Journal of the Society of Motion Picture and Television Engineers (1950-1954)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

film guiding through the soundhead is desired, the film may be threaded around the sprockets and pad rollers only. The upper sprocket is driven from the lower sprocket by means of timingbelt type of pulleys mounted on the rear of the sprocket shafts and a connecting precision-molded, tooth-type rubber belt shown in Fig. 5. This drive gives results comparable to a precision gear drive at considerably less cost. During operation with the film threaded for magnetic sound reproduction, as the film is pulled into the projector by the projector feed sprocket, the downward film pull causes the lower sprocket of the magnetic soundhead to rotate. The upper or feed sprocket is driven at the same speed as the lower sprocket since the belt drive is as positive as a gear drive and the pulley ratio is one to one. Both sprockets are of the 16-tooth type with tooth width and tooth pitch selected specifically for the new composite-type film and the new functional usage of the sprockets. The primary reason for incorporating two 16-tooth sprockets in the design rather than one 32-tooth sprocket is directly related to the type of filter system used and the desirability of keeping the height of the soundhead to a minimum consistent with good design practice. Use of the two sprockets simplifies film threading since a natural film wrap is afforded about the sprockets for the desired film path. The filter system is a film-pulled, drum-type, soft-loop system. Drumshaft assembly includes a solid flywheel mounted on the rear of the drum shaft. The flywheel is protected from accidental contact by operating personnel during operation of the unit by the rear cover of the soundhead. The double-roller assembly mounted between the magnetic-head assembly and lower sprocket comprises a second portion of the filter system. The two rollers are mounted on a common arm which in turn is mounted to a pivot shaft at a point midway between the two roller shafts. The assembly is biased by means of a clocktype spring enclosed in a cavity at the rear of the pivot-shaft housing. Damping is afforded by use of silicone grease in the spring enclosure and shaft bearing. The primary soft or compliance film loop is formed between the feed sprocket and drum. (Had a single 32-tooth sprocket been used, additional height would have been necessary to provide clearance between the soft loop and the film passing around the rollers of the double-roller assembly.) Most of the random irregularities in film motion on the feed side of the soundhead are absorbed in the compliance loop ahead of the drum. Tests were made on models of both tight-loop and soft-loop filter systems. Film motion was comparable on the two systems when used with a projector having good feed-sprocket motion and a feed magazine producing uniform drag or holdback. However, when projector feed-sprocket motion and feed-magazine drag were not uniform, a condition likely to be encountered in the field, film motion obtained with the soft-loop filter system was superior to that obtained with the tight-loop system. An improved method of construction for multiple heads* has been incorporated in the design of the magnetic-head assembly shown in Fig. 6. The four heads are contained within a single, precision-cast housing. The face of each half cluster is lapped on a precision flat which inherently makes all the gaps in true alignment when the half clusters are assembled together. The azimuth, head height and track location are accurately adjusted with respect to the mounting surface during assembly. After all assembly and final lapping operations are completed, the * Kurt Singer and Michael Rettinger, "Multiple-track magnetic heads," Jour. SMPTE, 67: 390-394, Sept. 1953. Phyfc and Kittle: Multitrack Sound Reproducer 219