Патент USA US2131669код для вставки
Sept. 27, 1938. A. POLIAKOFF' 2,131,669 SOUND REPRODUCING APPARATUS Filed May 31, 1935 2 Sheets-Sheet l / m. \ . w0 I000 4000 FF //nl?u nlu 7/ 7% 2000 FRE‘Ol/E/VC/ ‘ INVENTOR ALEXANDER POLIAKOFF B . ‘ y 47''”"'4 7142M ATTOHN}BYS ‘ SePt- 27, 1938- A. POLIAKOI~=F . SOUND REPRODUCING APPARATUS Filed May 31, 1935 2,131,669 2 Sheets-Sheet 2 INVEN‘I‘OR BY ALEXANDER PoLI‘AKoFF ATTORNEYS 2,131,669 Patented Sept. 21, 1938 UNITED STATES PATENT OFFICE 2,131,669 ‘ SOUND REPRODUCING ‘APPARATUS Alexander Poliako?, London, England Application May 31, 1935, Serial-No. 24,445 In Great Britain June 4, 1934 1 Claim. (Cl. 179-107) The present invention relates to all sound re producing devices in which head telephones and not loudspeakers are used to radiate sound, such as ordinary communication telephones, deaf-aid invention to a thermionic ampli?er used for deaf aid or ordinary speech frequency ampli?cation. . Figure 3 shows sound output characteristics of the circuit in Figure 2, and 5 ampli?ers, ?eld telephones, aircraft radio receiv ers and similar installations. , Hitherto, the majority of deaf-aids, both simple microteiephones and valve ampli?ers, utilized a single telephone. ~ ' Attempts have been made with‘valve ampli ?ers to shape the response curve of the apparatus to compensate partially the patient's “tonal deaf ness" as shown by his audiometric curve. Such 10 a curve ‘is commonly obtained by means of a valve oscillator provided with a calibrated at tenuator .or by means of a set of calibrated tun ing forks. In both cases the patient hears one note at a time, so that the disturbing or masking e?ect by low and middle notes on the high notes in‘ a complex sound is left out of consideration. ' This effect is known, however, to be ‘large and to increase rapidly with the sound intensity level; curves illustrating the effect may be seen in _ Harvey Fletcher, Speech and Hearing, 1929, part 3, ch. IV. r. . U in a complex sound by the other components of 10 such sound, by the use of two head telephones one on'geach ear, the-low and/or middle fre quency components in the sound output of one of which telephones being su?iciently reduced in intensity not to mask appreciably the high fre quency components in the sound output of one tact with that telephone. Since there isno mask ing of high frequency components received by one ear by low and middle frequency components received by the other ear, a given acoustic output » 20 of high frequency components in a complex sound thus produces far greater sensation than would _‘ be the case if the whole output were applied to one ear only, or were shared between the two. cars without frequency discrimination between’ 25. ' as 40 decibels greater loss at say 4,000 cycles than at 512 cycles. Witha portable valve ampli?er employing a carbon microphone and the usual ' 30 -magnetic telephone not only is it impossible to compensate for that loss but even to obtain a level response between these frequencies at a reasonable ampli?cation level, since both the microphone and the telephone have large high note losses and the number of valves used must necessarily be small. In addition, the high notes although present in the telephone of such an instrument will not be perceived by the listener on account of their 40 being masked by the noise in the room and by the low and middle notes in the sound particularly in the region of the principal resonance of the _ telephone ‘ The present invention" substantially eliminates the masking of high audio frequency components A common case of deafness will have as much , - Figure 4 is a circuit diagram ofa portion of the ampli?er in which separate valves are used to feed the level and high pass telephones. diaphragm. I them. ' v - An experimental verification of. the last state ment has been carried out as follows:—- ' Two thermionic ampli?ers were constructed with common input from a high ?delity non-v carbon microphone coupled to the ampli?ers by means of a valve common to both. One of the ampli?ers had an approximately level frequency response characteristic, while theother had a steeply risingcharacteristic. Two identical mag. netic telephones were connected in the output in such a manner that, by manipulating a switch, the-outputs of the‘ two ampli?ers, could be ‘either combined and shared equally'by the two tele phones, or the high-pass and level outputs were 40 delivered to different telephones.- _ ' Figure 1 shows the curve of the high-pass am pli?er relative to the level ampli?er in terms of ' Deaf aid ‘apparatus supplying each ear with a high ?delity signal ampli?ed separately to'com pensate accurately the audiometric curvesof the. in decibels, where V1. and V1; are respectively volt two ears, which are usually di?erent, apart from its prohibitive bulk will not be free from the ‘ masking effect and its attendant great diminution in high note perception, _ . . The invention is hereinafter described with ref — erence to the accompanying drawings in which: Figure 1 is a chart showing the curves of a , high-pass ampli?er relative to a level ampli?er. 55 Figure 2 shows a simple way of applying the ages applied to the ?rst and common grid for v ‘ equal outputs from the level and high-pass am ‘50 plifiers. . , - The output level of the high-pass ampli?er is below that of the level ampli?er at all frequen cies except 4,000 cycles at which the two outputs are equal. With a listener of normal hearing acuity, the 55 .. 2 2,181,669 experiment consisted of making speech in the room containing the microphone unintelligible than a pair of like telephones but the high notes by a controlled noise radiated by a loudspeaker > will still _be strongly masked by the middle notes. It is not suggested that isolation of high notes in the same room, the two telephones sharing equally the outputs of the two ampli?ers. On in one telephone should replace correction, that ’ switching over to an asymmetric output, that is is, shaping of the sound output frequency char 5 with one telephone connected to'the high-pass acteristic to suit approximately de?nite types of 10 deafness or special requirements of listeners of normal hearing acuity situated in noisy sur roundings. It is claimed however that with a givenavailable high note sound output in a com 10 plex sound the application of the invention re ampli?er only, intelligibility of speech was re stored. Noise of different nature such as a single note of SOD-1,000 cycles, imitation petrol engine noise and ampli?ed noise picked up by a-micro phone in a workshop were tried with the same re sult. Further the use of one phone only con sults in'a far greater sensation being produced by nected to the high-pass ampli?er did not pro-> 15 duce intelligible speech, while with both tele phones connected to the level ampli?er only and the masking noise increased to the point where speech was just unintelligible, intelligibility was ‘not restored by adding the-output-of the high 20 pass ampli?er which on account of its low level was entirely lost. Y coil telephone in the “high pass” position or 30 be applied to the simplest microphone systems em ploying ordinary magnetic telephone receivers. The output of the high-pass telephone alone must not be confused with a frequency corrected output, since in general the level of low and mid dle frequency components will be below the threshold of audibility so that the high-pass tele quency response of the output of the ampli?er 15 feeding telephones T1 and T2 by means such as an intervalve transformer described in U. S. Pat ent No. ‘1,996,685. ' In practice it has been found that sufficient low and middle frequency attenuation in the out 20 series condenser to meet the requirements of most under as the “level” telephone and the other as the “high pass” telephone. ' The invention is not dependent on the use of a special receiver such as a condenser or a moving even on the use of thermionic ampli?ers, and may ' It has been found useful to control the fre put of T2 may be produced by means of a simple To facilitate description, the telephone repro clucing the whole scale will be referred to here ~25 the high notes. deaf cases. Where space permits, however, a proper ?xed or variable high-pass ?lter ‘may be used, the construction'of which is common know 25 ledge. The use of separate thermionic valves to feed T1 and T2 need only be adopted with cases ‘requiring a very large output of high notes. In ‘such cases the two output valves V2 and V2, Fig ure 4, have their input from the valve V1, and the 30 high-pass output from the valve V2 to telephone T2 may be obtained for example, by using two intervalve transformers M1 and M2 with their primaries in parallel through a small condenser C2. The transformer M1 being of normal design, 35 phone alone will not usually provide intelligible feeds the grid of the level ouput valve V2 while the transformer M2 is of the type described in' audition. ' As shown in Fig.2, two telephones T1 and T2 ‘ U. S. Patent No. 1,996,685, the response curve of which is made more or less sharply rising with 40 which may be identical are connected in the out frequency according to the setting of the asso put, T1 direct, T2 through a condenser C1 the im ciated potentiometer. The function of the small pedance of which is high at low and middle fre quencies compared with Z1 and Z2. If Z1‘and Z2 condenser C2 is to prevent the primary of M2 un are the impedances of T1 and T2 respectively and duly lowering the impedance in the plate circuit Z1=Z2, then the sound output of T2 will have a of the valve V1 for low and middle frequencies. In some cases it is possible to do away with a 45 rising characteristic and will be at all frequen ?ltering arrangement by using receivers inthe _ cies at a lower level than T1. ~If Z1 is made higher than Z2 the sound outputiof T2 will be higher than high-pass position which by virtue of their elec of T1 at high frequencies and lower at low and trical or mechanical construction have a natural ly rising ‘response characteristic. A condenser middle frequencies. Curve I, Fig. 3, is the sound output of T1 with receiver for instance connected straight across a 50 magnetic receiver will in general reproduce high T2 disconnected. Curve 2 is the sound output notes only. ' of T1 with T2 in circuit, Z2 being slightly smaller It has moreover been found that with impaired than Z1. Curve 3 is the sound output of T2. There is no. increase in the total acoustic output hearing the high-pass telephone should generally on connecting T2 in addition to T1, but merely a be placed on the ear with better high note hear 55 transfer of half or more of the high frequency ing, which in the majority of cases is also the output to the other ear. GO - - ; The curves in Figure 3 should be contrasted with those published for dual speaker combina tions, the object of which is to reproduce a greater range of frequencies than can be covered by a single ‘speaker and in which the introduction of the high note speaker greatly increases the total high note output. more sensitive ear at all frequencies. The inven tion has then the additional advantage of putting‘ more energy into the bad ear than the good ear so that loud noises produce less distress than 60 would have been the case if .a single telephone were used on the better ear. ,' So far mention has been made principally of . vention does not consist merely in the use of two deaf aid ampli?ers, the invention is however of considerable value in sound reproducing systems 65 used by persons of normal hearing acuity. The existence of large high note losses in the ordinary communication telephone are of‘ course better than the other. It is common in dual 'speaker'dombinations for the output of the two units to be approximately equal at 1,000 cycles. surroundings may be usefully regarded as su?er-~ 70 ing from fairly acute deafness since such high notes as are transmitted will be largely masked by In my invention the low and middle notes par > ticularlythe latter are reduced in the high-pass telephone to a low intensity level. Thus my in 70 telephones, one of which reproduces high notes ‘ well known. The user of a telephone in noisy The headphone equivalent of such a pair of H 76 speakers may have slightly higher intelligibility the noise. - The same considerations apply in this case as in deaf aid ampli?cation, and a high-pass 75 ' 2,181,669 . 3 _' telephone added to the output greatly enhances response of low, middle and high frequency com ponents and‘ means for ‘altering the frequency intelligibility. ' response in the second receiver to cause the low I claim: . . a and middle frequencycomponents to be reduced Sound reproducing apparatus for deaf aid am to an extent that they do not mask the high fre- 5 pli?cation and communication in noisy surround quency component of said second receiver. ings, comprising two similar head telephone re ceivers one for each ear and arranged in di?erent _ ‘circuits, one receiver having a uniform frequency ALEXANDER POLIAKOFF.