Abstract:
Certain embodiments of the invention may be found in an insert earphone assembly. The insert earphone assembly may comprise a housing and a transducer located in the housing. The transducer may be for converting electrical signals received into sound energy. The insert earphone apparatus may further comprise an insert element. The insert element may be at, least partially integrated within the housing. The insert element may also comprise a main sound channel for communicating the sound energy from the transducer to a user. In certain embodiments, one or more of the body and the insert element may comprise one or more auxiliary ducts and one or more auxiliary volume spaces. The one or more auxiliary ducts and one or more auxiliary volume spaces may be separated by one or more auxiliary dampers. In certain embodiments, a diameter, length and/or shape of the one or more auxiliary ducts or one or more auxiliary volume spaces may be adjusted so as to modify an insertion response characteristic of the insert earphone assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE  
       [0001]     The present application claims priority under 35 U.S.C. §119(e) to provisional application Ser. No. 60/763,264, filed on Jan. 30, 2006, the entire contents of which are hereby expressly incorporated herein by reference. The present application claims priority under 35 U.S.C. §119(e) to provisional application Ser. No. 60/803,440, filed on May 30, 2006, the entire contents of which are hereby expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     Certain embodiments of the invention relate to sound processing devices. More specifically, certain embodiments of the invention relate to a method and system for insert earphone using a moving coil driver.  
       BACKGROUND OF THE INVENTION  
       [0003]     Use of insert earphones has risen considerably with the success of products like the Apple ipod. For the most part, the consumer&#39;s purchasing decision may be motivated by price-point more than by sound quality. The electro-acoustic transduction element traditionally used to create high-fidelity insert earphones is the device based upon the balanced-armature design. The complexity and subsequent high-manufacturing cost of this component is responsible for the high price-point of high-fidelity insert earphones.  
         [0004]     Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     An insert earphone assembly, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.  
         [0006]     Various advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.  
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0007]      FIG. 1  is an exemplary graph for estimating the average human ear response, which may be used in accordance with an embodiment of the invention.  
         [0008]      FIG. 2  illustrates exemplary graphs of responses at the eardrum of moving coil designs using methods described herein to achieve high accuracy frequency responses.  
         [0009]      FIG. 3  illustrates an exemplary graph of responses at the eardrum of concha mounted or partially/full sealing units currently on the market compared to the average human ear response as seen in  FIG. 1 .  
         [0010]      FIG. 4  illustrates an exemplary graph of responses at the eardrum of concha mounted or partially/full sealing units currently on the market compared to the average human ear response as seen in  FIG. 1 .  
         [0011]      FIG. 5A  is a diagram illustrating exemplary acoustic construction of a high accuracy moving coil design for an insert earphone assembly with a complete form factor designed to fit deeply into the ear canal of a user, in accordance with an embodiment of the invention.  
         [0012]      FIG. 5B  is a diagram illustrating exemplary acoustic construction of a high accuracy moving coil design for an insert earphone assembly with a complete form factor designed to fit deeply into the ear canal of a user, in accordance with an embodiment of the invention.  
         [0013]      FIG. 5C  is a diagram illustrating a portion of an insert earphone assembly using one or more acoustic resonant ducts, in accordance with an embodiment of the invention.  
         [0014]      FIG. 5D  illustrates exemplary graphs of frequency responses of an insert earphone assembly using one or more resonant ducts, in accordance with an embodiment of the invention.  
         [0015]      FIG. 5E  is a diagram illustrating a portion of an insert earphone assembly using one or more resonant ducts, in accordance with an embodiment of the invention.  
         [0016]      FIG. 5F  is a diagram illustrating a portion of an insert earphone assembly using one or more resonant ducts, in accordance with an embodiment of the invention.  
         [0017]      FIG. 5G  is a schematic diagram of an exemplary passive electrical filter, which may be utilized in connection with an embodiment of the present invention.  
         [0018]      FIG. 5H  is a schematic diagram of an exemplary electrical filter/bypass circuit for modifying bass response, which may be used in accordance with an embodiment of the invention.  
         [0019]      FIG. 5I  is a graph illustrating the effect of an exemplary high pass filter for shaping the response of an insert earphone, in accordance with an embodiment of the invention.  
         [0020]      FIG. 5J  is a graph illustrating the effect of an exemplary high pass filter for shaping the response of an insert earphone, in accordance with an embodiment of the invention.  
         [0021]      FIG. 6  is a graph that illustrates an exemplary response of an insert earphone with various levels of acoustic damping, in accordance with an embodiment of the invention.  
         [0022]      FIG. 7  is a graph that illustrates the effect on the frequency response when the sealed rear volume is varied, in accordance with an embodiment of the invention.  
         [0023]      FIG. 8A  is a graph that illustrates a varied acoustic notch filter and its effect on frequency response, in accordance with an embodiment of the invention.  
         [0024]      FIG. 8B  is a graph that illustrates changes in frequency response of an insert earphone utilizing an auxiliary diaphragm, in accordance with an embodiment of the invention.  
         [0025]      FIG. 9A  is a graph illustrating acoustic bass boost, in accordance with an embodiment of the invention.  
         [0026]      FIG. 9B  is a graph illustrating bass boost, in accordance with an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Certain embodiments of the invention may be found in a method and system for insert earphone using a moving coil driver. Driver designs based on the moving-coil structure are significantly less complicated and, therefore, less expensive. In accordance with an embodiment of the invention, an insert earphone may use a moving-coil driver to realize an insert earphone device with optimal sound quality and high isolation of external noise at a very affordable price-point.  
         [0028]      FIG. 1  is an exemplary graph for estimating the average human ear response, which may be used in accordance with an embodiment of the invention.  
         [0029]     Mead Killion, Elliott Berger and Robert Nuss have developed a composite curve to estimate the average human ear response, as illustrated in  FIG. 1 .  
         [0030]     Accuracy Score Defined. Accuracy score may be defined as a 25-band extension of a response accuracy rating system based upon the 1979 Consumers Union procedure applied to loudspeaker assessment. It employs Stevens Mark VI loudness values to weight the importance of defects or “compromises” in the frequency response. The Accuracy Score has been shown to correlate strongly to subjective (e.g. jury) assessments of signal (e.g. music) fidelity.  
         [0031]     In accordance with an embodiment of the invention, an insert earphone using a moving coil driver may be adapted to achieve a highest Accuracy Score of any moving coil design of 80% or higher. The highest accuracy score of moving coil designs in industry has been less than 70% accurate. This applies to either concha mounted “earbuds” or partial/canal sealing models.  
         [0032]      FIG. 2  illustrates exemplary graphs of responses at the eardrum of moving coil designs using methods described herein to achieve high accuracy frequency responses.  
         [0033]      FIG. 3  illustrates an exemplary graph of a response at the eardrum of a concha mounted or partially/full sealing unit currently on the market compared to the average human ear response as seen in  FIG. 1 .  
         [0034]      FIG. 4  illustrates an exemplary graph of a response at the eardrum of a concha mounted or partially/full sealing unit currently on the market compared to the average human ear response as seen in  FIG. 1 .  FIGS. 3 and 4  demonstrate the current state-of-the-art for earphone products that employ moving coil drivers.  
         [0035]     In accordance with an embodiment of the invention, methods of modifying insertion responses while obtaining external noise reduction may include, for example, the use of damping elements, auxiliary volumes, sound channels, and/or electronic components.  
         [0036]      FIG. 5A  is a diagram illustrating exemplary acoustic construction of a high accuracy moving coil design for an insert earphone assembly with a complete form factor designed to fit deeply into the ear canal of a user, in accordance with an embodiment of the invention. Referring to  FIG. 5A , the insert earphone  500 A may comprise a cap  502 A, a body  503 A, a moving coil driver  510 A, a diaphragm  512 A, an insert element  514 A, a plug. 520 A, and an eartip  518 A. In addition, the insert earphone  500 A may comprise damping elements  506 A,  524 A,  530 A,  534 A,  535 A,  538 A, and  544 A which may be used with sound channels  504 A,  522 A,  526 A,  532 A,  513 A,  536 A, and  542 A, respectively. The damping elements  506 A,  524 A,  530 A,  534 A,  535 A,  538 A, and  544 A may also be used in connection with auxiliary volumes  508 A,  528 A,  537 A, and  540 A, as well as with diaphragm  512 A. These acoustic combinations may also be aided by use of electronic components, such as the electronic filter illustrated in  FIG. 5C  and/or the electronic filter/bypass circuit illustrated in  FIG. 5D .  
         [0037]     The insert earphone  500 A, whose natural resonance may be at 4 kHz, may be tuned by these means so that a resonant peak may occur at or around 2.7 kHz, for example, which may be approximately 12 dB higher in level than measured at 500 Hz. The frequency response may then roll off at approximately 3 dB/octave. The insert earphone  500 A may be adapted for deep insertion in the ear canal of a user to achieve high levels of external noise reduction. Deep insertion of the earphone  500 A may be enabled by a slender form factor so that 20 dB or more of external noise isolation may be achieved by the earphone  500 A.  
         [0038]     Depending on the natural acoustic behavior of a the moving coil design of the insert earphone  500 A, the combination of response shaping, resonant peak shifting and/or smoothing may require any combination of damping values, sound channels, auxiliary volumes, auxiliary compliances and/or electronic filtering to shape the frequency response of the earphone  500 A. In this regard, the frequency response of the insert earphone  500 A may be varied by utilizing a different number of damping elements, sound channels, auxiliary ducts, resonant ducts, and/or auxiliary volumes. Furthermore, frequency response of the insert earphone  500 A may be varied by using one or more additional electronic components within the insert earphone, such as, for example, the components disclosed herein below with regard to  FIGS. 5C and 5D .  
         [0039]     In one embodiment of the invention, there may be two natural peaks close to the target peak frequency. In such instances, damping elements  524 A and/or  530 A may be used to reduce both peaks to a desired shape. If the peak closest to the target “damps out” before another un-desired peak, a change in one or more insert earphone components may be necessary. If an undesired peak is moved from 4 kHz down to 3 kHz, for example, the diameter of the front sound channel  522 A and/or the diameter of the sound channel  526 A may be reduced. In this regard, damping elements  524 A and/or  530 A may be used to smooth out the frequency response of the insert earphone  500 A.  
         [0040]     In another embodiment of the invention, the damping element  524 A may be mounted to a removable plug  520 A as a means of replacement in instances when the damping element  524 A becomes clogged with earwax or other contaminants. Damping element  530 A may also be attached to the insert element  514 A.  
         [0041]     In yet another embodiment of the invention, low-frequency bass response of the insert earphone  500 A may be increased by the use of a “modified Thuras tube” with regard to the sealed back auxiliary volume  540 A. In this regard, the size of the bass boost may be determined, for example, by the relative values of the diaphragm compliance and the volume of the auxiliary back volume  540 A. The frequency at which the bass boost begins may be determined by the resistance and inertance, or acoustic mass, of the connecting tube  542 A and/or  536 A, or the resistance of the damper  538 A and/or  544 A. The rate of rise of the low-frequency bass response may increase with the use of inertance. Such “modified Thuras tube” method of using a filter/bypass circuit within the insert earphone  500 A may be used to increase the low frequency sensitivity without changing the high-frequency sensitivity. In this regard, the insert earphone  500 A may be used as a means of bass compensation for devices such as MP3 players, for example, with output impedance that may be higher for low frequencies, thereby delivering less bass energy to the earphone as compared to devices with constant output impedance through the audio frequency band.  
         [0042]      FIG. 5B  is a diagram illustrating exemplary acoustic construction of a high accuracy moving coil design for an insert earphone assembly with a complete form factor designed to fit deeply into the ear canal of a user, in accordance with an embodiment of the invention. Referring to  FIG. 5B , the insert earphone  500 B is similar to the insert earphone  500 A of  FIG. 5A . However, the insert earphone  500 B comprises an integral body  502 B. In this regard, the insert element  514 A of insert earphone  500 A may be integrated with the body  503 A. Auxiliary volume  508 B and auxiliary damping element  510 B of insert earphone  500 B may correspond to auxiliary volume  528 A and auxiliary damping element  534 A, respectively, of insert earphone  500 A. Additionally, the auxiliary duct  506 B may be disposed within a removable plug  504 B, thereby making optional the use of the auxiliary duct  506 B and the auxiliary volume  508 B.  
         [0043]      FIG. 5C  is a diagram illustrating an insert earphone assembly using one or more acoustic resonant ducts, in accordance with an embodiment of the invention. Referring to  FIGS. 5A and 5C , in one embodiment of the invention, a resonant duct  502 C may be utilized by the insert earphone  500 A. In this regard, by utilizing the resonant duct  502 C, a deficiency in the response may be increased and excess energy in another frequency band may be simultaneously reduced. Therefore, by adding the resonant duct  502 C to the main sound channel  526 A, the frequency response of the insert earphone may be improved.  
         [0044]     The resonant duct  502 C may extend from the main sound channel  526 A and may be tuned to have, for example, a ¼ wave anti-resonance at 10 kHz. In this regard, the acoustic tube and the resulting anti-resonance effect may be utilized to decrease and/or prevent excess energy which may be present within the insert earphone  500 A. Furthermore, by utilizing the resonant duct  502 C in connection with the side cavity  528 A and the auxiliary damper  535 A may result in reduction of excessive energy at 10 kHz, as well as an increase of a deficiency in the frequency response from 4 kHz to 8 kHz. Consequently, the use of the resonant duct  502 C within the insert earphone  500 A may result in a smoother and accurate frequency response.  
         [0045]      FIG. 5D  illustrates exemplary graphs of frequency responses of an insert earphone assembly using one or more resonant ducts, in accordance with an embodiment of the invention. Referring to  FIG. 5D , graph  504 D may represent exemplary frequency response of the insert earphone  500 A using side cavity  528 A with the auxiliary damper  535 A and without additional acoustic volume, such as resonant duct  502 C. Graph  502 D may represent exemplary frequency response of the insert earphone  500 A using side cavity  528 A, auxiliary damper  535 A and the additional resonant duct  502 C for achieving an anti-resonance effect. In this regard, it may be noted from graphs  502 D and  504 D that a smoother downward slope of the frequency response may begin at about 2 kHz up to about 16 kHz, for example.  
         [0046]      FIG. 5E  is a diagram illustrating an insert earphone assembly using one or more resonant ducts, in accordance with an embodiment of the invention. Referring to  FIG. 5E , there is illustrated the insert element  514 A which is a part of the insert earphone assembly  500 A of  FIG. 5A . In one embodiment of the invention, the insert element  514 A may comprise a resonant duct (RD)  502 E. The RD  502 E may comprise the resonant duct  502 C of  FIG. 5C , and may comprise one or more interconnected volume portions of varying lengths. Furthermore, the RD  502 E may extend from the main sound channel  526 A and may be tuned to have, for example, a ¼ wave anti-resonance at about 10 kHz, as explained herein above with regard to the resonant duct  502 C.  
         [0047]      FIG. 5F  is a diagram illustrating a portion of an insert earphone assembly using one or more resonant ducts, in accordance with an embodiment of the invention. Referring to  FIG. 5F , there is illustrated a diagram of the RD  502 E. In one embodiment of the invention, the RD  502 E may comprise four interconnected volume portions  502 F, . . . ,  508 F. Each of the interconnecting volume portions  502 F, . . . ,  508 F may be of varying length, diameter and/or shape. In addition, the volume portions pairs  508 F- 506 F,  506 F- 504 F, and  504 F- 502 F may be connected at varying angles, resulting in the RD  502 E.  
         [0048]      FIG. 5G  is a schematic diagram of an exemplary passive electrical filter, which may be utilized in connection with an embodiment of the present invention. Referring to  FIG. 5G , the passive electrical filter may comprise resistors  502   c,    508   c,  and  510   c,  capacitors  504   c  and  512   c.  Inductor  506   c  may be functionally equivalent and may indicate a moving coil driver. The passive electrical filter may be used in connection with an insert earphone, such as the insert earphone  500 A of  FIG. 5A , to vary the frequency response of the insert earphone. In one embodiment of the invention, the electrical filter may be implemented within the insert earphone  500 A and filtering may be triggered automatically or upon an input from a user of the insert earphone  500 A. Even though one implementation of a passive electrical filter is disclosed in  FIG. 5G , the present invention may not be so limited and other filter implementations may also be used in connection with an insert earphone such as the insert earphone  500 A in  FIG. 5A .  
         [0049]      FIG. 5H  is a schematic diagram of an exemplary electrical filter/bypass circuit  606  for modifying bass response, which may be used in accordance with an embodiment of the invention. Referring to  FIG. 5H , the filter circuit  606  may comprise a resistor R 1 , a capacitor C 1  and a switch SW 1 . In one embodiment of the invention, the filter circuit  606  may comprise a high-pass filter. Furthermore, the filter circuit  606  may be coupled to a moving coil driver, such as the moving coil driver  510 A in  FIG. 5A . The electrical filter circuit  606  may be used within an insert earphone, such as the insert earphone  500 A in  FIG. 5A , to select between a flat bass response, represented by graph  604 , and a boosted bass response, represented by graph  602 .  
         [0050]     A boosted bass response  602  may be obtained when the R 1 -C 1  filter circuit is bypassed when the switch SW 1  is switched to the Low Frequency Boost (LFB) position. The flat bass response  604  may be obtained within the insert earphone  500 A when the switch SW 1  is switched to the “flat” position. Resistance and capacitance R 1  and C 1  may be selected to correspond to the impedance of the moving coil driver  510 A, for example.  
         [0051]     In one embodiment of the invention, the electrical filter/bypass circuit  606  may be implemented within the insert earphone  500 A and filtering may be triggered automatically or upon an input from a user of the insert earphone  500 A and a corresponding change in the position of switch SW 1 . Even though one implementation of the electrical filter circuit  606  is disclosed in  FIG. 5H , the present invention may not be so limited and other filter implementations may also be used in connection with an insert earphone such as the insert earphone  500 A in  FIG. 5A . By using the electrical filter/bypass circuit  606  within the insert earphone  500 A, a bass boost may be provided with fixed high-frequency gain without using a shunt capacitor. Bass boost may be achieved by, for example, utilizing a “modified Thuras tube” method, as described herein.  
         [0052]      FIG. 5I  is a graph illustrating the effect of an exemplary high pass filter for shaping the response of an insert earphone, in accordance with an embodiment of the invention. Referring to  FIGS. 5G and 5I , the graph of  FIG. 5I  demonstrates the effect of a high pass filter where a source may be connected through a resistor  510   c  parallel with a capacitor  504   c,  in series with a driver  506   c  to ground. The value of the resistance  510   c  may determine the sensitivity of the insert earphone  500 A for low frequencies. The low frequency impedance, Xc, of capacitor  504   c  may be high and thus resistor  510   c  may dominate and the current flow may remain low to the driver. At high frequencies, however, Xc of capacitor  504   c  may become low and may pass more current to the driver  506   c,  thereby resulting in higher output.  
         [0053]      FIG. 5J  is a graph illustrating the effect of an exemplary high pass filter for shaping the response of an insert earphone, in accordance with an embodiment of the invention. Referring to  FIGS. 5G and 5J , the graph of  FIG. 5J  illustrates another example of a high pass filter where capacitor  504   c  may remain and resistance  510   c  may be varied. In this regard, the low-pass filter in  FIG. 5G  may be tuned to apply a first order high frequency response roll-off where desired.  
         [0054]      FIG. 6  is a graph that illustrates an exemplary response of an insert earphone with various levels of damping, in accordance with an embodiment of the invention.  
         [0055]     Depending on the natural behavior of a given moving coil design, the combination of resonant peak shifting and/or smoothing may require any range of damping values. If, for example, there are two natural peaks close to the target peak frequency, damping may be used to reduce both peaks to the correct shape. However, if the peak closest to the target happens to “damp out” before another un-desired peak, a change in front plumbing may be necessary. If an undesired peak is moved from 4 kHz, for example, down to 3 kHz, for example, a reduction in front plumbing diameter may be necessary. In this regard, peak movement and/or damping may smooth out the response.  
         [0056]     Many moving coil drivers can produce extremely high sound pressure levels relative to their placement in the ear. In reference to the insert earphone  500 A, a reduced amount of power may be required to develop acceptable level of sound pressure at the eardrum while maintaining desired sound quality. In one embodiment of the invention, the low frequency of a moving coil driver may be tuned by changing internal capacitance or rear volume ( 540 A and/or  508 A). The size of the rear volume may depend on sensitivity and/or accuracy requirements. A smaller volume may reduce the low-mid frequency response sensitivity. However, the frequency response sensitivity of the earphone  500 A may be regained by electro-acoustic transfer efficiency realized with sealed insert earphone designs of the earphone  500 A.  
         [0057]      FIG. 7  is a graph that illustrates the effect on the frequency response when the sealed rear volume, such as the sealed rear volume  540 A and/or  508 A in  FIG. 5A , is varied, in accordance with an embodiment of the invention. Referring to  FIGS. 5A and 7 , auxiliary volume  540 A may be varied in connection with the auxiliary duct  542 A, auxiliary damping element  544 A, and auxiliary volume  508 A.  
         [0058]     In accordance with an embodiment of the invention, the speaker&#39;s internal capacitance may be reduced by encapsulating the volume of air around the back of the speaker similar to standard enclosed loudspeakers, which may be required for achieving external noise reduction. The size of this rear volume may depend on sensitivity and accuracy requirements. In this regard,  FIG. 7  demonstrates the effect on the frequency response when the sealed rear volume(s)  540 A,  508 A are varied. In some instances, auxiliary volume  540 A may be the only volume required in which case auxiliary duct  542 A may be blocked and auxiliary damping element  544 A may not be used.  
         [0059]     In some instances, resonant peaks may be present, resulting in detraction from the listening experience. In one embodiment of the invention, the resonant peaks may be smoothed out by tuning of the front port  522 A,  526 A and/or by application of acoustic resistance  524 A,  530 A. In some instances it may be necessary to augment such remedial methods by incorporation of one or more series of inertance  532 A resistance  534 A tanks terminated by an acoustic capacitance  528 A in the front acoustic path of the earphone  500 A. Such structure may create a notch filter aimed at reducing the intensity of the undesired spectral energy.  
         [0060]      FIG. 8A  is a graph that illustrates a varied notch filter and its effect on frequency response, in accordance with an embodiment of the invention. An alternate path or additional path to auxiliary volume  528 A from  532 A,  534 A is via auxiliary duct  513 A and auxiliary damping element  535 A. Referring to  FIGS. 5A and 8A , a notch filter effect may be achieved with acoustic components in combination to reduce the level in a specific frequency band. For example, the main sound channel  526 A and/or front speaker volume  535 A may be varied. In addition, the auxiliary duct  513 A and/or  532 A leading to auxiliary volume  528 A, may also be varied. Sound channel  526 A and auxiliary duct  513 A may comprise any geometric shape that results in the desired frequency response. The depth or “Q” of the notch filter may be limited by adding auxiliary damping elements  534 A and/or  535 A. Such notch filter combinations may be duplicated with different values and sizes to reduce energy in multiple spectral ranges.  
         [0061]      FIG. 8B  is a graph that illustrates changes in frequency response of an insert earphone utilizing an auxiliary diaphragm, in accordance with an embodiment of the invention.  
         [0062]     Undesired peaks in the response may also be reduced by use of one or more auxiliary diaphragms ( 512 A). In order to realize cancellation, the diaphragm(s) must have characteristic impedances that are tuned to change phase relative to the driver diaphragm, within the frequency band of interest. The unchanged response (AH- 13 C) may be compared to a response incorporating an auxiliary diaphragm (AH- 13 D).  
         [0063]     With one or more auxiliary diaphragms in place, an additional advantage may be realized within the insert earphone  500 A. Resonant peaks may be directly shifted closer to a target range that may not have been otherwise attainable. Notch filters as described herein above may also be used to enhance the effect of auxiliary diaphragms.  
         [0064]      FIG. 9A  is a graph illustrating acoustic bass boost, in accordance with an embodiment of the invention.  
         [0065]      FIG. 9B  is a graph illustrating bass boost, in accordance with an embodiment of the invention.  
         [0066]     In accordance with an embodiment of the invention, small scale speakers may be tuned to have an optional sub-frequency resonance by venting the rear volume through a highly inductive and resistive vent. In this regard, the correct band of sub frequencies may be increased.  
         [0067]     For example, a boost in a speaker may be tuned to create a mild boost ( FIG. 9A ) to correct a shortage of low frequencies typically occurring in a “bass adjusted system” so as to improve overall response accuracy. An additional increase in low frequency sensitivity above the reference may serve an application that requires/desires more bass response (refer to  FIG. 9B ). Such response adjustments may lower the accuracy score. A boost in a speaker may be tuned and a mild boost, such as illustrated in  FIG. 9A , may not adversely effect the overall accuracy.  
         [0068]     A method to tune these; small scale speakers to have an optional sub-frequency resonance can be accomplished when rear speaker auxiliary duct  536 A, vents either through auxiliary damping element  538 A or directly into auxiliary volume  540 A, which may be blocked at auxiliary duct  542 A. If a larger rear volume is required, any combination of auxiliary damping elements  538 A,  544 A, and/or  506 A may be used in conjunction with auxiliary ducts  536 A,  542 A, and/or  504 A that vent into either or both auxiliary volumes  540 A and  508 A.  
         [0069]     In this regard, the correct band of sub frequencies may be increased. For example, a speaker may be tuned to create a mild boost to correct a shortage of low frequencies typically occurring in a “bass adjusted system”. An additional increase in low frequency sensitivity may serve an application that requires/desires more bass response (refer to  FIG. 9A ).  FIG. 9B  demonstrates an extreme adjustment to the bass frequencies. The resulting sound quality may be characterized as “tubby” or undesirable.  
         [0070]     Accordingly, aspects of the invention may be realized in hardware, software, firmware or a combination thereof. The invention may be realized in a centralized fashion in at least one computer system or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware, software and firmware may be a general-purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.  
         [0071]     The present invention may also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context may mean, for example, any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form. However, other meanings of computer program within the understanding of those skilled in the art are also contemplated by the present invention.  
         [0072]     While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.