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The present invention relates generally to sound effects and sound reproduction. The present
invention is aimed at overcoming the problems of interrelated loudspeakers and sound effects,
which are particularly compelling in movie theaters. Significant progress has been seen in the
sound quality of the film over the past decade. However, problems with movie sound
reproduction remain between the theater speaker system and its acoustic environment.
Currently, most movie theaters are not equipped with speaker systems incorporating modern
technology, and in fact, most theaters use systems with components designed in the 1940s.
Typically, these systems use horn radiators in both the low and high frequency regions, and
perhaps complement the very low frequency subwoofer to overcome the lack of low frequency
response. In the case of content that includes a bus, it is common for audible distortion to occur
at high audio levels. The midrange sound distribution of such systems is suitable for balcony
theaters (i.e. the best midrange dispersion is vertical). Multi-cell radio frequency horns that have
been attempted to generate relatively constant amplitude output over a range of output angles
and frequencies are still substantially inferior to modern designs. Its crossover design and
dispersive properties result in a "combedback" shaped power response which is apparent when
making a moon octave pink noise measurement in a theater using such a system. In the article by
Mark Engebretson and John Agle, "5 HPTE Journal", published in 1982, pages 1046 to 1057,
entitled "Movie sound reproduction system-technical advances and system design considerations"
It is discussed. Engebretson and Agle have proposed to use a combination of speaker elements
that currently use a large amount of technology currently in speaker design. The method involves
the use of direct radiators placed in a perforated cabinet as woofer and the use of a so-called
"constant directivity" horn with wide dispersion as a tweeter. Although such a combination
provides a useful improvement to the systems normally used, the smoothness of the low and
high frequency responses in such systems is not optimal and the localization of the sound and
the stereo presence are not optimal. According to the teachings of the present invention, it has a
smoother response and a more uniform audience listening area, with significantly lower
distortion, better sound localization and stereo presence than presently used loudspeaker
systems A movie theater speaker system is provided.
The invention uses a direct-radius cone drive plate drive mounted in a perforated cabinet as a
low frequency or woofer speaker element. Such a speaker is designed to radiate in an
environment of 2? steradian radiation angle, and to imitate such an environment the woofer is
integrated with the acoustic boundary wall and the stage (IA unit) is this 2? simulated
environment Note that it is provided well above the stage floor so as not to cause any substantial
interference. A horn tweeter is used as a tweeter with a low-distortion compression drive in a
fixed range. A steep gradient O-over network is used which has a crossover frequency at which
the woofer and tweeter dispersions match to a first approximation. The low frequency and high
frequency speaker elements are disposed integrally with the acoustic boundary wall in close
proximity to the back of the cinema screen. The screen is increasingly reflective to high
frequency sound energy, so high frequency sound is captured between the screen and the wall,
with high frequency response and high end tone balance (as well as degraded sound localization
and stereo presence) In order to overcome the problem of causing a tone balance, a sound
absorbing material is placed on the wall so as to substantially eliminate secondary radiation of
high frequency sound energy from the wall. Referring now to the drawings, FIG. 1 shows the
inventive speaker system behind the movie screen to the audience placed in the intended
environment within the movie theater. The audience (not shown) has the same perspective as the
viewer in FIG. A screen (2) (partially removed to show the speaker system) is placed above the
stage (4) and below the proscenium arch (6). In the row of FIG. 1, the loudspeaker system
comprises five loudspeaker devices, ie a loudspeaker device with a combination of loudspeaker
elements (8a to 8e) arranged substantially straight above the far side of the separated stage and
behind the screen. Have. The system of the present invention can include one or more speaker
element combinations. In most movie theaters, when presenting multi-channel cinema films,
three sets of speaker elements may be sufficient to provide left, center, and right channel audio
reproduction. In very large theaters it may be necessary to use a two-phase loudspeaker element
for each such channel. Although it is preferable to place the speaker system behind the screen to
match the localization of audio events with visual events, the presence of the screen significantly
affects the audio heard by the audience.
This is not only the result of the attenuation of the sound by the screen, but also the result of the
back reflections coming from the screen towards the loudspeaker system and its surroundings.
Typical screens have only about 7-8% open area. Although the screen is substantially transparent
to low frequency sound (less than about 500 H7), the screen becomes increasingly reflective as
the sound enters the high frequency region. Above about 5 KH2 only about 7% of the sound is
transmitted through the screen and the rest is reflected. The reflected high frequency energy is
secondarily reflected on each surface behind the screen. The environment of the loudspeaker
rear area is in some cases a large open area, in other cases a very close wall. In some theaters
there are also curtains behind the speakers. Such environments can cause high frequency
combing effects, changes in high frequency response and tone balance, loss of sound localization,
and confusion in stereo presence. Another element of the loudspeaker system according to the
invention is an acoustic interface, or a rigid wall (10) fixed with the loudspeaker elements (8a to
8e). A frequency dependent sound absorbing member is provided adjacent to at least a portion of
the wall as described below. The wall (10) is generally spaced apart from the screen (2) and
extends at least partially parallel thereto. In the case of a curved screen as in FIG. 1, the walls
preferably follow the curvature of the screen. Each combination of loudspeaker elements
includes low and high frequency loudspeaker elements. The low frequency element or the woofer
element comprises at least one, preferably two direct radiation cone diaphragm transducers
mounted in a phase inversion cabinet. As discussed further below, the use of two direct radiators
results in a better match of the low frequency speaker dispersion to the high frequency speaker
dispersion at the crossover frequency. If two transducers are used, both are preferably arranged
vertically adjacent to each other so that the longitudinal dimensions of the cabinet are vertical
and the best dispersion is provided horizontally. This cabinet is placed sideways in the hall with a
long parconi. The rf element or tweeter element comprises at least one suitable driven horn.
These elements are then preferably arranged above the low frequency loudspeaker elements.
The phase reversal cabinet is preferably a perforated cabinet. There is a considerable amount of
literature, especially the work of Thiele, on the study of low frequency speakers using direct
radiators and perforated cabinets. Does he have a hole? He is one of the people who developed
and popularized the analog circuit of vignette system. Also, Small has made it progress based on
the results of Shier. See the following article as an example. An article entitled "Speaker in
Perforated Cabinet Part 1", A, N, An English Journal of Audio Engineering Society, 19th issue,
May 1971, pp. 382-392, by Sier. An article entitled "Speaker in Perforated Cabinet 2", A, N, The
Journal of Audio Engineering Society, 19th edition, June 1971, June 471, pages 471 to 483, by
Sier. 21 for the "Journal of Audio Engineering Society" by Richard H. Small, entitled "Perforated
cabinet-type speaker system (1)-Small signal analysis", Vol. 5, No. 5, June 1973, pp. 363-372.
article. "Round I with cabinet type speaker system (part 2)-large signal analysis" by Richard I.
Small's [Journal of Audio Engineering Husa 11 141 Vol 21 No. 6 1 Word for 3 July / August
Articles on pages 43-444. Journal of Audio Engineering Society by Richard H. Small, entitled
"Perforated cabinet type speaker system (Part 3)-Synthesis", 21 vol. 7 No. 1973, 9 549-554.
Article. An article entitled "Journal of Audio Engineering Society" by Richard Todtsmall, vol. 21,
No. 8, October 1973, pp. 635-639, entitled "Perforated cabinet-type loudspeaker system (Part 4)Postscript". In the small study, it was assumed that the direct radiation type perforated cabinet
speaker radiates to the environment (correct half space) of 2? steradian radiation angle. In order
to properly simulate such conditions in a real environment, the speaker front surface should be
acoustically bound, such as an acoustic boundary wall (10), sufficiently spaced from any crossing
boundaries (eg stage floor (4)) It is necessary to be equal to See, for example, an article by Roy F.
Allison in the "Journal of Audio Engineering Sosay Eddie", vol. 22 @ 5 @ June 1974, pp. 314-320,
entitled "The Influence of vJa on Speaker Output". .
Allison discusses the mirror image speaker effect that occurs when a speaker in front of the wall
produces an acoustic image behind a wall that produces a variety of audible anomalies, including
midrange dips. In fact, the use of the loudspeaker front surface and the adjacent contoured wall
not only provides a better match between the actual and the small theory, but it also prevents
irregularities in mid-bass and overall lows. The response is also aurally smooth, thus optimizing
the performance of the woofer drive and the cabinet. The loudspeaker elements should be
approximately midway through the screen vertical dimension to maximize the distance from the
low frequency elements to the stage floor (while optimizing the simulated 2? acoustic boundary)
while ensuring that the sound localization to the spectator is not too high. Be placed. Although
desirable from the point of view of low frequency sound reproduction, the acoustic boundary
wall (10) produces a comb filter effect by capturing ^ frequency energy, destroying the stereo
image, as well as frequency response and high end tone The result is a delayed reflection that
tends to upset the balance, which exacerbates the problem of high frequency screen reflections.
These problems are particularly acute as the distance from the screen to the wall is preferably
small (on the order of a few feet) in order to bring the sound source as close as possible to the
audience. The high frequency acoustic boundary created by the wall (10) and the screen (2) thus
has a high Q value and is acoustically "hot" at high frequencies. To overcome this problem, the
present invention applies a sound absorbing material (12) to the acoustic boundary wall (10) at
least in the vicinity of the frequency loudspeaker element. The sound absorbing material (12) is
preferably frequency dependent and has acoustical properties such that low frequency sound
energy is substantially transmitted while high frequency sound energy is substantially absorbed.
?? Ideally the acoustic properties of this sound absorbing material are complementary to the
high frequency reflection properties of the screen, such that the absorption also increases as the
degree of reflection increases with frequency. Suitable materials include (rust shaped acoustic
foam products and mineral cotton or glass fiber insulation for thermal insulation. One form of
acoustic foam wedge material is commercially available under the trade name Nnex. In particular,
mineral cotton sound insulation materials for sound blocking are sold by U, S, and Gibsam under
the brand name Thermafiber Sound Attenuation Blanket. The low frequency absorbance is
related to the thickness of the material used. Any suitable means may be used to secure the
acoustic boundary wall absorber.
One perspective partial cutaway view of the combination of speaker elements is shown in FIG.
The low frequency part or the woofer part of this combination preferably comprises two direct
emission cone-shaped loudspeakers (14) mounted in a perforated cabinet (18) having two
circular apertured holes (20, 22). (16). The radio frequency or tweeter element is preferably a
horn (24) and a matched compression driver (not shown). A wedge-shaped foam sound
absorbing material is shown as the sound absorbing material (12). This material is fixed to the
wall in the drawing and extends just above and just below the extended tweeter horn and over
the entire width of the wall (10). The area required for the sound absorbing material (12 can be
determined geometrically taking into account the dispersion of the tweeter, the angle of the
tweeter relative to the screen, and the distance from the tweeter to the screen. Although it is not
essential to the present invention to select a specific speaker element, the overall hearing effect
of this system can be obtained if system components with low distortion sufficient and smooth
characteristic responses used as these elements are obtained from commercial products. Raise.
For example, those of the type JBL 2225 H / J, which are suitable low frequency transducers
available from James B Lancing Company, have various measures taken to generate a
symmetrical magnetic field to reduce low frequency distortions, resulting in their working area It
is effective and smooth. The company also sells a suitable perforated cabinet JBL 4508, which
gives a smoother frequency response and a more normal polarity response than horns designed
for mid-bass. Suitable high frequency horns and drives such as the JBL 2360 horn and 2441 HA
moving parts are also available from this company. This horn is of constant directivity which
gives good dispersion over considerable spatial angles. In the practical embodiment of the
present invention a horn of angle 90 "X 40" was chosen, but this parameter should be chosen for
the specific theater so that the audience hears the largest possible ratio of diameter sound. is
there. Every spectator should be within the 16 dB effective angle of the horn. Conversely, for
surfaces that cause long delayed reflections, it should be possible to send a small amount of
sound that is practically possible. The compression drive is of a modern design incorporating the
structural improvements obtained by laser beam testing of the prior horn drive. An article by
Mark Enkebretson and John Agle co-authored "5 HPTE Journal", November 1982, pages 1046 to
1057, entitled "The movie sound reproduction system-technical advances and system design
ideas" in the same combination of speakers. Is suggested.
Although the woofer and tweeter are illustrated as being integral with and supported by the
structural members associated with the acoustic boundary wall, in principle the front wall of the
perforated cabinet (18) is the acoustic boundary wall (10) It is only necessary that they be
connected to ground or the like. However, from a constructional point of view it is also desirable
that the toe be integrated with and supported by the structural members associated with the wall
(10). In order to give the horn some degree of rotational freedom and to minimize system depth,
the horn should have its front edge slightly forward of the front of the woofer cabinet (about 6
inches (15, 240)) Be mounted. This wall is rigid and heavy gray wood (on the order of 3/4 to 1
inch (1,9 to 2.541)) or several meters <2 to 3 layers of gypsum board (1/3 to make it cheaper) In
any case, 2 to 578 inches (about 1,77 to 1.59 -a>) may be formed on a wooden frame or the like.
A mineral cotton or glass fiber type sound insulation (26) is preferably used behind the wall to
minimize any sound transmission through the wall due to echoes occurring in any open space
behind the system. The woofer cabinet (18) rests on a support shelf (28) integral with the wall
support frame. The details of the wall structure and the speaker element support structure may
not be as rigid as the structure has sufficient rigidity to properly support the speaker. If
necessary, subwoofers can be added to the system to add very low frequency response. Also,
ambient speakers can be additionally used on the side and back of the theater as required. FIG. 3
shows a block diagram of an apparatus for applying audio information carrying electrical energy
to a loudspeaker element, including a crossover network. Preferably, the crossover network is
located in the low level stage of the system. For example, they are placed after the preamplifier
and before the output amplification rather than placed on the speaker element itself. In this way,
the crossover network does not have to handle large amounts of power and can be adjusted
much more easily and accurately. For example, one audio channel is applied to the preamplifier
(40) and its output is split into two paths, a bypass and a low pass. The bypass path includes a
high pass filter (42) having the characteristic HH (Sn). This low-pass path comprises a low-pass
filter (44) with characteristic HL (Sn) and a time-delay paper fit (46), preferably consisting of a
cascaded second-order all-pass RC active network.
A time delay is required in the low pass path because in this preferred physical configuration the
woofer element is in front of the towder element, so that time compensation is necessary to
ensure temporal coherence. Alternatively, this time delay may be placed in the bypass and may
be omitted when the speaker system components take on other configurations. In a practical
embodiment of the invention the woofer is in a shallow box approximately forward of the tweeter
horn driver. As a result, the low pass path requires a 1.9 millisecond delay. Bi-amplification is
used so that the bypass and low-pass outputs are applied to separate amplifiers (48) and (50)
that drive the speakers and the woofer speakers respectively. These bypass and low pass filter
networks are acoustical fourth order Linkwitz-Riley filters as used in some advanced commercial
speakers. These networks are flat rovings, steep slopes for drive protection, acceptable pole
patterns, ie the smallest rovings obtained by having a short and well controlled crossover region
taking into account the phase response. (IobinO), and an acceptable system phase response. The
Linkwick Riley filter is 31 volumes for the Journal of Audio Engineering Society by Stanley P.
Lipschitz and John V. Nderkoy, entitled "High-Slope Linear Phase Crossover Networks Introduced
by Time Delay". Tube y is described in the article of January 2nd, 1983, pages 2 to 20. The low
pass and bypass sections have matched phase responses that can provide a combined all-pass
response where each intensity curve crosses at 1 6 dB, with the amplification and phase of the
speaker driver itself Have the effect of A more detailed description of such a network is given in
Volume 24 of the "Journal of Audio Engineering Society" by Sekfleet H. Linkwitz entitled "Active
Crossover Network for Non-coincidence Drivers". The January / February 1976 issue is described
on pages 2-8. In addition, the article "The design of the speaker system", "The article of Wireless
World J magazine May, 1978, pages 52 to 56" by "Speakfleet Linkwitz" and the design of the
"speaker system-part 2" the seekfleet link See the article in Wytz, 1 Wireless World, June 1978,
pages 67-72.
The time delay device is preferably formed by the required number of cascaded secondary Bessel
type full bus networks. Three such networks are cascaded to provide the sixth order Bessel-type
full "bus time-to-time delay network" to provide the one, nine millisecond delay required in this
practical embodiment. Such a network is described in the text "2nd full bus RC active network"
by George Wilson in the language of "1 EEE t-Lanzak John On Circuit and Systems" words CAS24 Vol. 8 No. 8 August 1917 446 It is described in the articles after the page. In the present
practical embodiment the crossover frequency is 500 H7. The exact loss-over frequency is not
essential but was chosen for several practical and theoretical reasons. The biggest reason is that
this crossover frequency was chosen to obtain a first order match between the woofer and the
toe eater at this frequency. By doing so, it is possible to avoid the classical trade-off between
direct radiated speech response and output response (e.g. response sum at any angle). The
vertical dispersion of the woofer collapses as the frequency increases towards 500 H 2 and
matches to a considerable degree the angle of the tweeter horn 40 degrees at crossover. Thus,
the audible tone (co + oratton) at the crossover frequency is avoided by substantially eliminating
all abnormal bumps in the output response at crossover. It should be appreciated that there is a
relationship between the choice of loudspeaker (different dispersion characteristics for different
operating frequency bands) and the appropriate loss over frequency to meet this requirement.
Another reason for choosing 500 Hz as the crossover frequency is that this frequency is well
within the operating frequency band of the preferred woofer driver and tweeter drive. Another
reason is that 500H2 has historically been widely accepted as the speaker speaker system over
frequency for Iil & i. The crossover network and time delay network of FIG. 3 are used in the
active circuit embodiment. 4 and 5 show the active circuit arrangements of the Linkwitz-Riley
lowpass and bypass networks, respectively. These active networks are entitled [Design of multiamplifier RC active filters with emphasis on GIC implementation], ?, [Modern active filter design]
by Bull-Ton, edited by Scalaman et al. Use the technology described in the document published in
the year (reprinted from "IEEE" -Lanzak John On Circuit System ", CA 325, October 1978, pages
830 to 845).
Ladder simulation networks are used for the development of this active circuit. In this active lowpass network (FIG. 4), the frequency-dependent negative resistor is simulated by a double
amplifier ladder network, and in the active bypass network (FIG. 5) a gyrator inductance
simulator is used. FIG. 6 shows details of a practical embodiment of three secondary Bessel
networks for providing time delays. Active networks are preferred as they are less sensitive to
component errors. The amplitude response curves of the practical embodiment of the low pass
and bypass networks of FIGS. 4 and 5 are shown in FIGS. 7 and 8, respectively. In practice, this
crossover network includes appropriate equalization which may be required to compensate for
one or more of the following conditions: 1) of the high frequency response of the high frequency
horn compression driver 2) Dropping of the high frequency component observed on the
objective side of the cinema screen due to 2) high frequency attenuation of the screen, 3) adding
so that the final theater response meets the world standard (eg 15 O 2969) Correction factor.
The high frequency response curve of FIG. 8 includes a high frequency boost beginning at about
1500112 to compensate conditions 1) and 2).
Brief description of the drawings
FIG. 1 is an elevation view of the speaker screen apparatus of the present invention disposed in a
movie theater.
FIG. 2 is a perspective view with parts removed to show details of the speaker screen apparatus
of FIG. FIG. 3 is a block diagram showing an electrical system with crossover network for
applying audio information carrying electrical energy to a speaker. FIG. 4 is a circuit diagram
showing an embodiment of a low pass crossover network. FIG. 5 is a circuit diagram showing an
embodiment of a bypass crossover network. FIG. 6 shows an embodiment of a time delay
network. It is a route circuit diagram. FIG. 7 is a response curve of a low pass crossover network
as in the embodiment shown in FIG. FIG. 8 is a cough network response curve when the bypass
crossover network in the embodiment shown in FIG. 5 is combined with additional high
frequency equalization. 8a to 8e ииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииииии Sound absorbing
material F1a-6 ░
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