully attain the properties of vibration
which the wood affords the cover is made up of two plates of which the inner is
cut longways of the fibre the outer however across the grain of the wood. The.
plate cut with the grain has a central hole for passage of the tube on the
diaphragm c but this hole is preferably faced at its edges with a metal ring which
does not touch the tube on the diaphragm. This tube is however firmly fixed in
the hole in the central boss of the upper plate which is cut across the grain of the
wood.
If for sake of greater simplicity of the construction the full capabilities of
vibration of the case are not required the cover and side walls may be cut out in
one piece the fibres lying vertically. As in such case the flange of the tube on
the diaphragm lies against the cover plate the most important of the vibrations
are obtained and utilized. With large telephonic transmitters which have great
power of resonance, it is however advisable to obtain all the advantages which the
vibrations of the wood will afford.
The covering disk should in all cases show vertical fibres, it is preferable to give
it the general form of a physicians stethoscope the size of which also it need not
exceed. The present form of disk used is acoustically very imperfect and its.
capabilities of collecting sounds is very small.
In the wooden casings of transmitters now in use the wood is arranged so that
vibrations must pass perpendically to the fibres of the wood. For this reason
the wave vibrations received and utilized in the instrument are mainly confined
to those of the air which comes into direct contact with the diaphragm, the
vibrations received by the wood are but very slightly utilized.
If a paraboloid speaking trumpet of the Rettig system referred to herein is
attached to the transmitter the volume of tone is increased.
A sound collector of this nature if of small focal distance is fixed on the
transmitter so that its focus falls on the middle diaphragm or as near as possible
thereto. If the sound collector is of a flat paraboloid form the reflector which is
placed in front of the parabola is so arranged that the focus of the reflected
waves lies in the middle diaphragm, or if desired the larger flat paraboloid may

page_text: be used behind the transmitter so that the focus of the paraboloid may lie in the
middle diaphragm.
The diameter of the tube g which is intended as a rule to receive such a sound
collector will be made according to the diameter of the collector which is
according to its focal length. The tube as drawn is intended for a sound collector
of 0:4 mm. focal length.
If the middle diaphragm is of rubber, then the upper diaphragmn c is fitted with
a cylindrical flange over which the rubber is stretched, it being secured thereon
by a ring with outstanding rim or lugs secured to the upper diaphragm by screws.
The resonance regulators may be secured either on the upper diaphragm inside or
outside the cylinder or to the cylinder. The spring lever k is here either carried
by the upper diaphragm or by the cylinder thereon or by the ring which secures
the rubber on the cylinder. This spring projects clear under the rubber diaphragm,
and is bent upward then horizontally so that it just lightly touches the rubber
diaphragm.
The pin a³ also only touches the lever very lightly; this pin is arranged as
before stated and the lever is also provided with a cushion on the under side for
the purpose before mentioned.
As the vibrations of the rubber diaphragm are much stronger than those of
the metal diaphragm b, the transmitter is stronger.
The sizes of the diaphragms
and c may be varied, the larger the diaphragms
the greater will be the power of the instrument, the resonance regulation must
however be made more accurate.
To avoid disturbing sounds when speaking directly into such transmitter the end
of the sound collector or equivalent may be provided with an elastic ring of
rubber or other convenient material against which the mouth of the speaker is
pressed.
For an automatically working transmitter which is intended not so much for
direct speech as to reproduce sounds arriving from the direction towards which the
sound collector is turned, it is preferable to use a flat paraboloid sound collector
and to place the transmitter so that the focus of the paraboloid is in the middle
diaphragm, the transmitter projecting but slightly, if at all, from beyond the front
of the sound collector.
The same acoustic reasoning is applied in the construction of the receiver shown
in Figures 5 to 8, only the construction is reversed and somewhat modified to suit
the different purpose.
The lower diaphragm d that is to say the one nearest the magnet, is circular and
of considerable size and is made of sheet metal and supported in a similar manner
to the small diaphragm a in the transmitter.
The metal diaphragm could be placed direct on the neck of the telephone and
be secured by screwing the ring of wood down upon it. In this case the grain of
the wood of the ring should stand perpendicular to the diaphragm to avoid cross
vibration. The construction does not however allow of the diaphragm being so
accurately adjusted with regard to the magnet as does the construction illustrated.
The resonance regulation is confined to four pins for groups of pins arranged
at 90° apart around the circumference as this arrangement gives the maximum of
power. The method of arranging these pins is similar to that before described.
When the diaphragm d is secured by the alternative method above described the
resonance pins may be arranged on small plates on the upper or under side of the
diaphragm as they are with the upper diaphragm c.
The sound vibration which allows the middle diaphragm to sink is omitted or
neutralized in the receiver and the metal diaphragm near the magnet is allowed to
rise in the center and this movement is utilized in place of the vibration of the
céntral diaphragm. With this view the lever k is secured on the upper side of the
lower diaphragm.
The small metal diaphragm a is secured in the central tube on the upper
diaphragm c being held in a sleeve screw threaded for adjustment in the said tube.

page_text: $
Its spring construction is arranged on the under side, and when no rubber
diaphragm is used as in Figure 7 these springs a a² work with pin a3 in direct
contact with the lever k in the same manner as with the transmitter only here
the lever works from below whereas in the transmitter it works from above.
When a rubber diaphragm is also used as in Figure 5 this diaphragm is interposed
between the large metal diaphragmn near the magnet and the upper metal diaphragm
and is supported as before described with reference to the transmitter. It thus
lies between the lever k and the springs on the little diaphragm d. The contact of
the lever with the diaphragm is produced by arranging on the end of the
lever a screw threaded vertically standing pin the rounded head of which
touches the diaphragm on the underside with a very light touch. The pin a³ on
the springs on the small diaphragma is approached to the rubber diaphragin on the
other side in a similar manner so as to lightly touch the same.
The receiver provided with the rubber diaphragm is more powerful than that
without.
The secure fastening of the metal diaphragm d which may naturally be done by
more than four arms if desired allows of the use of a larger diaphragm in front of
the magnet than before.
The rubber diaphragm and the metal diaphragm e may be of any convenient
size and will increase with their increased size the power of the instrument. The
regulation of the resonance must however be correspondingly increased.
Sound collectors may be used being fixed in the tube on the diaphragm c, the
tube as shown is suitable for a paraboloid reflector of about 4 mm. focal distance.
The flatter paraboloid reflectors may be arranged as before described for the
receiver.
To
If a paraboloid of small focal distance is desired the same may be divided so
that a part may be screwed on towards the apex, the listener can then hear at a
greater distance than otherwise. It is always possible to hear at the focus. Where
the receiver is used without a sound reflector it is advisable to use a special or
additional cover plate which lies close to the wooden cover at all points.
prevent access of disturbing sounds occuring in the place where such receiver is
put up, a carrying tube may be fixed in the tubular socket on the diaphragm e, or
when a narrow paraboloid reflector is used then on the latter or on its tube, this
carrying tube having a special end piece like an ordinary hearing trumpet or
speaking tube. In this way foreign sounds may be excluded from the ear.
If lateral noises are to remain without action on the instrument then very flat
paraboloid reflectors are used, and it is preferable to arrange the same so that the
focus of the reflector shall lie in the middle diaphragm of the receiver which latter
should not extend more than necessary outside the limits of the reflector; this is
the same as with the transmitter.
If desired there may be used a small rubber diaphragm e in place of the
diaphragm a this rubber diaphragm being circular and supported in an adjustable
sleeve similar to that holding the diaphragm a. In this case the arms for the
securing of the diaphragm would be somewhat differently placed so as to leave
room for a small sheet metal cylinder serving to stretch the diaphragm and bring
its surface into contact with the heads of the resonance regulating pins.
If there is no other rubber diaphragm in the receiver then the above is all that
is require but when there is also a middle diaphragm of rubber (') then a further
modification of construction is employed, a simple lever y being fixed on the sheet
metal cylinder which stretches the rubber diaphragmn on this lever is arranged
a screw threaded pin g projecting upward and downward over the middle of the
diaphragm . The lower rounded end of this pin lightly touches the diaphragm b'
and the diaphragm e is caused to lightly touch the upper end of the said pin.
Figs. 9 and 10 show this construction. The use of two rubber diaphragms gives
an instrument of greater power than where one only is employed.
As to the telephone, so is the invention applicable to the microphone with such
changes as the nature of the latter requires. If a receiving plate is made of this

page_text: wood and surrounded with a metal frame, it may be mounted in the face plate of
the microphone as a ground plate in the same way that the small metal diaphragm a
is mounted in the transmitter or the large metal diaphragm d in the receiver of the
telephone. The resonance regulators are so arranged that the pins touch the
metallic framing of the wooden disk.
All the constructions described greatly exceed all previous instruments in the
natural sound, clearness distinctness and strength of the sounds reproduced' and
increase the speaking and hearing distances, all this without use of sound reflectors.
The latter however still further increase the advantages of these instruments.
The speaking distance is especially noticeable; experiments having demonstrated
that whereas the transmitter, one of the ordinary kind chosen for comparison,
allowed a speaking distance of only 25 to 30 centimetres, a transmitter constructed
on the principles here described with a rubber diaphragm, but very roughly put
together and badly adjusted, with a sound collector of four millimetres focal
distance, 25 centimetres axial length and 41 millimetres width of opening, forwarded
every word and caused it to be reproduced clearly and distinctly, when spoken at
a distance of upwards of four meters, and this equally so whether the speaker was
in the same room, outside on the landing on the stairs or in the next room opening
on the landing. It was found that not only the speech but every movement of the
speaker was accurately reproduced as to the noise made just as if the speaker had
been present near the hearer.
By the constructions here shown tones may be exceedingly well reproduced, not
only those occuring near the instrument but also those at a distance, and this in a
manner not attainable with the methods hitherto employed for carrying the sound
waves to the receivers.
The better the construction of the telephone or microphone itself the better will
be the results obtained by the use of this invention.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is ;-
1. In telephones microphones and the like instruments intended to be influenced
by sound waves, the construction whereby the said waves are received and trans-
mitted and whereby the same are again constituted transmitted and delivered,
depending upon the use of several diaphragms so arranged and connected by spiral
springs, spring levers and the like and so chosen as to size and as to connection
with the wooden casing which itself is also constructed with a view to proper
transmission of the vibrations, that the waves are increased in strength from
diaphragm to diaphragm substantially as herein described.
2. In telephone receivers and transmitters and in microphones the combination of
the diaphragms herein described with a view to the increase of strength of vibration
as set forth.
3. The hereindescribed methods of combining metallic and rubber diaphragms
or diaphragms of like material.
4. The construction for damping for the regulation of the resonance of the
diaphragms consisting of pins ff arranged as herein described.
Dated this 16th day of September 1892.
HERBERT & Co.,
Agents to Applicant.