Showmen's Trade Review (Jan-Mar 1947)

E-8 SHOWMEN'S TRADE REVIEW, February 1, 1947 What's New In Sound Far Higher Poiver— Better Amplifiers— New Servicing Aids More reserve power in the sound system — much more — is one of the outstanding trends in sound development at the present time. Important further refinements in tone quality, revised and simplified apparatus, and improved servicing gadgets are also decidedly in the picture. The trend toward higher power is strikingly exemplified by two theatres just opened in California — the Crest and the Towne. Neither has as many as 1,500 seats, yet both have been equipped with 150 watts of sound output. The Academy Research Council's recommendations on the minimum power requirements for theatre sound systems specifies only 32 watts for houses of 1,500 seats. The owners of these new theatres, therefore, have seen fit to install five times as much power as the Academy calls for. Although the Academy's recommendations are not often multiplied to that extent, they quite generally are exceeded, now, whenever new equipment is installed. Last August, the members of STR's Projection Advisory Council voted the Academy's volume standards inadequate (see STR for August, 1946, Page E-4). The vote, however, was not unanimous, and no one then suggested that they ought to be exceeded five times. The Academy's standards actually represented a vast improvement over existing practices at the time they were issued. Theatres then quite commonly had only 10 or 12 watts of power for 1,500 seats, and thousands of houses of up to 1,000 seats or even more used as little as 2l/2 watts. The Academy recommendations were privately denounced by some, at the time, as excessive and beyond reason. The extent to which those once "excessive" standards are coming to be considered inadequate is to some extent exemplified by the new installations in the Towne and the Crest. Larger amplifiers are now on the drawing boards of manufacturers, and will be heard from before the end of 1947. In the past, and to a very considerable extent today, the favored way of getting more power into a theatre was and is to use two or even four output amplifiers, connected in parallel. The future unquestionably will see an increasing tendency to use only one ouput amplifier per channel — an amplifier large enough to do the job. Better Quality One reason for increasing sound power is to improve quality. When the reserve volume available is sufficient so that the system does not work near the overload point of any component under any circumstances, residual distortion is naturally reduced. Amplifiers, however, are not only being built now in larger ratings, but are being improved as to inherent quality. A type of distortion that was to some extent ignored by designers until recently — intermodulation — is being treated as of major importance. With present day testing equipments and methods intermodulation can be measured readily and accurately, and amplifiers improved to reduce the percentage of that distortion in their output. Intermodulation created by the loud speakers was materially reduced some years ago by the introduction of two-day speaker systems, with separate units for the low and high frequencies. Installation of the best available two-way speaker systems can be expected to increase as existing amplifiers are replaced or modified to reduce intermodulation in the amplifier. Only the best speakers known will be able to do justice to the new high quality of amplifiers. Another trend that appears to be growing increasingly popular is the use of dual channel sound systems to assure that no amplifier failure can ever interrupt the show. Some manufacturers are bringing out dual channel amplifier assemblies as regular equipment. This trend ties in with the increasing use of higher power in some cases. Where ample reserve power COMBINATION projector-andsoundhead, the Weber Machine Corporation's Synchro-Dynamic unit is in full production, with a limited number now ready for shipment. is installed, it can take the form of a double amplifying channel with the amplifiers wired in parallel — in case of any trouble the faulty channel can be switched out of service and its twin will still carry on the show without the audience noticing any difference except perhaps a not-toodrastic decline in sound quality. New Apparatus DeVry Corporation is now offering sound equipment that includes a line of amplifiers of recent design, delivering up to 80 watts of sound power. (Before the Academy standards were issued 24 watts was considered power enough for the largest 5,000 and 6,000 seat houses!) The new 40-watt unit amplifier is a dual channel assembly, consisting of two amplifiers each of which delivers 20 watts output at two per cent distortion — this rating being based on Academy standards. The wiring and switching arrangements are such that either amplifier can be used separately, with the other in reserve for emergencies, or both can be used in conjunction to provide a 40 watt output. The rated frequency range is flat within two db between 40 and 10,000 cycles. High-low tone compensation permits adjustment of quality to compensate for poor prints and for acoustical conditions; these controls also can be set to make the response curve conform exactly to Academy recommendations. A monitor speaker is built into the cabinet. The 20-watt DeVry amplifying assembly also contains two amplifiers — each of them of 20 watts output — but the wiring and switching are so arranged that they cannot be used in conjunction, only independently. The output rating is based on two per cent distortion and determined Academy standards; the frequency response is rated flat within one db from 50 to 10,000 cycles; high-low tone controls are included. The amplifiers have high impedance inputs for direct operation from photo-electric cells, and means for matching the volume from both cells. Microphone and record player input terminals are provided. Monitor speakers are built in. The same company's 80 watt amplifier assembly is wired to enable the projectionist to use 20, 40, 60 or 80 watts as needed; the DeVry line of amplifiers also includes a 20 watt single-channel unit. Complete sound installations are available with a DeVry combination projectorsoundhead, built as a single mechanical unit. Weber Machine Corporation has now (Continued on Page E-26)