THE IMPORTANCE OF SOUND IN WIRELESS
A few lines of history are desirable here. I do not mean the history controlled by the fact that William the Conqueror made many important appointments in A.D. 1066 or that Stephen was particularly busy in A.D. 1100. I mean the history of wireless, for, although Radio Science is new, it has a history; all time is relative, and we ourselves are functions of that phenomenon.
Only a few years ago the efforts of wireless experimenters were entirely directed to the converting of the extremely delicate wireless oscillation, still but little understood, into a mechanical movement, in order that the motion of electrons in a problematical aether (which may be nothing but a thought projection and which may exist in many different forms) might be altered into something readable by a man with a check waistcoat and a stock and share list in his hand.
That particular use, and the information that one army is about to kill another could be transmitted to headquarters, naturally occurred to everyone as the first valuable applications of Radio.
The many devices, the electro-magnetic receivers, tape machines, coherers, syphon recorders and the thousand and one electrical machines produced at the time for these purposes, have practically all gone.
Even when to-day we want to send messages quickly, we record them upon a Dictaphone and rely almost entirely upon the sense of hearing.
Sound, the regular oscillation, and noise, the irregular oscillation, of the air, are really the beginning and end of wireless as it is known to the public to-day.
I would go further when thinking of the public. They do not want to sit with a telephone upon their heads, even if their ears may be improved thereby. They require to walk into a drawing-room, and having stood for a moment upon the mat, they must be able to cross the room, touch a button in a fretwork cabinet, and by the movement of a lever be able to place themselves in touch with any part of the world. Paris, Hong-Kong, London, all must be one to them if we are to get their money for our art.
In other words, we are compelled to use what we now designate the “loud speaker.” We have got to project a sound into the room before we can sell our instruments, and therein lies one great difficulty.
In the first place we dare not exaggerate the movements of a delicate telephone very much or we shall spoil it—therefore we construct something which looks very much like a magnified telephone with a trumpet upon it. The mechanism is naturally rather heavy as regards the moving parts. In order to vibrate these heavy parts with the aid of our aetherial oscillations we have to amplify the available current, and during this process we naturally spoil the detail, or, in other words, we magnify it so much that electrical distortions occur through the whole range of various transformers and other items sold by every shop in the world—at double their value.
Most people are not content with a gentle sound: they find it necessary to express their joy at having reached their home by dancing; consequently they want plenty of sound, and they do not mind if it turns into noise.
They will tell you boldly that their wireless set with a couple of dozen foreign-made valves can be heard right across a large street, a street by the way in which we still permit as much nerve-shattering noise to occur as is thought necessary. This means that we must have quite a big movement on a diaphragm of large size, and a large diaphragm is made to move by the electrical oscillation, itself not very accurate; naturally, if it is heavy, like a poker or anything else, it has a will of its own, and therefore it continues to move when the wireless oscillation has told it to stop. It does not even commence to move when it is told to do so, as it would were it a thin delicate telephone diaphragm from which accurate music can be obtained.
This means further distortion, and so bad is it that a great many people say plainly that they will only listen to wireless concerts through a telephone and that they will only use crystals to obtain rectification because of the inaccuracies otherwise unavoidable to-day.
But this is not business, because do not forget we must have our cabinet with a fern upon it and beautiful music, if we are to be successful. Business always leads science, as we know.
Now think why it is that we need this big diaphragm moving so hard to get a big noise; let us neglect electrical details and consider what produces the noise; or sound, if we are lucky.
Sound is unfortunately purely a mechanical phenomenon as we chiefly understand it, and is produced by oscillations, alternate compression and rarefaction of the atmosphere. Unlike the aether, which sometimes oscillates only too readily, air is a heavy material and has great mass.
You will soon find this out if you put your head out of a railway carriage window, because the air is so heavy that we have got to really kick it and hit it hard before we can obtain a reasonable degree of noise.
When a speaker is standing at one end of a room, irrespective of what he says, the actual temperature-rise of the air can be measured, a fact which was used during the war for the inspection of sound.
Sound is a very complicated thing. It can be reflected in much the same way as light, and I suppose most school-boys know that if a concave mirror is at one end of a room and a similar mirror at the other with a watch hanging at its focus, the watch cannot be heard by an observer walking across the room, yet as soon as he places his ear at the focus of the other mirror he will hear the tick clearly, showing that sound is easily reflected. Everybody who has heard an echo should know this.
Sound travels also very slowly, and there is plenty of time for wind and different mechanical scraping effects to spoil the purity and partially absorb its delicacies.
Remember that if I am addressing a man by wireless who is one hundred miles away, someone who is listening on a telephone will hear my voice before I am heard at the end of the big hall where I am speaking, because the velocity of sound is only 1100 feet per second, and wireless, like light, travels much faster. Sound can also be actually refracted. Just as the old-fashioned jeweller used a globe of water to concentrate the light upon his work, so will a collodion balloon filled with carbon dioxide, the ordinary gas product of average combustion, act as a lens for sound, which can be actually focussed by these means.
This exemplifies the complication of our subject, and indicates that the heavy diaphragm and other details of the loud speaker must produce serious distortion.
Let us be honest at once. We can only hear such distant places as America by the grace of heaven. Even Sunlight can tune sweet song into vague cracklings. Until true tuning can be obtained we are largely at the mercy of the reproducing instrument, which too often exaggerates every fault and gives the impression that wireless and music are in no way related. No loud speaker of to-day really produces voice and song which sound exactly like voice and song. It all too much resembles a bad gramophone, but without the advantage of the user having the choice of the music.
If user and manufacturer would concentrate upon obtaining purity, if they would try the effects of damping upon loud speakers, which are easily obtained; if they would realise that the horn of the loud speaker should be without resonance, that it should be also damped and pocketed, that its goose-necked shape is not adopted without an object, and if they would aim at the delivery of true music instead of noise—then, we should make a great advance. The average loud speaker can often be greatly improved by padding the horn with some kind of tape, and as an example of the great difficulties of proper transmission let it be made quite clear that with most cases of wireless communication the sending is nearly perfect. Reception is greatly at fault: it is the reception that mangles the sound and makes it too often almost unbearable to anybody of reasonably sensitive hearing.
At some large transmission stations it was at one time quite common to use three separate microphones for the modulation. One received notes of high pitch, one of low, and a third attempted to obtain the “S” sound with the result that, when this “S” microphone was adjusted for a man who did not say his “S” very loudly and someone appeared who did, it sounded exactly as if the speaker had dropped his false teeth.
All this is now avoided. The ordinary diaphragm is no longer in use, but a very small coil of aluminium wire is suspended between the poles of an electro magnet, allowed to rest against an ordinary pad of cotton wool, and that is all!
The infinitesimal movements of this aluminium coil will reproduce speech up to about 40,000 periods per second in oscillatory speed, yet speech is well recognisable if all frequencies over 4,000 per second are gridded out.
How difficult it is going to be to make a large, heavy, and rapidly moving diaphragm reproduce accurately when we have had to take all these precautions to obtain accuracy of transmission! It is not impossible; it will come one day.
Now let us see what is the result of our sound troubles.
We are told that before long it will be quite easy to hear birds singing in trees and the waves beating against the seashore. Quite right, quite easy to do it now, but if a bird singing in a tree sounds like a man moving his condenser or walking about with a pair of squeaky boots, is it progress?
Perhaps it is. The whole point of wireless is that it brings a man into your room, but it must sound like the man himself if it is to be really effective; it is this pitiful quality of reproduced sound that has wrecked the talking cinema.
It is very easy to photograph sounds and to reproduce them simultaneously with the projection of a picture, but to reproduce all the sounds of a cowboy scene accurately is, at present, almost impossible. If a hero says “Good-bye” to a heroine with a kiss like a creaking board, in the middle of a twenty-reel drama, instead of improving upon the effect of your imagination, which tells you that it is real, and which acts the scene for you better than it can be shown in life or sound, it would be like putting up a blackboard across the screen with the words written upon it, “this is not real—it is only a fake.” That is what is wrecking the talking cinema. As a scientific proposition it is easy, but the results are not good enough at present, and, if we can improve, let us first consider the loud speaker.
The talking cinema will come as a matter of course. It is so easy to record sounds upon the film by photography with reproduction by the selenium cell or the neon tube; it is easy to photograph the wave; it is easy actually to impress the sound wave upon the film with the picture, or to use a gramophone; but reproduction is not like a human voice. Neither as yet is any reproduction ever like the voice itself. Let that painful fact be remembered.
Unfortunately, from the business point of view, the long distance reproduction effect is usually satisfactory even when re-broadcasted upon telephones, and for business purposes it is immaterial whether the voice that records the profit or loss is harsh or pleasant.
So the greatest effects we shall soon see from wireless and sound are these: we shall be able to speak to people all over the world by relaying and a combination of land-line and radio; we shall easily be able to connect our office with a wireless station on the coast, radio across the Continent, and then connect by land-line to another office on the other side of the Atlantic.
All this is so easy that no one can doubt that we shall soon listen in to native jamborees; no one can doubt that we shall hear the strange cries of partisans at a baseball match taking place a few miles from New York; no one can question these things, and when reproduction becomes so accurate that the very nature of the people is revealed to us through their speech, surely we might be a little more neighbourly even with those whom we now pretend to love? Relations are notoriously quarrelsome.
If you are in a concert hall and the number of people is varied, it will alter the effect of the sound. You have only to look at a sound-wave photograph produced from a violin to realise from its dainty intricacies that the least variation of any of its harmonics or the very exact shape of its wave beats will reveal all the difference between a beginner and the finest musician in the world. But these things are seldom noticed in wireless.
It is quite easy to photograph a sound, by means of a diaphragm beside which a soap bubble is thick, and to compare wireless sound with the original; even then we have the great difficulties of resonance, and a diaphragm cannot reproduce properly. How, therefore, dare we neglect the dreadful sounds we hear in the name of radio music?
If a piece of silvering, one thirty-secondth of an inch, be scraped from the back of a mirror and fastened to the outer part of a celluloid diaphragm (made by water-floating a drop of amyl acetate in which celluloid has been dissolved), it only requires a horn and a beam of light to render visible the waves of sound. A diaphragm movement of a millionth of a millionth of an inch is sometimes audible.
It is the science of wireless that is beautiful; it is the possibilities that are wonderful; but to talk of pure sound and to judge of it by the human ear which varies after every meal, is like measuring the amount of current passing through an electric-light bulb by feeling its heat with the hand.
It is not generally known that, during the War, experiments were made with a sound-reflector for listening to different types of aeroplane and submarine, by means of a microphone placed at the centre of a concave mirror. The difficulty was that of distortion, which is the whole source of trouble with sound producers to-day. Distance is no difficulty and when we can obtain purity and realism as well as distance, the latter is no difficulty at all; then only will be the time when we shall have that spontaneous mental realism of vision that will help radio to alter the world.
In a few years time we shall be able to chat to our friends in an aeroplane and in the streets with the help of a pocket wireless set, and be able to do practically everything by the aid of radio that we now do with our voice.
The only thing that will seem intensely strange will be that these comforts never existed before!