Abstract:
By combining an earphone with an extra audio splitter and jack, it becomes possible to share the audio being played over one set of earphones with another set of earphones in a sanitary manner using ordinary, unmodified earphones.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Earphones, also known as headphones or earbuds, are commonly used to listen to music or other audio media. They provide relative privacy in listening, permit others not to be bothered by the sound, consume relatively little power, and add portability. 
         [0002]    One disadvantage of conventional earphones is that sharing of audio among multiple persons is difficult. The difficulty arises from their very purpose, to provide sound to one person without disturbing others. One common method, having the left and right earphone shared between two people, is unsanitary and therefore undesirable. 
         [0003]    Another method is to purchase an earphone splitter. This requires one to purchase and carry around extra equipment and may not always be available. A similar method, described in WO 2008/086279 A2 to Gantz, is to provide a second set of earphones that can be stored in combination with a first set and optionally separated and used. This has the disadvantage of being forced to pay for and carry around a second set of earphones. 
         [0004]    Another method is to add some sort of radio transmitter, but this requires the purchase not only of the transmitter but also of special earphones to receive the audio. A similar method, described in US 2013/0016849 A1 to Senemaud, is to have an external apparatus that combines two audio inputs and drive two sets of earphones. This also requires the purchase of special electronics. 
         [0005]    It is desirable to add features to earphones to permit persons to share the audio among multiple earphones. The features should enable users of ordinary, unmodified earphones to hear the audio, and should not require the primary user to carry around extra earphones. Additionally the features should permit multiple persons to listen to the same audio without disturbing others and in a sanitary manner. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In the following, terms such as “earphones,” “headphones,” “headsets,” and “earbuds” are used synonymously to refer to portable audio devices usually placed in or near human ears. The term “plug” is used to describe the metal tip that carries audio signals (and the plastic casing adjacent to it that is used to hold it) and the term “jack” is used to describe the hole or receptacle that holds the plug (and the plastic casing surrounding it). This patent anticipates and therefore includes well-known variants of earphones, plugs, and jacks, including versions that are monaural and stereo, versions with and without microphones, and versions with various pin orderings. 
         [0007]    In order to enable another set of earphones to listen to an audio source, an extra earphone jack and audio splitter are added to the earphones. This enables another set of earphones to attach and render the same audio for another listener. In an alternate embodiment, a source of power (such as a battery) and an audio amplifier are added to compensate for the extra load added by the extra set of earphones. 
         [0008]    The extra jack permits ordinary, unmodified earphones to connect to the same audio source. By using an extra set of earphones, the arrangement is sanitary and the primary listener does not need to pay for or carry around the extra set of earphones. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]      FIG. 1  is an illustration of the primary and secondary earphones and the jack-and-plug arrangement that permits the attachment of an extra set of earphones. 
           [0010]      FIG. 2  is an alternate embodiment including a power source and amplifier. 
           [0011]      FIG. 3  is an exemplary unity-gain circuit to add drive strength and drive multiple sets of earphones. 
           [0012]      FIG. 4  is an exemplary amplifier circuit that adds volume control. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The following description is presented in order to enable persons of ordinary skill in the art to make and use the invention without undue experimentation. Various modifications to the disclosed embodiments will be readily apparent to persons of ordinary skill in the art, and the principles disclosed herein are applicable to other embodiments of the invention without departing from the spirit and scope of the present invention. Specifically, certain elements of the invention, such as the amplifier circuit, monaural/stereo earphones, presence or absence of a microphone, and arrangement of pins, are capable of numerous modifications and variations known to persons in the art. The invention explicitly discloses that there are numerous combinations of invention elements, and all combinations are therefore disclosed herein. 
         [0014]    As shown in  FIG. 1 , a set of earphones  100  has a plug  101 . This set of earphones is specially modified so that the plastic casing of plug  101  includes a jack  102  for receiving the plug of a different set of earphones. If no earphone plug is inserted into the jack  102 , the earphones  100  operate normally. If an extra earphone plug  103  of second earphones  104  is inserted, both earphones  100  and earphones  104  present sound to their respective listeners. 
         [0015]    The shape and size of the casing of jack  102  may vary, and the jack  102  may be located a distance up the cable away from plug  101  (in an embodiment not shown). The casing of jack  102  may be decorated or molded into a creative shape, such as the mouth of an animal, or may be plain and unmodified. The jack  102  may have a cover or door over it to prevent dust or dirt from accumulating when not in use. The jack  102  is of a design to accommodate the plugs of widely sold earphones. (The jack  102  is normally of the corresponding size and shape to, and will therefore mate with, plug  101 .) One common size is the 3.5 mm phone jack widely used in smart phones such as those sold by Apple, Inc. of Cupertino, Calif. 
         [0016]    More than one jack  102  may be added to earphones  100 , so that more than one extra set of earphones can be optionally attached. 
         [0017]    If the earphones that are attached to jack  102  are also modified with their own jack  102 , additional earphones can be added. Conversely, the earphones that are attached to jack  102  need not be modified and can be ordinary, already existing, commercially sold earphones. 
         [0018]    One disadvantage of this simple circuit is that the audio drops in amplitude (that is, loudness) as additional earphones are attached. This is because the audio energy (emitted by the device to which the earphones are attached) is being split among multiple earphones. This can be compensated by additional circuitry. 
         [0019]    As shown in  FIG. 2 , the earphones  100  may include not only the plug  101  and jack  102  but also a casing  201  for an amplifier and power source. The power source may be a removable battery or rechargeable battery. If the battery is rechargeable, the casing  201  may have a port  202  for attaching a charger. The casing  201  may also include a volume control  203  such as a volume-control knob or button-operated controls. As before, the plug  101 , jack  102 , and casing  201  may be arranged and/or combined in any order and may be molded into decorative shapes. 
         [0020]      FIG. 3  shows an exemplary electronic amplifier circuit that may be contained in casing  201 . This circuit uses an op-amp  301  in a well-known unity-gain configuration. Capacitors  302  may be used so that the DC op-amp circuit can drive the AC audio waveform. Resistor  303  may be needed so that the audio appliance to which the plug  101  is attached drives an ordinary, single headphone impedance. (For example, some headphones manufactured by Apple, Inc. of Cupertino, Calif. have an impedance of 23 ohms.) The use of capacitors  302  and resistor  303  are optional and their use depends on the design of the overall circuit. This particular circuit drives on its output the same voltage that it receives on its input, and the op-amp  301  adds drive strength, so that multiple earphones can be attached without loss of amplitude. 
         [0021]      FIG. 4  shows another exemplary electronic circuit. In addition to op-amp  301 , resistor  303 , and capacitors  302 , a second op-amp  401  and variable resistor  402  are used. The variable resistor  402  is used to vary the gain of the second op-amp  401  and therefore vary the amplitude (that is, loudness) of the audio output. The variable resistor  402  may be attached to a knob for human control of volume. 
         [0022]    This illustrates one variable-amplitude circuit; other variations may include a microprocessor and/or volume-control buttons (such as one to increase volume and one to decrease volume) or other circuits commonly used and well known in the art. 
         [0023]    In the case of either amplifier circuit, additional circuits such as electrostatic discharge (ESD) protection may be added. Circuitry to limit output amplitude, to protect the hearing of listeners, may also be added. Numerous variations in amplifier circuits are possible, known and used in the art, and may be used within the scope and spirit of this patent. 
         [0024]    In all cases using an amplifier, a source of power is needed, which is usually a battery. Disposable batteries, such as commonly used alkaline AA or AAA batteries, may be used. Rechargeable batteries, such as lithium-ion, lithium-polymer, and nickel-cadmium, may be used. As noted above, a recharging port  202  may simplify the process of recharging, or the rechargeable battery may be removable. 
         [0025]    Numerous variations of the circuits and earphones may be used. For example, the earphones may be attached to a structure that holds the earphones against one&#39;s ears and on one&#39;s head. All of these variations are within the scope and spirit of the patent.