Loudspeaker

“ 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.” ”

“ The action is the same on the voice of the speaker. The sounds he utters are complex and as they reach the walls certain components are reinforced and the quality of the sound is changed. This action of resonance may also be caused by the air in a room. Each room has a definite pitch to which it responds, the smaller the volume of the room the higher being the pitch. A large auditorium would respond to the very low pitch of the bass drum. ”

“ 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. ”

“ A loud speaker when connected with a wireless receiving set makes it possible for a room, or an auditorium, full of people, or an outdoor crowd, to hear what is being sent out by a distant station instead of being limited to a few persons listening-in with headphones. To use a loud speaker you should have a vacuum tube detector receiving set and this must be provided with a one-step amplifier at least. ”

“ 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 [Pg 30] 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. ”

“ The cure for the trouble is brought about by the introduction of materials such as carpets, tapestries, and the like, which act as absorbers of sound and reduce the time of reverberation.
When music is played in an auditorium with a prolonged reverberation, the tones following one another blend and produce the same effect as that of a piano when played with the loud pedal in use. A reverberation is more advantageous for music than for speech, since the prolongation and blending of the musical tones is desired, but the mixing of the words in a speech is a distinct disadvantage. ”

“ A phonograph seems almost miraculous. Yet it works on an exceedingly simple principle. When you talk, the breath passing out of your throat makes the [pg 175] vocal cords vibrate. These and your tongue and lips make the air in front of you vibrate.
When you talk into a dictaphone horn, the vibrating air causes the needle at the small end of the horn to vibrate so that it traces a wavy line in the soft wax of the cylinder as the cylinder turns. ”

“ In the phonograph, a diaphragm replaces the tuning fork and a cylinder (or a disk) coated with wax replaces the glass plate. When the speaker talks or the singer sings, his voice [305] strikes against a delicate diaphragm and throws it into vibration, and the metal point attached to it traces on the wax of a moving cylinder a groove of varying shape and appearance called the "record." Every variation in the speaker's voice is repeated in the vibrations of the metal disk and hence in the minute motion of the pointer and in the consequent record on the cylinder. ”

“ Next we were favoured with a song in bass, accompanied with the piano—in which a male voice was so closely imitated as to defy the most acute ear to make it anything else; a male voice, however, highly refined—deeper, stronger, sweeter—than ever before fell upon our ear. The feelings of all present were delightfully stirred,—even the atmosphere in which we sat seemed trembling with emotion.
These were followed by other songs, enough to exhibit the vocal charms and operatic talent of this wonderful cantatrice, in all their strength and compass. ”

“ Now, the speaking diaphragm in the telephone, as in the phonograph, presently to be described, must reproduce not only all the varieties of sound-wave corresponding to vowel sounds, with their intermixtures of the fundamental tone and its overtones and their inflexions or sliding changes of pitch, but also all the effects produced on the receiving diaphragm by those interruptions, complete or partial, of aerial emission which correspond to the pronunciation of the various consonant sounds. ”

“ 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. ”

“ No human voice, however, has so great a range of tone; the highest soprano notes of women correspond to [282] but 1000 vibrations a second, and the deepest bass of men falls but to 80 vibrations a second.
While the human voice is limited in its production of sound,—rarely falling below 80 vibrations a second and rarely exceeding 1000 vibrations a second,—the ear is by no means limited to that range in hearing. ”

“ 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. ”

“ By speaking into the phonograph and reproducing the words, we are enabled for the first time to hear ourselves speak as others hear us; for the vibrations of the head are understood to mask the voice a little to our own ears. Moreover, by altering the speed of the barrel the voice can be altered, music can be executed in slow or quick time, however it is played, inaudible notes can be raised or lowered, as the case may be, to audibility. ”

“ 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. ”

“ The acoustic quality of a room may be improved by breaking up the smooth surfaces by curtains or by arrangement of furniture. The echo is then broken up into small waves, none of which may be sufficiently distinct to interfere with the direct voice. Sometimes a sounding-board over the head of a speaker improves the hearing probably by preventing echo from a smooth wall behind him. A large bare floor is undoubtedly bad for acoustics, for when a room is filled by an audience the hearing is much improved. ”

“ All voice-sounds are made by two elastic bands or cushions, called vocal chords, stretched across the end of the tube or windpipe through which we breathe, and as we send the air through them we tighten or loosen them as we will, and so make them vibrate quickly or slowly and make sound-waves of different lengths. But if you will try some day in the woods you will find that a bird can beat you over and over again in the length of his note ”

“ The air column in the tube of the French horn, and the sounding-board of the pianoforte develop the vibrations caused by the lips and strings into musical tones pleasing to the ear. The tuning-fork alone can scarcely be heard, while the induced vibrations it sets up through properly adjusted resonance may be audible far away.
The vocal cords alone cannot make music any more than can the lips of the cornet player apart from his instrument. The tone produced by the vibrations alone of the two very small vocal bands must, in the nature of things, be very feeble. ”

“ Any sound that is made in front of the large orifice will not meet any response, unless it be that particular one which the globe can naturally re-enforce, when it will be plainly heard. Suppose, then, one has a series of twenty or more of these, graduated to the proper size for re-enforcing sounds in the ratio of one, two, three, four, and so on. Take any instrument, say a flute: have one to blow it upon the proper pitch to respond to the largest sphere, then take each of the spheres in their order, applying them to the ear while the flute is being sounded. ”

“ In a later investigation6 Sabine showed that the reverberation depended also on the pitch of sound. As a concrete example, the high10 notes of a violin might be less reverberant with a large audience than the lower tones of the bass viol, although both might have the same reverberation in the room with no audience. Again, the voice of a man with notes of low pitch might give satisfactory results in an auditorium while the voice of a woman with higher pitched notes would be unsatisfactory. ”

“ We recognize at once a difference between the sound of a vowel, say ah, sung by different persons to the same note of the piano and with the same loudness. There is a personal element, an individuality, about voices which at once arrests our attention, apart altogether from the tone or loudness. This sound-quality is determined by the form of the wave-motion, that is, by the nature of the movement of the air-particle during its little excursion to and fro in which it takes part in producing a zone of compression or rarefaction in the air and so forms a sound wave. ”

“ If it vibrates 256 times a second, it will [282] produce the same tone as middle C on a piano; if it vibrates 512 times a second it will produce the C which is an octave above, and if 128 times a second an octave below middle C. The human voice is produced by vocal cords in the throat, which vibrate with the proper frequency to give any required tone. But how can we make the human voice act as an interrupter of the primary circuit? An examination of the telephone transmitter will supply the answer to this question.
Fig. 165
Fig. ”

“ The third quality of sound is due to the form of the vibrations regardless of the pitch or the loudness. The trained ear recognizes, for instance, in the note of the tuning fork, the violin, the clarionet and the piano, the same tone howsoever made. ”

“ PITCH. The various degrees of pitch in the compass of the voice depend upon the rate of vibration of the vocal cords. This rate of vibration, the pressure of breath being the same, is caused by the different degrees of tension of the vocal cords. If the vocal cords are drawn thin and short, the pitch will be high; as the tension diminishes, the pitch will be lower. The greater the number of vibrations to the second, the higher will be the pitch. A sound consisting of sixteen vibrations to the second produces the lowest pitch that has been recognized by the human ear as sound ”

“ The general terms—loudness and quality, embrace all the distinctions heard in a noise, as in the collision of two unelastic sticks. Pitch and duration can scarcely be considered as belonging to common noise. Thus we have— (1) noise whose audible distinctions are comprehended under the general terms loudness and quality; (2) common sound, whose audible distinctions are comprehended under the general terms—loudness, quality, duration, and every varying pitch; (3) musical sound, whose audible distinctions are comprehended under the general terms—loudness, quality, duration, and uniform pitch. ”

“ While the vocal cords serve the purpose of the reed, the resonator forms the body of the vocal instrument. Every sound passes through it; every vowel and consonant in the production of syllables and words must be formed by it, and the whole character and individual qualities of the speaking as well as the singing voice depend in great part upon the manner in which it is used. ”

“ To practise this, dwell on various voiced sounds for a long time, emitting the breath slowly and regularly.
Only the voiced sounds can be produced with varying pitch; they are musical, the rest are noises. Notice, in church for instance, how the tune is carried by the voiced sounds; the voiceless ones seem to break the course of the tune.
When the vocal chords are short they vibrate more quickly than when they are long, and quicker vibrations give a higher pitch. This explains why the average pitch of a woman's voice is higher than that of a man. ”

“ 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. ”