REPRODUCING LOW NOTES

Sun (Auckland), Volume III, Issue 675, 29 May 1929, Page 16

REPRODUCING LOW NOTES

Most loud-speakers of the horn type fail as perfect reproducers, because they tend to repress the lower notes in the musical scale in comparison with the manner in which the midle and higher notes are reproduced. If two notes, one high on the scale, and one low of equal intensity, are impressed in the average speaker horn, the higher note will appear to be very much stronger than the low note as it leaves the horn.

The reason for this is that, for true reproduction, the length of the speaker horn must bear a definite relation to the wave-length of the sound being reproduced. As the waves corresponding to the lower notes are several feet long, a very long speaker horn would be required to reproduce them in their correct perspective with the higher notes. It will be seen from this that if the actual intensity of the higher notes, as they are fed into the speaker, could be diminished, without at the same time diminishing the intensity of the lower notes, a state of balance would be reached in which the reproduction from the speaker would be approximately accurate. A simple means of bringing about this diminution of intensity of the higher notes consists of the connectting of a fixed condenser of suitable value across the terminals of the loudspeaker. Since the frequency of the currents

which produce the high notes is great, compared with that of currents producing the low notes, portion of the high note currents will be short circuited in the condenser, reducing the intensity of the higli-note currents which reach the speaker. As the tendency to this leakage across the condenser depends on the frequency, a substantial proportion of the high-note energy will be lost, but as the frequency of the low notes is too low for them to pass the condenser, they will be fed into the speaker at full volume. The actual value of the by-pass condenser will depend oil the characteristics of the speaker used, and must be found by trial. In most cases it will lie between .001 microfarads and .01 microfarads, depending on the length of the speaker horn. The shorter the speaker horn the larger will be the condenser value required. As fixed condensers having values lying within the range indicated can be bought very cheaply, no difficulty will be experienced in finding the correct condenser value by the trial and error method.