Patent Publication Number: US-2012033822-A1

Title: Earphone having sound insulation means

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Application No. 2010-206088, filed on Aug. 30, 2010, with the Japan Patent Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an earphone, and more particularly, to an earphone having sound insulation means for blocking a portion of a space formed between an earphone body and an external auditory canal. The present invention also relates to a sound insulation material, a sound absorption material, an environmental noise reduction, an earphone manufacturing technology and an electronic circuit filter. 
     2. Description of the Related Art 
     In recent years, earphones or players having an environmental noise reduction capability have been being sold. Such devices may be generally classified into an active type and a passive type. The present invention involves a passive type earphone. 
     Throughout the specification including the claims, technical terms indicated by {.} take precedence over other technical terms. Technical terms defined in the claims are equally applied to the specification. 
     As a background art for passive type earphones, there are two important factors, i.e., a method of enhancing an external noise blocking performance of an earphone while maintaining an earphone regeneration performance of the earphone in order to block a sound propagation path ranging from an environmental noise source to an auditory organ, and improvement of material and shape of sound insulation elements for enhancement of sound insulation performance of {gap between an ear and an earphone}. 
     For this purpose, Japanese Patent Application Publication No. H08-275298 discloses an earplug-typed earphone mounting mechanism and an earphone and Japanese Patent Application Publication No. H10-511832 discloses an ear cushion-attached headset and a cushion compression limiting device. However, in some case, since environmental noises propagate through an earphone structure to reach an auditory organ, the techniques disclosed in these documents cannot provide a high level of satisfaction of a noise reduction performance. 
     In addition, Japanese Patent Application Publication No. 2002-200109 discloses an earplug-typed electroacoustic transducer which reduces noises by directly delivering {vibration of a diaphragm of an earphone} to a {sound insulation element as the earplug}. However, with this transducer disclosed in the Patent document, it is difficult to obtain high quality of sound performance since a sound insulation material is inherently incompatible to {direct propagation of sound using a mechanical vibration from a material having different propagation characteristics}. 
     Conventional sound insulation elements cannot have sufficient sound insulation effects under noisy environments such as {in subways, trains, engines and wind of aircrafts, etc.} making environmental noise of 87 dB or more. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an inexpensive environmental noise reduction type inner earphone which allows a user to listen music with high quality of sound and with a small volume even under noisy environments making environmental noise of 86 dB or more such as in aircraft seats, subways, trains and so on. 
     It is another object of the present invention to provide noise reduction which satisfies conditions of {inexpensiveness, easy manufacture, convenient use, high reduction performance and high quality of regeneration sound} and which allows a user to listen music and call sound with high quality without increasing a volume under noisy environments making environmental noise of 87 dB or more. 
     To achieve the above objects, according to an aspect of the invention, there is provided an earphone including an earphone body which includes a voice coil and outputs a regeneration sound through radiating holes; a sound insulation element which is made of deformable sound insulating porous plastic, covers the radiating holes of the earphone body, and fills a space formed between the earphone body and an entrance of an external auditory canal; and a hollow tube which is mounted on the radiating holes of the earphone body and forms an aggregate such that the sound insulation element is combined to the earphone body. 
     Preferably, the hollow tube includes an engagement projection formed on the circumference of the hollow tube and by which the sound insulation element is fixed to the hollow tube. 
     Preferably, the earphone includes a high sound range attenuation correction circuit including a capacitor and a resistor connected in parallel between the voice coil of the earphone and a plug of the earphone. 
     The present invention can be applied to a wide range of goods since it is {simple, highly efficient and inexpensive} and provides {regeneration environments having environmental noise reduction}. 
     In addition, the present invention can provide more stable regeneration environments against apprehensive auditory disturbance since a small volume is delivery to an eardrum of a user and the user can listen music with {high quality of sound}. 
     In addition, since the earphone of the present invention is inexpensive, a majority of persons can comfortably enjoy with {moderate volume and high quality of sound} for a long time in {trains, aircrafts and so on}. 
     In addition, {mobile phone call conditions} are highly improved under noisy environments, which can serve to reduce loud call {as may be often the case under noisy environments} as well as convenient use. 
     On the other hand, although the attenuation characteristic of the earphone of the present invention requires appropriate adjustment, since the attenuation characteristics can be simply adjusted according to a margin of output of a player which is likely to be used under highly noisy environments, compensation of attenuation in a middle and low sound range can be covered by increasing a playback volume. 
     For example, a {volume of seat entertainment in an aircraft} is designed to be {sufficiently heard under noisy environments}. Therefore, an appropriate volume can be secured when such noise is blocked along with a playback signal. 
     In reality, results of experiments in an aircraft showed that the earphone of the present invention is sufficiently used with a range of from a conventional level to a small volume of 10 dB to 20 dB although an {earphone equipped within the aircraft} has to significantly increase a volume for listening. 
     Accordingly, it is possible to greatly reduce an auditory fatigue due to a large volume even when the earphone is used for a long time. Further, the earphone of the present invention can be employed for conventional players, which may result in lowering the barrier to market entry. 
     On the other hand, the earphone of the present invention has substantially the same effect of sound leakage as conventional. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view for an embodiment of the present invention; 
         FIG. 2  is an explanatory view for use condition of the embodiment of  FIG. 1 ; 
         FIG. 3  is an explanatory view for a conventional technique; 
         FIG. 4  is an explanatory view for an embodiment of the present invention; 
         FIG. 5  is an explanatory view for a sound insulation characteristic of a conventional technique; 
         FIG. 6  is an explanatory view for a sound insulation characteristic of an embodiment of the present invention; 
         FIG. 7  is an explanatory view for a regeneration characteristic of an embodiment of the present invention; 
         FIG. 8  is an explanatory view for a regeneration characteristic of an embodiment of the present invention; 
         FIG. 9  is an explanatory view for a regeneration characteristic of an embodiment of the present invention; and 
         FIG. 10  is a CR type high sound range attenuation compensation circuit diagram of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In general, in order to enhance an earphone regeneration performance, it is preferable that {rear side of a diaphragm} is outwardly opened. However, it is preferable that an earphone of a conventional type of {blocking environmental noise} has a {structure where a rear side of a diaphragm of an earphone is sealed} in either {active type or passive type} for {the purpose of blocking environmental noise}. Although the rear side of the earphone may be simply sealed, a generation performance may be affected by such a sealing. 
     In particular, there is a product subjected to delicate workmanship such as installing a duct from a rear side of a diaphragm and opening an ear side opposing the duct in order to avoid {noticeable deterioration due to sealing} of a low sound regeneration performance. In brief, {enhancement of sound performance of earphone itself} cannot be substantially compatible with {enhancement of low sound regeneration performance of earphone}. 
     Accordingly, in the present invention, by filling a space formed between an ear and an inner earphone with a sound insulation element made of porous soft plastic, a regeneration sound is blocked along with a high level of environmental noise passing the inner earphone. In this case, according to an embodiment of the present invention, a frequency characteristic correction circuit, which serves to correct a sound insulation characteristic of the sound insulation element and is composed of resistors and capacitors, is interposed between a voice coil and a plug of the earphone. 
       FIGS. 5 to 9  are views showing measured characteristics, where a horizontal axis represents a frequency and a vertical axis represents a {{relative voltage measured through an amplifier} of a measurement microphone output}. All of the figures having the same reference level show {measurement data in sufficient measurement environments} {in comparing respective characteristics}. 
     In the present invention, by filling a {space formed between the inner earphone and an entrance of an external ear (a portion of an external auditory canal)} with a sound insulating material, both of {environmental noise to be reduced} and {music or announcement signal to be listened} are attenuated. This method performs {sound insulation using a material having a high performance sound insulation effect for regeneration sound}, which results in attenuation of volume of regeneration sound, particularly high sound. 
     Sound quality can be corrected by correcting a dependency of attenuation on frequency. {Noise reduction type earphone with high convenience} can be realized by {providing this correction for an earphone regeneration characteristic} or {inserting an {electronic or electrical circuit} in an earphone}. 
     As a result, sound insulation performance of environmental noise can be enhanced and {attenuation of regeneration sound} is corrected to achieve normal sound quality and improve a S/N ratio. 
       FIG. 1  is a view showing one embodiment of the present invention. 
     Reference numeral  1  denotes an earphone body, reference numeral  2  denotes environmental noise, reference numeral  3  denotes friction noise, reference numeral  4  denotes an earphone regeneration signal, reference numeral  5  denotes a {combination of environmental noise and friction noise} which reaches an auditory sense via the earphone body, reference numeral  6  denotes a hollow tube which {facilitates mounting of a soft sound element, which will be described later, on the earphone body and promotes stability of sound insulation performance of a sound insulation material (in use)}, reference numeral  7  denotes a sound insulation element which is made of {deformable sound insulation porous plastic} for {blocking a portion of a space which is formed between the earphone body and an external auditory canal}, and reference numeral  8  denotes a space which is formed in an inner side of the sound insulation element. 
       FIG. 2  is a view showing a state where the embodiment of  FIG. 1  is mounted on an ear. 
     In  FIG. 2 , reference numerals  1  to  8  denote the same elements as  FIG. 1 . Reference numeral  9  denotes a contour of the external auditory canal, reference numeral  10  denotes the external auditory canal, reference numeral  11  denotes an earphone regeneration signal which reaches the auditory sense via the sound insulation element, and reference numeral  12  denotes environmental noise which reaches the auditory sense via the sound insulation element. 
     The {earphone regeneration sound}  4  and the {environmental noise and friction noise which enter via the earphone}  5  reach the auditory sense via the external auditory canal while being attenuated by a sound insulation effect of the sound insulation element  7 . As apparent from the figure, the environmental noise and the friction noise reaching the auditory sense are greatly attenuated by the {sound insulation effect of the sound insulation element} as a portion of the external auditory canal is blocked by the sound insulation element. Although the earphone regeneration sound is naturally attenuated likewise, by applying a {reverse characteristic of an attenuation effect by the sound insulation element} to the {earphone regeneration sound} in advance using a {high sound range attenuation compensation electronic circuit or high sound range attenuation compensation type signal processing}, the {attenuation by the sound insulation element} can be corrected. As a result, the original regeneration sound quality can be recovered to {substantially the same {sound quality} as a state where no sound insulation element is installed}, which results in reduction of the {environmental noise and a friction sound of a cord} by only {a degree of sound insulation effect of the sound insulation element}. 
     At this time, the hollow tube  6  serves to {secure stable sound insulation performance} under a {state where the sound insulation element is mounted on the ear} by promoting stability of a {shape of a sound exit of the earphone}, that is, by {securing the space  8  stably}. Many experiments showed that {quality of material of the sound insulation element}, {volume of a portion of the sound insulation element blocking the external auditory canal} and {shape of the space  8  in the inner side of the sound insulation element} had a great effect on the sound insulation characteristic under a state where the earphone is inserted in the ear, the role of the hollow tube is important to obtain a stable sound insulation characteristic. 
       FIG. 3  is a view showing a state where a conventional earphone is inserted in an ear. 
     An earphone regeneration signal reaches an auditory sense via an external auditory canal without being blocked. Naturally, since {environmental noise and friction noise of a cord} reach the auditory sense via the earphone without being shielded, sound insulation performance of {environmental noise and friction noise} of the earphone itself has to be high. 
       FIG. 4  shows one embodiment of a composite sound insulation element of the present invention. 
     In the figure, the same reference numerals as  FIG. 1  have the same functions as  FIG. 1 . Reference numeral  13  denotes a key-shaped projection of the hollow tube.  FIG. 4A  shows a combination of the sound insulation element, the hollow tube and the earphone. The projection is provided on the circumference of the hollow tube such that the sound insulation is prevented from being easily fallen out under a state where the sound insulation element is put on the hollow tube. The projection is key-shaped so that it can be easily inserted and prevented from being easily fallen out. A positional relationship between the hollow tube and the sound insulation element is important in obtaining a stable sound insulation characteristic.  FIG. 4B  is an enlarged view of the key-shaped projection of the hollow tube. The key-shape projection may be positioned in any places in the hollow tube. In addition, it is necessary and sufficient if only the key-shaped projection is shaped to be prevented from being separated. 
       FIG. 10  shows a high sound range attenuation compensation circuit of the earphone according to one embodiment of the present invention. 
     An embodiment of changing a regeneration characteristic of  FIG. 7  to a regeneration characteristic of  FIG. 8  is given by way of example as follows. In  FIG. 10 , VC represents an earphone voice coil, R represents a resistor, C represents a capacitor, and IN represents an earphone input terminal. A signal of a low sound range is attenuated by the resistor and a signal of a high sound range passes through the capacitor, thereby obtaining a low sound-limited and high sound-enhanced characteristic. In this embodiment, assuming that impedance of the voice coil is 16Ω, the resistor has resistance of 32Ω and the capacitor has capacitance of 4.7 μF, a −10 dB attenuation is achieved in a middle and low sound range, thereby obtaining a high sound range-enhanced characteristic providing a gain of octave of +6 dB from a frequency of about 3000 Hz. The −10 dB attenuation in the middle and low sound range has no practical problem since a general player outputs a large volume required to listen music under noisy environments. 
       FIG. 5  shows an {earphone sound insulation characteristic} of an available goods attached with a {highest performance sound insulation piece}. 
     In the figure, a dashed line represents a level of sound when a vertical axis is at a 0 dB position and no earphone is mounted. Although the earphone sound insulation characteristic seems to show a sound insulation effect below a frequency of 80 Hz, which is because a source of simulation environmental noise does not regenerate a sound of less than 80 Hz, there is no attenuation of a range of less than 80 Hz in an actual sound insulation characteristic. A small change in a frequency range of less than 30 Hz is attributed to natural environmental noise in which a measurement instrument is placed. 
     A frequency range of less than 400 Hz shows a right and down falling attenuation characteristic from {6 dB to 7 dB}. The attenuation slowly increases near a frequency range of more than 400 Hz and an attenuation of about 35 dB is shown in a frequency range of more than 1500 Hz. This sound insulation characteristic is sufficiently useful under relatively light noise environments but insufficient under noisy (for example, 80 dB) environments such as in a subway.  FIG. 5  shows a sample having excellent sound insulation performance among available earphones, however, most of cheap ones have a sound insulation characteristic as poor as not to be put in practical use. 
       FIG. 6  shows a sound insulation characteristic when a composite sound insulation element is mounted on an earphone having the characteristic shown in  FIG. 5 . 
     In  FIG. 6 , a dashed line represents a level of sound when a vertical axis is at a 0 dB position and no earphone is mounted. Although the earphone sound insulation characteristic seems to show a sound insulation effect below a frequency of 80 Hz, which is because a source of simulation environmental noise does not regenerate a sound of less than 80 Hz, there is no attenuation of a range of less than 80 Hz in an actual sound insulation characteristic. A small change in a frequency range of less than 30 Hz is attributed to natural environmental noise in which a measurement instrument is placed. 
     A frequency range of less than 400 Hz shows a right and down falling attenuation characteristic from {17 dB to 18 dB}. The attenuation slowly increases near a frequency range of more than 400 Hz and, unlike  FIG. 6 , noticeably increases even in a frequency range of more than 1500 Hz. This sound insulation characteristic is sufficiently useful even under heavy noise environments such as in a subway and a jet liner. In reality, field experiments showed improved sound insulation performance of 10 dB to 20 dB as compared to conventional types. 
       FIG. 7  shows a regeneration characteristic of an {earphone equipped with the {composite sound insulation element} of the present invention. 
     Since the sound insulation element blocks a regeneration sound as well, the regeneration characteristic is attenuated from above 500 Hz. An unequal characteristic in a range of from 1000 Hz to 10000 Hz is attributed to an inherent property of a measurement system. An actual attenuation characteristic is attenuated with an {inclination of octave of about 6 dB}. Such an attenuation characteristic provides insufficient quality of high sound. 
       FIG. 8  shows a regeneration characteristic when an {example of the CR type high sound range attenuation compensation circuit} is interposed {between the voice coil and an earphone plug} of the {earphone on which the composite sound insulation element of the present invention is mounted}. Specifically, this figure shows a regeneration characteristic when a {volume of a signal source is preset to be large} such that {regeneration performance in a range of from 100 Hz to 500 Hz} is equal to that shown in  FIG. 6 . Considering an error of a measurement system, it is shown that the CR type high sound range attenuation compensation circuit maintains an ideal regeneration characteristic up to near 10 kHz. 
       FIG. 9  shows a regeneration characteristic when an {example of a precise high sound range attenuation compensation circuit} is interposed {between the voice coil and the earphone plug} of the {earphone on which the composite sound insulation element of the present invention is mounted}. In this case, since the compensation circuit uses a digital signal processor, it is shown that substantially the same fine correction is made in a range of from 40 Hz to 10000 Hz as compared to that of  FIG. 8 . 
     As described above, by employing a {structure where the {sound insulation element mounted on the earphone blocks a portion of the external auditory canal}, it is possible to implement high performance noise reduction {even in a rear open type earphone}. 
     On the other hand, from the fact that a {close type earphone which seldom obtains good low sound regeneration performance} has a high sound range attenuation compensation characteristic similar to that of the present invention, the spirit of the present invention can be applied to a close type earphone having a simple structure. 
     Thus, it is possible to simply reduce environmental noise and obtain high quality of sound having little distortion and electronic circuit noise at a low cost and with stability using {conventional manufacture technology and equipment}. 
     In addition, since the {sound insulation} is inexpensive, it may be easily replaced with a new one {even if it is dirtied, damaged or lost}. 
     In addition, there is no need of a {difficult signal processing technique} that a {point of compromise of contradictory problems has to be considered} in connection with {stability of a closed loop including a complicated filter} and a {problem of noticeable deterioration of controllability due to a nonlinear characteristic of a system}. 
     Embodiment 1 
     An environmental noise reduction type earphone which is commercialized separately. 
     A sound insulation element with various exchangeable {designs and forms}. 
     A sound insulation element for earphone. 
     An earphone mounted with a sound insulation element. 
     An earphone with a removable sound insulation element. 
     A sound insulation element which can be mounted on an earphone. 
     An earphone for mobile phone. 
     An earphone for potable player. 
     An earphone for aircraft seat. 
     The earphone of the present invention has an extremely wide range of application since it is practical, inexpensive, simple to be manufactured, easy to be used, and provides high reduction performance and high regeneration quality. Accordingly, the present invention can be applied to almost all apparatuses with which user are likely to hear sound under noisy environments.