SEEKING PURE REPRODUCTION

Radio Record, Volume I, Issue 15, 28 October 1927, Page 14

SEEKING PURE REPRODUCTION

A FEW NOTES ON THE LOUD-SPEAKER 4 ;

In selecting a loudspeaker of either type, there.is no method equal to that of hearing several demonstrated at the dealer’s, and taking home ‘the two you fancy best to try on your own set undér actual conditions under which the speaker is to be used, ‘There are a number of makes of good cone speakers, but for a set giving liberal volume, a speaker that will carry plenty of volume, without overloading, is essential, and in such a case a small speaker will do scant justice to your sect, Very often the set gets the blame for trouble that is solely due to the londspeaker. ‘ "AN INTERESTING EXPERIMENT. Readers having a horn speaker al-. ready on haud «an try an iteresting experiment if they care to go to a little trouble. ¥rom thin cardboard, stiff brown paper, or the large manila sheets used to make office folders, an experimental horn can be sade, the thin eud just a fit for the aperture when the ordinary horn is removed, and the wide end'teighteen inches in diameter, the total length of the horn being four feet six inches, ‘The speaker .unit can be placed on the floor with the horn standing upright and pinned to the wall. The use of this should prove to be a_ pleasant surprise, as the lower or bass frequencies will be heard as they never were before from the same unit. The only thing that could prevent these low motes from being heard would be faulty audio transformers, incapable of reproducing and passing on such frequencies. A convenient and quick method of securing the lower half of the ‘horn when rolled up is to wind round twine in a spiral direction, securing it as soon as possible with glue. The top portion is easily secured by paper fasteners passed through at suitable points, The sheets of paper must first be glued together on the flat, to form a large triangle of suitable dimensions, the wide part sixty-four inches across. This experiment shows that length is the essential to good reproduction from a horn speaker, and the increased length also gives extra volume. As most horn speakers have not more than a two-foot horn at the most, and many are much shorter than that, it is a wonder thnt they are us good as they are, but careful design is made to compensate to some extent for the lack of length. CONE SPEAKERS, Cone speakers are improving rapidly, great attention being centred upon the driving mechanism, in the direction of securing volume approximating that from a horn type under the same conditions. Many corte speakers are efficient on low notes, but discriminate badly against high tones. For the lower

frequencies, at any rate, they are mostly less directional than the liorn-type, and for ordinary rooms and moderate’ volume a cone. is excellent. It is, quite likely that before very long a cote type will he produced that will actually respond to-.as low as 60 cycles, and equally to ail intermediate audio frequencies up to 7000. Such a speaker would cover the whole range of musical sounds, ‘ There are in use in America at- the present time orthophonic horhis 40° feet in length, yet mathematically designed, with a correctness that allows equal response to the lowest bass notes and also to the high C of the soprano. _. ~ Fxperimental cones up to ten feet in diameter have heen built in a factory laboratory, and though only driven by an ordinary small unit, the ‘voices of, singers are reproduced with great faithfulness, and most wonderful musical reproductions. When rewinding old transformers for choke-coupling for the loudspeaker, if it is possible, the laminated core should be réassembled so that all the joins come together at the one place, and in the space where the two ontside lots meet, a square of thick paper should be inserted, the whole pushed together tight, and clamps screwed on.. This gives a core with gaps, which is flie correct thing for a low-frequency choke.