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Патент USA US2411004

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_ A. A... SAW.
Filled Sept. 1, 1945
2 Sheets-Sheet 1
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?ri/zur I Jazz/a!
FL4. _.
INov. ~12,. 1946.
Filed Sept. 1, 1945
2 Sheets-Sheet 2'
?riitur .I Sauz'al
Patented Nov. 12, 1946
Arthur J. Sanial, Flushing, N. Y.
Application September 1, 1943, Serial No. 500,785
13 Claims.
(01. 179——1)
This invention relates to sound amplifying
apparatus, more particularly to electronically
trating the sound focusing operation of the unit;
powered sound amplifying apparatus embodying
both microphone and loudspeaker units.
Fig. 5 is a schematic view of the electrical cir
cuit of the embodiment of Fig. 1.
In accordance with the illustrative embodiment
of the invention, the electronic megaphone unit
Objectsand. advantages of the invention will
be set forth in part hereinafter and in part
will be obvious herefrom, or may be learned by
practice with the invention, the same being re
alized and attained by means of the instrumentali
ties and combinations pointed out in the ap 10
pended claims.
The invention consists in the novel parts, con~
is made up of a microphone and a loudspeaker,
each of special type, positioned in de?nite, and
preferably ?xed, spatial relationship and inter
connected by an ampli?er.
The microphone has both sides of its dia
phragm, or other sound wave sensitive element,
open to the atmosphere, at least to the extent
that sound waves will have access to both back
and front. Thus, sounds directed at it from a
structions, arrangements, combinations and im»
provements herein shown and described.
The accompanying drawings, referred to herein
distance will travel’ substantially along paths
and constituting a part hereof, illustrate one
of almost the same length from the source to the
embodiment ‘of the invention, and together with
front and back of the diaphragm, so that they
the description, serve to explain the principles
will have a comparatively small vibrating effect.
of the invention.
On the other hand, however, sounds directed at
An object of this invention is to provide an
the front of the diaphragm from a source close
electronic megaphone unit with which sounds
thereto will not be subject to this cancelling effect
delivered to the input will issue from the output
due to the large difference in path length of the
in greatly ampli?ed volume.
sound from the sound source to front and back
Another object of this invention is to provide
25 of the diaphragm, respectively.
nev»7 and improved electronic sound-amplifying
The loudspeaker is of such construction that
apparatus which is compact and portable so that
the sounds emanating therefrom will be con
it can readily be carried by an individual and
with which the ampli?ed sounds can be readily
verged and directed thereby toward a region on
the central axis in front of the horn. Project
directed where desired.
30 ing the sound to a region in space a distance
Another object of this invention is to provide
in front of the horn actually creates what may be
a combination microphone and loudspeaker unit
thought of as a virtual source of the radiated
of which the microphone and loudspeaker are in
sound. This gives the effect of a longer horn than
close physical relationship and which when held
the physical length of that actually used. The
close to a person’s mouth, but not touching, will
source of sound is thus removed farther from the
amplify the voice to a very great volume without
microphone so that the acoustic feedback tend
acoustic feedback.
ency is reduced. Even though the sound ulti
Another object of this invention is to provide
mately diverges beyond the focal region, the
a combination microphone and loudspeaker unit
degree of divergence is much less from this device
which will be free of undesirable energy transfer
than from a conventional horn exit. Hence,
either by electrical, acoustical or mechanical
even such sound as does diffuse backwards from
means between the loudspeaker and‘ the micro
beyond the focal region is largely attenuated in
phone, when they are interconnected by means
the distance it must travel back to the micro
of an ampli?er.
Of the drawings:
Fig. 1 is a view in side elevation of an electro—
acoustic megaphone unit and its ampli?er con
stituting a typical and illustrative embodiment
of this invention;
Fig. 2 is a sectional view in elevation of the
megaphone unit of Fig. 1;
Fig. 3 is a view in end elevation of the mega~
phone location and is of substantially no conse
45 quence at the microphone because of the cancel
lation effect arising from both sides of the micro
phone diaphragm being open to the atmosphere.
A spatial relationship of the microphone and
loudspeaker is established such that the micro
phone is centered on, and is normal to the cen
tral acoustic axis of such sound waves as may
radiate backward from the loudspeaker mouth.
This is not necessarily the geometric central axis,
so that the microphone is located by trial in this
megaphone unit of Fig. 1 schematically illus~ 55 null position when ?rst mounted, or the mount
phone unit of Fig. 2, as viewed from the left;
Fig. 4 is a somewhat diagrammatic view of the
ing is provided with means to permit it to be
adjusted to the null position when in use.
The microphone and loudspeaker may be sepa
rately supported having regard to the require
ment of the null position of the microphone.
at its outer end substantially in the plane of the
outer periphery of the bell 4.
The annular passageway which the plug forms
with the members 3 and 4 comprises front and
Preferably, however, suitable means are provided
convenience are sometimes hereinafter referred
for incorporating them in a single unit which
may also incorporate the ampli?er if so desired.
to as the annular passageways 3! and 32 re
Suitable provision for reducing mechanical vi
rear sections 32 and 3! respectively, which for
, The annular passageway 3! .may follow any
‘oration impressed by one upon the other or upon 10 desired rate of ‘acoustic expansion. The pas
sageway 3| serves to conduct the sound waves
either or all from external sources is preferably
‘issuing from the horn 2 angularly outwardly
made in the form of cushioning devices of resil
therefrom in a con?ned path to the junction at
lent material located at the most advantageous
P with the‘annular passageway 32. Thus, in the
points of support. Similarly the various electri- ~
initial portion of their travel through the outer
cal circuits that are above ground potential are
horn, the sound waves are carried radially out
grounded and dissimilarly polarized, to prevent
wardly from'as well as along the central axis
regeneration and electrical feedback.
A—,A of the assembly.
It will be understood that the foregoing gen
The annular passageway 32 diverges from its
eral description and the following detailed'de
junction at P with the passageway 3! to the
scription as well are exemplary and explanatory
outer periphery of the bell '4 so as to provide
but are not restrictive of the invention.
an expanding passageway from which the sound
Referring now more particularly to the ac
waves issue in the form of annular rings travel
companying drawings, there is provided as is
ling in the forward direction. This annular pas
best shown in Fig. 2 a conventional loudspeaker
sageway is of uniform width at any plane normal
driver unit 5 of any suitable type, to which is
connected an intermediate or inner baffle mem
ber or horn 2, of any suitable type which may be
straight, folded or re-entrant, the latter termi
nated by a second or outer horn of novel type
comprising ba?le members 3, 1i and 5, for the so
purpose of providing a focusing effect for the
radiated sound.
It is not intended to con?ne the rate of ex
to the central axis A—A, the rate of expansion
being uniform, exponential or at such other rate
as may be most suitable to the purpose. It will
be understood in this regard that the ‘rate of
expansion of the air column so chosen may have
different values in different portions of the horn
as a whole, this being governed by theacoustical
design requirements of the particular type of
frequency characteristic.
pansion through the inner horn 2 to ‘any speci?c
The minimum diameter of baffle member 3
formula. On the contrary, the rate may be in
where it joins baffle member 45 is substantially
accordance with any conventional design for
equal to the maximum diameter or" member 4
mula familiar to one skilled in the art. However,
where it is exposed to the atmosphere, that is,
a speci?c con?guration of the second or outer
the open end. in this manner the diameter of
horn should preferably be adhered to from the
the annular ring section of the air column in the
point where it joins the inner horn. For pur
plane of the greatest diameter of plug 5 can be
poses of illustration in Fig. 1 the inner horn 2 is
made as large as the maximum limiting diameter
shown as of the straight horn, tubular extension
of the structure as awhole will permit. In addi
type, which expands uniformly at a chosen rate
tion, the actual width of the annular ring section
along the center axis A--A.
The outer or terminal horn is attached to " that results is as small as can be obtained at this
maximum diameter for a given expansion rate of
the end of the inner horn 2 in the following
the air column. Each element of the thin annu
manner. The external portion of the terminal
lar ring of sound at the opening, P, can be then
horn comprises a ba?le member 3, preferably
considered as a small source of sound originating
frusto-conical, the small end of which is sealed , at the small end of the expanding air column
to the terminal periphery of inner horn 2. At
formed by the outer section of plug 5, and the
the large end of member 3, a second ba?le mem
bell 4.
ber ‘01' bell it, preferably frusto-conical in con
As the acoustic axis, indicated by the dash-dot
tour, is secured and sealed in the same manner.
lines in Figs. 2 and 4, of any section of the an
The internal portion of the terminal horn com
nular horn formed by these members is directed
prises a plug baffle member 5 forming an annu- ’ toward the central axis A-—~A. of the assembly as
lar expansion passageway with the ba?ie mem
a whole and substantially to the same region R,
bers 3 and d serving to direct and focus the
Fig. 4, because of symmetry, the greater portion
sound issuing from the terminal horn at a focal
of the sound emanating from the horn is thus
point R, Fig. 4, in front of and on, or substan 60 focused in a manner similar to that occurring
tially on, the central axis A—A of the assembly.
with light in an optical lens system.
The plug 5 may be solid, but as here preferably
It is recognized that due to thev relatively wide
embodied, is of hollow construction and tapers
frequency spectrum embraced in‘ acoustic sounds
from a locus of maximum diameter and circular
that the focusing point B will not be exactly'the
contour intermediate its ends, in either direction 65 same for all frequencies. However, the converg
to its endsso as to form front and back tapered
ing effect is present over the entire band of im
surface portions having a common axis of sym
portant speech frequencies as contrasted to the
metry, The plug is nested in the space formed
more diverging pattern present with conventional
by the ba?ie members 3 and 6., being supported
types of loudspeaker horns.
‘therefrom in annularly spaced relation thereto, 70 It is apparent thatyif the amount of sound
as‘by means of studs 30, coaxially with the center
radiating backwards from the region in front of
axis A-A of the assembly. > The plug is suitably
the loudspeaker is reduced to a low value, less
dimensioned'in length so as to‘terminate at its
energy will be available to cause acoustic feed‘
inner end substantially in the plane of the ter
back between the radiated sound and the micro
minal periphery of the horn 2 and to terminate 77 5 phone. The design of the outer radiating horn
cordance with a requirement described herein
greater proportion of the sound emanating from
the horn 2 toward a region on the central axis
It will be apparent to one familiar with the art
in front of the horn at a distance that can be de
that a microphone so mounted is most efficient
termined within limits by the designer. As the m for close talking purposes, as sounds directed at
natural tendency of radiating sound from a
it from a distance will travel substantially along
is therefore such as to converge and direct the
large portion
is to diverge,
of it to athe
to results
in a
greater transfer ef?ciency.
There is thus less
' Mills of almost the same length from the source
to front and back of the diaphragm, so that they
will have a comparatively small vibrating effect.
sound radiated in diverse directions i. e. toward
When talking close to the front of the diaphragm
the rear, hence the great reduction in the tend
‘i -is cancelling effect is insigni?cant due to the
large difference in path length of the sound from
the talker’s mouth to the front and back of the
ency for the device to cause acoustic feedback into the microphone.
Even though the sound ultimately diverges be
diaphragm, respectively.
yond the focal region, the degree of divergence is ‘
This effect of cancellation of sounds other than
those originating close to the front of the dia
much less from this device than from a conven
tional horn exit. Projecting the sound to a re
phragms is utilized in this combination. With
gion in space a distance in front of the horn actu~
the microphone located on the acoustic axis of
ally creates what may be thought of as a virtual
the sound which radiates backward from the
source of the radiated sound, which gives the - loudspeaker opening, as described above, the path
effect of a longer horn than the physical length
lengths from any point in a sound wave in space
of that actually used. The source of sound is
originating from the loudspeaker, to opposite
thus removed farther from the microphone which
as one skilled in the art knows, reduces the acous~
tic feedback tendency. Hence, even such sound
as does diffuse backwards from beyond the focal
region is largely attenuated in the distance it
must travel back to the microphone location.
A tubular housing 5 is secured to the horn
structure as by means of screws 33 engaging the
loa?le member 3, to serve as an enclosure to pro»
tect the inner working parts, but is proportioned
points on either side of the diaphragm is substan
tially the same. This effect is assisted by the
shape and size of the tubular housing 6 and the
space between the microphone l’ and housing 6,
which tend to bend the direction of travel of the , ’
stray sound from directly backwards parallel to
the axis, to a, direction more nearly parallel to
the plane of the microphone diaphragm.
Thus, the sound pressure of a sound wave
strikes opposite sides of a point on the diaphragm
to guide any backward radiated sound as dc~
substantially simultaneously, so that the net
exerted on the microphone diaphragm by
A microphone unit I’ is provided which is of a 35 sound radiating back from the loudspeaker is
type so designed that both sides or” its diaphragm
practically zero, provided the constants of the de
or other sound wave sensitive element, are open to
vice are correctly designed and constructed, The
the atmosphere to the extent that sound Waves
tendency for acoustic feedback between the loud
have access to both back and front. Covering
40 speaker and the microphone is therefore reduced
screens 8 of such design that will pass the sound
to an insigni?cant value, permitting very large
waves but prevent foreign matter, spray, etc,
ratios of ampli?cation to be used between the
from reaching the diaphragm may be added.
microphone and the loudspeaker, without produc
The microphone is held in. a position separated
ing audible oscillation or howling.
from the rear of housing 5, as by adjustable legs 45
Thus it will be seen that because the con?gura—
or similar means 9, suf?ciently far so that sound
ti-on of the horn, the housing, and the micro
waves can freely pass between it and the housing.
phone and its mounting, and the spatial relation
Further, the microphone is so positioned that it
ship between these parts, a much greater increase
is centered on, and is normal to, the central
in volume of ampli?ed speech than has hereto
acoustic axis of such sound waves as may radiate 50 fore been possible with similar devices, can be
backward from the loudspeaker mouth. This is
obtained without acoustic feedback.
not necessarily the geometric central axis A-A
A handle i3 is attached to the assembly under
although it may coincide substantially therewith,
the center of gravity for ease in holding the unit
so that the microphone is located by trial in this
A push button switch l4 such as used on portable
null position when ?rst mounted, or the mounting 55 electric tools, etc., is mounted in the handle to
is provided with means to permit it to be adjusted
permit the electric circuits to be turned on and
to the null position when in use, by adjustable
off easily when using the electronic megaphone,
mounting means, 9 and it, or other methods.
so that current is only drained by the ampli
The front opening to the microphone dia
?ers from its batteries or power supply, when it
phragm is substantially equal to, or less than, the 60 is desired to talk.
size of the average mouth when talking, to pro
Separately shielded conductors are run through
vide_as high
acoustic impedance as possible
the handles and switch from the microphone 7
without sacri?cing efficiency. Any chamber
and the loudspeaker driver unit 1, respectively.
scribed hereinafter.
formed by an aperture or mounting means on
They cannot be connected haphazardly however.
front and back of the diaphragm is constructed 65 It is necessary to electrically phase the two cir
so that its cavity resonance is at a frequency
cuits so that the input and output conductors that
other than those uniformly transmitted in the
are above ground potential are dissimilarly polar
speech frequency band of the system.
ized, to prevent regeneration and electrical feed
Some means of protecting the microphone from
mechanical vibration, in accordance with are 70
The microphone is connected through the cable
quirement well known by those skilled in the art,
i5 to the ampli?er input. Means are provided,
is provided in its mounting, such as pads of resil
such as the rubber insulation 62, to have the
ient material I l and I2, (rubber, etc.). This ma—
structure of the microphone electrically separate
terial may be used to electrically insulate the mi
from that of the horn housing, and the micro
crophone housing from the horn structure in ac
phone is connected to the electric shield of the
. 2,41 1,004
cable l5 to isolate the microphone from the horn
to be free to the atmosphere not only on the front
The loudspeaker I, is connected through cable
l5 to the ampli?er output, the shield of this cable
being connected to the horn structure as shown
of the diaphragm but also on the back. -
It is thereby understood that although the pro
portions of the horn, the radiating mouth, and
other parts of the loudspeaker will be maintained
in Fig. 2. The shields of cables I 5 and I6 are
as described hereinbefore, the absolute values of
properly connected into the ampli?er circuit as
the dimensions are only limited by the maximum
is shown diagrammatically in Fig. 5. The switch
size within which it is desired to keep the device.
l4 may interrupt either circuit I5 or IE or pref
However, it is well known to the art that all acous
erably the circuits to the power supply of the am 10 tic radiating devices tend to produce more diver
pli?er unit I9 through a separate cable such as
gent sounds at lower frequencies, particularly be
low the frequency at which the diameter of the
The combination comprising the complete sys
radiating aperture is less than approximately 1/2
wave length of the sound. It is a common prac
tem, Fig. 1, shows how the input and output con
tice to attenuate proportionately frequencies be
ductors referred to above are connected through
low this value in acoustic loudspeaker systems,
a receptacle IS in a conventional manner, to a
a practice which is intended to be followed in the
suitable electronic tube ampli?er l9, such as, a
invention described herein.
portable type operated by batteries. Fig. 5 shows
In like manner following conventional prac
the electrical schematic connections between the
microphone ‘and the ampli?er input, and the 20 tice known to the art, mechanical vibrations and
mechanical energy transferred from external
loudspeaker and the ampli?er output.
sources and from the body of the loudspeaker por
It will be apparent, therefore, that this de
vice is to be used with an ampli?er, such as a
portable type, which can be carried by a strap
over the shoulder or rest on a convenient support 25
within the limits of the extension cables i5, i6
and I1, so that the electronic megaphone unit
may be held by the handle to the user’s mouth.
tions are reduced to an insigni?cant amount by
cushioning the microphone in its support.
Other combinations of the electronic mega
phone and its ampli?er may be used, such as in
corporating the two in one unit or detaching the
microphone from its supports on the loudspeaker
in the event that it may be desirable to mount the
As soon as ready to talk the operator closes the
switch in the handle thereby energizing the am 30 loudspeaker on a separate support such as a tri
pod, with the user holding the microphone in his
pli?er circuits so that speech directed into the
hand. In this event the user only has to observe
microphone diaphragm opposite the talker’s
the restriction of holding the microphone on the
mouth generates electrical currents in the micro
null acoustic axis at the rear of the loudspeaker
The electric energy from the microphone is fed 35 as described above in order that the device may
be operated at optimum e?iciency. In like man
through the cable IE to the ampli?er input and is
ner a conventional power operated ampli?er in
increased many-fold in power by the ampli?er.
place of a battery operated ampli?er may be used,
The ampli?ed output is fed through the cable l6
if power from an electric generator is convenient.
to the loudspeaker driver unit I. The force ex
The invention in its broader aspects is not
erted by these amplifiedv currents actuates the 40 limited
to the speci?c mechanisms shown and
diaphragm,'setting up sound waves of a great
described but departures may be made therefrom
ly ampli?ed pattern of those directed into the
In this way the power of a human
voice is ampli?ed tremendously and is then di
rected by the electronic megaphone to the desired
location by simply aiming the device at this
The operation is therefore, similar to that when
using an ordinary megaphone except for one
great dilference: whereas with an ordinary mega
phone the talker may, and usually does, bring
the small end up to and touching the area around
his mouth without mu?ling the speech so as to
render it unintelligible, with the electronic meg
aphone, the megaphone must not actually touch
within the scope of the accompanying claims
without departing from the principles of the in
vention and without sacri?cing its chief advan
What is claimed is:
1. An electronic megaphone comprising in com
bination a loudspeaker; and, a microphone located
out of the direct soundpath of the loudspeaker,
the microphone having openings for the entry
of sound waves on opposite sides of its diaphragm
so that sound waves emanating from a source
relatively remote therefrom will strike opposite
sides of said diaphragm substantially simulta
neously and eifect substantially no energizing of
said diaphragm whereas sound waves emanating
the speaker’s mouth which is open to the atmos
phere, no matter how small this space may be, and
from a source closely adjacent to one side of said
indeed it is desirable for the greatest e?iciency
diaphragm will strike opposite sides of said dia
to keep the distance betwen the two as small as 60 phragm successively and energize said diaphragm.
possible. Inasmuch as the inlet of the microphone
2. An electronic megaphone comprising in com
must be at all times open to the atmosphere, by
bination a microphone and a loudspeaker, with
virtue of this spacing, in all known devices or sys
the microphone positioned behind the exit of the
tems using a microphone and ampli?er and loud
loudspeaker horn, said horn comprising an inner
speaker, so as to maintain intelligible speech re
horn of conventional exponential or conical de
production, all such devices are inherently sub
sign, terminated by an additional outer horn com
ject to acoustic feedback due to the sounds from
prising outside ba?‘le members and an inner plug
the speaker entering the front of the micro
ba?ie member together forming a sealed annular
This invention therefore greatly overcomes this
inherent tendency to acoustic feedback by sounds
entering the front of the microphone both by
converging the projected sound from the loud
I speaker toward the region to which communica
tion is desired and by permitting the microphone
passage extending forwardly from the inner horn
to the exit of said outer horn for sound to follow
from the inner horn through said passage to the
exit of the outer horn.
3. An electronic megaphone comprising in com
bination a, loudspeaker; and, a microphone sup
ported therefrom, said microphone having both
sides of its sound sensitive unit open to the at
mosphere and said loudspeaker having its mouth
facing in the opposite direction to the far side of
annular sound passage from said inner horn to the
loudspeaker mouth, said sound passage com
mencing at said inner horn being directed out
both sides to the atmosphere, said diaphragm unit
being substantially centered on and substantially
er in front of its mouth; and a microphone car
wards from the central axis of symmetry so as
said unit.
4. Electronic sound amplifying apparatus com 2.21 to form at the junction of said intermediate and
terminal ba?ie members an annular ring of sound
prising in combination a loudspeaker having a
of large diameter substantially equal to the diam
driver unit and baf?e members forming a sound
eter of said terminal baffle member and said pas
passage from said driver unit to the exit of the
sage commencing at said junction having a cross
loudspeaker for focusing the sound waves gener
ated by said unit at a locus in front of said exit -. section in the plane of the axis of symmetry which
has a geometric axis from said junction to the
substantially on the geometric axis of the loud
loudspeaker mouth which slants toward a point
speaker; and, a microphone back of the loud
on the central geometric axis of the loudspeak
speaker mouth having a diaphragm unit open at
normal to the central acoustic axis of said loud
speaker so as to be in an acoustic null position
with respect to sound waves which radiate back
ward from the mouth of said loudspeaker.
5. An electronic megaphone comprising in com- ~
bination a loudspeaker capable of focusing sound
Waves at a locus ahead of its mouth; and a micro
phone in back of the loudspeaker at a ?xed dis
tance therefrom, said microphone being normal
to the central acoustic axis of the loudspeaker and
adjustable relative thereto whereby said micro
ried by said loudspeaker in a position out of the
direct soundpath of the loudspeaker.
11. An electronic megaphone comprising in
combination a microphone ‘and a loudspeaker of
which the horn focuses a substantial portion of
the radiated sound to a region on the central
geometric axis of the loudspeaker in front of its
mouth, housing means for the rear of said loud
speaker of such shape that sounds from the loud
speaker which diffuse to the rear are refracted to
wards the central axis of the loudspeaker, a micro
phone unit spaced from the rear of said housing
means so that the refracted sound may pass be
phone may be centered on said axis.
tween the microphone and housing, the front
6. An electronic megaphone comprising in com
and rear of the microphone diaphragm being open
bination a loudspeaker capable of focusing sound
Waves at a locus ahead of its mouth, said micro 30 to sound waves in the atmosphere and said dia
phone having both sides of its sound sensitive unit
open to the atmosphere; a housing for the rear
phragm being so positioned that the diffuse sound
from the loudspeaker acts upon opposite sides of
any point on the diaphragm at substantially the
of said loudspeaker; and, a microphone supported
same time and with the same pressure.
by said housing out of the direct soundpath of
12. Electronic sound amplifying apparatus
said loudspeaker.
comprising in combination a sound focusing loud
7. An electronic megaphone comprising in com
speaker unit, a microphone unit carried by said
bination a loudspeaker, said loudspeaker com
loudspeaker, an electronic ampli?er, electric con
prising baffle members forming an annular sound
ductors interconnecting the microphone, loud
passage terminating at the mouth of the loud
speaker, the acoustic axis of said passage at the 40 speaker and ampli?er, a handle unit for the loud
speaker-microphone assembly by which the oper
exit converging toward the central geometric axis
ator can direct the focused ampli?ed sound to a
of the loudspeaker; and, a microphone supported
chosen region, and a switch in said assembly for
from said loudspeaker.
energizing the electronic circuits, said micro‘
8. An electronic megaphone comprising in com
phone having a diaphragm unit open at front and
bination a loudspeaker, said loudspeaker com
prising baffle members forming a sound passage
of annular shape having a central axis of sym
metry, said passage increasing in maximum diam
eter for a distance and thereafter increasing in
width to the loudspeaker mouth so as to provide
a terminal portion converging toward a point on
said axis; and, a microphone located out of the
direct soundpath of the loudspeaker.
9. An electronic megaphone comprising in com—
rear to sound waves in the atmosphere, and said
ampli?er unit having high ampli?cation such
that if the back or front of the microphone dia
phragm were closed to the atmosphere, acoustic
feedback would occur between the loudspeaker
and microphone.
13. An electronic megaphone comprising in
combination a microphone and a loudspeaker, the
loudspeaker comprising an inner horn terminated
bination a loudspeaker capable of focusing sound ,
waves at a locus ahead of its mouth; a housing for
by an outer horn with a two section sound
outer horn comprising a terminal ba?ie member of
larger diameter than the exit diameter of said
inner horn, an intermediate ba?ie member con
necting said inner horn with said ?rst baffle mem
to provide an annular entry to said second sec
tion equal to the exit of said ?rst section, the
cross section of said second section from its en
passage of substantially annular shape, the ?rst
section of said passage forming the sound into
said loudspeaker; a microphone having its sound
thin annular rings during its passage there
sensitive unit exposed at opposite sides to the
through from the exit of said inner horn, said
atmosphere; and, means for adjustably support
ing said microphone from said housing in a posi 60 ?rst section soundpath being directed angularly
outwards from the central axis of symmetry to
tion out of the direct soundpath of said loud
the junction with said second section so as to form
speaker and with its sound sensitive element sub
an annular ring of sound of large diameter sub
stantially centered on and normal to the central
stantially equal at said junction to the diameter
acoustic axis of the loudspeaker.
10. An electronic megaphone comprising in P of the second section of said passage, said second
section being formed by an outer ba?le member
combination a loudspeaker, said loudspeaker com
and an inner plug baffle member positioned so as
prising a driver unit, inner and outer horns, said
ber; and a plug ba?le member positioned in the
chamber formed by said ?rst mentioned, ba?lc
members and forming with said baffle members an
try to its exit having a geometric axis which slants
toward a point on the central geometric axis of
the loudspeaker.
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