Boxoffice (Oct-Dec 1963)

for 35mm and 70mm projection. Instant change from one film width to the other, a THE MOST ADVANTAGES LOTS OF LIGHT FOR SALE at a Bargain with this marvel of projection lamp. See your Strong dealer or write for literature. lYi* Electric Corp. PCity Park Ave., Toledo, Ohio 43601 TELEPHONE: 248-3741 AREA CODE: 419 NEW ^ ^FUTURA MOST LIGHT PER CARBON DOLLAR NEW ^ g^FUTURA TOP LIGHT OUTPUT for indoor and drive-i theatres. NEW ^ g^FUTURA Low original cost. Greater operator convenience. Efficient use of standard 20-inch carbons. ACHIEVING HIGH-QUALITY SOUND Continued from preceding page ment, the best check on any sound system is the “listening” test in various parts of auditorium. The crossover plays a very important part in sound equipment installation. When two loudspeakers (high and low-frequency speaker combination) are installed, the frequency below which the low-frequency speaker receives the electrical signal, and above which the high-frequency unit receives the signal, is called the crossover frequency. Generally, this crossover frequency is in the region of 500 and 2,500 cps. This will depend, of course, on the particular make of speaker combination installed, and the manufacturer’s data should be consulted to make sure you have the “right” type of crossover setup for your particular setup or you can mar the quality of the sound output. A crossover network must be used to perform this function, located in the projection room or backstage. The crossover network should present a constant impedance to the amplifier, and deliver power to the speakers. There should be provision for setting the volume output equal for both speakers. This is generally taken care of at the crossover network in a high-quality loudspeaker setup. ONLY FOR A SMALL THEATRE There are quite a few installations, in small auditoriums, using bass-reflex cabinet with a 15 -inch speaker inside and high-frequency unit mounted on top. This will do very well in a small theatre, but is not recommended for large auditorium. Usually a crossover arrangement is made up by the installation engineer at the time of installation and works fairly satisfactory. The type of low-frequency speaker for this kind of installation should be a permanent type using highly magnetic material and a high quality cone of wellknown make. Cheap speakers always give inferior sound and will not faithfully reproduce all the frequencies without some distortion. This same advice applies to a small, high-frequency, metal-type speaker. The above loudspeaker will “get by” in theatres seating around 200-250, but is not highly recommended. We find quite a few installations using only a 12-inch conetype speaker on a large baffle, but such a setup is not for a motion picture theatre that wants to compete with high-fidelity sound in homes. You must have highquality sound reproduction to meet TV and high-fidelity sound competition. Loudspeakers seldom give any trouble if given proper care and they are kept free of dirt accumulation. Often, when we have given a sound system a complete check, we have found speakers covered with dust, connections corroded and the interior of cone speakers full of dirt. This condition will certainly mar sound reproduction and should never be allowed to exist in any theatre. DAMAGE TO VOICE COIL Troubles — Damage to the voice coil, the most delicate component in your speaker, may impair the quality of sound obtained from a speaker, or may render it entirely inoperative. The voice coil may burn out, but, due to rugged construction of modern theatre speakers, this trouble is not very common. But, keep this in mind: If the speaker is subjected to prolonged and excessive volume (overload), especially at low frequencies, this may cause it to burn out and a new voice coil will have to be installed before it will operate again. We find that open circuit in a voice coil is rather more likely to be caused by a break at the point where flexible leads are joined to it. Check with your ohmmeter for opens. Another cause of broken leads can be traced to continuous vibration of the coil — excessive vibration. In many high quality loudspeakers the construction of the leads is such as to make a break of this kind impossible, but should one of your speakers “go dead” you should check at the connections with an ohmmeter. These leads are larger than those in oldtype speakers, and a terminal block is generally used for connection. The field coil, on the contrary, is commonly wound of heavy wire, little subject to open-circuit, and a speaker built for the motion picture theatre very seldom gives trouble unless excessive voltage is applied. Too, the voice coil is more rugged in construction and special wire is used for long, trouble-free operation, but trouble can develop if overloaded or if dust is allowed to accumulate. Most all speakers today are of the permanent magnetic type and no power is wired to the field coil; only the transmission line to the cross The next time your projection equipment needs repairs ask your dealer to install genuine LaVezzi Super Service replacement parts. Their unexcelled performance and long life make them your best buys . . . Only the finest— since 1908. MACHINE WORKS 4635 W. LAKE ST.. CHICAGO 44. ILL. TELEPHONE— AREA 312-376-1636 12 The MODERN THEATRE SECTION