Richardson's handbook of projection (1930)

1208 HANDBOOK OF PROJECTION FOR by condenser blocks and transformers which have twice the capacity they normally operate at. The input transformer has a very wide impedance range, which makes it adaptable to use with any high grade commercial pick-up system. The entire amplifying unit has a practically flat curve from thirty (30) to eight thousand (8,000) cycles. The output is designed for use with either high or low impedance speakers, the low impedance secondary being designed in two ways, having an impedance of ten (10) ohms for use with the dynamic air column horns and twenty (20) ohms for use with dynamic cone loud speakers. A little more clearly in explaining high and low impedances as well as flat curves, etc., we might say that everything works at its very best in a certain cycle or place. An automobile will derive more miles per gallon at one certain speed than any other speed it may travel. A dynamic cone derives best results with an input of 20 ohms, which is said to be low in impedance. A dynamic horn unit has the same appropriate low impedance input. If we were to pour the entire volume into a dynamic cone or horn unit at, say, 1,000 ohms which is, as will be seen, a great deal higher in impedance, the same effect would be had as if the entire gas tank was poured in the carburetor of the automobile. It would merely choke up and stop. A high impedance unit would be represented by an average commercial air column unit or commercial dynamic cone speaker which has the transformer to lower the impedance to the proper level, selfcontained in the speaker. The advantage of the specified impedance of the output for speakers such as 20 ohms, 10 ohms, etc., is: If a certain speaker or repro