Measuring up the hearing. The physician at the audiometer reduces the loudness until his patient can no longer hear'the tone and releases the push button By Paul B.'Findley IT WAS just about ten years ago, says my friend Wilkinson, that he began to wonder if his hearing was “going be .” He noticed, so he said, thaghe was replying to many a quickly fiung. remark. “What d'you say?" After he’d killed a good story or two by missing the key sentence, he forced himself to pay more attention and so kept up with most conversations. Then he noticed his friends “straining their ears or asking him to repeat. Finally it came to a point where the subway was his favor- ite conference room, for only in its roar would people talk loud enough to make themselves heard. Now Wilkinson is not the only man I know who is plodding the weary road of enforced seclusion. Changeghis name to Jones. or Steele. or Halleran and he is some one in your own circle— soms one you like‘immonsely, but have little real fellowship with. becausehe is nearly or quite "incommunicado," as thefipanisrds say. There are 10,000,- 000 of him, more or less, and his per— ' eentage in our population seems to be Increasing, especially in our seacoast regions. He comes from every class in the community; a locomotive engineer may be forced into other employment because he can no longer hear the con- ductor's whistle, a banker may go to the hospital because he could not hear the text's horn. Tests of hearing have long been required in the army and navy and many industrial jobs. - Accurate measurements are the very foundation of definite programs ofrelief for both individuals and the community as a whole. This has been recognized by the Franklin Institute at Philadel- phia in its recent award of the, Louis Edward Icvy Medal, “founded for the recognition of papers descriptive of the author's researches—which have aided at-iy the well-being of mankind}? The recipient .is,Dr. Harvey Fletcher, of the Bell Telephone laboratories, the research laboratories of the American Telephone and Telegrdph Company and the West- ern Electric Company. who has placed ment of hearing on a sound, the measure is and has contributed merical has he‘d-gel}? to the design of electrical aids to hearing. " TO SPEND an hour with Dr. Fletcher" is a fascinating experience. One learns a great deal about how we hear, and yet is quite unconscious that many of these interesting things were discov- ered by the man who tells of them: Solo- mon or one of his contemporaries re- -marked that the tongue could not be relied on to tell the truth, and Dr, Fletcher can prove that the ear is a deceive: too. You will swear that the tone you are hearing is an octave below middle C, and Dr. Fletcher will demon. strate that such a note is not being sounded at all. Or he will make one note Vanish by. sounding axiother one, and then show you why recognizing a friend's voice and identifying the words he speaks require different properties in. your ears. ' , ‘ Since its earliest days the telephone system has been making investigations. out of which our present-day telephone has grown. Of recent years «this work figs-been done largely in laboratories ‘ ' maintained jointly by the American Tele- phone andeegi-aph Company and the Western. Electric Company _ and now brown as the Bell Telephone Labora- tories. Inc. . ‘ ‘ In 1916 Dr. Fletcher was invited to visit the laboratories. There he found We old friends of his Chicago]. days, Dr. H. D. Arnold and Dr. H. W. Nichols. Interesting problems were there for solution, good research work was being done; Fletcher wanted to share init; he joined. ' The telephone.’s job is to transmit your words to some one else, be he in the next room or across the continent. so that he can understand you. A sys- tem can be built by which he could hear you as well over the wire as face to face. But perfection costs money-via, this case so much more than the cost of a “practical” system that people would not care to pay the difference. A compromise must be made, and to make it intelligently~ it is necessary to know all about the human voice and how the ear interprets it. Dr. Fletcher was assigned to this investigation. I Recall your early studies in physiology When you say “am-ah” your lungs force. a stream of air up the larynx and be- tween the vocal corde, which vibrate like the rubber whistle of s toyballoon. The pitch of your voice is regulated by the tension of the cords. Its other char- acteristics are determined by the sin and shape of your throat, mouth and nose. As the sound waves leave your month they contain not only the funda- mental note which you recognize as pitch, but a long series of harmonic waves, each an octave of the 1 mental. It is the relative ”Doing“; each of these harmonics that makes your voice difi’erent from every one else’s. ‘ So much for the vowels. When you say “cat" you press your tongue against the soft palate and allow the rush of air to force it away. Then you termiv nate the a sound by bringing your tongue against your teeth. ' These beginnings and endings of vowels are the consonants. and thsy bring a lot of new air waves into being. In‘general, the lowar pitches are most important for the vowels and the higher IMAGINE a steam gauge . Which could register etcu~ 'ratcjly‘ ally presents between onc‘ . pound and One million poundsle ‘But‘ the car must cover this range; it must respond. to a4 change in thc‘air pressure equal ‘ to the weight of a bit of human: f . hair one-thousandth of an inch“ long, and not “blow up”‘on‘ pressure ancs a million times“ asgrcat. !. . . Within' a given area Dr. Fletcher and his associates csti- ’ mated a total‘of 300,000‘simple. tones which‘can be distinguish- ed from each other in loudness, in'pitchor in both. Yet so mar- velous is the humancar that out of all thc noise and tumult of a busy city we can isOlatc and dis- tinguishany one familiar sound. Yod‘ wOuld imagine a lot of energy in such a voice as a col- lege cheer leader or a powerful bass ‘singcr,yct thcsc scientists tell us that if all the energy of the voice could be put into heat ing loafer, it would take 5.000,- 000 people all talking at once toboil a cup of teal On a giant model a: the ear. Dr. Fletcher(ri8ht)l!01nt8 out the author ’(leit) looks into the‘oval ‘1“semlclrcular" canals which give the sense 0 pitches for the consonants. The human voice used _a pitch range from about ‘ fifty waves per second‘up to well above 5000 per second. Most of its energy is , in the lower pitches, around 200 waves ' per second. But there is mighty little of it at that; one of Dr. Fletcher's abso- ciates, Dr. Irving B. Crsndall, has meas- ured it and found that if all the'energy of this voice could be put into heating water, it would take 5,000,000 1100910. allgtalking at once to boil a cup of teal NOW the air treats all waves alike; they all fade away equally as they travel. Apparatus, however, plays favor- ites. It is an expensive matter to make anything except perhaps ths'marvelous vscuum tube so that it will be oqually edicient at 100. 1000 and 5000 waves \ \\\\\\\\\\\\\\\\ \\\\\.\\\ r/// a“ om slum turnout BOW. bk . , nu sens nous umwnioourititmjrsr min on reticent meant-our someones cams - , . (any arcane? estrous) » L 7 I "» 'Bu'cmmt - ”tits: COMThlIS in. season users readiness. _ ‘ t This shows how we heir. 'Malleus. ineusandstapea are three " little bones thattraneter enemas-g enemy-mm“ ‘ “‘9 Ovalwindowg Then it, cool down ‘. e” cochlea and becomes“ , - ‘ aneryostiinulatlong . q :1!“ , O our experimental telephone syste‘m.”.. par second. So Dr. Fletcher had to find out what would be the eflcct_ on the intelligibility of your words 11 30!!“ pitches were not transnntted as eil'ec‘ tively as others. To do this a perfect telephone system was built and in it was inserted a device, called a filter, whichwill cut 08 certain. pitches eno tirely. “If you should listen at the end of said Dr. Fletcher. “and filter out all the low pitches. the ‘taik’ might still be intelligible. but it would be thin and colorless, and you could hardly recognize the speaker's' voice. 0n the other hand, if the high tones were eliminated. you . from , natural might recognise this speaker’s voice, even if you could not understand him. To test the intelligibility of speech under various conditions, We had to eliminate the effect, of context, which is such a help in daily conversation. So we tool: the thirty-six sounds of the English language and from them made up 8700 syllablesnevery pronounceable combina- tion of one vowel and two or three con- sonants. , You couldn't help laughing if you overheard one of our. testers gravel! reading oi! in measured tones ‘chush.’ "thupr? "\von'g,’ ‘jum,’ 410°; lzek} ‘nam.’ As' the filter cuts of! more and more tones the listener-at the other end makes more and more'errors. I won't bore you with figures; the experimen , that, while good intelligibility is; btained with that range of pitches from 500 waves per-second up tol2500. speech. and especially‘musictwould sound for if only this range; were transmitted. Broadcast programs are to be enjoyed.-ss well as understood, and ' . so our broadcasting equipment is built , to 5000 waves per second. Unfortunate”; * to. transmit the full range from 500 ‘ much .of‘the receiving equipment on the market does not transmit all this range. Many loudspeakers sndv'other devices fell. for instance, to reproduce tones jhslow middls‘O of the pisno,‘hnd Were a“ s .‘ ltnotxfo‘ra remarkable‘property of the human ear they :Would'lesve the lower. ' half of the musical scale a perfect blank.‘ . 1- “The ear. seroufilrnow. has s dis? , whose vibrations . move a”: chain of threetiny boner-tbssmfll'eet stream window of the‘codllea ' i balance showed ‘ Science Has Acquired a. New Meihodvof Measuring the Hearing, "What 0... Bars Must: Do 5 _ pm] With It, Has‘Come the Application .. in on body. rs." last of these bones], , touches lightly against a membrane-v covered window in a bony chamber call“! the cochlea. Inside is a fluid down which the vibrations'trsvel until they die out. and the/distance fley travel-rue more ' than an inch atwthe most—is what gives us our sense of pitch. . Marvelous. isn‘t 2’it. that withthis simple implement we. can sense pitches over so wide a ram and, more yet, pick out dozens of sep-‘ arate sounds from the city's roar! . ' “Now this apparatus doesn’t treat all sounds alike. In fact. it is fortunate that it do'esn’ . Imagine a steam, gauge which could register accurately any press; sure between one pound and one Quinlan poupdsl .But the car must cover this range; it must respond to a. change in‘ air pressure equal'to the weight of a". hit of“ human hair one one-thousandth» of an inch long and. noti‘biow up’f‘vonv pressure waves a million times'ss great; ' So its response falls of! as the mom. thethroe ,littlewbones, while Above the window are the mini b’ I"...- in tori. tude of the air waves increases, and from this property comes your ability to hear. tones that never came out of your loud- speaker. _ ~ “In our laboratories it is well known that any device whose output is not directly proportional to its input Will do strange things to waves «which it transmits. One of themis thus: Putin two ‘waves of different pitch or frequency and you will get out the original two, one whose frequency is the sum of the original frequency and one the dlflerence., Put into the, car tones of Wind 600 per second and with some practice you can hear these tones, and also one of 1100 and one of ‘100. Put in 500, 600. 700, 800 and the common difierencsél tone is unmistakable. In fact. you'd swear that all you heard was the 100, note. but that it sounded rather ‘tinny.’ Now the piano and many other instruments when one note is struck sound as many as sixteen harmonic tench—for example, hen the 100 key is struck the ' will he waves sent out at 100, 200, 800. 400 and so, up to 1600 per second. Even: if your loud-speaker kills the first'four. there will be twelve tones left. with a common diil'erence‘ of 100. ‘ “So your ear fools you into believing that you hear the original note. when all it gets'is a string of harmonies. The tone doesn’t have the richness of the original, but sounds like the .‘tin pisno‘ of dance hall fame. The market is full of these loud-speakers and lather. ‘ devices that cause distortion. but already there are signs that the radio‘llstoner ' wants something more than more noise. 'And as soon as he insists on faithful reproduction of the original program he will get it,” ‘ .‘ . ‘ UT this was far afield from helping . the deaf to hear. 1A question started our conversation on its new tracks. “No. not every oneesn hssr by making the sounds louder,” replied Dr. Fletcher. “There is a limit to what the ear can stand withoutlpain‘. "and this‘, limit is, not scootod by dehfness. 3 his the power limit “which is raised. As a mulch: ‘mgon many-people of normal hearing we" have plotted curves .showihg but! about uppersnd lowpr limits vary with pitch. These curves in fiiuclosing l ‘ x ‘of New Principles lathe Prbblcm of fl" i . W origing Out’ Electrical Aids for Those 1 W boss Auditory Ne mes A re Impaired vi. , g ~ ' .i ., p x a song . oval seed. .Withbi this ared are roux y 800.000 simple tones which can he. istinguished from each other by differences.» loudness. in pitch or in both. Apperson whoselcwer limit is raised to out on somerodi this area has thus losts definite percents“ of normal hearing. 1 “One who hasless than 80 per cent ~ loss of hearing will have little diillculty in understanding ordinary conversation at a distance,“ three feet from the speaker. Only the i, th sndm sounds are seriously affected. One having 40 per cent less begins to miss the conse- 'nants and would experience some diiii. ' culty in following the conversation, but by P175112 strict attention would probes bly be able to understand what is being said. One having 60 per cent in hearing can. hear only the loud vowel sounds and“: consequently could “not follow ‘the conversatlbn; 'It is only those, who have a greater loss than 40 per cent hearing who are seriously inconvenienced in the ordinary. aflsirs of life. However, the loss from 40 per cent to 50 percent - becomes a serious handicap in being able to understand ordinary conversation. To make a person understand who has a 50 per cent lo‘ss labouring. people must , t, either tell: very much louder or get closer to the ear. A person having as much less as 00 cent would not , 1‘ hear anything when s erson was talking at s three-foot ‘ M ll ", , . ', “‘NIIY is it ‘t s s people claim .to hear better in the subwiy than in a quiet‘room‘l" I asked. “Is it Just ’ their. imagination?" - “No, indeed, there is a‘ real reason. and a simple one. In the subway every one instinctively r’aiseschis voice.: our tests show that subway noise is'equiva- lent to a loss of 60 per cent of normal hearing, so that the normal person can hear no better than one whose hearing 1. 60 per cent down. When both are on a par and both raise their voices.» both can hear. The no!» in on ordinary room is equivalent to a 25 per cent hearing loss. ‘That is why one only ,Jhyhflv' 4...: is scarcely conscious of his infirmity-4n average surroundings he can beer as well asany one “else. Only when everything is quiet and people are tglkinuh in appropriate tones does he begin to lose some of the consonants. 1 might add that lip reading is of great assistance to, this class of people, because tbs sounds they cannot hear—z, t, 'p, a and others—are formed by muscular mévementa which include the lips. This fight canbe trained to help out their hearing. while the latter sense still func- 'tlons for the loudgrtonsa such on a. s ando. 33“ _ . ' ‘ "We have recont‘ ly~had ' with a case of this kinda A" young ‘ woman of abhut i7’who had an inipair. merit of hearing since she was 7 years old bad‘her hearing tested and found - that above a pitch corrospondlng to 2000' her hearing became very deficient. She had gone through the publle'schools and is new in high school and has passed all of her courses subousfully, but she had a noticeable defect in her speech. Shesdid not say any of her ‘s’s. th’s or f' . I calledher attentionto this fact and by using a system which amplified the speech in the right, way was able to make her hear 'these‘ particular sounds. In a very short time she was able to say the words containing these it. ’t. sounds in a more normaliwlwd’ . , ,. ‘ p .. ”1 “W. A”. s new is less-paladin or a sea! . _ person being able to 1: electrical amplifier?" was “third?” on “It depends on how much of his hear- ing has gone." replied Dr. Fletcher. “‘Up to 00 per cent loss. amplification will enable: the suites-er to understand nine unions" outfof no. Minsk the speech still louder will do no good. he...» ,. already Some Of. the vowels are a. loud as the ear can sttnd. At the same certain consonants are; ineudiblgfim- their number» increases with increasing deafness. There-is. however. a really practical and yet simple in; of whether .n' amplifierlwill be beneficial. Your own voice.‘speaklngdlrectiylnto a listen- ing canton begraised to. give all the loudness that the flop!“ “N‘stsudp If. . sheik“! thus is a loud tone.‘ the sulfate: cannot understand you then an 3!? wouldbe of no valu’eii ' But if chan I uncut-unions. then probably on snow ,_fisr.eanbsdeslgnedtogivethe same '“ilm: .. . . ‘ q. .gmwwrwugm‘mm m ‘_ s‘ .. > s‘ t. . ‘ . 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Norwalk Chronicler