Transmission Apparatus Research Articles

Studies of Acquired and Inherited Deafness in Animals

These studies of deafness in animals were chiefly of the end organ for the reception of sound (organ of Corti). The functions of the organ of Corti were studied by means of the Wever and Bray phenomena, then correlated by histological examination. Animals studied were chiefly cats, dogs, guinea pigs and mice. In all these animals the organ of Corti is the same as in the human. The difference between human and animal hearing is the interpretation of sound detected by the organ of Corti. The interpretation of sound stimulating the organ of Corti is done by the brain. The function of the organ of Corti is to analyze the sound stimulation and transpose this stimulus into nerve impulses. The nerve from the organ of Corti (cochlea nerve) transmits these nerve impulses to the brain and the brain interprets these impulses. The chief causes of deafness are: (1) disturbances of the transmission apparatus (the middle ear apparatus), usually called conduction or middle ear deafness; (2) disturbances of the end organ for reception of sound, usually called perception or nerve deafness. Deafness resulting from intercranial lesions cannot as a rule be differentiated from perception deafness. Conduction deafness in animals shows a similar pathology to that found in the human. Changes occur in the middle ear cavity, resulting usually from infection, preventing sound from reaching the organ of Corti in a normal manner. To overcome this increased resistance of the middle ear to transmission of sound, the intensity of sound must be increased. It must be remembered that the organ of Corti does not care how sound reaches it, for if it is a normal organ of Corti, it will respond in a normal manner; if abnormal, in an abnormal manner. Bone conduction is just another means of sound reaching the organ of Corti. The studies of the organ of Corti in animals deafened by disease, toxic poisoning and exposure to loud sounds for long periods of time, have given definite clues to the cause of perception deafness in the human. The lesions found in these animals are of a similar character, showing that the end result is the same in the organ of Corti. This is a degeneration of the external hair cells in the organ of Corti, and in more marked cases, a loss also of the internal hair cells, followed by a degeneration of the nerve cells. The loss of these special sensory hair cells in animals, when studied by the Wever and Bray method, has shown changes of response to sound similar to those found in the human being suffering from perception deafness. Studies of inherited deafness have shown that deafness of this type may vary from complete degeneration of the organ of Corti to only partial degeneration. The evidence at present from studies of the waltzing guinea pig shows that the organ of Corti develops to normal before birth and then degenerates after birth. This degeneration is similar to that found in animals deafened by toxic poisoning, by disease and exposure to loud sounds. From these studies the following conclusions with regard to perception deafness are drawn. (1) Degeneration of the external hair cells of the organ of Corti causes partial loss of hearing. (2) Internal and external hair cells when degenerated cause a complete loss of hearing for the region involved. This may result in (a) loss of part of the range; (b) an island of deafness. (3) External hair cells are for the detection of sounds of minimum intensity and are not concerned primarily with pitch. (4) Internal hair cells are more for the detection of pitch and do not begin to function until the intensity of sound has been increased to about 20 db above the threshold of the external hair cells. These conclusions are amplified in the main article and the difficulties of developing hearing aids for the perception type of deafness are also discussed.

LXXVIII Testing of the Transmission Apparatus with the Bone-Conduction Receiver

LXXVIII Testing of the Transmission Apparatus with the Bone-Conduction Receiver

Transient Response of Multistage Video-Frequency Amplifiers

The response to a Heaviside unit voltage is set forth as the most logical and relevant criterion of the fidelity of video-frequency amplifiers. The part of the transient response that is governed by the high-frequency amplitude and phase-delay characteristics of amplifiers may be approximated closely by the steady-state response to a square wave having a suitable period and thus may be expressed in a Fourier series. Simplicity and rapidity of numerical calculation are the outstanding advantages of the steady-state formulation. As an illustrative example of the method the transient response of several multistage compensated resistance-coupled amplifiers are computed. Considerable data helpful in the design of amplifiers of this type are presented. It is concluded: (1) The wave-shape distortion of a Heaviside unit voltage is accumulative as the number of stages is increased. (2) The value of the damping constant K= RVL/ C should lie between 1.51 and 1.61. (3) The resonant frequency fo = 1/( 2r, rVLC) determines the slope of the wavefront of the transient response. R is load resistance; C is the total shunt capacitance; and L is the compensating inductance in series with R. It is proposed that the oscillographic response of video-frequency amplifiers and the associated transmission apparatus to a square wave be considered as a part of performance tests of future television systems.

Utility of Variable-Displacement Oil-Pressure Pumps for Hot-Pressing in Plywood Operations

Abstract Variable-displacement pumps or generators form the primary part of a complete hydraulic energy transformer, the secondary part of which is a hydraulic motor. Hydraulic transformers of fluid drives are becoming more and more useful for all kinds of modern production machinery, such as presses, machine tools, automotive engines, cranes, etc., because of certain advantages offered along the line of the modern power-transmission problems. The flow of chemical energy occurs in the form of a fuel and air compound, into an internal-combustion engine, where it will be transformed to thermal and partly mechanical energy. The mechanical energy flows further in periodic impulses to the crankshaft of the engine in the form of a mechanical direct-current energy, where through the flywheel of the shaft it will be somewhat smoothed out, so that in a mechanical-electrical energy transformer it will be transformed to direct-current or alternating-current energy. These currents finally reach the electromotor of the shop, which operates the drive shafts of mechanical or hydraulic energy transmission apparatus, transmission-belt shafts, gear transmissions of machine tools, electromotors of press pumps, etc.

Acoustic Insulation and Cancellation Effects at the Basilar Membrane

The perceptive mechanism presents an apparatus of phenomenal sensitivity and of equally phenomenal capacity to withstand acoustic insult. The physiological requirement calls for a place of reasonable quiet in which the end organ may analyze the vibrations conducted to it. This is fulfilled by immersion of the end organ in the liquid of the internal ear, and the insulation (a factor of 40 db.) is overcome by the sound transmission apparatus which is about equally efficient throughout the audiorange. The auditory cells act as selective transformers and rest on the basilar membrane which is flanked by the two scalae. Vibrations pass into the internal ear through both windows and the basilar membrane is placed nearly edge-on to the advancing wave front. This would result in a cancellation effect at the basilar membrane and would present a shock absorber which is instantaneously operative at all frequencies. The interpretation is opposed to the generally accepted ideas both on transmission of vibrations to the internal ear and to the function of pitch analysis as dependent on mechanical factors which lie extrinsic to the auditory cells themselves. This is supported by both morphological and experimental evidence.

An Acoustic Probe.

The writers first described the bone activating telephone receiver in this journal. The apparatus was used in studying the problem of the minimum audition for bone transmitted sound in normal and pathological cases. The results of these researches have appeared from time to time in the Annals of Otology, the Laryngoscope and the Archives of Octololaryngology. Attention has already been attracted in various papers to the fact that not until the character of the physical disability in the sound transmission apparatus has been established may we hope to arrive at a proper operative solution for the amelioration of some types of deafness. The acoustic probe is nothing more than a miniature bone activating receiver provided with a long slender stalk which is to be used as a probe. When the appliance is hooked up with an electric adiometer the minimum acuity for bone transmitted sound may be determined when the tip of the probe is applied to the handle of the malleus, the long process of the incus and the stapes. This necessarily must be done with reflected drum membrane and under light local anesthesia. It is hoped that in selected cases this method of “feeling one's way” along the sound transmission system will show where a blocking of the drum membrane vibration takes place. Once a mechanical lesion is determined and'rocated, operative correction of the disability may be anticipated. The probe is also to be employed in determining the location of the “hot spot” found in individuals who in the absence of drum membrane and outer ossicles find the cotton plug prothesis of great benefit to air acuity.

QUANTITATIVE TESTS ON BONE AND AIR ACUITY IN PARACUSIS WILLISI: REPORT OF TWO CASES, TOGETHER WITH A NOTE ON THE INTERRELATION OF AUDIOMETRIC TESTS

REVIEW OF THE LITERATURE There are several explanations of the testimony of deaf persons that they hear better in a noisy than in a quiet place. Probably the best known explanation is that put forth by Politzer, 1 who believed that the noise agitated the sound transmission apparatus and thereby made it more permeable to the accompanying sounds. Roughly in modern parlance, the noise acts like a carrier wave for sounds which would otherwise be inaudible. Another explanation is that of Urbantschitsch, 2 who believed that the paracusis was entirely dependent on an increased efficiency in the end-organ or the central apparatus. This, he believed, was substantiated by finding that the paracusis was prolonged after the noise had ceased, and in some cases did not appear until the subject had again come into a quiet place. Objections were raised to the Urbantschitsch's findings by Siebenmann, who did not believe