Field of the Invention
[0001] This invention relates to a dome-like speaker system and, more particularly, to a
dome-like speaker system which has a spherical wave horn baffle to diffuse into an
acoustic field space, acoustic waves from a dome-like vibrating plate so as not to
cause reflection and/or refraction, on the basis of the fact that the acoustic waves
from the vibrating plate are similar to spherical waves.
Prior Art
[0002] Many of recent speaker systems employ a dome-like vibrating plate in a tweeter and/or
a midrange.
[0003] As shown in Fig. 4, when such dome-like speaker is mounted on a flat baffle 2, disturbances
in the frequency characteristic of the speaker are often encountered. This is due
to the reflection caused by rapid expansion of acoustic waves into the acoustic field
space and the interference of acoustic waves between the baffle surface and vibrating
plate 1.
[0004] When acoustic radiation by the vibrating plate 1 placed in the flat baffle 2 as shown
in Fig. 4 is measured, it is understood that as shown in Fig. 5, the frequency characteristic
and directional characteristic of the vibrating plate exhibit many crests and valleys
therein and it is hence presumed that reflection, interference and refraction have
occurred.
[0005] When the state of acoustic waves in the vicinity of the vibrating plate 1 is observed
using acoustic intensities diagram at 6320 and 8000 Hz, it is seen that as shown in
Figs. 6A and 6B, the acoustic waves exhibit a wave front close to that of a spherical
wave at a place near the dome-like vibrating plate 1 while the wave front is disturbed
at a place remoter slightly from the vibrating plate 1.
[0006] It is confirmed from this fact that, basically, the acoustic waves radiated from
the vibrating plate 1 may be handled as spherical waves and that disturbances in the
wave front is due to reflection, interference or refraction of acoustic waves caused
by an improper shape of the baffle 2. Therefore, in order to flatten the characteristics
of the dome-like speaker, it is necessary to take the shape of the baffle into account.
[0007] As just described above, it is confirmed in the dome-like vibrating plate 1 that
the wave front of acoustic waves generated due to the shape of the vibrating plate
1 may be handled as spherical waves, so that in order to provide flat characteristics,
it is necessary to expand those spherical waves into an acoustic field space so as
to avoid reflection or refraction.
[0008] Thus the applicant has previously proposed as a new baffle shape through Japanese
U.M. application 59-189547 filed December 15, 1984, the "spherical wave horn baffle"
which introduces the concept of a horn thereinto.
[0009] The reason why the concept of such spherical wave horn baffle is basically introduced
is that the horn is conventionally used as means for diffusing acoustic waves into
an acoustic field space without causing reflection or refraction.
[0010] It is designed that when the dome-like vibrating plate is constituted as a part of
a spherical surface, the horn is formed so as to prevent rapid expansion of acoustic
waves from the vibrating plate into the acoustic field space and that the cross sectional
area of the horn is gradually expanded relative to the surface of the vibrating plate.
In the conventional horn, the cross sectional area of the horn is calculated by handling
the wave front in the horn as plane waves while in the applicant's speaker the horn
is formed by calculating the cross sectional area of the horn by handling the wave
front in the horn as spherical waves. This horn is used as a dome-like speaker baffle
to be defined as a spherical wave horn baffle. In that case, the problem is where
the center of the spherical waves is. In this respect, it is assumed that the initial
wave front as the origin of spherical waves substantially coincides with the surface
shape of the dome-like vibrating plate. Here, the dome-like vibrating plate is handled
as a part of a spherical surface and the center of the sphere is handled as the center
of the spherical waves.
[0011] The spherical wave baffle horn proposed previously by the applicant takes the form
of a horn such as that shown in Fig. 7 by giving partial surfaces of the horn using
the following formulas,
Sx = 2π(R + x) Hx (1)
So = 2πRHo (2)
[0012] The shape of this horn varies as shown in Fig. 8 by changing the cut off frequency
fc.
[0013] As will be seen in Fig. 7, in the spherical wave horn baffle 21 defined here, the
horn wall 21a extends behind the vibrating plate 1 and is closed. Thus the resulting
wave front may be regarded as being equivalent to that generated by a breathing sphere.
[0014] Therefore, the characteristics provided by the spherical wave horn baffle 21 may
be replaced theoretically by those generated by a breathing sphere. It is to be noted
that the breathing sphere does not theoretically exhibit directionality, but as the
wave front propagates actually behind the vibrating plate 1, the acoustic pressure
attenuates, so that the breathing sphere will have directionality.
[0015] As shown in Fig. 8, even at the same dome-like vibrating plate, the size of baffle
varies as the cut off frequency fc is changed. It is to be noted that when the baffle
is employed in an actual dome-like speaker, it is necessary to specifically take into
account how the characteristics to be desired should be and to determine the size
of the baffle.
[0016] Fig. 9 shows an example of a dome-like speaker SP for reproduction of a high frequency
band, employing a spherical wave horn baffle 21.
[0017] Fig. 10 shows the frequency and directionality characteristics of the horn baffle.
[0018] It will be seen in Fig. 10 that the characteristics have no crests and valleys and
that acoustic waves radiated from the dome-like vibrating plate causes neither reflection
nor refraction. Particularly, the features of the directionality are that the 30°
characteristic exhibits substantially the same curve as the 0° characteristic and
that the level difference is 3 - 4 dB, which is large on average compared to that
between the characteristics obtained when the flat baffle 2 shown in Fig. 4 is used.
This tendency is applicable to the 60° characteristics. This implies that the frequency
characteristic of a direct sound is substantially the same in a range of about 30°
right and left relative to the central axis irrespective of the position where the
sound is heard, and that the acoustic energy reflected by side walls, etc., is small
to thereby improve the location or positioning of an acoustic image. Therefore, the
spherical wave horn baffle is an excellent one which satisfies both opposing matters
of irrelevance to the hearing position and excellent location or positioning of an
acoustic image.
[0019] Figs. 11A and 11B show the results using acoustic intensities in order to see the
state of acoustic waves in the vicinity of a dome-like vibrating plate. Comparison
of Figs. 11A and 11B and Figs. 6A and 6B exhibits that disturbances in the wave front
of Figs. 11A and 11B are extremely small even at a position remote from the dome-like
vibrating plate 1 compared to Figs. 6A and 6B.
[0020] The dome-like speaker provides the flat characteristics, and improves the directional
characteristic, and the location of an acoustic image by employing the new spherical
wave horn baffle in the speaker.
Summary of the Invention
[0021] It is now obvious from the foregoing that the horn baffle of Figs. 7 and 9 has a
very excellent shape for a dome-like speaker to radiate acoustic waves without causing
reflection, interference and refraction.
[0022] However, with such shape, it is difficult to mount such horn baffle onto the flat
baffle 2 of the cabinet although it is possible to mount such horn baffle on a conventional
speaker cabinet.
[0023] There is the problem that when a dome-like speaker SP with a spherical wave horn
baffle 21 is mounted on the flat baffle 2 of the cabinet by performing required processing,
as shown in Fig. 12, a discontinuity portion ⓐ is produced at the junction of the
horn wall 21a of the baffle 21 and the flat baffle 2 to cause disturbances in the
acoustic waves to thereby adversely influence the frequency characteristic and acoustic
quality.
[0024] In order to solve this problem, it is necessary to join the horn wall 21a of the
baffle 21 and the flat baffle 2 surface of the cabinet so as not to produce a discontinuity
portion therebetween.
[0025] Thus the applicant previously proposed a structure in which the horn wall 21a was
joined to the flat baffle 2 surface at a junction ⓑ without forming any discontinuity
portion therebetween, as shown in Fig. 13.
[0026] Such structure of Fig. 13 serves to decrease disturbances in the acoustic waves due
to reflection and refraction in the frequency characteristic. However, with such structure
of Fig. 13, it is impossible to use a long horn, and the dome-like vibrating plate
adversely influence the acoustic quality because the dome-like vibrating plate 1 is
disposed considerably deeply within the cabinet rather than at the surface of the
flat baffle 2.
[0027] This invention derives from contemplation of the above problems. The object of this
invention is to solve the above problems, and to provide a dome-like speaker in which
the horn wall of the spherical wave horn baffle and the flat baffle surface of the
cabinet are joined to each other without any discontinuity portion therebetween to
thereby improve the frequency characteristic and acoustic quality.
[0028] A dome-like speaker according to this invention solves the problems by forming a
slope on a spherical wave horn baffle provided on the outer periphery of the dome-like
vibrating plate and joining the slope to the flat baffle surface of the cabinet so
as not to produce any discontinuity portions with the flat baffle surface.
[0029] By the slope continuous to the horn wall of the spherical wave horn baffle provided
on the dome-like speaker, the baffle can be joined to the flat baffle surface with
no or little discontinuity portions to make it difficult to cause reflection and refraction
of acoustic waves and provide a smooth frequency characteristic.
Brief Description of the Drawings
[0030] Figs. 1 - 3 show embodiments of a dome-like speaker according to this invention.
Fig. 1A is a cross section view of the essential portion of a first embodiment, Fig.
1B is cross section view of the essential portion of a second embodiment, Figs. 2A
and 2B show frequency characteristics, Figs. 3A and 3B show characteristics illustrating
the state of acoustic waves in the vicinity of the dome-like vibrating plate. Figs.
4 - 13 show a conventional speaker. Fig. 4 is a cross section view of the essential
portion of a structure in which the dome-like speaker is mounted on the flat baffle
of the cabinet, Fig. 5 is a frequency characteristic diagram, Figs. 6A and 6B are
characteristic diagrams showing the state of acoustic waves in the vicinity of the
dome-like vibrating plate, Fig. 7 illustrates the principle of a spherical wave horn
baffle, Fig. 8 illustrates a change in the size of a baffle required when the cut
off frequency of the dome-like vibrating plate varies, Fig. 9 is a cross section view
of the essential portion of a high-frequency band reproducing dome-like speaker which
employs a spherical wave horn baffle, Fig. 10 is a frequency characteristic diagram,
Figs. 11A and 11B are characteristic diagrams showing the state of acoustic waves
in the vicinity of the dome-like vibrating plate of Fig. 9, Fig. 12 is a cross section
view of the essential portion of a dome-like speaker having a spherical wave horn
baffle mounted on the flat baffle of the cabinet, Fig. 13 is a cross section view
of the essential portion of an example which a spherical wave horn baffle is joined
to the flat baffle surface of the cabinet.
Detailed Description of the Drawings
[0031] An embodiment of a dome-like speaker according to this invention will now be described
with reference to Figs. 1A, 1B to Figs. 3A, 3B.
[0032] Fig. 1A is a cross section view of the essential portion of a first embodiment of
this invention and Fig. 1B is a cross section view of the essential portion of a second
embodiment.
[0033] Figs. 2A and 2B are frequency characteristic diagrams and Figs. 3A and 3B show the
state of acoustic waves in the vicinity of the dome-like vibrating plate using acoustic
intensities at 6320 and 8000 Hz.
(Embodiment 1)
[0034] The first embodiment of this invention will now be described with reference to Fig.
1A.
[0035] When a spherical horn baffle 21 provided on the dome-like speaker SP is mounted on
the surface of a flat baffle 2 of the cabinet, they are not simply joined as shown
in Fig. 12, but the baffle 2 surface and the horn wall 21a are continuously joined
through a slope 4.
[0036] The slope 4 is formed such that the tangent line at an end point ⓒ on the spherical
wave horn baffle is smoothly connected to the surface of the flat baffle 2 at a point
ⓓ without discontinuity.
[0037] Reference numeral 3 inFigs. 1A and 1B denotes the front surface of the opening in
the horn 21.
[0038] By such structure, the frequency and directional characteristics of the speaker do
not substantially show disturbances, as shown in Fig. 2A. The relationship between
the 30° and 60° characteristics and the 0° level is substantially similar to that
of Fig. 10 and sufficiently maintains the closed characteristic of Fig. 7.
[0039] By use of the acoustic intensity diagrams in the vicinity of the vibrating plate
1, the characteristics of Figs. 3A and 3B exhibit significantly reduced disturbances
compared to those of Figs. 6A and 6B.
[0040] As shown in Fig. 2B, comparison with the characteristic ⓔ of Fig. 12 having a discontinuity
portion ⓐ at the junction exhibits that the speaker of Fig. 1A having the slope 4
considerably suppresses the reflection and refraction of acoustic waves to thereby
provide smoothed characteristics, as shown by ⓕ in Fig. 2B.
(Embodiment 2)
[0041] A second embodiment of this invention will now be described with reference to Fig.
1B.
[0042] This embodiment shows a structure in which the slope 4 which comprises an extension
of a tangent line to the horn wall 21a of the spherical wave horn baffle 21 mounted
on the dome-like speaker SP and the surface of the flat baffle 2 of the cabinet on
which a dome- like speaker SP is mounted are joined with a discontinuity portion
or a step at ⓖ therebetween.
[0043] In the particular embodiment, the rise or discontinuity portion at the junction ⓖ
is formed to be sufficiently small compared to the wavelengths in the frequency band
used of the speaker SP.
[0044] Thus, the influence of the discontinuity portion on acoustic waves is substantially
negligible and an effect similar to that of the first embodiment is obtained.
[0045] According to the inventive dome-like speaker, the influence of reflection and refraction
of acoustic waves by a discontinuity portion at the junction where the spherical wave
horn baffle mounted on the dome-like speaker is joined to the flat baffle surface
of the cabinet in which the speaker is mounted is reduced, so that disturbances in
the frequency characteristic are greatly reduced and the acoustic quality is improved.
The horn length can be increased compared to that of Fig. 13, so that the effect of
the spherical wave horn baffle is improved. Furthermore, the dome-like vibrating plate
can be disposed further forwardly compared to that of Fig. 13, so that the inventive
structure is very preferable in acoustic characteristic.
[0046] Thus the dome-like speaker having the spherical wave horn baffle can be easily mounted
on the flat baffle surface of the cabinet to thereby improve greatly the characteristic
of the speaker.