Abstract:
A dedicated stereophonic bridged type amplifier and headphone or earbud system in which the amplifier provides at least one of low frequency compensations and high frequency compensations calibrated to substantially match the coefficients of acoustic coupling for the corresponding headphones or earbuds. In preferred embodiments, the dedicated amplifier is integrated into the headphone or earbud body(s), head strap or audio input cable as applicable.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority from U.S. Provisional Application Ser. No. 60/631,117, filed Nov. 24, 2004, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to headphones and earbuds. More particularly, it relates to bridge amplifier driven acoustic coupling compensated headphones and earbuds for optimal sound reproduction accuracy.  
         [0004]     2. Description of the Prior Art  
         [0005]     Headphones fall into two basic categories—“open air” or on-the-ear type, and “cup” or over-the-ear type, each having left and right headphone bodies, left and right transducers incorporating left and right transducers respectively, and an audio input cable. On-the-ear headphones generally include a pair of substantially flat surfaced, acoustically transparent (open air) cushions disposed over the left and right transducers of the headphones, which press against, but do no envelop, the corresponding outer ears of a listener. Over-the-ear headphones generally include a pair of ear cups disposed over the left and right transducers of the headphones, which substantially envelop the corresponding outer ears of a listener.  
         [0006]     The open air cushions in on-the-ear headphones do not form air tight fits to the ears, and, it has been determined by the inventor, therefore exhibit a low frequency ‘coefficient of acoustic coupling’ to the ear that is approximately unity between 150 Hz and 7 kHz, and decreases as a function of frequency below 150 Hz. Additionally, the diameters of such transducer diaphragms are typically significantly larger than the exposed openings of the ear canals, and therefore provide a high frequency coefficient of acoustic coupling to the ear that decreases as a function of frequency above substantially 7 kHz.  
         [0007]     Variances in the 150 Hz and 7 kHz frequency points and the magnitude of required compensation, occur as a function of several influencing factors, including: 1) the electro-acoustic characteristics and frequency response of the transducers; 2) physical size of the diaphragms; 3) shape and density of the open air cushions; and 4) pressure between the air cushions and the ears.  
         [0008]     Contrary to conventionally held assumptions in the field, even very high quality on-the-ear headphones require compensation of low and/or high frequency coefficients of acoustic coupling in accordance with the above described influencing factors, for optimal sound reproduction accuracy.  
         [0009]     A dedicated amplifier having low and high frequency compensation calibrated to substantially match the coefficients of acoustic coupling for a specific on-the-ear headphone design is therefore required for optimal sound reproduction accuracy. As a practical matter, such dedicated amplifier is best integrated in-line with the headphone input cable.  
         [0010]     The ear cups comprised in over-the-ear headphones form more air tight, although not perfect, fits to the ears than that provided by on-the-ear headphones. It has been determined that over-the-ear headphones also exhibit a low frequency coefficient of acoustic coupling to the ear that decreases as a function of frequency below 100 Hz, however, generally to a less severe extent than that of on-the-ear headphones. The over-the-ear headphones also provide a high frequency coefficient of acoustic coupling to the ear that decreases as a function of frequency above 7 kHz, each for the same reasons and subject to the same variances as identified above for on-the-ear headphones. Over-the-ear headphones therefore also require a dedicated amplifier having specific low and high frequency calibrations for optimal sound reproduction.  
         [0011]     Similarly, earbuds (or earphones) exhibit low and high frequency coefficients of acoustic coupling to the ear, and therefore require a dedicated amplifier having specific low and high frequency calibrations for optimal sound reproduction accuracy. Variances in the low frequency coefficients of acoustic coupling for earbuds, however, can be quite large relative to that of headphones and is a function of physical design and ear fitting effectiveness. Variances in the high frequency coefficients of acoustic coupling in earbuds occur for various reasons, including sound direction misalignments and/or resonances occurring between the earbud diaphragms and the ear canals.  
         [0012]     A unique earbud design described in specific embodiments of the present invention optimizes both such variances by means of a transducer diaphragm having a diameter substantially larger than an output tube that is acoustically coupled to the diaphragm through a coupling channel. The radial center of the output tube is misaligned with the radial center of the diaphragm in order to position the transducers of the earbuds further from the listener&#39;s head. The acoustically confining surfaces of the coupling channel are, at least to a limited extent, non-parallel to the radial axis of the diaphragm. The output tube fits into the ear canal opening and preferably comprises a pliable solid or hollow annulus about its diameter and near its open end to facilitate a comfortable fit to the ear.  
         [0013]     As is the case for conventional earbuds, the earbuds of the present invention insert into the ear canals of a listener, and have left and right transducers and an audio input cable, but do not include a head strap. A dedicated bridged type amplifier having low and/or high frequency compensation calibrated to substantially match the coefficients of acoustic coupling for a specific earbud design, such as the above unique earbud design, is required for optimal sound reproduction accuracy. As a practical matter, such dedicated amplifier is best integrated in-line with the earbud input cable.  
         [0014]     A unique dedicated amplifier as applies to driving headphones or earbuds is described in several embodiments of the present invention, and includes a stereophonic pair of bridged amplifier output stages having + and − output signals that are generally direct coupled (no coupling capacitors) to the left and right transducers of a pair of corresponding headphones and earbuds, wherein such amplifier incorporates low and/or high frequency compensation of the coefficients of acoustic coupling for the corresponding headphones or earbuds. In another embodiment, the dedicated amplifier may be used with various headphones and earbuds, and comprises selectable low and/or high frequency calibrations matched to at least two specific and differing headphone/earbud models.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention is a dedicated bridged type amplifier, having + and − outputs for each stereophonic channel, and headphone or earbud system in which the amplifier provides low and/or high frequency compensation calibrated to substantially match the coefficients of acoustic coupling for the corresponding headphone or earbud. Such dedicated amplifier is integrated in-line with the audio input cable of such headphone or earbud.  
         [0016]     A unique earbud design described in the present invention comprises left and right earbud bodies, left and right transducers and an audio input cable. Each transducer comprises a diaphragm having a diameter substantially larger than an output tube that acoustically couples the diaphragm to a corresponding ear canal of a listener. The radial center of the output tube is substantially misaligned with the radial center of the diaphragm in order to position the output tube at an angle that is conducive to deep insertion into the listener&#39;s ear canal. The output tube preferably comprises a pliable solid or hollow annulus about its diameter and near its open end to facilitate a comfortable fit to the ear.  
         [0017]     A unique dedicated amplifier as applies to driving headphones or earbuds is described in several embodiments of the present invention, and comprises a stereophonic pair of bridged amplifier output stages having + and − output signals that are generally direct coupled (no coupling capacitors) to the left and right transducers of a pair of corresponding headphones and earbuds, wherein such amplifier incorporates low and/or high frequency compensation of the coefficients of acoustic coupling for the corresponding headphones or earbuds. Bridged amplifiers are not used in prior art headphone or earbud in-line cable applications because such amplifiers require separate left and right ground lines and therefore cannot drive common ground input cables and connectors used in commercially available earbuds and headphones. Since the bridged amplifier of the present invention is dedicated and integrated in-line with corresponding headphones or earbuds, separate left and right ground lines may be utilized between such amplifier output signals and the left and right transducers, while the necessary conventional input cable and connector having a common ground may is utilized as input to the amplifier. Alternatively, unconventional male and female audio connectors and cables, each having at least four electrical contacts, may be used to couple between the dedicated amplifier and the left and right transducers. In another embodiment, the dedicated amplifier comprises selectable low and/or high frequency calibration matched to at least two specific headphone and/ or earbud models.  
         [0018]     Other combinations and equivalent variations of the above described concepts and embodiments may be practiced by those skilled in the art without altering the general principles of the present invention.  
         [0019]     Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     In the drawings wherein like reference numerals denote similar components throughout the views:  
         [0021]      FIG. 1  is a block diagram of prior art headphones driven by a typical audio source and interconnected by a conventional 3-conductor connector;  
         [0022]      FIG. 2  is a block diagram of the headphones and dedicated bridged amplifier driven by a typical audio source according to an embodiment of the present invention;  
         [0023]      FIG. 3  is a block diagram of the headphones and dedicated bridged amplifier, according to an embodiment of the invention, interconnected by an unconventional 4-conductor audio connector and driven by a typical audio source;  
         [0024]      FIG. 4  is a block diagram of prior art earbuds driven by a typical audio source and interconnected by a conventional 3-conductor audio connector;  
         [0025]      FIG. 5  is a block diagram of the earbuds and dedicated bridged amplifier of the present invention driven by a typical audio source;  
         [0026]      FIG. 6  is a block diagram of the earbuds and dedicated bridged amplifier of the present invention interconnected by an unconventional 4-conductor audio connector and driven by a typical audio source;  
         [0027]      FIG. 7  is an illustration of the preferred embodiment of the earbud design of the present invention;  
         [0028]      FIG. 8  is a block diagram of the first embodiment of the dedicated bridged amplifier of the present invention for use with one specific headphone or earbud design or model; and  
         [0029]      FIG. 9  is a block diagram of the second embodiment dedicated amplifier of the present invention for selectable use with at least two specific headphone or earbud designs or models.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]      FIG. 1  is a block diagram of prior art headphones H 1  driven by typical audio source SS 1 , in which headphones H 1  do not include a dedicated or integrated amplifier. Audio source SS 1  provides source ground S 1 , source left signal S 2 , and source right signal S 3  to conventional 3-conductor female audio connector F 1 . Conventional 3-conductor male audio connector M 1  couples to connector F 1  and provides connector ground S 4  applied to the − inputs of left driver D 1  of headphones H 1  and right driver D 2  of headphones H 1  respectively, connector left signal S 5  to the + input of driver D 1 , and connector right signal S 6  to the + input of driver D 2 .  
         [0031]      FIG. 2  is a block diagram of headphones H 2  and dedicated bridged stereo amplifier DA 1  of the present invention, in which DA 1  is driven by typical audio source SS 2  and introduces compensation for at least one coefficient of acoustic coupling matched to headphones H 2 . Audio source SS 2  provides source ground S 7 , left source signal S 8 , and right source signal S 9  to conventional 3-conductor female connector F 2 . Conventional 3-conductor male connector M 3  couples to connector F 2  and provides connector ground S 110 , and connector left and right signals S 11  and S 12  respectively to corresponding stereo inputs of amplifier DA 1 . DA 1  provides left output ground S 15  to the − input of left driver D 3  of headphones H 2 , left output signal S 16  to the + input of driver D 3 , right output ground S 13  to the − input of right driver D 4  of headphones H 2 , and right output signal S 14  to the + input of driver D 4 .  
         [0032]      FIG. 3  is a block diagram of headphones H 3  and dedicated bridged stereo amplifier DA 2  of the present invention, in which DA 2  is driven by atypical audio source SS 3  that does not have common stereo ground outputs. Amplifier DA 2  introduces compensation for at least one coefficient of acoustic coupling matched to headphones H 3 . Audio source SS 3  provides left source ground S 17 , left source signal S 18 , right source ground S 19 , and right source signal S 20  to unconventional 4-conductor female audio connector F 3 . Unconventional 4-connector male audio connector M 3  couples to connector F 3  and provides left connector ground S 23 , left connector signal S 24 , right connector ground S 21 , and right connector signal S 22  to corresponding stereo inputs of amplifier DA 2 . Amplifier DA 2  provides left output ground S 27  to the − input of left driver D 5  of headphones H 3 , left output signal S 28  to the + input of driver D 5 , right output ground S 25  to the − input of right driver D 6  of headphones H 3 , and right output signal S 26  to the + input of D 5 .  
         [0033]      FIG. 4  is a block diagram of prior art earbuds E 1  driven by typical audio source SS 4 , in which earbuds E 1  do not include a dedicated or integrated amplifier. Audio source SS 4  provides source ground S 29 , source left signal S 30 , and source right signal S 31  to conventional 3-conductor female connector F 4 . Conventional 3-conductor male connector M 4  couples to connector F 4  and provides connector ground S 32  applied to the − inputs of left driver D 7  of E 1  and right driver D 8  of E 1  respectively, connector left signal S 33  to the +input of D 7 , and connector right signal S 34  to the + input of driver D 8 .  
         [0034]      FIG. 5  is a block diagram of earbuds E 2  and dedicated bridged stereo amplifier DA 3  according to an embodiment of the present invention, in which DA 3  is driven by typical audio source SS 5  and introduces compensation for at least one coefficient of acoustic coupling matched to earbuds E 2 . Audio source SS 5  provides source ground S 35 , left source signal S 36 , and right source signal S 37  to conventional 3-conductor female connector F 5 . Conventional 3-conductor male connector M 5  couples to connector F 5  and provides connector ground S 38 , and connector left and right signals S 39  and S 40  respectively to corresponding stereo inputs of amplifier DA 3 . DA 3  provides left output ground S 43  to the − input of left driver D 9  of earbuds E 2 , left output signal S 44  to the + input of driver D 9 , right output ground S 41  to the − input of right driver D 9  of earbuds E 2 , and right output signal S 42  to the + input of driver D 9 .  
         [0035]      FIG. 6  is a block diagram of earbuds E 3  and dedicated bridged stereo amplifier DA 4  according to an embodiment of the present invention, in which DA 4  is driven by atypical audio source SS 6  not comprising common stereo ground outputs, and introduces compensation for at least one coefficient of acoustic coupling matched to earbuds E 3 . Audio source SS 6  provides left source ground S 47 , left source signal S 48 , right source ground S 45 , and right source signal S 46  to unconventional 4-conductor audio female connector F 6 . Unconventional 4-connector male audio connector M 6  couples to connector F 6  and provides left connector ground S 51 , left connector signal S 52 , right connector ground S 49 , and right connector signal S 50  to corresponding stereo inputs of amplifier DA 4 . DA 4  provides left output ground S 55  to the − input of left driver D 11  of earbuds E 3 , left output signal S 56  to the + input of driver D 11 , right output ground S 53  to the − input of right driver D 12  of earbuds E 3 , and right output signal S 54  to the + input of driver D 12 .  
         [0036]      FIG. 7  is an illustration of earbud E 4  according to a preferred embodiment of the present invention. Earbud E 4  includes a magnetic assembly MA 1  having + and − input terminals, and which drives driver diaphragm DD 1 . Sounds produced by DD is coupled by collection chamber CC 1 , which collects sound produced by diaphragm DD 1 , to output port P 1 . The axial center c 1  of P 1  is asymmetrically aligned with the axial center c 2  of DD 1 , thereby comfortably displacing the earbud from the outer ear when inserted into the ear canal of a listener. P 1  is surrounded by annulus A 1  for comfortable fitting to the ear canal.  
         [0037]      FIG. 8  is a block diagram of dedicated bridged stereo amplifier DA 5  for use with one specific headphone or earbud design according to an embodiment of the present invention. Amplifier DA 5  includes left and right input signals Lin and Rin which are applied to acoustic compensation networks ACC 1  and ACC 2  respectively. The compensation networks ACC 1  and ACC 2  are calibrated to one specific headphone or earbud design. The outputs of ACC 1  and ACC 2  are applied to the inputs of left and right bridged amplifiers PA 1  and PA 2  respectively, which provide left and right + and − output signals to the left and right drivers of the intended headphone or earbud respectively. The left and right − output signals are independent and therefore do not constitute a common ground signal.  
         [0038]      FIG. 9  is a block diagram of dedicated bridged stereo amplifier DA 6  according to another embodiment of the present invention. Amplifier DA 6  is used with a selected one of at least two specific headphone or earbud designs, and includes left and right input signals Lin and Rin which are applied to acoustic compensation networks ACC 3  and ACC 4  respectively. The compensation networks ACC 3  and ACC 4  are calibrated to a selected specific headphone or earbud design by means of ganged switches (or controls) SW 1  and SW 2 , respectively. The outputs of ACC 3  and ACC 4  are applied to the inputs of left and right bridged amplifiers PA 3  and PA 4  respectively, which provide left and right + and − output signals to the left and right drivers of the intended headphone or earbud respectively, wherein the left and right − output signals are independent and therefore do not constitute a common ground signal.  
         [0039]     While there have been shown, described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions, substitutions and changes in the form and details of the methods described and devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed, described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.