Business screen magazine (1967)

The Sight and Sound of History: (CONTINUED FROM llll PRKCl DING PAGU 45 ) from masters and enables them to change and upgrade the program at any time. Each 14-track tape machine uses seven twotrack Ampex professional audio recorder electronics units, modified to include a muting relay to short line outputs in every mode but "play". These units have been transferred to deeper chassis for more effective cooling, since they are operating 1 1 hours a day. New connectors were installed to mate electronics with the AG-300-14 head assembly. Tour Leader's Key Start.s a Performance The Ampex equipment is set for virtually automatic operation of the entertainment cycle. A tour-leader needs only to insert a key in a tamper-proof lock in a door casement to start the presentation. To accomplish this, engineers installed photo cell assemblies and memory systems in the control boxes of the recorders. Lights and photocells are mounted in the tape path. As the tape runs between the cells, they sense transparent leaders spliced at the beginning and end of the program. At the end of the program, the machine goes into rewind; this takes about a minute. When the start of the program is sensed, a forward relay cues the show up automatically. 14-Channel Recorders Posed Some Problems Special problems were posed in building the 14-track recorders. Takeup and wind motors with double the normal torque were used in the modification to take the wider tape. Locking-type holddowns were permanently attached to the assemblies. Wider capstan and reel idlers were added, and longer shafts were made for the capstan assemblies. Heavier solenoids were used for the capstan idlers, and heavy duty silicon rectifiers were installed in the transport power supply. Staggered, optically-aligned, fixed audio heads with low impedance, 200 microinch gaps were designed to give adequate signal-to-noise ratios from the narrow tracks and retain good tracking and frequency response. This design also gives minimum crosstalk between channels, and provides good separation. Patch Panels Interconnect the Equipment Two patch panels, one for each recorder, were installed and interconnected so that the Speaker sijstcms were placed faee-ihncit in fireplace casements of the Assembly Room. output, which normally comes from the reproducer, may be jumpered to lead from the recorder, and the recorder input, which nomially is connected to an external source, may be jumpered to lead to the reproducer. The automatic control circuit for the visual effects and audio special effects employs frequency-sensitive circuits with solid-state silicon-controlled rectifier switching to control the house lights and candles, and to switch the three audio special effects channels to any or all of ten surrounding speakers. Speakers Placed for Most Natural Effects Eight JBL S-4000 solid-state power amplifiers were built into one rack to handle the 14 channels at 40 watts per channel. Allen Bradley lock pots are located in the same rack. The fourth rack in the system carries a 14-channel monitor system. In the Assembly Hall itself. 38 JBL speakers are built into window casings on either side of the room, out of sight of visitors. Six are mounted in the wall paneling, using balsa wood panels as cone resonators. These also provide audio effects — rain, the Town Crier's voice and bell, carriages and horses' hooves, and so on — but since they weren't required for such low-frequency sounds as thunder, very small units could be used, thus increasing the natural quality of the sound. Two standard JBL S-7 speaker systems — standard studio monitors — are mounted face Closeup of SpiiuUer & Sauppe continuous slide projectors used within the Little Theater down in the fireplace casements; these highquality, wide-range systems reproduce the thunder, cannon and similar sound effects. Ten modified S-8 systems are located under tables, concealed by the homespun cloths. These systems use JBL 375 theater drivers for mid and upper-ranges, and S-7 wooders tc give the desired bass quality. These large speakers had to be selected and adjusted to create the realistic effect of someone's sitting at a table and speaking from there. A great deal of experiment was needed for the best combination of JBL components. A Door Slams and Footsteps Are Heard . . . Unseen — and not showable in picture — special effects units in the doorway are used tc re-create the sound of a slamming-door and the footsteps of delegates coming into the room. Part of the door frame actually is vibrating panel, driven by the speaker mechanism. No voices are heard here, and the sound moves quickly on toward the front of the room More than $6500 in speakers are installed in the Assembly Room alone, all powered by JBL transistorized amplifiers. Although a multiplicity of channels were involved, each wa; a straightforward wiring job. Nearly a month was required to set up and balance the system. The Liberty Bell Tolls from the Belfry A special high-power JBL loudspeaker i^ located in the belfry to reproduce the sound ol the Liberty Bell. That is supplied by a tup., which reproduces an engineering estimate what the original sound must have been . a project in which the engineering ran a constant "clang clang" on endless tape, going up a notch in frequency periodically and using sound-spectrum analyzer which checks an; sound in any and all frequencies and provide; a chart-readout. There's enough power in th( belfry of Independence Hall/West to matcl three full symphony orchestras. JBL engineer say — and that's just enough to reproduce thi bell in its probable original power. James B. Lansing Sound, Inc., one of thi pioneers in high-quality theater loudspeakesystems, was incorporated in 1946 and ha: marketed many basic advances in loudspeakei design. Among them are the acoustic lens, thi ring radiator, passive radiator, and the Paragot stereophonic reproducing system. Under the di rection of President William H. Thomas, the company has grown to a position of majo importance in the production of highest-qual ity-component high fidelity equipment. Historic E\ents on Little Theater Screen . While emphasis has been given the uniqui sound reproduction facilities of Independenci Hall/West and the adjacent Heritage Hall equal and careful attention was given to botl lilm and slide projection. The theatre pictured in these pages (see 11 lustration on page 45) is set up to providi visitors with an overall "feeling" for the tou they are about to begin. Highly-precise Spind ler & Sauppe continuous slide projection vi: lour of this company's machines brings scenl background on Americana to viewers. In thi Independence Hall theatre (on the secom lloor") seating by Heywood-Wakefield (install (CONTINUED ON THE FOLLOWING PAGE 48 46 BUSINESS SCREEr