US 3849602 A
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United States Patent [191 Gendin i Nov. 19, 1974 EARPHONE WITH FREQUENCY CORRECTION  Inventor: Gennady Semenovich Gendin,
Proletarsky prospekt, 50, kv. 20, Moscow, U.S.S.R.
22 Filed: Dec. 23, 1971 21 Appl. No.: 211,545
 US. Cl. 179/1 D, 179/182  Int. Cl. H04r 3/08, H04r H28  Field of Search 179/1 D, 1 G, 156, 182; 333/15  References Cited UNITED STATES PATENTS 2,063,148 12/1936 Bischoff et al. 179/1 D 2,253,186 8/1941 Loye et al. 179/] D 2,946,862 7/1960 Wadsworth et a1. 179/182 R OTHER PUBLICATIONS Proceedings of the Institute of Radio Engineers, July 1951, Vol. 39, pages 819-821, Available in Patent Office Library TK 5700 17.
Primary ExaminerWilliam C. Cooper Attorney, Agent, or FirmWaters, Roditi, Schwartz & Nissen 5 7] ABSTRACT Each earphone of a stereo headset comprises an electroacoustic transducer with an audio-frequency signal applied to its input. The electroacoustic transducer is provided with an electric filter connected in series in the current path of the audio-frequency signal and the filter has frequency characteristics which, added to the frequency characteristic of transducer radiation, compensate for frequency attenuation of the high and low end thereof and provide a linear overall radiation characteristic within the assigned frequency band.
5 Claims, 3 Drawing Figures ,fidelity broad-band dynamic, piezoelectric or electromagnetic transducers, as, for instance, electrodynamic transducers with a reproduced frequency band of about 20 to 20,000 Hz with a deviation of about 2-4 db.
The use in such earphones of low-fidelity transducers with a limited reproduced frequency band and with a considerable deviation of the frequency characteristic is impossible in principle for it fails to meet the quality requirements of stereophonic equipment.
On the other hand, the manufacture of high-fidelity transducers of any type always involves considerable technical and technological difficulties, requires the use of extra high-quality materials, a high precision in manufacturing and superior workmanship.
Naturally, such special high-fidelity stereo earphones are very expensive.
The object of the present invention is to produce stereo earphones with a high fidelity of sound reproduction, using transducers with a limited reproduced frequency band, thus considerably reducing the earphone production costs.
This object is achieved in stereo earphones each of which comprises an electroacoustic transducer with an audio-frequency signal applied to its input, wherein the electroacoustic transducer is, according to the invention, provided with an electric filter connected in series with the transmission path of the audio-frequency signal and having frequency characteristics which, added to the frequency characteristic of transducer radiation, compensate for the irregularity of the latter and provide a linear overall radiation characteristic within the assigned frequency band.
The present earphones make it possible to obtain high fidelity response while using transducers with a limited reproduced frequency band and thereby to reduce considerably their production costs.
The invention will now be described in detail by way of example with reference to the accompanying drawings in which:
FIG. 1 is an axial sectional view a stereo earphone, according to the invention;
FIG. 2 is a circuit diagram of the electric filter of each of the stereo earphones; and
FIG. 3 illustrates the frequency characteristics of the filter arms of each of the stereo earphones and the total filter frequency characteristic.
Each of the stereo earphones comprises, according to the invention, a plastic case 1 (FIG. 1) housing a plastic ring 2.
One of the sides of the ring 2, facing the interior of the case 1, holds an electroacoustic transducer, the functions of which are performed in the present embodiment by a miniature electrodynamic speaker 3 with a cone 4. The internal diameter of the ring 2 is selected to be equal to the diameter of the radiating part of the cone 4.
A latex seal 5 with an opening whose diameter equals the internal diameter of the ring 2 is pasted onto the outside of the ring 2. The opening of said seal 5 and the ring 2 form a sound chamber 6.
An electric audio-frequency signal is applied from a source (not shown in the drawing) via a wire 7 to the speaker 3 through an electric filter 8 (FIG. 2).
The earphones are also provided with a headband stop adjustment range to enable each user to obtain the most comfortable earphone position.
The electric filter 8 (FIG. 2) is an incomplete double T-bridge. The audio-frequency arm of the bridge com prises two series-connected resistors 9 and 10 whose junction point is connected to the zero-potential point via a capacitor 11. The radio-frequency arm of the bridge comprises a capacitor 12 placed between the input and output of the filter 8.
The speaker 3 is connected to the output of the filter 8.
The electric filter 8 uses a printed-circuit board mounted on a magnetic circuit 13 (FIG. 1) of the speaker 3.
The operation of the present stereo earphones is based on the use of electrodynamic speakers from pocket-type transistorized radios, the frequency characteristic of which is corrected by the electric filter and the sound chamber.
It is common knowledge that the operating band of the frequencies, reproduced by a speaker, is a frequency band within which the efficiency attenuation at the cut-off frequencies does not exceed an assigned level (usually between 14 and 18 db). This, however, does not mean that beyond this band the speaker does not reproduce sound at all. In fact, at higher or lower frequencies attentuation increases to 30-40 db or more thus bringing the speaker efficiency to the vanishing point so that at very low or very high frequencies the signals become practically inaudible. But even such a low radiation at these frequencies makes it possible to expand several times the actual range of frequencies reproduced by almost any speaker, provided an electric filter is used.
If the signal is applied to the speaker not directly but through an electric filter which attenuates the midrange of the incoming signal to the level of the frequencies higher and lower than the cut-off frequencies of the speaker being used, the response in the frequency range reproduced by the speaker can be flattened.
The input of the filter 8 (FIG. 2) receives a broadband signal comprising signals below 1,000 Hz and above 10,000 Hz. At frequencies lower than a reference mid-band frequency (e.g. 1,000 Hz) the reactance of the capacitor 11 increases as the frequency is decreased and at the threshold low frequencies (20-40 Hz) it practically ceases to affect the shape of the frequency characteristic.
At frequencies higher than the reference mid-band frequency, the reactance of the capacitor 11 drops as the frequency is increased, and at threshold high frequencies (18-20 Kc), there is practically no voltage across the output of the filter 8. The shape of the frequency characteristic for this case (without the capacitor 12) is represented by a curve 14 of the graph shown in FIG. 3, where frequency f in Hz is plotted on the X- axis and filter attenuation K in db on the Y-axis.
The capacitor 12 (FIG. 2) closes the filter 8 to frequencies higher than 1,000 I-Iz., while its reactance at frequencies below 1,000 Hz is so high that it practically does not effect this section of the frequency characteristic whereas at the threshold high frequencies (18-20 kHz it is practically a short circuit (curve 15, FIG. 3).
As a result of the interaction of both arms of the filter 8 its frequency characteristic assumes a shape represented by curve 16 FIG. 3). The parameters of the filter 8 depend on the characteristic of the speaker 3 and are selected experimentally.
Thus the use of the above filter 8 provides the necessary correction of the speaker characteristic. The frequency characteristics of the filter 8, added to the frequency characteristic of the speaker 3, compensate for the irregularity of the latter and provide a linear overall radiation characteristic within the assigned frequency band.
Apart from electric correction with the aid of the filter 8, provision is made for acoustic correction by adjusting the volume and configuration of the sound chamber 6.
As in any other stereo earphones, a stereophonic effect in the present earphones is achieved by applying an audio-frequency signal to each speaker from a separate signal source.
The present earphones provide high-fidelity sound reproduction with the use of transducers with a limited reproduced frequency band thereby considerably reducing the production costs.
What is claimed is:
1. An earphone comprising a case; an electroacoustic transducer adapted to reproduce sound in the audio 1,600 Hz and attenuated output in both high and low frequency ranges, said filter being effective in the midband frequency of the transducer for attenuating said mid-band frequency to compensate for the attenuation of low and high frequencies and provide a substantially linear overall radiation characteristic within the assigned audio-frequency band.
2. An earphone as claimed in claim I wherein said transducer is mounted in said case and has a radiating portion of given diameter, a ring secured in said case and mounting said transducer, said ring having an opening with a diameter equal to the diameter of said radiating portion of the transducer, and a seal on said ring and having an opening with a diameter equal to the opening in said ring, said opening in the ring and seal forming a sound chamber.
3. An earphone as claimed in claim 1 wherein said filter comprises two resistors connected in series, and a capacitor connected in parallel with said resistors.
4. An earphone as claimed in claim 3 wherein said filter further comprises a second capacitor connected to the junction of the series-connected resistors and to ground.
5. An earphone as claimed in claim 1 wherein said transducer is a miniature electrodynamic speaker.