Radio broadcast .. (1922-30)

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Authorities Describe the Year's Improvements PROGRESS IN LOUD SPEAKER DESIGN NATHANIEL BALDWIN, INC. E. W. SMITH, Research Department: Fundamental and accurate data on vibration instruments has enabled manu- facturers to set a new standard n moving-iron reproducers as regards efficiency. A very satisfactory response is now obtained with a reduction of the "peaks" that have charac- terized the performance of these instruments hitherto. The Baldwin line reflects all the improvements enumer- ated in a new moving-iron instrument. The improvements are listed as follows: one-piece cast-aluminum frame, laminated pole pieces and armature, new double permanent magnets which offer nearly twice the magnetic flux of the old type, and an improved "Burtex" acoustic diaphragm. JENSEN RADIO MFG. COMPANY PETER L. JENSEN, President: Loud speaker manufacturers that employ competent and progressive engineering staffs will present to the trade this year new models of dynamic (moving- coil) loud speakers somewhat better in every respect than the 1928 models. The main improvements are made along the following lines: greater dependability on high power; larger cones with consequently less motion for the same output of sound; eliminating stresses and danger of breakdowns; larger voice coil capable of carry- ing 250 push-pull input without overheating, and finally and most impor- tant extending the re- sponse to include more of the higher voice fre- quencies. The voice coil problem has been overcome in the new 1929-30 model Jensen dynamic loud speakers by the use of aluminum wire. As aluminum has about 60 per cent, the conduc- tivity of copper and only about 30 per cent, its weight, its employment gives the required increase in current carrying capacity with- out correspondingly adding to the weight of the moving parts. The Jensen Concert Speaker employing a lighter movable system has a response well above a frequency of 5000, and the "boom-boom" characteristic of many dynamic loud speakers has been entirely eliminated without the sacrifice of the pleasing true low notes. It employs a shallow 9i" cone. Due to the increased demand, dynamic loud speaker manu- facturers have been able to plan more economical production this year by being assured of a larger output and set manu- facturers can procure good dynamic speakers at a cost prob- ably not exceeding 25 per cent, over the cost of a good mag- netic unit. OXFORD RADIO CORPORATION FRANK RE CHMAN, Radio Sales Division: Dynamic loud speakers will hold the front rank in loud speaker styles dur- ing 1929. The dynamic loud speaker has proven its merit and Peter Jensen, president, Jensen Radio Mfg. Co. Frank Reichman, Radio Sales Division, Oxford Ra- dio Corp. with another year of development behind it outranks, in fidelity of performance, any other design. Practically all of the leading set manufacturers are planning on using dynamic loud speakers exclusively. Dynamic speakers will be ever so much lower in price due to set manufacturers incorporating in the power pack of the set the means for supplying the field current to the speaker. This eliminates almost half of the manufacturing cost of the loud speaker proper. However, this means the speaker and the set have to be engineered and sold together. Oxford loud speakers this year will be available in every type of dynamic. This will include all d.c. models for setmanufacturers. The line will also include "hum free" a.c. models in both the dry rectifier and tube types, and theatre models designed to operate on the most powerful amplifiers. All types are made in two sizes, the 9" and 11". Cabinet manufacturers, this year, are designing their cabinets as "baffle boxes" quite as much as beautiful furniture. They realize that the dynamic loud speaker is not a com- plete operating instrument without its "baffle" and that the cabinet is the "horn," and is an essential, vital part of the loud speaker. STROMBERG-CARLSON TELEPHONE MFG. COMPANY RAY MANSON, Vice President and Chief Engineer: Last year, the dynamic type (moving-coil) loud speaker came into its own, due to the small space required for a powerful driving unit. Many detailed improvements have been made in this type of unit which provide for increased audio-frequency range and increased electrical efficiency. This result will be obtained by various detailed improvements, such as the use of larger diameter driving cones, more flexible supports for the cone, lighter weight cone materials, the use of stiffening means in the cone structure, etc. The so-called "magnetic" (moving-iron armature type) loud speaker also will be offered in greatly improved forms, which are sure to give better repro- duction than many of the dynamic loud speaker offerings of last season. Condenser-type loud speakers will be available as a commercial product before the end of 1929 and no doubt will create considerable interest. Stromberg-Carlson loud speakers meet these trends in a full line of improved "magnetic" types, model Nos. 14, 15, 16, and 17, and in an improved electrodynamic floor model, known as the No. 25. All of these loud speakers use "large diameter" cones of special construction, arranged to provide the correct frequency range for natural reproduction of speech and music, and a combination electrical and mechanical sys- tem which provides high efficiency of sound output as com- pared to electrical input 84 • • JUNE • 1929 •