U.S. patent number 3,648,801 [Application Number 05/013,886] was granted by the patent office on 1972-03-14 for sound radiator.
This patent grant is currently assigned to Elektroakusztikai Gyar. Invention is credited to Denes Huszty, Andras Illenyi.
United States Patent |
3,648,801 |
Huszty , et al. |
March 14, 1972 |
SOUND RADIATOR
Abstract
A series of at least three loud speakers is set one in each of
at least three walls forming alternately oppositely opening
dihedral angles with each other. The center-to-center distance
between the loud speakers is less than 10 times the wavelength of
the upper limiting frequency of the sound frequency band. The loud
speakers are excited by the same signal source, and a stronger
interference field is produced than if the sound emanated from a
planar or spherical surface.
Inventors: |
Huszty; Denes (Budapest,
HU), Illenyi; Andras (Budapest, HU) |
Assignee: |
Elektroakusztikai Gyar
(Budapest, HU)
|
Family
ID: |
10995317 |
Appl.
No.: |
05/013,886 |
Filed: |
February 25, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Nov 26, 1969 [HU] |
|
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EE 1750 |
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Current U.S.
Class: |
181/147 |
Current CPC
Class: |
H04R
1/323 (20130101) |
Current International
Class: |
H04R
1/32 (20060101); G10k 013/00 (); H04r 001/28 () |
Field of
Search: |
;181/31R,31A,31B |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Publication "A Four-Speaker Bass-Reflex Enclosure" by Dr. Richard
C. Hitchcock, Popular Mechanics, June, 1957, pp. 142-144,
181-318.
|
Primary Examiner: Tomsky; Stephen J.
Claims
What we claim is:
1. A sound radiator comprising at least three loudspeakers excited
by the same signal source and each having a flat front panel
perpendicular to the radiating axis of the speaker, the panels
being on a common level and meeting each other at angles
substantially different from 180.degree. along lines that are
parallel to each other, a flat panel perpendicular to and below and
common to all said front panels, said front panels meeting said
perpendicular panel in a zigzag line, said axes of adjacent
speakers intersecting each other alternately before and behind said
zigzag line, adjacent speakers having radiating centers that are at
a distance from each other less than 10 times the wave length of
the upper limiting frequency of the speakers.
2. A sound radiator as claimed in claim 1, and a second flat panel
perpendicular to and above and common to all said front panels and
parallel to the first-mentioned perpendicular panel, said front
panels meeting said second perpendicular panel in a zigzag line
congruent to the first-mentioned zigzag line.
Description
The object of the invention is a sound radiating element and a
sound radiator built up of such elements, in which the subjective
sensation of the radiated sound is a better one than that of prior
sound radiators.
Experts dealing with problems of electroacoustical transmission are
well aware of the fact that no high sound power can be obtained
from a loudspeaker consisting of only one single sound radiator of
small dimensions. By sound radiator it is meant a loudspeaker (s)
built in a box, horn, baffle etc. Further it is well known that the
radiation properties, i.e., the characteristics of the sound field,
the frequency response curve and the directivity pattern (1) (It is
to be noted that the parenthetical numerals throughout this text
relate to the bibliographical references at the end thereof.) of
sound radiators consisting of a number of radiating elements are
influenced by the arrangement of the construction. It is to be
mentioned that in some cases even one of the sound radiating
elements can be used as a sound radiator itself. By such
arrangements nonhomogenity sound field, i.e., a sound field with
strong interference is energized in the neighborhood of the sound
radiator. Its extension, its nonhomogenity depends on the utilized
radiators, their dimensions and their arrangement relative to each
other (2). Investigating the different solutions already realized,
a correlation can be observed between the nonhomogenity of the
nearfield and the directivity pattern of the radiator.
Theoretically the directivity pattern of the surface radiator
becomes narrow at high frequencies. By this the sound pressure is
diminished deviating from the axis of the radiator. In FIG. 1, 1
indicates the radiator from side-view, 2 the vector leading to the
observer's point in the far-field, .alpha.(.degree.) is the angle
between the vector of the observer's point and that of the axis of
the radiator. FIG. 2 shows the idealized frequency response curve
p= p(f) in the axis (.alpha.= 0.degree.) and in a certain angle
.alpha. 0.degree. off the axis the directivity pattern gradually
diminishes at high frequencies. These theoretical considerations
are well proved by practice. It has been the practice to design
convex radiators and concave ones too. In FIG. 3, 3 indicates a
convex and 4 a concave sound radiator while 2 here also marks the
vector of the observer's point in the far-field. In such radiators
the former effect increases and even the frequency response
belonging to the axis (.alpha. =0.degree.) is irregular. The
corresponding frequency response curves p= p(f) of the usual
aforementioned arrangements as a function of .alpha. (.degree.) are
shown in FIGS. 4 and 5. In practice in both arrangements further
irregularities occur. On convex surfaces between 2 and 5 kHz. a
characteristic dip can be observed. On concave surfaces due to the
focusing effect in the range of low and middle frequencies where
the wavelength, the distance of the focus and that of the measuring
microphone are about the same-- a maximum of sound pressure occurs.
At high frequencies due to the diminishing of the wavelength a
diminishing of the focal length can be observed. Hence, the
observer or the microphone-- as in the case of convex surfaces-- is
surrounded by a sound field in which the frequency response, as a
function of frequency, is falling even in the axis, i.e., at
.alpha. = 0.degree.. The fulfillment of the abovementioned
considerations may be well observed even in line radiators that can
be considered to be a limiting case of surface radiators.
Spherical radiators are to be mentioned particularly as being the
most general forms of convex radiators. The classical type of this
kind of radiators, the so called Kosters' radiator (3) was followed
by a number of constructions--used in the industry extensively--
among which the patent descriptions (4), (5) and (6) are to be
mentioned as examples. By these radiators a weak interference field
is produced in free field, as the elemental radiation has a
divergent character. In a living room, i.e., in the neighborhood of
reflecting surfaces the interference of the sound field is
increased by the reflections from the walls (7), (8), (9). Thus,
the subjective sensation of the "sound image" produced by the sound
field is enlarged, the origin of the sound cannot be determined
exactly and the effect of the room surrounding the sound source is
to be felt considerably.
Although these systems represented a great step forward as compared
to prior systems having one single loudspeaker only-- which
improvement is due to the increased nonhomogenity of the produced
sound field-- for further progress the requirements set in
connection with the radiator and the subjective experience have to
be revised. In the course of revision efforts are to be directed
toward finding which are the desirable characteristics of a sound
radiator reproducing sound with remarkable fidelity and the why of
it.
In sound radiators the frequency response and the directivity
pattern within the transmitted band ought to be smooth and as
independent of the frequency as possible, or these conditions
should be fulfilled at least within a broad band (10), (11). This
is an especially important requirement when radiating perspective
sound (12). Further to the abovementioned conditions, according to
our practice, it is also very important that the frequency
responses measured in free field and in a living room should be as
equal as possible. In this case namely almost the same sound
pressure-- and therefore the same subjective sensation-- can be
obtained in small and in middle size rooms i.e., the reproduced
sound image will be independent of the room. This statement can be
explained by the equality of the radiated power when the
aforementioned conditions are fulfilled.
There emerges, however, the question under what conditions a
transmitted band can be considered to be a smooth one.
The program signal to be reproduced-- be it speech, music, natural
or another sort of noise-- in fact, never is a vibration with a
line spectrum i.e., a sinusoidal vibration, but always a signal
with practically finite bandwidth. The natural sounds, namely, be
they speech sounds or musical ones have needs a beginning and an
end, i.e., they are of finite duration. Applying Fourier's theorem
it is obvious that the ear almost never is excited by pure
sinusoidal sounds. Furthermore, in the case of finite duration the
spectrum of sounds that could be characterized at infinite duration
with a single spectrum line will widen to the bandwidth .DELTA. f
according to the equation .DELTA. f=2/.DELTA. t (13). Here .DELTA.
t means the duration of the signal, .DELTA. f its bandwidth the
value of which, in the case of t= 50 ms for example, is 40 Hz. The
investigations of Winckel (14) show that the phonems of speech and
the swift passages of music comprise signals with a duration of
about 50 ms. Hence, the system is in fact mostly energized not by a
pure sound but by sounds having spectra of considerable bandwidth
with a configuration varying with time.
It is well known that the intensities of components within the
critical band of hearing (15), at an excitation longer than 10 ms
are added by the ear unmindful of the components frequencies within
the critical band of hearing (16). The irregularities within the
critical band, however, cannot be observed, which fact is proved by
the following experience. Let us consider that in a direct hearing,
i.e., free of electroacoustical chain, the acoustical surrounding
of the listener is an interference sound field, due to reflections
on the boundary surfaces and diffraction on objects including the
human body (17). The nonhomogenity of this interference field--
although considerable-- according to practice cannot be observed,
not even in an idealized surrounding, free of reflections, in the
so-called anechoic chamber. If namely a natural sound source e.g.,
a speaking person is listened to in an anechoic chamber and the
speaking person i.e., the sound source slightly turns away from the
listener, the ear of the listener-- due to the changing of the
geometrical arrangement-- is in a different sound field, which fact
can be well measured physically, yet the turning of the sound
source cannot be observed (18). This phenomenon is obviously due to
the fact, that the signals of speech-- as it is well known-- are
signals of finite bandwidth. A similar experience can be made when
hearing natural sounds, or music, or noise. In a natural
surrounding having reflecting surfaces this irregularity will occur
even stronger. Let us mention for example the well known highly
irregular character of the frequency response curve-- measured with
the help of sinusoidal signals-- of sound radiators operating in a
room having reverberation (19).
Similar conclusions can be drawn-- among others-- from the results
of Flohrer (20): according to his experience a dip having a
relative bandwidth .DELTA.f/f.ltoreq. 0.1 in the frequency response
curve cannot be observed.
It follows from the aforementioned that there is no practical
reason for taking into consideration the irregularities of the
frequency response within the critical band or the narrow dips
having an interference character of the directivity pattern. On the
other hand the larger dips and peaks of the frequency response are
worth noting, as, when reaching the critical bandwidth, their
presence-- even if they are of interference origin-- may be heard
and is of disturbing character (21).
Out of the usual specification for sound radiators let us consider
the shape of the frequency response curve within the transmission
band. Rather often an irregularity of .+-.5 db. can be observed
here. According to Shorter's experience (11) irregularities of
.+-.2 db. may be observed in some ranges of the frequency response
curve.
He observed that for example the quality of the sound-- due to the
irregularities of a frequency response curve of some db., having
dips or peaks broader than the critical band-- becomes colorless,
hard and metallic, and that a broad dip at frequencies of 2-5 Hz.
provides the sensation of the sound source being far off while at
the same place a small size peak gives the impression of the sound
source being rather near the observer.
The requirements set in the aforementioned from the subjective side
lead to very strict requirements in the technological realization
of sound radiators, all the more so, if it is taken into
consideration that during monitoring further irregularities are
caused in the sound field surrounding the listener.
In the design of the prior sound radiators, on the basis of the
aforementioned theoretical considerations, efforts had been
directed toward reducing the interference field in order to
possibly avoid nonhomogenities. As already mentioned in connection
with FIG. 1-5 and when describing the different types of sound
radiators, these efforts were only partly crowned by success and
even the best loudspeakers have dips and peaks which can be
measured objectively, and which can be observed by the listener
subjectively. At the same time the task to eliminate the always
existing nonhomogenity of the interference field seems to be rather
hopeless.
When realizing the object of the invention the basic consideration
is not to eliminate the interference field but to create a rather
strong one in which dips and peaks occur so frequently that the
subjective sensation of their existence is no more possible. Thus,
in spite of the fact that these said irregularities of the sound
field can be measured objectively, the observer has the subjective
impression of being in a homogenous field. Hence, the object of
this invention is a sound radiator producing a soundfield the
interference nonhomogenity of which is rather strong. If namely the
irregularities of the sound field-- which is changing in space and
time-- actually are falling within the critical bands of hearing,
these irregularities cannot be observed any more and the subjective
sound impression will be a good one. For this purpose-- on the
basis of the aforementioned-- such a strong interference field has
to be produced at which the condition .DELTA.f/f.ltoreq. 0.1 is
satisfied. In this case even the disturbing factors of the room or
the surroundings are compensated by the strong inhomogenity of the
field, i.e., the electroacoustical transmission becomes almost
independent of the surroundings. For better comparison between the
subjective sensation and the parameters, measured objectively, it
is advantageous to carry out measurements by help of signals having
statistical properties like program signals have instead of the
common sinusoidal signals. This condition is fairly satisfied by a
noise of one third octave bandwidth.
Obviously the abovementioned requirements can only be met with by a
compound sound radiating element comprising a plurality of
loudspeakers, respectively a sound radiator built up of such
elements.
In this invention the strong interference sound field of the
element comprising a plurality of loudspeakers (from now: sound
radiating element) which is a constituent part of the sound
radiator, is produced immediately at the aperture of the sound
radiating element. By aperture we means that real or fictive
boundary surface of the sound radiating element through which the
produced sound field is immediately passed on to the medium outside
the sound radiator. In most of the possible arrangements the
aperture in the solid angle of the main radiation of the
loudspeakers is at one or more points in contact with the wall
elements carrying the individual loudspeakers. On the surface of
the aperture, being in the nearfield of the sound radiating
element, the amplitude and the phase of the excitation of the air
particles is rapidly changing from point to point. By this strong
nonuniform phase distribution produced along the surface of the
aperture as a function of place it is made possible for the sound
radiating element to show superdirective properties (22), i.e., to
prevent the actual narrowing of the main lobe of the directivity
pattern at increasing frequency.
Utilizing this sound radiating element arranged according to the
invention as a building block, sound radiators can be composed
variable in a wide range with a view toward the actual acoustical
task. The sound radiating element may be composed of a plurality or
at least three single unit and/or multiple unit loudspeakers
arranged in such a manner that the planar surfaces through the
radiating surfaces of the loudspeakers have an angle different from
180.degree. and their intersecting lines are parallel, while in the
planar surface perpendicular to these intersecting lines the
intersecting line is a broken one, so that the radiating (main)
axes of the individual neighboring loudspeakers, respectively their
projection on the aforementioned perpendicular planar surface are
intersecting each other before and behind the broken line
alternately, and the radiating centers of the neighboring
loudspeakers are at a distance from one another less than three
times the wavelength of a sound wave belonging to the upper
limiting frequency of the transmitted frequency band.
The upper limiting frequency-- according to the draft
recommendation of the International Electrotechnical Commission
(IEC)-- is that frequency at which the frequency response of the
loudspeaker, measured on the reference axis, has decreased a stated
amount (normally 10 db.) below the mean response averaged over a
bandwidth of one octave in the region of maximum sensitivity. Sharp
peaks and troughs in the response curve narrower than 1/8 octave
shall be neglected for both the upper and the lower limits (23). If
over an even number of planar surfaces identical loudspeakers are
arranged symmetrically, a radiation with symmetrical directional
effect will be obtained, if, however, an odd number of planar
surfaces is utilized a special directional effect will result,
i.e., the main lobe of the directivity pattern can be tilted. This
tilting effect of the sound radiating element utilizing a plurality
of loudspeakers is rather weak and is increasing with diminishing
the number of loudspeakers building up the sound radiating element
and its most expressed form is obtained at an element comprising
three loudspeakers.
In fact, the loudspeakers may be arranged asymmetrically too, they
can have different dimensions and different forms by which further
desirable effects can be attained.
Moreover, to the planar surface over the radiating opening of a
loudspeaker-- as to aperture plane-- more than one loudspeaker may
be assigned.
The object of the invention shall be described in detail by way of
example with preferred embodiments using the following
drawings:
FIG. 6 gives a diagrammatic view of an element arranged according
to the invention comprising five loudspeakers and suitable for the
explanation of the concept of the invention.
FIG. 7 is the perspective view of an elemental one-line sound
radiating element comprising three components.
FIG. 8 illustrates the perspective view of a one-line sound
radiating element consisting of four components.
FIG. 9 shows the perspective view of a one-line sound radiating
element comprising five components.
FIG. 10 is the perspective view of a sound radiator comprising two
times four components. At this embodiment the same planar surface
can be laid over the opening surfaces of the loudspeakers placed
two over two other ones.
FIG. 11 shows the perspective view of a sound radiator comprising
two times three components. In this embodiment the same planar
surface can be laid over the opening surfaces of the loudspeakers
placed two over two other ones.
FIG. 12 also illustrates the perspective view of a sound radiator
comprising two times three components with the difference as
compared to the embodiment shown in FIG. 11 that the components of
the sound radiating element are turned away from one another.
FIG. 13 as embodiment is similar to the embodiment shown in FIG. 12
with the difference that the sound radiator is built up of two
times four sound radiating elements.
FIG. 14 as embodiment showing a high power sound radiator system.
The individual loudspeakers are special surface or line radiators
which may also be used independently, the directional effect of
which is-- at the arrangement according to the invention-- modified
according to the advantages to be mentioned later.
FIG. 15 illustrates the perspective view of a sound radiator in
which more than one loudspeakers belong to the planar surface-- as
aperture surface-- through the individual loudspeakers of the sound
radiating element. In this case and with these components wide band
transmission is made possible by a multichannel system with the
ability of radiating independently. For reasons of construction the
two components in the middle of the embodiment shown in the FIG.
are individual widerange loudspeakers each.
The sound radiating element to be seen in FIG. 6 is built up of
five either single or multiple loudspeakers 5 which are arranged so
that the planar surfaces 6 over the radiating surfaces have an
angle 7 different from 180.degree. and the intersecting lines 8 of
the said surfaces 6 are parallel to each other while the
intersecting line 10 between the planar surface 9 perpendicular to
the parallel intersecting lines 8 and the planar surfaces 6 is a
broken one, the loudspeakers 5 are placed so that the main
radiating (symmetry) axis 11 of the neighboring loudspeakers 5
respectively their projection 12 on the planar surface 9 intersect
each other alternately before the broken line 10 in the
intersecting point 13, respectively behind the broken line 10 in
the intersecting point 14, and the radiating centers 15 of the
neighboring loudspeakers 5 are at a distance from each other
shorter than 10 times the wavelength of the sound wave belonging to
the upper limiting frequency of the already defined sound frequency
band.
FIGS. 7-15 show different embodiments the building up of which-- in
consideration of FIG. 6-- needs no further explanation than already
given for the said figures. Suffice it to say, for FIG. 7 as for
the others of FIGS. 8-15, that the loudspeakers 5 are set in flat
front panels 6a that meet perpendicular upper and low flat panels
9a and 9b in zigzag lines 10.
The sound radiators are excited by the same signal source. By the
sound radiating element, respectively sound radiator arranged
according to the invention a stronger interference field is
produced than by prior sound radiators having a planar or a
spherical surface. Its special advantage is that as compared to
other systems-- for example the 1/8 spherical radiator mentioned in
reference (9)-- its frequency response does not comprise any dip
between 2,000 and 5,000 Hz. and the directivity pattern becomes
more independent of frequency. For comparison, FIG. 16 shows
frequency response curves under similar measuring conditions and
using similar types of parallel connected loudspeakers, eight
pieces each. In FIG. 16 curve 16 relates to the sound radiator
arranged according to the invention shown in FIG. 10, while 17 is
the frequency response curve of the 1/8 spherical sound radiator
described in reference (9), both measured with a noise of one third
octave bandwidth. Both measured sound radiators were built in boxes
of equal width so that two loudspeakers were placed under each
other subsequently. The boxes were damped inside with cotton wool.
The angle between the loudspeakers was in the arrangement according
to the invention .beta.=145.degree. --where .beta. is the angle 7
in FIG. 6-- and .beta.=135.degree. in the prior arrangement. The
width of the box was 0.6 m. in both cases. The volume of the room
used for measurement was 125 m..sup.3 having a reverberation time
of 0.45 .+-. 0.05 s between 100 to 10,000 Hz. A Bruel and Kjaer
measuring microphone Type 4135 was used. It was verified by the
comparing measurements of the chosen two different sound radiators
that taking similar loudspeakers and similar dimensions the
arrangement according to the invention shows considerable
advantages as compared to the prior arrangement imitating a
spherical radiator. The same was verified also by the directivity
patterns measured in free field. This time the sound radiators
already measured in a living room were measured afresh-- for
comparison-- in a field free of reflections. The measuring
microphone was placed in a distance of 2 m. from the sound
radiators. The exciting signal was a noise with a bandwidth of one
third octave. The directivity patterns obtained with the
arrangement according to the invention with a midfrequency of the
noise of 1, 2, 4, 8, 16 Hz. are shown in FIG. 17 a, b, c, d, e. In
FIG. 18 a, b, c, d, e the directivity patterns of the prior
arrangement are to be seen. In connection with FIGS. 17 the
directivity patterns gradually become steady as a function of
frequency and the connecting superdirectivity may be well observed
in the arrangement according to the invention.
A symmetrical directivity pattern results from the sound radiating
element built up according to the invention symmetrically and
utilizing an even number of loudspeakers which may be considered to
be equal. If, however, an asymmetrical arrangement or an odd number
of loudspeakers it utilized, or an even number but differing in
sensitivity, the main lobe of the directivity pattern will tilt the
direction of the more numerous loudspeakers or in that of the
loudspeakers of a higher sensitivity. Applying the arrangement
according to the invention-- as already mentioned-- a sound
radiating element with a tilted main lobe and with the appropriate
combination of such elements a sound radiator having the same
properties may be built up.
Measurements were carried out with the embodiment shown in FIG. 11
and the obtained directivity patterns, to be seen in FIGS. 19 a. .
.e clearly show the tilting of the main lobe by which a special
effect can be obtained. The measuring conditions and the used
mid-frequencies-- here too-- were equal to those mentioned in
connection with FIGS. 17 and 18.
If the sound radiating elements are built up so that the angles
between the elements are different from 180.degree., the symmetry
of the directivity pattern, respectively its asymmetry may be
produced even on planar surfaces perpendicular to each other.
In order to increase the nonhomogenity of the interference field,
i.e., to influence the directivity pattern of the sound radiating
element as a function of frequency it is suitable to place in the
area in front of the loudspeakers obstacles the dimensions of which
are comparable to the wavelength. By the diffraction occuring along
the surfaces of such obstacles the phase variation at the aperture
of the sound radiating element is further increased. If the
dimensions of the obstacle placed in the area in front of the
loudspeakers are half the wavelength of the sound belonging to the
upper limiting frequency of the transmitted sound frequency band,
the described effect will follow. For verifying this statement
FIGS. 21 a, b, c, d and e show the directivity patterns obtained
when measuring the arrangement according to FIGS. 20a and 20b, and
using cylinders 18 of wood built in the sound radiator 19
comprising loudspeakers 5. When comparing FIGS. 17 and 21 it is
well to be seen that after building in the obstacles the
superdirective character of the directivity pattern increased more
and more and-- due to the diffraction of the sound waves at the
cylinders-- the directivity pattern widens from the axis. The
character of the effect is also depending-- as a function of
frequency-- on the wave impedance of the built in obstacle as
compared to that of the air.
FIGS. 22, 23 and 24 show free field frequency responses. For the
measurements the same geometrical arrangement and the same noise
signal of one third octave bandwidth were applied as for the
measurements of the directivity patterns. In FIG. 22 the results of
the measurements with the arrangement according to the invention,
shown in FIG. 10, are to be seen, while in FIG. 23 those of the
prior spherical radiator. FIG. 24 shows the measuring results of
the arrangement according to FIG. 10, embodied according to FIG.
10. When comparing FIGS. 16 and 22 it is obvious that the
arrangement according to the invention provides the properties that
the frequency response curves in the free field and in the living
room are equal, that the directivity patterns are independent of
frequency and even have a superdirective character. Comparing the
measured results with the subjective experiences, dealt with in
this description, and with the resulting technological task it is
obvious, that by the use of the sound radiating elements arranged
according to the invention a good subjective effect can be obtained
which at the same time-- by objective parameters - can be firmly
kept in hand technologically.
It is apparent that those skilled in the art may make numerous
departures from the specific arrangement described herein without
departing from the inventive concepts.
* * * * *