Laboratory Jottings

Radio Record, Volume III, Issue 43, 9 May 1930, Page 30

Laboratory Jottings

-- ae Farrand Inductor Dynamic Speaker M. SILVER and Co. have secured * the’ New Zealand agency for the Farrand inductor dynamic speakers, the principle of which type was described last week. One of these speakers. has been tested by our laboratory; and has. put. up a very record. In external appearance the ‘Farrand | resembles # magnotie -eone -unit with

two very large permanent. magnets. Lk is ‘light, being only slightly heavie than.a good cone. The cone is suspend? ed somewhat similarly. to. the dynamic, and as:a result of the lateral movement between the pole -pieces there is fully qin. play. . The. cone is 10 inches in diameter, and it-is intended to be placed behind a baffle, which can quite conveniently ‘be. that: of a," dynamic speaker. The delicate moving parts are enclosed: so that they will stand hard knocks, and it appears. not easy to put the speaker out of adjustment. For our. tests the speaker was placed behind a baffle, and fed in turn by a power amplifier and an ordinary twovalve amplifier, by weak and strong signals, and by constant frequency notes’ from 48 to 8000 cycles a. nd, It was compared with both our ater ard moving coil and magnetic speakér. As a result the following data has been acquired :- 1. It will take at least four watts without distortion or rattle. As comfortable room strength is one to twowatts, depending on the size of the room, it will handle ample power for most general purposes. In fact, at one stage an amplifier such as that used with small sound film plants was em-ployed-and the Farrand stood up to the output: without | signs of" overlonding. 2. It is almost as sensitive’ ag a cone and slightly more sensitive than our standard moving coil. It works satisfactorily- from a two-valve amplifier on both broadcast and: gramophone. reproduction. .Hven when 90 volts are on. the plate the speaker. performs well. ' 8. The frequency range is from below" 43 to 8000, a. range consistent with excellent reproduction., The curve is practically flat between 50 and 6000 cycles with very few peaks. A range such as this is not usual. During the test at the lower-frequencies the cone could be observed vibrating at least 1-8-inch, and yet there was room for further movement. We did -not locate any resonance peaks; 4. The reproduction is both pleasing and natural, giving a freedom from boom and screech-a pleasing quality in these times when the tendency is grossly to’ over-emphasise the bass. Within the range, which includes that of all notes within the working musical range, there is even amplification. The instruments in both bass and treble are clearly defined, and there is an absence of mushiness. The introduction of a speaker ch as this. will mean a great step fo d in loudspeaker design.