Projection engineering (Sept 1929-Nov 1930)

Projection Engineering, October, 1929 Page 21 harmonics of both voice and music lie in the high-frequency range, as well as some of the fundamental frequencies, these are lost also. This condition is indicated by curve No. 3. For the reproduction of voice and speech, which are within the band of 500 to 4,000 cycles, we find that by adding 100,000 ohms resistance to the reactance of the choke coil, this curve will be broadened as indicated by curve No. 1 of Fig. 4 which will include this band of frequencies, and at the same time eliminate the background of base which has a tendency to make the voice d rummy ; also as some of the distributed capacity of the winding is still taking effect, most of the photoelectric cell hiss will be eliminated. For the faithful reproduction of music, the value of the resistance is increased to 250,000 ohms which will broaden the curve still more as indicated by curve No. 2. This seems to be of about the right value for the best reproduction of music for the average recording. Manual Pitch Control However, as all recordings are not of the same pitch, some being high pitched and others low, the value of this resistance can be adjusted to suit the individual requirement. This is a valuable asset and most of the commercial sound installations have in the main amplifier some method of controlling the pitch, but if the damage has been done at its source before it ever gets to the main amplifier, there cannot be much done about it. This variable resistor can be conveniently located on the peck amplifier with different markings etched on it to show the resistance values, and instant changes can be made by the operator in changing from speech to music with little or no trouble. Reducing Capacity Effect of Shield "With the combination of impedance and resistance coupling, as shown in the circuit of Fig. 3, the same conditions exist as in the straight resistance coupling, shown in Fig. 2, i.e., the capacity between the high potential lead and the shield. Most of this capacity effect can be eliminated by placing the peck amplifier as close to the head of the projector as possible without actually being attached to it. It has been proven that it is bad practice to actually fasten the peck amplifier to the projector as the vibrating of the latter will set up microphonic noises in the amplifier which are practically impossible to eliminate. This high potential lead should be separated from other leads that run to the head of the projector and placed in a separate shield. A piece of copper tubing of about one-half inch in diameter makes an ideal shield for this lead. As the wire does not have to be any larger than No. 30 B & S gauge, the spacing between the wire and the shield is great enough to make the capacity practically negligible. After the wire is placed in the tubing, the tubing should be filled with some kind of insulating compound to eliminate vibration. The circuit combining resistance and impedance has now been in use in a number of theatres for several months and has proven its merits. General Report of the S. M. P. E. Extracts From a Report of the Activities of the Society of Motion Picture Engineers by L. C. Porter, the President DURING the past six months our Committee Chairmen have worked hard and faithfully. They have initiated and are carrying out some interesting things. The Studio Lighting Committee, for example, reports as follows : "The Committee on Studio Lighting has so far been able to do only fundamental planning for what we hope will eventually result in something like a manual which will be of very practical value to the lighting departments of the various studios. "The first step along this line will be a bibliography of articles which have appeared in the Society's Transactions and also in other magazines, such as the Transactions of the Illuminating Engineering Society, on studio lighting and the characteristics of light sources. From this either entire articles or abstracts of the essential particulars in each article will be put together, so that they may be readily accessible and useful." The Journal Committee reports that they unanimously favor the publication of a technical journal in place of our present Transactions. They are busy securing detail data on costs, and ways and means of doing this. The Publicity Committee puts in a plea for the publication of more S.M.P.E. material in the trade papers, more support from the theatre owning *From The S. M. P. E. Bulletin. interests, and more co-operation from the Society's members in general. The Standards and Nomenclature Committee has some new propositions to consider for standardization. They also recommend changing our present method of adopting standards by vote at our conventions to vote by letter ballot, after propositions are presented and discussed at the conventions, and published in our Transactions. The work of the Membership Committee speaks for itself. The fact that we now have well over 600 members is mute evidence of hard, efficient plugging. In connection with the work of this committee, the Board has given most careful consideration to the advisability of extended foreign expansion. This seems to be closely tied up with the question of the publication of a journal. After about two hours discussion of the matter at the last Board meeting, the following resolution was passed : "The Membership Committee be instructed to temporarily curtail activity in all foreign countries until such time as the question of the publication of a journal is definitely settled." The Board of Governors in a strenuous 12-hour session on July 26th, considered the above reports at length. Other matters of minor importance which the Board has discussed are : (1) The advisability of presenting an annual medal for meritorious work in the motion picture field. (2) Changes in our present letterheads. (3) Definition of "Foreign residence." (4) Revision of Qualifications for Associate Membership. (5) Honorary Memberships. (6) Distribution of "Aims and Accomplishments" booklet. (7) Possibility of holding a convention in London. Our Pacific Coast Section continues active and is proposing a series of joint meetings with various other motion picture organizations. This is fine! The S.M.P.E., its Sections and members, should be co-operators. The London Section is growing steadily and holding almost monthly meetings which, from the reports received, are quite successful. It is to be hoped that each of these Sections will be well represented at future conventions, and that they will contribute freely to the Society's Transactions. It is my firm conviction that we have grown to the point where it becomes urgent that we have a permanent office, and at least one full time paid officer to conduct much of the Society's business. The burden is becoming too great to be carried in addition to a man's regular business, even though divided among as many men as practical. To meet these changing conditions will require quite some changes in the Society's conduct, particularly in its finance. We are facing a turning point, as it were, in our history.