Abstract:
An audio speaker ( 10 ) including an electrical circuit that is interconnected within the speaker circuitry within the speaker enclosure ( 14 ) to selectively alter the resistance of the speaker ( 10 ), such as from 4 ohms to 8 ohms. It therefore allows the owner to use the speaker as a replacement speaker for both 4 ohm and 8 ohm amplifiers. It also allows the owner to engage additional speakers to an amplifier ( 58 ) without causing damage to the amplifier ( 58 ). In a preferred embodiment, the speaker includes two drivers ( 18/22 ) that are electrically engaged in parallel in the speaker circuit, wherein a plurality of capacitors ( 44 ) are engaged in parallel within the speaker circuit, and an electrical switch is engaged to selectively shunt electrical current around said plurality of capacitors ( 44 ) to alter the resistance of the speaker.

Description:
CROSS-REFERENCED TO RELATED APPLICATION  
       [0001]     This application claims priority to U.S. Provisional Patent Application Ser. No. 60/536,753, filed Jan. 13, 2004, entitled: Audio Speaker Impedance Matching Circuit. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to audio speakers and speaker circuits, and more particularly to such speaker circuits having a user operable impedance altering circuit therewithin.  
         [0004]     2. Description of the Prior Art  
         [0005]     In audio systems including an amplifier and a plurality of speakers, the amplifier output circuit is typically designed to be connected to speaker systems having a resistance such as 8 ohms or 4 ohms, and the speakers are therefore designed to have a matching resistance such as 8 ohms or 4 ohms. The owners of such audio systems often have a desire to change speakers and/or to add more speakers onto the amplifier in order to obtain an improved sound quality.  
         [0006]     When changing speakers for an existing amplifier, the replacement speakers must have the same resistance as the prior speakers to match the amplifier output circuit.  
         [0007]     The process of adding additional speakers to an existing system is typically attempted by adding a new speaker in parallel with the existing speaker. However, as is well known, the total resistance of the two speakers in parallel will be less than, typically approximately half of, the resistance of one of the speakers. That is, two 8 ohm speakers when connected in parallel will have a total resistance of approximately 4 ohms. Where a cumulative resistance of 4 ohms from the two parallel speakers is engaged to the 8 ohm speaker output of an amplifier it can cause overheating and damage to the amplifier output circuit.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is a speaker including an electrical circuit that is interconnected within the speaker circuitry within the speaker enclosure to selectively alter the resistance of the speaker, such as from 4 ohms to 8 ohms. It therefore allows the owner to use the speaker as a replacement speaker for both 4 ohm and 8 ohm amplifiers. It also allows the owner to engage additional speakers to an amplifier without causing damage to the amplifier. In a preferred embodiment, the speaker includes two drivers that are electrically engaged in parallel in the speaker circuit, wherein a plurality of capacitors are engaged in parallel within the speaker circuit and an electrical switch is engaged to selectively shunt electrical current around said plurality of capacitors to alter the resistance of the speaker.  
         [0009]     It is an advantage of the audio speaker impedance matching circuit of the present invention that it provides a speaker with user selectable resistance.  
         [0010]     It is another advantage of the audio speaker impedance matching circuit of the present invention that it provides speakers with a plurality of drivers therewithin, and a user selectable resistance of the speaker.  
         [0011]     It is a further advantage of the audio speaker impedance matching circuit of the present invention that it includes a speaker with two drivers and an electrical circuit that includes a user operable switch for altering the resistance of the speaker driver circuit.  
         [0012]     It is yet another advantage of the audio speaker impedance matching circuit of the present invention that it provides a speaker with user selectable resistance, such that additional speakers may be added to an amplifier circuit without overloading the amplifier.  
         [0013]     These and other features and advantages of the present invention will no doubt become apparent to those skilled in the art upon reading the following detailed description which makes reference to the several figures of the drawing. 
     
    
     IN THE DRAWINGS  
       [0014]     The following drawings are not made to scale as an actual device, and are provided for illustration of the invention described herein.  
         [0015]      FIG. 1  is a schematic diagram of a speaker including two drivers and the impedance matching circuit of the present invention.  
         [0016]      FIG. 2  is a schematic diagram of an amplifier with two speakers engaged in a parallel circuit configuration. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     As depicted in  FIG. 1 , a speaker  10  includes a speaker enclosure  14  having two drivers  18  and  22  disposed within the enclosure  14 . An audio signal input jack  26  at the rear of the speaker enclosure includes a positive lead  30  and a negative lead  34 . Driver  18  is directly connected to the two leads  30  and  34 . Driver  22  is connected in parallel with driver  18 . Significantly, the impedance matching circuit  40  of the present invention is connected to one of the two leads to driver  22 ; in this instance it is connected to the negative lead  34  connection to driver  22 .  
         [0018]     The impedance matching circuit  40 , as shown in  FIG. 1 , includes a plurality of capacitors  44 , preferably electrolytic capacitors, that are engaged in parallel. A bypass switch  48  is engaged across the capacitors, and in the preferred embodiment, the bypass switch  48  will be located at the rear exterior of the speaker enclosure for access by the user of the speaker.  
         [0019]     An example of the use of the present invention is as follows. Initially, assume that each of the drivers  18  and  22  is an 8 ohm driver, and assume that the bypass switch  48  is closed, such that the capacitors  44  are bypassed and essentially not part of the electrical circuitry. The total resistance of the speaker  10  with its two 8 ohm drivers connected in parallel will be 4 ohms. This speaker  10  is designed to be connected to an amplifier having a 4 ohm audio output for connection with a speaker. Significantly, the speaker  10  is designed to also be connected to an amplifier having an 8 ohm audio output for connection with a speaker. Specifically, where the bypass switch  48  is opened, the DC resistance of the second driver  22  is greatly increased because the capacitors now act as an open circuit in the lead to driver  22 . Therefore, when the bypass switch  48  is open, the DC resistance at the speaker input  26  is only the resistance of the first driver  18 , which is 8 ohms, and it can be connected to an 8 ohm amplifier speaker outlet.  
         [0020]     By way of a further example, if the two drivers  18  and  22  have a 16 ohms resistance, the impedance matching circuit  40  would give the user a choice of an 8 ohm speaker resistance when the bypass switch is closed or a 16 ohm resistance when the bypass switch is open.  
         [0021]     The speaker  10  is also suitable for engagement as an additional speaker in a parallel circuit configuration. Specifically, with reference to  FIG. 2 , assume that the user of the audio system desires to engage a second speaker  50  that is identical to speaker  10  to an amplifier  58  using the amplifier&#39;s 4 ohm speaker outlet. The user accomplishes this by attaching the second speaker  50  in parallel with the first speaker  10  to the amplifier  58  as is depicted in  FIG. 2 . Where prior art speakers that lack the impedance matching circuit of the present invention are engaged as depicted in  FIG. 2 , the parallel connection of the two 4 ohm speakers will create a total speaker impedance to the amplifier of approximately 2 ohms, which input impedance is so low as to probably damage the amplifier. However, where the two speakers  10  and  50  that are connected in parallel include the impedance matching circuit  40  of the present invention, the overall impedance of the speaker circuit can be properly modified.  
         [0022]     Specifically, returning to  FIG. 1 , where the bypass switch  48  is opened, the DC resistance of the second driver  22  is greatly increased because the capacitors now act as an open circuit in the lead to driver  22 , and the DC resistance at the speaker input  26  is only the resistance of the first driver  18 , which is 8 ohms. Thus, by opening the bypass switch  48 , the impedance of the speaker  10  is altered from 4 ohms to 8 ohms. Therefore, returning to  FIG. 2 , where each of the speakers  10  and  50  includes the impedance matching circuit  40  of the present invention, the bypass switch  48  of each speaker  10  and  50  is opened, such that the DC resistance of each speaker becomes 8 ohms, and the total resistance of the two 8 ohm speakers  10  and  50  engaged in parallel becomes 4 ohms, which matches the impedance of the speaker outlet of the amplifier  58 . Thus the use of the impedance matching circuit  40  of the present invention allows the user to engage additional speakers in parallel without the threat of damage to the amplifier.  
         [0023]     By way of a further example, when the two speakers  10  and  50  include  16  ohm drivers, the total resistance of the two speakers  10  and  50  in parallel will be 4 ohms when the bypass switch of each circuit  40  of each speaker  10  and  50  is closed, and the total resistance of the two speakers  10  and  50  in parallel will be 8 ohms when the bypass switch of the circuit  40  of each speaker  10  and  50  is open.  
         [0024]     Returning to  FIG. 1 , it is seen that the impedance matching circuit  40  of the present invention includes 6 capacitors  44 . However, the present invention is not to be so limited, and may include an impedance matching circuit having one, two, three, four, five, six or more capacitors. However, an impedance matching circuit having a plurality of capacitors, such as 6, is preferred over an impedance matching circuit having one or even two capacitors. This is because the capacitance of the impedance matching circuit is desirably chosen to be large enough that the impedance circuit does not act as a high pass filter circuit. That is, it is desired that all of the amplifier&#39;s audio signal, even down to as low as 2 Hz, be transmitted to the driver  22 . To accomplish this, a total capacitance of approximately 1,200 microfarads is desired for the impedance matching circuit for an 8 ohm driver. A single capacitor having a 1,200 microfarad capacitance will generally be quite large, whereas a plurality of capacitors (as shown), connected in parallel is considerably smaller and is easily mounted upon a printed circuit board for installation within the speaker cabinet  14 . A second reason for the utilization of a plurality of capacitors  44  is that each capacitor will generally have a certain resistance, termed its equivalent series resistance. It is desirable to minimize this resistance as it will affect the quality of sound from the driver  22 . Where a plurality of capacitors, each having an equivalent series resistance is connected in parallel (as shown in  FIG. 1 ), the overall total resistance of the circuit is reduced to insignificance. In the preferred embodiment, 6 capacitors are engaged in parallel with an 8 ohm driver, as shown, where each capacitor has a capacitance of approximately 220 microfarads, where each capacitor is an electrolytic capacitor that is rated at 150 volts. If the driver were a 4 ohm driver then the six capacitors would preferably be approximately 440 microfarads each, and if the driver were a 16 ohm driver the six capacitors would be approximately 110 microfarads each.  
         [0025]     The capacitance in this circuit is set so high that it will pass all audio frequencies of interest. It is not designed to block any audio signals such that the driver  22  receives the full range of signal from the amplifier. The capacitance is selected to pass all frequencies above a low point which is set at approximately 2 Hz, such that all of the audio sound above 2 Hz is passed to the driver  22 . Additionally, the audio feed to the first driver  18  is not affected because it does not have the impedance matching circuit in it, so the first driver receives the full audio signal from the amplifier.  
         [0026]     While the present invention has been shown and described with regard to certain preferred embodiments, it is to be understood that modifications in form and detail will no doubt be developed by those skilled in the art upon reviewing this disclosure. It is therefore intended that the following claims cover all such alterations and modifications that nevertheless include the true spirit and scope of the inventive features of the present invention.