Auditory tube

“ If a person on blowing the nose violently, feel a swelling in the ear, from the membrane of the tympanum being forced outwards, the tube is open; and though the tube be closed, if the beating of a watch placed between the teeth, or pressed against the side of the head, cannot be heard, the operation cannot relieve, as the sensibility of the auditory nerve must have been destroyed. In a closed Eustachian tube, there is no noise in the head, like that accompanying nervous deafness. ”

“ If this process is going on in the same medium (the air) in which our ear is situated, the membrane will at every condensation be forced toward the hollow of the drum, and at every rarefaction will move itself in the opposite direction.
These vibrations necessitate a similar motion of the auditory ossicles, and thereby a transference to the auditory nerves is effected.
The greater the condensation of a sound-conducting medium at any given moment, the greater also will be the amplitude of vibration of the membrane and of the auditory ossicles and of their action ”

“ But the primary use of this tube is to afford a free communication between the middle ear and the external atmosphere, and thus secure an equal pressure upon both sides of the membrane of the drum of the ear, however the density of the atmosphere may vary. If, from undue tension of the membranes, pain is experienced in the ears, when ascending into a rare atmosphere, as in a balloon, or descending into a dense one, as in a diving-bell, it may be relieved by repeating the act of swallowing, from time to time, in order that the inner and outer pressure may thus be promptly equalized. ”

“ The auricle of the human ear presents many irregularities of surface. If these irregularities are abolished by filling them up with a soft material such as wax or oil, leaving the entrance to the canal free, experiment shows that the intensity of sounds is weakened, and that there is more difficulty in judging of their direction. When waves of sound strike the auricle, they are partly reflected outwards, while the remainder, impinging at various angles, undergo a number of reflections so as to be directed into the auditory canal. ”

“ A tuning-fork in vibration disturbs the surrounding air, and sets up air waves which produce the effect called sound when they strike against the drums of our ears. In a similar way the discharge of a Leyden jar disturbs the surrounding ether, and sets up electric ether waves; but these waves produce no effect upon us in the shape of sight, sound, or feeling. There is however a very simple piece183 of apparatus which acts as a sort of electric eye or ear, and detects the waves for us. This consists of a glass tube loosely filled with metal filings, and having a cork at each end. ”

“ The tube is known as the Eustachian tube. Its walls are ordinarily collapsed, so it is not an open passage, but every time one swallows the tube is pulled open, thus allowing differences in air pressure on the two sides of the eardrum to equalize. Whenever one ascends a high hill quickly, as by train or automobile, or even in going to the top of a high building by elevator, the difference in air pressure behind and in front of the eardrum can be felt. The sensation is disagreeable, and there is definite impairment of hearing. Repeated swallowing gives relief. ”

“ I’ll say this much, however, it is 64 the vacuum or audion tube detector that gives results, and the application of a loud speaker is only possible with a vacuum or audion tube. It is as easy to build a vacuum tube set as a crystal set and only a very little more expensive. So, whether you are building or buying a set, make it a good set, something that you can hear with a good many hundred miles.
“Now, you can buy the parts and build a receiving set that will generally give more satisfaction than a bought set.” (Bill stepped over to the blackboard and took up a pointer.) ”

“ If it were always open, all the sounds produced in the throat would pass directly into the drum of the ear, and totally confuse us. We should hear every breath, and live in a constant bewilderment of internal sounds. At the same time the closure, being but a light contact of the walls of the tube, easily allows a slight escape of air from the drum, and thus not only facilitates and regulates the oscillations of the air before the vibrating membrane, but provides a safety valve, to a certain extent, against the injurious influence of loud sounds. ”

“ Let a simple sound be now made in the tube, consisting of 256 vibrations per second: the membrane carrying the iron will vibrate as many times, and so many pulses of induced electricity will be imposed upon the constant current, which will each act upon the receiver, and cause so many vibrations of the armature upon it; and an ear held at P will hear the sound with the same pitch as that at the sending instrument. If two or more sound-waves act simultaneously upon the membrane, its motions must correspond with such combined motions ”

“ Vibrations which cause hearing are communicated by the chain of bones. When the base of the stirrup is pushed into the oval window, the pressure in the labyrinth increases, and, as the only mobile part of the wall of the labyrinth is the membrane covering the round window, this membrane is forced outwards; when the base of the stirrup moves outwards a reverse action takes place. Thus the fluid of the labyrinth receives a series of pulses isochronous with the movements of the base of the stirrup, and these pulses affect the terminal apparatus in connexion with the auditory nerve. ”

“ 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 a very common ear disorder. The opening into the ear is about an inch long, or a little more, and is separated from that part of the ear within, which is known as the middle ear, by the eardrum membrane. The drum membrane is a thin, skinlike membrane stretched tightly across the bottom of the external opening in the ear or auditory canal, and shuts it off completely from the middle ear within, and in this way protects the middle ear from the entrance of germs, dust, and water, but only secondarily aids hearing. ”

“ They are also transmitted by liquids and solids. When a tuning-fork screwed into a little wooden foot vibrates, nobody, except the persons closest to it, hears its sound. On dipping the foot into a glass of water a musical sound is audible: the vibrations having been transmitted through the water to the air. The tube M N, Fig. 30, three feet long, is set upright upon a wooden tray A B. The tube ends in a funnel at the top, and is now filled with water to the brim. The fork F is thrown into vibration, and on dipping its foot into the funnel at the top of the tube, a musical sound swells out. ”

“ These physical agitations or vibrations are transmitted to the air. Omitting the account of the anatomical path by which they reach the inner ear, we find them at last setting up vibrations in a many-fibred membrane, the basilar membrane, which is in direct connection with the ends of the auditory nerve. It is supposed that to every possible rate of vibration, that is, every possible tone, or partial tone, there corresponds a fibre of the basilar membrane fitted by its length to vibrate synchronously with the original wave-elements. The complex wave is thus analyzed into its constituents. ”

“ It is believed that each is sensitive to a particular vibration rate and that each is also attached to a nerve fiber. The sound waves of the air transmitted by the tympanum, the ear bones and the liquid of the internal ear start sympathetic vibrations in the strings of the cochlea which affect the auditory nerve and we hear. The highest tones perceptible by the human ear are produced by from 24,000 to 40,000 vibrations per second. The average person cannot hear sounds produced by more than about 28,000 vibrations. ”

“ The length of the tube (K) is such that the sonorous vibrations from the receivers (F G) reach the common hearing-tube (M) in opposite phases. Under these circumstances silence is produced when the vibrations in the receivers (F G) are of equal intensity. When the intensities are unequal, a residual effect is perceived. ”

“ An alternative type of hydrophone consisted merely of a hollow enclosure without a microphone, sometimes with a metallic diaphragm, and sometimes simply a rubber tube, filled with air and connected by long tubes to stethoscopes applied to the ears. These are operated by the transference of the pressure vibrations from the sea to the air cavity and thence to the ears. Electrical hydrophones have the advantage over non-electrical ones that their sensitivity can be readily augmented by various means, e.g., bv the use of thermionic amplifiers (see WIRELESS TELEGRAPHY) . ”

“ Let R and R' be two resonators accurately tuned to the note given by the vibratory body at S. Suppose both resonators at the same instant on the wave-surface, then they both receive, at the same instant, the same phase of vibration, on the planes of their mouths. If two tubes of equal length lead from the resonators and join into one tube just before they reach the ear, E, then the sound-pulses will act together, being of the same phase, and the ear will receive double the action which it would if only one resonator were connected with the ear. ”

“ If the experimenter alone wishes to hear as well as possible when faint sounds are produced, he should carry a piece of smooth india-rubber tube about half an inch in diameter from the open end to his ear. ”

“ The wire passes through the perforated handle, D, and is exposed only at the extremity. When the point, A, was rested against the center of a diaphragm upon which was focused an intermittent beam of sunlight, a clear musical tone was perceived by applying the ear to the hearing tube, c. The surface of the diaphragm was then explored with the point of the microphone, and sounds were obtained in all parts of the illuminated area and in the corresponding area on the other side of the diaphragm. ”

“ If the patient before operation hears conversation at a greater distance than 12 feet he should be told that the hearing power may be reduced to this amount. If, however, there be considerable deafness, due to polypi or granulations blocking up the tympanic cavity and auditory canal, the hearing power may be improved by the operation. The ultimate hearing depends on the condition of the stapes within the fenestra ovalis: if it remains freely movable, the hearing power may be extremely good. ”

“ Moreover, this instrument is so sensitive that it is capable of taking up the vibrations of any sound, and of varying the electric current in accordance with them, so that the sound is reproduced at a distance in an ordinary telephone which may be placed in the circuit. If the tube is placed upon a resonating-box, the delicacy is increased. The tube in such an arrangement serves as the transmitting and the telephone as the receiving instrument. Other substances may be substituted for the white silver powder with good results. ”

“ To get the most out of an audion see that the telephone, or whatever circuit or piece of apparatus is connected to the output terminals, shall have a resistance of RP ohms. When the resistance of the circuit, which an audion is supplying with current, is the same as the internal resistance of the output side of the tube, then the audion gives its greatest output. ”

“ About 25 per cent. of the diameter of the tube must be added to the length of the air column to make it just one-fourth the wave length. The sound heard in seashells and in other hollow bodies is due to resonance. Vibrations in the air too feeble to affect the ear are intensified by sympathetic vibration until they can be heard. A tuning fork is often mounted upon a box called a resonator, which contains an air column of such dimensions that it reinforces the sound of the fork's sympathetic vibration. ”

“ If the person who wishes to hear by means of the Audiphone will hold the fan against the upper teeth,—the convex side of the fan outward,—he or she will hear distinctly, for the vibrations of sound are collected and strike upon the teeth and bones, and act upon the auditory nerves from within, precisely as the vibrations act from without through the auricle. ”

“ Placing its resonant tube in front of one of its nodes, a sound is heard, but nothing like what is heard when the tube is opposed to a ventral segment. The reason of this is that the vibrations of a bell on the opposite sides of a nodal line are in opposite directions, and they therefore interfere with each other. By introducing a glass plate between the bell and the tube, the vibrations on one side of the nodal line may be intercepted; an instant augmentation of the sound is the consequence. ”

“ This bending of the tuning wires, however, takes place to a much larger extent than most organ builders imagine. It is the chief reason why reeds fail to stand in tune.
When point A on the reed tuning wires is rigidly supported and held by force in its normal position, reeds can be made to stand in tune almost as well as flue pipes.
Figure 34 represents the Hope-Jones method of supporting the tuning wire at point A. It consists of having a brass tube T inserted in the block moulds before the block is cast. This tube T therefore becoming an integral part of the block itself. ”