Note: Descriptions are shown in the official language in which they were submitted.
i27628~
Description of the Invention
The invention relates generally to loudspeakers
and particularly to an improved multidriver loudspeaker.
Ideally, a loudspeaker-driver should be capable
of reproducing all frequencies so that the source of, for
example, the high and low frequency sound waves is a
single location. This would result in the time and phase
coherence of all sound waves, thereby producing
undistorted natural sound. It is difficult, however, to
build a conventional driver that is both big enough to
reproduce the low frequencies and light enough to
reproduce the high frequencies. Therefore, most
loudspeaker systems utiIize two or rnore drivers and are
terrned multidriver loudspeakers. Several major problems
arise when multiple drivers are used in a single
loudspeaker. Specifically, at some frequencies several
drivers are functioning and the actual location of the
sound is not fixed for the listener. In addition, as tne
listener moves around the listening area, the distance
fro~n each driver to the listener changes in a non-uniform
manner, such that at one location the listener is closer
to the low frequency driver and at the second location the
listener is closer to the high frequency driver. This
results in the non-synchronization of the wave fronts
reaching the listener at all frequencies. Finally, at the
crossover point, where both drivers are producing the same
~,
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amount of output, phase shifts will exist between the
sound waves emanating from the two drivers caused by the
difference in path lengths from the drivers to the
listener. To a great extent, these problems are inherent
in any multidriver loudspeaker system and are caused by
the fact that the apparent acoustical source of the
drivers are not all at the same location. The apparent
acoustical source of a driver is the point in space where
the sound wave front from the driver appears to a listener
to originate at the time the input is applied to the
driver. Typically, in view of the inertial
characteristics of the driver, the apparent acoustical
source of a driver is behind the voice coil - cone
junction and within the magnetic structure of the driver.
15 Obviously, if the apparent acoustical time
source for all of the drivers were the same point in space
many of the problems described above would be solved. In
fact, several complex mechanical structures have been
developed in an attempt to achieve this, resulting in the
embedding of the high frequency driver inside the magnetic
structure of the low frequency driver. Practically, these
speakers are too expensive to manufacture and as such, are
not manufactured. ~urther, even if speakers of this type
could be manufactured at a reasonable cost, they
incorporate other disadvantages since the sides of a low
frequency driver tend to act somewhat like a horn with
respect to the sound emanating from the low frequency
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driver (horn loading) thereby dis~orting the sound
produced thereby.
Other at~empts ~o solve the problems inheren~ in
multidriver loudspeakers include positioning the high
frequency driver in front of ~he low frequency driver.
This solu~ion is unsatisfactory as i~ creates a constant
time delay in ~he sound waves emana~ing from the low
frequency driver which becomes acu~e a~ the crossover of
the two drivers. Further, the high frequency driver in
such an arrangement serves as a diffrac~ing object and
interferes with the sound produced by ~he low frequency
driver.
It is ~herefore an object of ~he presen~
invention to provide an improved mul~idriver loudspeaker
which overcomes the problems inherent in mul~idriver
loudspeakers of the prior art.
Ano~her object of ~he presen~ inven~ion is to
provide an improved mul~idriver loudspeaker in which the
apparent acoustical source of both ~he high and low
frequency drivers appear to a listener to be at a single
location.
Still ano~her objec~ of ~he presen~ invention is
to provide an improved mul~idriver loudspeaker in which
the wave fron~s from the high and low frequency drivers
are synchronized wi~h respec~ to time, phase and response.
A fur~her objec~ of the present invention is to
provide an ~mproved multidriver loudspeaker which is
simple in cons~ruc~ion and inexpensive to manufacture.
~276Z85
In accordance with ~he presen~ inven~ion an
improved mul~idriver loudspeaker includes a low frequency
driver having an elongated voice coil former ~ermina~ing
in an inverted speaker cone and a high frequency driver
S located along the voice coil former. The voice coiL
former is formed so as ~o move ~he apparent acous~ical
source of ehe low freqnency driver along the voice coil
former tO a loca~ion substan~ially coincident wilh the
apparen~ acoustical source of the high frequency driver.
The above brief description as well as further
objects, features and advantages of the present inven~ion
will be more fully unders~ood by reference ~o ~he
following de~ailed descrip~ion of the presently preferred
bu~ none~heless illus~ra~ive embodimen~s in accordance
wi~h ~he presen~ inven~ion, when ~aken in conjunc~ion wi~h
tl-e accompanying drawing, wherein:
FIG. 1 is a fron~ eleva~ional view of ~he
multidriver loudspeaker of ~he presen~ inven~ion;
FIC. 2 is a righ~ side elevational sec~ional
view of ehe multidriver loudspeaker ~aken subs~an~ially
along the line 2-2 of FIG. l and looking in ~he direc~ion
of ~he arrows;
FIG. 3 is a fron~ eleva~ional view of an
aL~erna~e embodimen~ of ~he mul~idriver loudspeaker of the
presen~ inven~ion; and
FIG. 4 is a righ~ side eleva~ional sec~ional
view of ~he mul~idriver loudspeaker ~aken subs~antially
along the line 4-4 of FIG. 3 and looking in the direc~ion
~Z76285
of the arrows.
Referring first ~o FI~S~ 1 and 2 a mul~idriver
loudspeaker, indicated generally by ~he reference numeral
10, includes both a high frequency driver and a low
frequency driver and is formed from a base 7 2 adapted ~o
support a steel basket enclosure 14 and a magne~ assembly
16 for the low frequency driver. Disposed within ~he
basket 14 is an inverted conical diaphragm or cone 18
which is a thin, curved sheet, ~he surface of which is of
a shape such as would be genera~ed by ~he rota~ion of a
straigh~ or, alternatively, a curved line about an axis.
Such a surface, generated by a curved line, is no~ a ~rue
cone, but is generally referred ~o as such in ~he industry
and is included wi~hin ~he ~erm "cone" as used herein.
The cone 18 may be made of a stiff material, such as
felted fiber, paper, a fel~ed fiber and paper composition,
or plastic.
The cone 18 is associa~ed wi~h ~he low frequency
driver and includes an inner concave sound radiating
surface 18a and an outer convex sounà radiating surface
18b. The cone 18 also includes ~wo coaxial ends; the
upper, smaller end of ~he cone 18 is referred ~o as the
driving circle 20 and ~he larger end of ~he cone 1~ is
referred to as ~he surround 22- The angle ~' of the cone
18 refers ~o ~he angle formed be~ween a line perpendicular
~o ~he base 12 and ~he inner surface 18a a~ ~he surround
22. Tlle angle X in ~his par~icular embodiment
approxima~es 60 degrees. A damping ring 24 secures the
~2~7628~;
surround 22 of cone 1~ ~o the bas~e~ 14. ~lle driving
circle 20 is secured to one end of an elongated voice coil
former 26, the opposi~e end of which is cen~ered in ~he
annular gap between ~he pole pieces of ~he magne~ assembly
16 and includes a voice coil 18. A damping ring 30
secures the end of the voice coil former 26 proximate eo
the voice coil 2~, to ~he basked 14. The damping rings 24
and 30 serve ~o cen~er ~he voice coil former 26 and the
cone 18 within ~he basket 14 bu~ permi~ ~he cone and
former freedom ~o move axially.
The voice coil 23 is glued tO ~he former 26 and
positioned in ~he air gap of ~he magne~ assembly 14, which
together wi~h coil 2~3 forms a conven~ional loudspea~er
motor. Varyin~ curren~s proportional ~o audio frequencies
genera~ed by a sound source such as a record or ~ape are
suitably amplified and are applied ~o conven~ional input
terminals (not shown) of ~he voice coil 2~ which ~hen
in~erracts with the magne~ic field in ~he ~ap ~o cause the
coil to undergo mechanical longi~udinal ~ran51ational
movements a~ 2 ra~e which is proportional ~o the audio
frequencies. I~hen ~he voice coil 2~ undergoes i~s
longi~udinal ~ransla~ional mo~ion, ~hat mo~ion is imparted
~hrough the former 26 ~o ~he cone 1i3 and audible sound (in
~he low frequency range) is produced in ~he air.
~ conven~ional high frequency driver 32 is
loca~ed wi~hin ~he former 26 a~ ~he end proxima~e ~o ~he
driving circle 20 and is supporced by a pin 34 and a
housing 36 ex~ending alonq ~he leng~h of ~he former 26.
~27~2~5
As such, the high frequency driver is coaxial with ~he low
frequency driver.
The multidriver loudspeaker described ~hus far
shows the coaxial arrangemen~ of both ~he low frequency
and high frequency drivers. I~owever, in this arrangemen~,
the apparent acous~ical source of ~he low frequency driver
is not the same as ~he apparen~ acous~ical source of ~he
high frequency driver. Specifically, the apparent
acoustical sources of both ~he high frequency driver and
low frequency driver are located just in fron~ of their
respective magnet assemblies. Different apparent
acoustical sourccs for ~he low frequency and high
frequency drivers crea~es a ~ime delay dis~or~ion in which
tthe re~roduced sounds are vaguely unnatural. This
dis~ortion is due ~o ~he fac~ ~ha~ ~he reproduced sounds
from the high frequency driver and ~he low frequency
driver do not simul~aneously arrive a~ ~he lis~ener's ear.
The ins~ant invention minimizes ~his problem by
moving the apparent acoustical source of ~he low frequency
driver to a point substantially coincident with the
location of ~he apparent acous~ical source of ~he high
frequency driver. This is accomplisiled by manipulating
~he ~ime delay of the low frequency driver in a manner co
be more fully described hereinbelow.
Specifically, ~he cone 18 will ~ove similarly to
the voice coil 28 but delayed by the time i~ ~a~es for ~he
sound ~o ~ravel ~he length of ~he voice coil former 2~.
This time delay is represen~ed by ~he follcwing equation:
1Z76Z~3~
Time Delay = Lena~h of Former
.,
Soeed of sound ln Former
as a mul~iple of ~he speed
of Sound in Air
Typically, drivers are formed wi~h as shor~ a voice coil
former as possible so as to minimize this time delay.
However, ~he creation of an appropriate ~ime delay serves
to move the apparen~ acous~ical source of ~he low
frequency driver out of ~he magnet assembly 16 and forward
along the voice coil former 26. Placing ~he high
frequency driver 32 wi~hin ~he former 26 and crea~ing a
time delay which moves the apparent acous~ical source of
the low frequency driver to approxima~ely ~he same
location as the high frequency driver 3 resul~s in ~he
in-phase ou~pu~ of both ~he lligil and low frequency
drivers. ~s such, bo~h drivers, while no~ a~ ~he same
physical loca~ion, are perceived ~o have ~he same
acoustical source in view of ~he synchronized wave fronts
emanating from both ~he low and high frequency drivers.
The appropria~e ~ime delay may be accomplished by
ex~ending ~he leng~h of ~he voice coil former 26, which is
made of a ma~erial which ~ransmi~s sound a~ a speed
grea~er ~han ~he speed of sound in air. For example, if
the former is 5 inches long and has a speed of sound
~ransmission ~en ~imes ~hat of air, the acoustical
apparent leng~h of ~he former would only be .5 inches. By
placing ~he high frequenc'~ driver .5 inclles into ~he end
of ~he former 26, oroximate to ~he driving circle 20, the
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apparen~ acoustical source of bo~h the high and low
frequency drivers would be at approxima~ely the same
location. The specific length of the voice coil former 26
and the material chosen for its construction may be varied
to suit the particular application. For example, voice
coil formers made from metal instead of paper are
contemplated. Specifically, a longer former will result
in a longer time delay while a shorter former will usually
result in a shorter time delay, with the increasing speed
of sound transmission of the ma~erial serving ~o shorten
the time delay.
Ic is no~ necessary to achieve the exact
coincidence of the apparenc acoustical sources of the ~wo
drivers. A lis~ener hearing cwo sources of sound that are
within one-six~h of a waveleng~h of each other will not be
able tO perceive the ~wo sources separacely and ins~ead
perceives the sound waves coming from ~he cto sources as
if they were coming from a single source. As such, it iS
only necessary ~o posi~ion ~he cwo apparen~ acous~ical
sources such ~hac the sound waves emanacing cherefrom are
wichin one-six~h of a waveleng~h of each o~her. The
lis~ener will perceive ~he ~wo sources as being only one.
Referring now ~o FIGS. 3 and 4 an al~erna~e
embodimen~ of che mul~idriver loudspeaker of che present
inven~ion is indicated generally by che reference numeral
40 and includes bo~h a hic3h frequency driver and a low
frequency driver. A base 42 is adap~ed to support a steel
baske~ enclosure 44 and a magnet assembly a6 for the low
i276Z85
frequency speaker.
Disposed within ~he basket 44 is an inverted
conical diaphragm or cone 48 which is associated with ~he
low frequency driver and incLudes an inner concave sour.d
radiating surface 4~a and an outer convex sound radia~ing
surface 48b. The cone 48 also inclucles ~wo coaxial ends;
the upper, smaller end of the cone 48 is referred ~o as
the driving circle 50 and the larger end of ~he cone 48 is
referred to as the surround 52. A damping ring 54 secures
the surround 52 of cone 48 ~o che '~aske~ 44. The driving
circle 50 is secured ~o one end of an elonga~ed voice coil
former 26, ~he opposi~e end of which is centered in ~he
annular gap becween ~he pole pieces of ~he magne~ assembLy
46 and includes a voice coil 58. A damping ring 60
1~ secures the end of the voice coil former 56 proximate tO
~he voice coil 28 to the basket 44. The damping rings 54
and 60 serve to center ~he voice coil former 56 and the
cone 48 within the basket 44 but permit the cone and
former to move axially.
The voice coil 58 is glued or otherwise
permanently affixed to the former 56 and posi~ioned in the
air gap of the magne~ assembly 44, whic'l ~ogether ~ith
coil 53 forms a conven~ional loudspeaker motor for ~he Low
frequency driver.
A conventional hi~h frequency driver S2 is
located along and partially within ~he former 56 a~ ~he
end proxima~e ~o the drivin~ circle 50. E~igh frequency
driver 62 is secured to an L-shaped moun~ing bracket 64
12~6Z~S
which is supported by a pin 66 and a housing 68 extendins
along ~he leng~h of ~he former 56. The high frequency
driver 62 is can~ed wi~h respec~ ~o a plane perpendicular
to the axis of ~he low frequency driver and formed at ~he
driving circle 20, at an angle Y. The angle Y in ~his
particular embodiment approximates 105 degrees.
The voice coil former 56 is formulated in
accordance with the principles ou~lined above tO create an
appropriate time delay in low frequency driver by moving
the apparent acoustical source of the low frequency driver
out of the magnet assembly 46 and forward along the voice
coil former 56 to approximaeely ~he same location as the
apparent acoustical source of ~he high frequency driver
62. In ~his particular embodiment the voice coil former
is cons~ructed so as ~o move the apparent acoustical
source of ~he low frequency driver as close as possible to
~he end of the voice coil former 56 proximate the driving
circle 50. ~ ~his loca~ion, ~he sound waves emana~ing
from the low and high frequency drivers are within one
sixlh of a wavelength of each o~her, and a listener will
perceive ~he ~wo sources as being only one.
This embodimen~ is par~icularly adap~ed for use
as an au~omobile loudspeaker. The use of ~he can~ed high
frequency driver 62 is well sui~ed for ~he placemen~
loca~ions available for loudspeakers in automobiles.
Typically, these locations include ~he package shelf
(si~ua~ed behind ~he rear seats), ~he dash board and ~he
lower portions of ~he car doors. The limited number of
1Z76Z8~i
possible loudspeaker locations coupled wi~h the fact tha~
the position of ~he lis~eners in automobiles is generaLly
stationary wi~h respect to the loudspeakers, permi~s the
use of the can~ed high frequency driver 62 arrangement ~o
direct the sound emana~ing from ~his smaller, lower power
driver directly a~ the lis~eners. As a result, ~he sound
emanating from the high frequency driver 62 is not
directed against ~he rear window, windshield or into the
footwells of the au~omobile. This is accomplished without
the problems normally encountered when ~he high frequency
driver is placed in fron~ of ~he low frequency driver in a
mul~idriver loudspeaker. Fur~her, ~he listeners will
perceive the separa~e sound waves emana~ing from the high
and low frequency drivers as origina~ing from a single
loca~ion.
As will be readily apparen~ ~o ~hose skilled in
~he ar~, ~he inven~ion may be used in o~her specific forms
or for o~her purposes withou~ depar~ing from i~s spirit or
central characteristics. The presen~ embodiment is
~herefore ~o be considered as illus~ra~ive and no~
res~ric~ive, the scope of ~he inven~ion being indicated by
~he claims ra~her ~han bv ~he fore50ing descrip~ion, and
all embodimen~s which come within ~he range of equivalence
of ~he claims are in~ended to be embraced.
