Earphone

“ We ask in vain for an answer to the question which is upon the lips of every one-What next? The microphone has proved itself highly useful in strengthening the sounds given out by the telephone, and it is probable that we shall soon see those three inventions working unitedly; for the microphone might make the telephone sounds so powerful as to enable them to be printed by phonograph as they are received, and thus a durable record of telephonic messages would be obtained. We can now transmit sound by wire, but it may yet be possible to transmit light, and see by telegraph. ”

“ In using the Audiphone during conversation there is no movement or vibration felt by the teeth; in listening to a piano there is a very faint sensation as if the Audiphone vibrated slightly, while with the handle of the Audiphone resting on the sounding-board of the piano the vibrations are so violent as to be painful to the teeth. By closing the ears a person with even acute hearing can observe the admirable manner in which the instrument conveys spoken words to the ear. ”

“ 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 [Pg 34] beautiful; it is the possibilities that are wonderful ”

“ The sound that is heard in the receiving-instrument of the microphone, when a fly is walking across the board on which the transmitter is placed, is not the sound of the fly's footsteps, any more than the stroke of a powerful electric bell, or sounder, is the magnified sound of the operator's fingers tapping lightly, and it may be inaudibly, upon the key. ”

“ Just the same, only in radio telephony we are confronted by a problem not met with in wireless telegraphy. We have not only to transmit sound, such as isolated dots and dashes, but to send through the air every rise and fall and inflection of the human voice just as it is recorded in the minute lines of a phonographic record. ”

“ The amount of current flowing in the circuit thus keeps step with the changes in the resistance, and accordingly produces sounds in the telephone receiver. The vibrations emitted from the receiver are usually much greater than those of the original sounds, and so the microphone may be used to magnify weak sounds such as the ticking of clock-wheels or the footfalls of insects. If a watch is laid on the base of the microphone, the ticking of the escapement wheel can be heard with startling loudness. ”

“ The ear is constructed on the same principle, its diaphragm being actually moved by the vibrations of air, being what we call hearing. With these facts about sound understood in connection with those given in connection with the substitution of a magnet for a battery current, it is entirely possible for any non-expert to understand the theory of the construction of the telephone. ”

“ To serve as an ear, the telephone must be able to take up quickly and nicely the sound-waves of the air. A tightened drum-head will do that; or better, a strip of goldbeaters'-skin drawn tightly over a ring or the end of a tube. But these would not help Professor Bell, the inventor of the telephone we shall describe, since he wanted an ear that would translate the waves of sound into waves of electricity, which would travel farther and faster than sound-waves could. ”

“ The telephone enables us to speak to distances far beyond the reach of eye or ear, 'to waft a sigh from Indus to the Pole; 'the phonograph enables us to seal the living speech on brazen tablets, and store it up for any length of time; while it is the peculiar function of the microphone to let us hear those minute sounds which are below the range of our unassisted powers of hearing. ”

“ Let me tell you how it is that you can hear over the telephone, whether made of a simple box and string like this, or with a wire and electric battery, for in one respect they are both alike.
If you will place your finger gently on your throat, against what is sometimes called "Adam's Apple," but what is really the delicate little instrument with which we speak, and then utter some words in a strong, clear voice, you will doubtless feel a vibration or trembling in your throat, just the same as I now feel in my throat while I am talking. ”

“ It may be here noted that in a paper on experiments in audition published in 1827 Wheatstone said: “The great intensity with which sound is transmitted by solid rods at the same time that its diffusion is prevented, affords a ready means of augmenting the loudness of external sounds and of constructing an instrument which, from its rendering audible the weakest sounds, may with propriety be named the microphone.” ”

“ Although the audion is familiar to all amateur radio-operators, we shall have to give a brief outline of its construction and operation for the benefit of those who have not had the opportunity to dabble in wireless telegraphy.
The audion is a small glass bulb from which the air is exhausted to a high degree of vacuum. The bulb contains three elements. One is a tiny filament which is heated to incandescence by a battery, so that it emits negatively charged electrons. The filament is at one side of the bulb and at the opposite side there is a metal plate. ”

“ In speaking of the Telephone, we must not lose sight of the facts before mentioned, as regards our sense of hearing, and the manner in which the ear acts by the series of bones termed the hammer, the anvil, and stirrup. In the process of reproduction of tone in the magnetic instruments, the mechanism of the human ear was, to a certain extent, imitated, and a diaphragm, by vibrations, generates and controls an electric current. ”

“ Not only is the vacuum tube a detector of electric wave signals and speech and music but it can also be used to amplify them, that is, to make them stronger and, hence, louder in the telephone receiver and further its powers of amplification are so great that it will reproduce them by means of a loud speaker, just as a horn amplifies the sounds of a phonograph reproducer, until they can be heard by a room or an auditorium full of people. ”

“ It is usual to have a transmitter and a receiver on one handle for the greater convenience of the user. The arrangement is shown in Fig. 32, and it will be seen that when the user places the receiver to his ear the transmitting mouthpiece is in position for speaking. The microphone with its carbon dust is placed at A, just below the mouthpiece, and the earpiece or receiver B contains a little magnet and coil with a diaphragm in front, so that it is really a Bell instrument. ”

“ The three nails I have spoken of will not only do all, and that far better than Edison's carbon telephone in telephony, but has the power of taking up sounds inaudible to human ears, and rendering them audible, in fact a true microphone; besides it has the merit of demonstrating the molecular action which is constantly occurring in all matter under the influence of sonorous vibrations. ”

“ At the other end of the wire the pull of the magnet of the speaking telephone is varied exactly in proportion to the strength of the electric impulses that come over the wire; the varying pull of the magnet sets the diaphragm in motion, and that sets the air in motion in waves precisely like those of the distant voice. When those waves strike the listener's ear, he seems to hear the speaker's exact tones, and so, substantially, he does hear them. The circumstance that electric waves, and not sound-waves, travel over the wires, does not change the quality of the resulting sound in the least. ”

“ Before the description of the necessary apparatus is followed out, it might be necessary, however, to go back to the point how our ear perceives the vibrations of a given tone, and the total vibrations of all the tones simultaneously acting upon it; because by this means will be determined the various requisite conditions which must be fulfilled by the transmitting and receiving apparatus for the solution of the problem that has been set.
Let us consider first the processes which take place in order that a single tone should be perceived by the human ear ”

“ The function of the organs of hearing, therefore, is to impart faithfully to the auditory nerve, every condensation and rarefaction occurring in the surrounding medium. The function of the auditory nerve is to bring to our consciousness the vibrations of matter resulting at the given time, both according to their number and their magnitude. Here, first, certain combinations acquire a distinct name: here, first the vibrations become musical tones or discords (Misstöne) . ”

“ The discovery of the microphone by Professor Hughes has enabled us to understand the reason of this failure. The transmitter of Reis was based on the plan of interrupting the current, and the spring was intended to close the contact after it had been opened by the shock of a vibration. So long as the sound was a musical tone it proved efficient, for a musical tone is a regular succession of vibrations. ”

“ Reis met this difficulty in his own way by mounting his steel wire upon a small sounding-box to strengthen the sounds, and added a flat upper case against which the ear of the listener can be pressed, and which can be removed, or opened as a lid, when a whole audience is to hear simultaneously the tones of the instrument when working in a loud and disagreeable manner, as a transmitter of the coarser vibrations of a loudly sung melody. ”

“ Sound needs a Material Medium to Travel Through.—In order that the ear may be affected by a sounding body there must be continuous matter reaching all the way from the body to the ear. This can be shown by suspending an electric bell in the receiver of an air-pump, the wires conveying the current passing through an air-tight cork closing the hole at the top of the receiver. ”

“ The efforts to make the audiphone and denta-phone useful as regular instruments of hearing to the deaf have not had satisfactory results. Dr. Thomas acknowledges that the expectations which have been excited on the subject are likely to be disappointed. Those who are able to hear with the aid of the audiphone hear their own voices perfectly without it; while those who are unable to hear their own voices without it can hear nothing with it. ”

“ On applying the ear to a telephone joined into a circuit working in such an office, a curious sound is heard, comparable most nearly to the sound of a pot boiling. But the practised ear could soon separate the boiling into distinct sounds. There was one masterful Morse instrument—probably on the wire lying nearest the one on which we were joined up—whose peremptory 'click, cli-i-i-ck, click,' representing 'dot, dash, dot' on the printed slip we read from, could be heard over all. ”

“ When a telephone is placed in circuit with a telegraph line, the telephone is found seemingly to emit sounds on its own account. The most extraordinary noises are often produced, the causes of which are at present very obscure. One class of sounds is produced by the inductive influence of neighbouring wires and by leakage from them, the signals of the Morse alphabet passing over neighbouring wires being audible in the telephone, and another class can be traced to earth currents upon the wire, a curious modification of this sound revealing the presence of defective joints in the wire. ”

“ When the nature and laws of the waves of sound became fully known a great field of inventions was opened. Then came the telephone, phonograph, graphophone and gramophone.
The telephone depends upon a combination of electricity and the waves of the human voice. The phonograph and its modifications depend alone on sound waves—the recording of the waves from one vibrating membrane and their exact reproduction on another vibrating membrane. ”

“ When sound waves are prevented from dispersing the voice can be carried a great distance. Speaking tubes and trumpets, as well as ear trumpets, are examples of this principle, and of the reflection of sound.
There are many very interesting experiments in connection with Acoustics, some of which we will now impart to our readers. We shall then find many ingenious inventions to examine,—the Audiphone, Telephone, Megaphone, and Phonograph, which will occupy a separate chapter. ”

“ The optophone translates light into sound by means of that wonderful little element, selenium, which in darkness is a poor conductor of electricity, but in light is a good conductor. This property is used in the optophone in transmitting an electric current which is interrupted by a special clockwork interrupter. It makes light and darkness audible in the telephone. This thing over my head is like a wireless telephone receiver, capable of detecting a current of even a quarter of a microampere. ”

“ While no sound can be heard in the headphones at the receiving station so long as the points of the key are not in contact, when they are in contact the oscillations are modulated and sounds are heard in the headphones that correspond to the frequency of the buzzer in the key circuit. ”