Award in the Frequency Test

Radio Record, Volume II, Issue 5, 17 August 1928, Page 4

Award in the Frequency Test

Decision made by

M.I.R.

E.

[N giving consideration to the award of the prize, it has been necessary to take into consideration various factors in order that all listeners throughout the Dominion should be on an equal footing. 1. The more distant listeners would require to use more valves in order to get reception and would therefore be handicapped with respect to those close to 2YA and especially to many in Wellington using a loudspeaker or headphone crystal combination. 2. Obviously those happy individuals in possession of expensive equipment should be expected to get the best results. 83. In considering the results obtained and information gained by reason of the tests it has been necessary to take into account the different individuals technical knowledge as evinced by the subject matter sent in ard give equal credit to the layman’s observations and the useful technical comments forwarded by others obviously qualified so to do. It has to be pointed out that any distortion or variation of sound intensity occurring in the transmission system of station 2YA can be discounted

equal disadvantage except those who were in a position where fading would cause trouble. A listener who lost the signals through this cause just at in that every listener would be at an the critical point when he would ordinarily be straining to hear can be counted as unfortunate, but he should smile his acceptance of the fortunes of war -or wireless becaus. fading is incurable in the light of present knowledge. The human ear is not a standard and those whose ears are high-pitched are at an advantage in such a test as this. However, the winner did not show the best results but was a good average so that there need be no heartburning on that score. Taking an average of the results as shown by those returns considered reliable, the signals were loud up to 3000 and commenced to weaken rapidly after 6000 and were ‘ost at 8000. Highclass equipments maintained touch to 10,000, but beyond this any results were freakish and probably due in

many cases to imagination. This statement will probably put to rest the lack of confidence in their equipment expressed by correspondents. Returns show a certain proportion of faulty equipment, but as far as can be judged the class of apparatus in use is generally good. Where really good designs of receivers and speakers were used the cut-off frequencies were obviously the limitation of aural response on the part of the listeners and cases were guoted where several people listening to the same equipment arrived at varying conclusions. The number of charts which came in without comments was disappointing and many good results had consequently to be ignored. A great deal of irrelevant matter was also sent in, although of interest in other directions. The decision in this matter was only given after ve carefu? consideration of the twenty contestants who were in the final selection and the other 19 can all be considered as.close runner-ups.-M.I.R.E. The Winner’s Report. ‘PH winning paper is adjudged to be that of Mr. R. Lake, 24 Leighton Street, Avonside, Christchurch. He uses a three-coil regenerative set with audio stages, one resistance, one transformer, and a gramophone att:.chment with a wide gramophone horn. He heard normal signals up to 1024 frequencies, after which a slight degree of fading, gradually intensifying, became apparent in the frequencies up to 7178. Frequencies were lost from 8192 on, although the generator hum was heard on 8192.

Mr. Lake’s letter was as follows !- [ PROPOSE to divide my report on the frequency test carried out by 2YA into three sections, the first of these to deal with the results achieved on my owl loudspeaker, the second with the general conclusions I have drawn from the test, including some remarks which will, I hope, mitigate to an extent the disappointment some listeners, probably most, may have felt in the performance, or lack of performance, of their speakers. The third section will deal with the broadcast itself. May I, at the outset, stress the ‘point that in all my remarks I am guided only by the position as it appeals to a layman in the theory of harmonics and overtones. Whilst, therefore, I.- lay myself open to correction on certain points, I feel, nevertheless, that suflicient excuse for rushing in where perhaps even angels may fear to tread is provided in the fact that the majority of listeners also view the position from a similarly non-technical standpoint, and if this is not sufficient excuse, then the "Record" must shoulder the blame, as it calls for reports from all and sundry. | A little elaboration of the notes made on my coupon (attached) is perhaps necessary. As this section is likely to be of small interest to the majority, dealing, as it does, with the results,. on one make of speaker only, it will bf as short as possible. A few points, however, seem worthy of note, and it may be that the same conclusions may have been reached by otherse with different makes of speakers. I BELIEVE it is very difficult for the human ear accurately to gauge the intensity of sound. One person hear-

ing the same note sounded at two different intensities will say the sound is three times as loud as the first, another that it is twice as loud, whereas measurement shows it to be but half as loud again. When to this human aural disability is added the effect of the decreasing sensitiviity of the ear to increasing sound vibrations, it becomes harder than ever to say definitely that a certain note is equal in intensity to a note an octave lower. Further reference will be made to this in my second section. In marking all the frequencies ex- _ cept that of middle C on my coupon as fading, it must not, therefore, be assumed that I considered this fading was in any way excessive until near the limit of the frequency range of my speaker. To be absolutelly faithful to my impressions, however, and to avoid exaggeration contributed to by pride of ownership of a_ certain speaker, I have, as stated above, confessed to a fading right from middle C. The word "fading" really needs qualification according to degree, and with this in view I have placed my crosses in the form of a curve which will give an approximate "‘ea of thi degree. . POINT that surprised me-using a .. horn type speaker-was that the fading increased at a quicker rate above middle C than below it, vibra tion 2048 (8rd octave above middle C) being appreciably less in intensity than frequecy 32 (8rd octave below middle C). In other words, although not having in an exponential horn, my speaker appears to deal better with low notes than with high ones. This is, I believe, contrary to the accepted theory governing the performance of horn speakers. To come now to the second section of my report. Assuming the re. sult obtained from my speaker to be equivalent to the average-a fair assumption I think, as it is a speaker with a good reputation-many people may have been disappointed with their results. Before taking such drastic ‘action as throwing them into the dustbin, however, it as well to consider one or two aspects of the case which may not occur readily to the mind One of these I touched on in my first section-the question of the sensitivity of the human ear. It was stated in the "Radio Record" that all the notes put out were of the same volume. Whether this means that the same power was used to produce them, or that the intensity of the produced notes, measured on recording instruments would have been the same, I do not know. Even in the latter case, however, I do not find cause to condemn a speaker because it will not produce a frequency of 4000 as loudly (apparently) as it wil produce a frequency of 256. While this failing may be, and undoubtedly is, present in loudspeakers, I think some of the apparent lessening in in. tensity is due to the merciful natural] law which decrees that our ears shal) not respond so easily to extremes in sound frequencies. Imagine frequency _.4000 sounding as loudly in the ears "Ys. does frequency 256. It would be / comparable to standing beside a rail way engine blowing off steam at high pressure through a whistle-little short of deafening. ; I THINK, then, that in judging a speaker, one should endeavour to forget that a certain high or iow-frequency note sounds less in intensity than a

middle frequency note, and try to judge the result impinged on the ear, by comparison with the actual sound, as remembered, of the instrument being broadcast. ‘I think if the highest note on the violin were produced with as much intensity, recorded on a sound-measuring instrument, as, say, middle © or the first C above middle C, it would still be said in a concert hall that "it didn’t sound so loud." Make allowance, therefore, for this human failing, if you care to call it that, though I think it would be more correctly described as a protective adjustment of nature. Lest I should be deemed to have fallen into the manner of one who advances proved theories, let me here reiterate that all I have said in this question is a matter of opinion only en my part, and quite open to correcion. N speakers themselves. The sound is produced roughly in the same fashion as it is received by the earby vibration of a diaphragm. Until something revolutionary occurs’ in speaker design, therefore, it is hardly

~- fair to blame them for having the same tendency as the ear, ie, to quieten high notes, especially when one makes allowance, as one must, for the fact that mechanical disabilities cannot fail to add even more to this tendency, to the detriment of the speaker compared with the ear. Moving-coil speakers are reputed to give the most natural reproduction. Kiven these fall short of perfection. They are also very costly. A cone or horn speaker at an average cost can, therefore, be expected to have failings. In view of all these points, and in spite of the fact that technically, my speaker reproduction may have been Shown to be a dismal failure, I shall continue for the present to use it, satisfied that at to-day’s stage of speaker development at a reasonable price I am obtaining as nearly perfect reception as possible. . OF the transmission itself I. have little to say. The generator hum was rather in evidence on my speaker, and possibly this may have overpowered one or two of the lower high frequencies I failed to hear. Again

EN 5 I will give my speaker the benefit of. the doubt. It may be relevant here to say that perfect speaker reproduc: tion can, of course, only be attained hand in hand with perfect transmission, and as the latter is admittedly not achieved yet, here is a further small argument in favour of the retention for the time being of the notperfect speakers we already may possess. Bete following point I mention in view of the fact that repetition of this test is possible from other stations. After one or two of the very lowest frequencies had been sounded, mention was again made of the possibility of hearing the harmonic an octave higher, and mistaking it for the fundamental. Then the frequency an octave higher was sounded. In one case it seemed to me that the lowest frequency was a border-line case, that is, I could not be quite sure if I heard the fundamental and harmonics, or the harmonics only. Memory slightly faded during the musical director’s remarks.