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JBL CINEMA SOUND SET UP Manual

Cinema sound system
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C I N E M A
S O U N D
S Y S T E M
M A N U A L
January, 1998

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Summary of Contents for JBL CINEMA SOUND SET UP

  • Page 1 C I N E M A S O U N D S Y S T E M M A N U A L January, 1998...

  • Page 2: Table Of Contents

    A. Hardware Class vs. Room Size..............B. Advantages of Biamplification ..............C. Cinema Playback Level Calibration............D. New JBL Driver Developments ..............E. Mechanical Details of JBL Screen Loudspeaker Systems ......18 F. Subwoofers ....................G. Surround Requirements................H. Screen Losses...................

  • Page 3: Introduction

    Electrical interface and system checkout will be covered in detail. JBL believes that the more dealers and installers know about the basics of sound in the cinema, the better will be the results of their work in all areas.
  • Page 4 loudspeakers. Options are to use the two remaining magnetic tracks for subwoofer signals and/or split (dual channel) surrounds. The 35 mm format was modified during the 1950’ s to handle four magnetic tracks: three screen channels and a single surround channel. At the same time, the standard monophonic variable area optical track was maintained.

  • Page 5: Digital Film Formats

    rOUTPUTS I N P U T S - - - - --QL LT 0 + M A S T E R -_o C ADAPTIVE LEVEL --_o R MATRIX CONTROL -_o SURROUNDS SUBWOOFER B~TYPE i kHz AUDIO L O W - P A S S - DELAY DECODER FILTER...

  • Page 6: A- And B-Chains

    100 Hz. This is commonly referred to as a “ 5.1’ channel system and uses an elaborate perceptual encoding process known as AC-3. timecode data btween optical tracks and picture Figure 3A. Dolby SR-D Figure 38. DTS Figure 3C. SDDS Figure 3B shows the format used in DTS.
  • Page 7 SIGNAL OUT FILM NOISE SOLAR --$-I_ ___) --) P R E A M P --) REDUCTION - CELL ‘ I ’ LAMP Figure 4A. Block diagram of analog A-chain SIGNAL OUT Figure 48. Block diagram of digital A-chain SCREEN CHANNEL I1 of31 ,:,pg MASTER...

  • Page 8: Evolving Dynamic Range Requirements In The Cinema

    The B-chain is comprised of one-third octave equalization, dividing networks (low- or high-level), power amplification, and loudspeakers. JBL Professional products are used extensively used in the B- chain of the system. D. Evolving Dynamic Range Requirements in the Cinema Figure 4D shows details of the headroom requirements of current and future cinema formats.
  • Page 9 differences between high and low frequency sections. The chief weakness of these systems was their lack of uniform coverage. System design stressed output conversion efficiency, because of the small power amplifiers available at the time. Figure 5A shows the on- and off-axis curves of a typical horn/reflex system, while polar response of a typical multicellular horn is shown at B.

  • Page 10: Power Response And Power-Flat Systems

    200 Hz. The net result of this pattern narrowing in the horizontal and vertical planes is that they make a good match for the pattern control of the JBL 2360A horn at the normal crossover frequency of 500 Hz.

  • Page 11: Coverage Requirements For Proper Stereo Reproduction

    JBL pioneered the concept of flat power response in the cinema (2,3). It has become the guiding principle in much of JBL’ s product design, and it has been adopted by the industry at large. G. Coverage Requirements for Proper Stereo Reproduction In the cinema, it is expected that all patrons will be able to appreciate convincing stereo reproduction.
  • Page 12 This performance is seen in Figure 8. At A, we show in plan view the direct field coverage given by a JBL 2360 horn aimed at the absorptive back wall of a large theater with sloped floor. Coverage at 2 kHz is within a range of +/- 3dB, front to back. If the horn is aimed downward to a point two-thirds the distance from front to back, the coverage is as shown at B, and coverage at the rear of the house is compromised.

  • Page 13: Acoustical Considerations

    The surround ensemble of loudspeakers, if properly specified, can easily produce a sound field that is uniform throughout the back two-thirds of the house, and level variations can often be held within a range of 2 to 3 dB. Details of surround system specification will be covered in a later section. When all of the above points are properly addressed, the sound in a cinema can approach that which we take for granted in a post-production screening facility - which is, after all, how the picture director intended it to sound.

  • Page 14: Control Of Reverberation And Discrete Reflections

    Acoustical engineers make use of what are called Noise Criterion (NC) curves in attempting to. set a noise performance goal for cinemas. The octave band values of these curves are shown in Figure 9. In implementing this data, the acoustical designer settles on a given criterion and then determines the cost and other factors involved in realizing it.
  • Page 15 frequencies tends to lower the reverberation time. Figure 11 shows the normal range of reverberation time, as a function of the value at 500 Hz, while Figure 12 shows the acceptable range of reverberation at 500 Hz as a function of room volume. .

  • Page 16: The Role Of The Acoustical Consultant

    IV. SPECIFYING THE CORRECT LOUDSPEAKERS AND AMPLIFIERS A. Hardware Class vs. Room Size In all but the smallest cinemas, dual low-frequency systems, such as the JBL 4670D and the 4675C, should be specified. Normally, there will be three of the systems behind the screen in left, center, and right positions.
  • Page 17 800W (200,ooo al. ft.) Table 1A: Maximum Reverbwant Levels1 for JBL 467OD and 467% Systems in Cinsmas of various sizes (non-b&m plifiedmode) Taking the information presented in Table lA, we can now determine the actual power requirements to produce target levels in the house of 105 dB per channel:...

  • Page 18: Advantages Of Biamplification

    LF:4oow (200,ooo cu. ft.) HF:2!5OW Table 1C. Maximum Reverberant Levels’ for JBL 4675C Systems in Large Cinemas (biimpliied mode). B. Advantages of Biamplification The importance of biampiification in large cinemas cannot be overestimated. Even though the systems detailed in Table 1 B use the same amplifier model as the systems detailed in Table 1 A, the reallocation of the power through biampiification has important beneficial effects.

  • Page 19: New Jbl Driver Developments

    As a result of this, many cinema applications ordinarily will not require the high power Vented Gap Coolingm (VGC) performance designed into the JBL 2226 driver. A more recent model, the 2035, was subsequently designed with a 76 mm (3 in.) voice coil, retaining the same sensitivity of the 2226.
  • Page 20 lrn’ 17s/r’ - FQure 14. Complete system assembly diagram for 46700 and 46756.
  • Page 21 JBL4670D-HF Figure 15 COMPONENT EXPLODED VIEW Driver, Hiih F req 2446t-t Gasket 20810 Bracket - Inner Binding Post Driver/Horn Red. 33750 Blk, 33751 $%n Sale) screw No.8xV2 FWHD PH BLK Bracket - Outer Mounting Base 72109 (Not For Sale) Assembly Hardware Kit 72110 (IlkJstrated)
  • Page 22 JBL4671B :OMPONENT EXPLODED VIEW Horn 2370A Network 3llOA 6486641 Fwyf$$fz t-bhft3 Instattation Kit 55343 Port Tube 57932 (Not For Sale) Gasket, Vinyl 34499 Cabinet 4507 63299 (Not For Sele) Use Mounting Hardwar IfIchled With In~tion Kit 55340...
  • Page 23 Figure 17 ZOMPONENT EXPLODED VIEW Driver. High Freq 2446J Diaph Rept Horn 2380A D18R2448 64889 tJMyJ$fif Hardware Installation Kit 57538 support 2508 80851 Use Mounting Hardware Included With Unit Network 3115A 47031 lose Mounting Hardware Included With Installation Kit 55343 Port Tube 57932 (Not For Sale)
  • Page 24 JBL4675GHF Figure 18 VIEW COMPONENT EXPLODED Drhw Hiih Fmq 2446H Bolt (4) 114-20x l-111) Gasket 60718-01 Bindin Post EzY$Et Adapter 60705 Washer l/4-20 x 2-114 Lockwasher Washer Hom236OA 60703-01 Bracket Assy 25068 And Mounting Hardware 72144...
  • Page 25 Figure ZOMPONENT EXPLODED Scmw (4) EE6xW PHLRGHDhlSSLK\ ,g%%; screw Port Tube (2) 56144 56460 (Not For Sale) No.6x3l4 FLHD PH ELK Gasket (2) 34499 Inseri, Threaded (16) 63154-01 10-32x l/2 Sg$er, Low Freq (2) Cone Rep1...
  • Page 26 Figure 20 BLACK LFSPEAKER FROM RED EIACK BLACK RED AWLIFIER FRcA4 AMPLIFIER NETWORK FLANGE DN RIGHT SIDE OF LF ENCLOSURE 46700 wiring diagram 4671 B wiring diagram HF DRIVER LF SPWER AMPLIFIER FROM AMPLIFIER I N PUT 46738 wiring diagram 4675C wiring diagram NOTE: Input comctions as shown here provide coned EIA polarity.

  • Page 27: Subwoofers

    F. Subwoofers Subwoofers are an integral part of cinema loudspeaker systems installed in mid- and large-size ‘ L houses. In specifying them, the designer must take into account the reduced sensitivity of the ear to low frequency sounds. Figure 21 shows the Robinson-Dadson equal loudness contours. Note that, for a reference level of 85 dB at 1 kHz, frequencies in the range of 30 to 40 Hz will have to be reproduced 15 to 20 dB louder in order to be perceived at the same subjective level.
  • Page 28 8 ohms. A pair of subwoofer modules can be driven by a single JBL model MPX1200 amplifier, which is capable of producing continuous sine wave power of 606 watts into each of two 8-ohm loads.
  • Page 29 JBL 4645B :OMPONENT EXPLODED VIEW I = / Port Tube (Not For Sate) winat 60669-01 Speaker, Low Freq Screw 2242HPL 65555...

  • Page 30: Surround Requirements

    As a general rule, the total ensemble of surround loudspeakers should be capable of producing as much acoustical power as a single screen channel. Today, the new JBL 8340 surround loudspeaker is capable of producing total acoustical power output in the range of about 2 watts. Since a typical dual woofer JBL screen loudspeaker is capable of producing continuous acoustic power output of 28 watts, it is clear that 14 of the 8340’...

  • Page 31: Screen Losses

    A driver must be specified which can handle this increased input -- and at the same time be able to provide a good match with the low frequency system. All JBL cinema systems have been engineered with this requirement in mind.

  • Page 32: Use Of Multiple High Frequency Elements

    In mid-size screening rooms there is less air loss to deal with, and it is often the case that no 1 0-dB more than a boost is required to meet the equalization requirements above 10 kHz. Many conservative engineers feel that a lO-dB boost should never be exceeded. I.

  • Page 33: Subwoofer Mounting

    !mDNTvEw AoED3r4eR&xs(Ar3 Frameandbag~,2~4 lumber -. . . Bracing mquimd TOPVIEW onhwsium. Figure 25. Isometric view of a pl$fonn. Figure 26. wings between screen loudspeakers. When possible, large wings should be mounted between systems, as shown in Figure 26. The surfaces should ideally be finished with sound absorptive material, as.should any exposed wall areas behind the screen should be finished with sound absorptive materials.

  • Page 34: Surround Mounting

    D . Surround Mounting The JBL 2502 mounting bracket will accommodate both the 8330 and the 8340 surround systems. The user has a choice of mounting the loudspeakers for horizontal projection or for 15” downward projection. The electrical response switch on the 8330 and 8340 surrounds should be placed in the IS0 2969 X-curve position for cinema application.
  • Page 35 JBL8340 Figure ZOMPONENT EXPLODED “ IEWO Screw (8) 762-61 CM@75 No. 6 x 3I4 FLHD 100” BLK Horn/Driver 127-10000-00 (Not For Sale) T-Nut (8) Screw (8) =6x1 Speaker, Low Freq BTHD HEX BLK 124-21000-00 screw (4) 67375 No. 8 x l-114 FLHD PH BLK PNHD PH BLK...

  • Page 36: Wiring For Non-Biamplified Installations

    IM-12 module that is included in the ‘ Open Input Architecture’ options available for JBL’ s MPA-series power amplifiers. FROM...
  • Page 37 833oort3Nosurrcundloudspeakecstypicaloftwosets four to loudspeakers wired sefieslparallel. Figure 30. Typical passive network cinema system -ii!+ cinemaPr~asw lwd2 8330or8340smnmdlodswkerstypiceloftwosets of four to six budspeakers wired in seri~ralld. Figwe 3 Typical biamplified cinema system...

  • Page 38: Wiring For Surround Channels

    6 ohms, as shown in Figure 32A. Twelve 6 ohm loudspeakers, such as the JBL 6340, can be series-parallel wired to give a resulting impedance per side of 5.3 ohms. Both wiring arrangements provide equal feed to all loudspeakers.

  • Page 39: Wire Gauges And Line Loss Calculations

    D. Wire Gauges and Line Loss Calculations Good engineering practice requires that line losses result in no greater than a level loss of 0.5 dB at the load. In making the calculations to determine the smallest wire gauge that will ensure adherence to this, the engineer must keep in mind that the loss at the loudspeaker is due to actual losses in the wiring as well as to losses due to impedance mismatching caused by the added resistance in the line.

  • Page 40: System Setup And Checkout

    16 dB/octave, and a fourth order network will provide transitions of 24 dB/octave. The most common mistake made in field assembly of non-biamplified JBL cinema loudspeaker systems is mis-wiring of the dividing network. The data presented in Figure 20 should be studied carefully, inasmuch all network details are spelled out clearly.
  • Page 41 106d8@lm 62dBQ2Om~Ims t6dBu - 2dE@2omuas 2kdB@lm Setiprtdan@ierso,Ihat -100 t6dBuinpmducesoutputd t6av(&3mlts)inb6dnw Figure 35. Tvpical gain-loss diagram for the B-chain of a cinema system Note that the gain-loss diagram for this system indicates clearly maximum output levels of each component in the system as well as the noise floor of each component. The goal in proper systems engineering is to ensure that the widest possible dynamic range is preserved through the chain.

  • Page 42: References

    References J. Lansing and J. Hilliard, ‘ An Improved Loudspeaker for Theaters,’ Journal SMPTE, vol. 45, pp. 339-349 (1945). M. Engebretson and J. Eargle, “ Cinema Sound Reproduction Systems: Technical Advances and System Design Considerations,’ Journal SMPTE, vol. 91, no. 11 (November 1982). J.
  • Page 43 JBL Professional @Copyright 1998 JBL Professional Printed in USA 8500 Balboa Boulevard Northridge, California 91329 USA A Harman InternatoM Company...

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