Radio mirror (Jan-Oct 1923)

September 22, 1923 RADIO DIGEST — Illustrated Human "Earful" M easured by Aid of Radio Tubes Device Shows 300,000 Tones Audible to Normal Ear By C. W. Tucker LEND us your ears: In a few minutes we can tell you by means of the audt■'ometer whether you receive full measure when you get an "earful." You know there are eart'uls and earfuls, just as there are types of ears. Most everyone has observed the many different kinds of ears. Some are small, some large; some are pinned back close to the head; others stand out like wings; some can be wiggled and others can't. But, of course, that is only the outer ear. The inner ear. the part that actually does the hearing, is inside the head; its peculiarities cannot be observed by the Innocent bystander. But from what the scientists of the Bell System laboratories of the Western Electric company tell us, there are as many variations in the inner ear and its hearing quality as there are in the outer ear. Therefore, there has never been evolved a standard unit of measure for an earful. By measuring the hearing of a number of normal ears there has now been established a standard for the normal hearing. This is done by finding out the total number of pure tones audible to the person ■with normal hearing. A pure tone is one in which there is no mixture of other tones; it is specified by pitch and loudness. The pitch is determined by the rate of vibration and the loudness by the intensity of the vibration. These findings are plotted on a chart, as shown below. The lower line is established by finding the lowest intensity at which the tones can be heard. The tones are 6i>aced an octave apart on the musical scale. You will see by this figure that the intensity or loudness of the higher and lower tones must be considerably greater to be audible than the tones near the middle of the scale. This makes the line of minimum audibility a curved line, as shown, instead of a straight one. The upper line, marked "maximum audibility." shows the maximum intensity at which these tones can be heard without hurting the ears. Likewise this is a curved line, because the higher and lower tones hurt the ears with less intensity or loudness than do those "near the middle of the scale. The area between these two lines shows the area of normal hearing. The question naturally arises in the reader's mind as to how many pure tones are audible to the normal ear. It has been determined that at high C, or C3, there are 270 graduations of volume which can be sensed one from the other. At the line of intensity or loudness, where the area is widest on the normal chart, 1,500 tones can be perceived as having different pitches. If the ear were equally sensitive PROTECT The Heart of Your Radio Set Vacuum Tubes are c o e t 1 y and extremely delicate. B battery or any other excessive current applied for only a fraction of a second to the filament leads will burn out your tubes. You have probably already had this experience and It is apt to happen again at any time. A burnt out tube means money lost — the set out of commission — inconvenience to you. WHY TAKE THESE CHANCES WHEN RADECO SAFETY FUSES will absolutely protect your tubes. Applied in an instant to the filament terminals. Will fit any standard tube or go in any standard socket. Fully guaranteed. 50 cents each. gent Postpaid. Delay may be costly. Write now. Specify type of tube used. DEPT. 6 RADIO EQUIPMENT COMPANY CM Washington Street Boston, Mass. New England's Oldest Exclusive Badlo House Distributors of maiiy other successful Radio Specialties. Dealers: — Write for our proposition and full detail*. to all pitches and intensities within its ranso. the total number of pure tones perceptible to the normal ear would be the product of these two numbers, or 405,000 tones. But as the ear is not as sensitive to the higher and lower tones there are ^S ** Ss s J / ( 1 \ s, / -^. / HEARING =5&?» only 12 per cent, of the news that the person with the normal hearing gets under the same conditions. B hears 58 per cent, of all that the person with normal audibility hears. One of the distinct advantages of this 300,000 sounds which are audible to the normal ear. Having determined the number of pure tones audible to the normal ear by the same method, the degree of deafness of a person with abnormal hearing can just as easily be ascertained. The upper charts show the percentage of the normal hearing that two persons, A and B, possess. Mr. A when he gets an earful gets v -% \ y' A y •> „ i 1 \ i i / .,,/ / HEARING =\2 7o method of measuring the hearing is that it is possible to find just what tones cannot be heard. This gives the doctors a very good clue as to what is causing the deafness. It may then be possible to remove the cause and in some cases restore normal hearing to the afflicted. The audiometer is very useful in legal cases. Considerable confusion exists in courts where the degree of deafness is involved, as there are a number of laws which prevent persons with poor hearing from engaging in certain kinds of work. For example, one cannot operate an automobile if he has a certain degree of deafness. At the present time there is a wide variation between the standards of various doctors in different parts of the country. The audiometer measures deafness with such accuracy that there is little opportunity for dispute. The audiometer is composed of vacuum tubes, coils and adjustable resistances. By a proper arrangement of circuits the vacuum tube is capable of generating an oscillating electrical current of any desired frequency. This electrical vibration is transferred into sound vibration by means of a telephone receiver. Between the receiver and the oscillator a wire network, called an attenuator, is interposed which makes it possible to regulate the volume of sound. The theory of the receiver used to calibrate the audiometer has been worked out so that it is possible to calculate its acoustic output from the electrical energy it is absorbing. In this way it is possible to calculate the pressure produced in the outer ear canal while a tone is perceived. WTW You Can't Afford to Miss THE SECOND ANNUAL American Radio Exposition Under the auspices of the American Radio Exposition Company of New York OCTOBER 6-13, 1923 (EXCEPTING SUNDAY) Grand Central Palace NEW YORK Hundreds of Features for the Fans! A big Amateur Contest for the best home-built set Open to ALL Amateurs — Valuable Prizes — Write for details Sets from all over the country will be entered. Motion Pictures on Sensational Radio Topics. Unusual Scenics and Educational Displays, Showing Recent Developments in Radio Industry. Applications for space and all communications regarding the Exposition should be sent to American Radio Exposition Co., 120 Broadway, N. Y. J. C. JOHNSON, GENERAL MANAGER