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JBL 300 Series, Manual

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35

XI. LOUDSPEAKER SIGNAL PROCESSING FOR JBL DSC260A

 

The following loudspeaker signal processing settings are intended for the JBL DSC260A digital system 

controller.

 

Different loudspeaker controllers may have channel-to-channel differences in delay settings. They  

 

may also have different definitions and implementations of parametric filter Q or bandwidth.  As a result when 
alternative processors are used, field measurements, both electrically and acoustically, will ensure the maximum 
performance is retained.

 

Note that equal voltage gain for all amplifier channels is assumed.  If power-amplifiers with different 

voltage gain are used then this difference must be compensated for.

Summary of Contents for 300 Series

Page 1: ...CINEMA SOUND SYSTEM MANUAL ...

Page 2: ...ay Loudspeaker Systems 19 V Mounting Requirements 21 A General Comments 21 B Screen Loudspeaker Aiming 22 C Subwoofer Mounting 22 D Surround Mounting 22 VI Electrical Interface 23 A JBL Polarity Conventions 23 B Wiring Diagrams for 3000 Series Screen Systems 24 C Wiring Diagrams for 4000 Series Screen Systems 24 D Wiring Diagrams for 5000 Series Screen Systems 25 E Wiring Diagrams for ScreenArray ...

Page 3: ...a strong commitment to the cinema market We have become the acknowledged leader in the field and our products are routinely specified for major studios and post production houses throughout the world JBL continues its rapid pace in new product development aimed at increasing performance levels in the cinema This manual has several goals First it will provide a background in basic systems concepts ...

Page 4: ...r through a combination of gain control and altering of separation coefficients within the matrix In a similar manner information intended for the surround channels is fed to both stereo channels so that there is a 180 phase relationship between them This phase relationship triggers the playback matrix to steer that information primarily to the surround loudspeaker array Figure 2B shows details of...

Page 5: ... format used in most cinemas but SDDS also supports as many as 5 screen channels for special applications making a total of eight channels All digital formats discussed here have a fall back failsafe mode in which the analog tracks will be used in case of failure of the digital portion of the systems C A and B Chains For convenience in defining responsibilities for system specification and alignme...

Page 6: ...Figure 4 Analog A chain A Digital A chain Dolby SR D B Digital B chain DTS C Block diagram of B chain with split surrounds D Dynamic range requirements for Dolby A Dolby SR and and Dolby Digital formats E ...

Page 7: ...cessors the new systems were two way in design With the coming of digital sound tracks during the early 1990 s the need was felt for greater power output capability with even lower distortion The answer here was to be found in newly engineered three way systems F Power Response and Power Flat Systems The discrepancy between on axis and reverberant room response in the older systems was solved with...

Page 8: ...appreciate convincing stereo reproduction By contrast standard two channel stereo in the home environment often imposes strict limitations on where the listener must sit in order to perceive correct stereo imaging The factor that makes the big difference in the cinema is the presence of the center channel Not only does the center loudspeaker lock dialog into the center of the screen it further red...

Page 9: ... cinema with the center channel aimed at the audience approximately two thirds from front to back A side section view of the stadium theater is shown at 7D Typical response in the Goldwyn Theatre is shown at 7E Figure 7A Figure 7B Figure 7C Figure 7D Figure 7E Figure 7 Center channel coverage in traditional and in stadium cinemas Computer acoustical modeling plot at 2 kHz in traditional house A ce...

Page 10: ...g this data the acoustical designer settles on a given criterion and then determines the cost and other factors involved in realizing it Low noise air handling requires large ductwork and is expensive Even more likely to be a problem is through the wall isolation from adjacent cinemas The general recommendation made by Lucasfilm 6 is that interference from adjacent cinemas should be audible no mor...

Page 11: ...gh frequencies are not very effective sound absorbers at low frequencies At higher frequencies there is additional absorption due to the air itself and this excess attenuation of high frequencies tends to lower the reverberation time Figure 10 shows the normal range of reverberation time as a function of the value at 500 Hz while Figure 11 shows the acceptable range of reverberation time at 500 Hz...

Page 12: ...roof are just a few of the offenders here Once the installation has been made the problem is very expensive to correct and a good consultant will have an eye out for such things at the design stage of the project Related problems such as projector noise and other noises associated with concession activities need to be identified early in the project and corrected before construction begins As stan...

Page 13: ...ing 105 dB at the required distance in the 250 seat house JBL recommends driving these models with amplifiers equal to their rated power regardless of the application We will now consider the maximum output capability of the 4675C 4 8 LF system in biamplified mode taking into account the 6 dB crest factor of the test signal This is the absolute peak output capability of the system JBL recommends t...

Page 14: ...allows additional headroom of 6 to 8 dB above this so it is clear that the values we have listed in Tables 1A through 1D are not excessive in the cases of the larger houses In the smaller houses we can certainly use smaller amplifiers than indicated in the table but even then the cost of the added power is very slight while the benefit is substantial The amplifier output powers recommended in Tabl...

Page 15: ...678 B Figure 14 4000 Series screen systems Perspective and side drawings of 4670D Figure 15 Drawings of 4000 Series screen systems Front and side drawings of 4622N Figure 16 4000 Series screen systems Perspective and side drawings of 4675 Figure 17 Model 5671 screen system front and side views ...

Page 16: ...16 Figure 18 5672 screen system front and side views Figure 19 5674 screen system front and side views Figure 20 Robinson Dadson equal loudness contours ...

Page 17: ... number of subwoofers specified for a given cinema must bear some relationship to the total volume in the space JBL s experience in specifying subwoofer units has led us to the following empirical recommendations 1 For each 5 666 cubic meters 25 000 cu ft specify one 2241 or 2242 transducer in a suitable enclosure 2 All systems should be mounted in very close proximity to one another in order to m...

Page 18: ... acoustical power output in the range of about 2 acoustical 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 8340A s will be required for power matching Typically in a large house 12 to 16 units will suffice The careful designer should not specify less than this quantity In smaller houses a simi...

Page 19: ...inema systems have been engineered with this requirement in mind In mid size screening rooms there is less air loss to deal with and it is often the case that no more than a 10 dB boost is required to meet the equalization requirements above 10 kHz Many conservative engineers feel that a 10 dB boost should never be exceeded H JBL s New ScreenArray Loudspeaker Systems The ScreenArray series consist...

Page 20: ...20 Figure 26 ScreenArray loudspeakers Front A and side B views of model 4632 front C and side D views of model 3632 ...

Page 21: ... as logos and polished transducer frames should be painted matte black so that they will not show through the screen 4 Platforms for loudspeaker mounting should be rigid and completely free from rattles all exposed vertical surfaces should be finished with sound absorptive materials 5 All other wall areas behind the screen should be finished with sound absorptive materials Figure 27 Performance of...

Page 22: ... the requirements for masking for various aspect ratios the spacing between left and right loudspeakers should be broad enough to produce ideal stereo for the widest format Acoustically transparent masking material should be used so that when masking is in place there is negligible high frequency loss The wider loudspeaker spacing when used for a narrower projection format will be quite acceptable...

Page 23: ...stency in the field many of JBL s older transducer and systems groups have what is called negative polarity convention that is a positive going voltage on the or red terminal will result in an inward motion of the cone or driver diaphragm Positive polarity so called EIA polarity specifies that a positive going voltage on the or red terminal will result in an outward motion of the cone or driver di...

Page 24: ...Series Screen Systems Figure 33A shows proper amplifier loudspeaker hookup for the models 3677 and 3678 both operating in a single amplifier mode The model 3678 is also configured to operate in biamplified mode as shown at Figure 33B Note that this change requires removing four jumpers from the terminal strips of the dividing network C Wiring diagrams for 4000 Series Screen Systems Figure 34A show...

Page 25: ... quadruple set of LF units makes use of four amplifier sections All aspects of frequency division time correction power response equalization and room equalization are carried out by the JBL model DSC260A digital controller Pertinent wiring diagrams are shown in Figure 35A and B Figure 34 Wiring diagram for 4000 Series Passive network operation of 4675C A and 4670D B biamped operation of 4675C C ...

Page 26: ...y Systems The model 3632 wired for biamped operation is shown in Figure 36A The model 4632 is shown biamped in Figure 36B triamped wiring of the 4632 is shown at 36C Figure 35 Wiring diagram for 5000 series systems 5671 and 5672 A 5674 B ...

Page 27: ...in future A chain technology Since all of JBL s surround models are nominally 8 ohms impedance the parallel load of two of them will of course produce a 4 ohm load Amplifiers should then be chosen that can deliver twice the loudspeaker rated power into 4 ohms as compared with their 8 ohm ratings Be sure in surround amplifier specification 1 That the amplifier will not be overdriven in normal opera...

Page 28: ...28 Figure 37 Typical stereo surround hookup Figure 38 Surround EX hookup ...

Page 29: ...the system prior to making any adjustments on the system An example is given in Figure 39 Here we have shown the gain structure for the model 5674 We show here only the LF system section at full output the MF and HF sections operate at lower power amplifier levels so that the individual acoustical outputs of LF MF and HF sections will all be proportional All aspects of A chain calibration should b...

Page 30: ...30 Figure 39 Level diagram for 5674 LF section ...

Page 31: ...s with more than 500 seats consider specifying systems with four LF drivers per channel for maximum performance REMEMBER You can always specify a larger system for a smaller house but not vice versa 3 Placement of screen channels Space horizontally to match the widest anticipated picture format Elevate systems so that HF sections are about 2 3 the screen height Place the systems so that the HF sec...

Page 32: ...ways use a home run from the booth to each surround loudspeaker Do all of the loudspeaker paralleling in the booth Select wire gauges that will ensure insertion loss no greater than 0 5 dB 5 How to position the surrounds The front most surrounds are normally 2 3 the distance from the back wall to the screen The back most sidewall surrounds should be about nine to 12 feet from the back wall Surroun...

Page 33: ...ectives C Specifying and Installing Subwoofers 1 Subwoofer assumptions Use 18 diameter drivers Sensitivity no less than about 97 dB 1 W at 1 m Power rating per driver should be no less than about 400 watts continuous 2 How many subwoofer drivers are necessary A safe rule is to specify one sub driver for each 25 000 cubic feet of house volume Always round upward if your calculations indicate 5 1 2 ...

Page 34: ...enty of neoprene padding for isolation See Figure 45 VIII LISTING OF THX APPROVED JBL PROFESSIONAL PRODUCTS A Screen systems 3678 3678 HF and 3678 LF 3632T 3632 M HF T and 4639 4632T 4632 M HF T and 4639 4675C 8LF 4675 HFA and 4648A 8 5671 5671 M HF and 5641 5671 5674 M HF and 4648A 5674 5674 M HF and 5644 B Subwoofers 4641 4645C 4642A 4642A GS with grilles C Surround Systems 8330A 8340A Figure 45...

Page 35: ...es in delay settings They may also have different definitions and implementations of parametric filter Q or bandwidth As a result when alternative processors are used field measurements both electrically and acoustically will ensure the maximum performance is retained Note that equal voltage gain for all amplifier channels is assumed If power amplifiers with different voltage gain are used then th...

Page 36: ...ay 1 396 0 000 1 396 0 000 Output Delay Link Off Off Off Off Polarity Normal Normal Normal Normal Output Lo Shape BUT18 BUT18 BUT18 BUT18 Output Lo Frequency 29 1 392 0 29 1 392 0 Output Hi Shape L R24 BUT12 L R24 BUT12 Output Hi Frequency 482 0 Out 482 0 Out Output EQ1 Type Bell Bell Bell Bell Output EQ1 Frequency 153 0 659 0 153 0 659 0 Output EQ1 0 5 2 0 0 5 2 0 Output EQ1 Bandwidth 1 00 0 45 1...

Page 37: ...ay 1 396 0 000 1 396 0 000 Output Delay Link Off Off Off Off Polarity Normal Normal Normal Normal Output Lo Shape BUT18 BUT18 BUT18 BUT18 Output Lo Frequency 29 1 392 0 29 1 392 0 Output Hi Shape L R24 BUT12 L R24 BUT12 Output Hi Frequency 482 0 Out 482 0 Out Output EQ1 Type Bell Bell Bell Bell Output EQ1 Frequency 153 0 659 0 153 0 659 0 Output EQ1 0 5 2 0 0 5 2 0 Output EQ1 Bandwidth 1 00 0 45 1...

Page 38: ...ut Delay Link Off Off Off Off Polarity Normal Normal Normal Normal Output Lo Shape BUT12 BUT24 BUT12 BUT24 Output Lo Frequency 25 3 840 0 25 3 840 0 Output Hi Shape BUT24 BUT12 BUT24 BUT12 Output Hi Frequency 683 0 Out 683 0 Out Output EQ1 Type Bell Bell Bell Bell Output EQ1 Frequency 406 0 1 46k 406 0 1 46k Output EQ1 5 5 6 0 5 5 6 0 Output EQ1 Bandwidth 0 05 1 40 0 05 1 40 Output EQ2 Type Bell B...

Page 39: ... Output Delay 0 396 0 000 0 396 0 000 Output Delay Link Off Off Off Off Polarity Normal Normal Normal Normal Output Lo Shape BUT12 BUT48 BUT12 BUT48 Output Lo Frequency 30 1 450 0 30 1 450 0 Output Hi Shape BUT48 BUT12 BUT48 BUT12 Output Hi Frequency 378 0 Out 378 0 Out Output EQ1 Type Bell Bell Bell Bell Output EQ1 Frequency 138 0 6 06k 138 0 6 06k Output EQ1 2 0 4 0 2 0 4 0 Output EQ1 Bandwidth ...

Page 40: ...l Normal Normal Normal Normal Normal Output Lo Shape L R12 L R24 BUT18 L R12 L R24 BUT18 Output Lo Frequency 25 0 450 0 1 31k 25 0 450 0 1 31k Output Hi Shape L R24 BUT18 BUT12 L R24 BUT18 BUT12 Output Hi Frequency 353 0 1 46k Out 353 0 1 46k Out Output EQ1 Type Bell Bell Bell Bell Bell Bell Output EQ1 Frequency 176 0 707 0 2 37k 176 0 707 0 2 37k Output EQ1 5 0 3 0 2 0 5 0 3 0 2 0 Output EQ1 Band...

Page 41: ...y 0 354 0 000 0 354 0 000 Output Delay Link Off Off Off Off Polarity Normal Normal Normal Normal Output Lo Shape BUT12 BUT48 BUT12 BUT48 Output Lo Frequency 30 1 250 0 30 1 250 0 Output Hi Shape BUT48 BUT12 BUT48 BUT12 Output Hi Frequency 225 0 Out 225 0 Out Output EQ1 Type Bell Bell Bell Bell Output EQ1 Frequency 138 0 307 0 138 0 307 0 Output EQ1 3 0 3 0 3 0 3 0 Output EQ1 Bandwidth 0 45 0 30 0 ...

Page 42: ...ff Off Polarity Normal Normal Normal Normal Normal Normal Output Lo Shape BUT12 BUT48 BUT24 BUT12 BUT48 BUT24 Output Lo Frequency 30 1 258 0 1 51k 30 1 258 0 1 51k Output Hi Shape BUT48 BUT24 BUT12 BUT48 BUT24 BUT12 Output Hi Frequency 225 0 1 1k Out 225 0 1 1k Out Output EQ1 Type Bell Bell Bell Bell Bell Bell Output EQ1 Frequency 138 0 1 23k 3 03k 138 0 1 23k 3 03k Output EQ1 3 0 6 0 3 0 3 0 6 0 ...

Page 43: ...width in Octaves dB D1 Frequency Hz Highs 9 18k 9 18k 11 7k Bandwidth in Octaves 12 Hi Shelf 12 Hi Shelf 12 Hi Shelf dB 5 5 7 5 D2 Frequency Hz Highs 2 82k 2 82k 3 36k Bandwidth in Octaves 0 4 0 4 0 3 dB 2 5 2 5 3 5 CROSSOVER A Gain dB Subs Not Used Not Used Not Used Limit Slope low hi FR low hi Hz B Gain dB Lows 0 3 5 Limit 2 2 2 2 2 2 Slope low hi LR 24 LR24 LR 24 LR24 LR 24 LR24 FR low hi Hz 32...

Page 44: ...way Surround 8 75 Watt system XLS202 CL1 NA CTs600 NA 4000 Series Model Description Nom Imp System Power Handling 4670D 2 way Passive 4 600 Watt thru network XLS602 CL4 NA CTs2000 NA 4675C 2 way Passive 4 600 Watt thru network XLS602 CL4 NA CTs2000 NA 4675C 4LF 2 way Bi Amp 4 8 1200 100 Watt CL2 XSBSCJBL4675 CTs2000 IQPIPUSP3 4675C 8LF 2 way Bi Amp 8 8 1200 100 Watt XLS602 Bridged XLS402 CL2 XSBSC...

Page 45: ...tical Background Noise Levels in Dubbing Stages EG 14 1987 6 T Holman THX Sound System Instruction Manual Architects and Engineers Edition Lucasfilm Ltd 1987 7 I Allen Technical Guidelines for Dolby Stereo Theaters Dolby Laboratories September 1992 8 T Holman Motion Picture Theater Sound System Performance New Studies of the B Chain Journal SMPTE vol 103 no 3 March 1994 9 M Gander and J Eargle Mea...

Page 46: ... Copyright 2003 JBL Professional Revised 6 11 03 JBL Professional 8500 Balboa Boulevard Northridge California 91329 USA ...

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