High back EMF, high pressure subwoofer having small volume cabinet, low frequency cutoff and pressure resistant surround

Abstract

A subwoofer cabinet having a volume less that 1 ft 3 axially aligned openings in opposed cabinet walls; first and second cages mounted on respective ones of the walls in alignment with the openings; a voice coil driven driver including an annular 225 oz. magnet affixed to the first cage; a stationary pole piece extending through the magnet and defining a magnetic gap therebetween; a voice coil mounted on a cylindrical voice coil former positioned within the gap; a cone affixed to one end of the former; a first flexible surround secured to the outer end of the cone and attached at its periphery to the first cage; a flexible spider secured to the former and at its outer periphery to the first cage; a mass driven driver including a 1.7 lb. mass; a second flexible surround secured to the mass and to the second cage; a flexible spider attached to the second cage and to the mass; both surrounds having a uniform thickness of at least 0.1″, an edgeroll having a diameter of at least 1.5″, and capable of standing off internal pressures of 1.5 lbs./in 2 to 3 lbs./in 2 ; a drive amplifier capable of delivering 2,700 watts to a nominal 4 ohm resistive load and swinging 104 volts for delivering (+)-v and (−)-v drive signals to the voice coil for driving the voice coil driven driver through a peak-to-peak stroke of about 2.5″ while generating a large back emf sufficient to counter the applied emf and minimize current flow in the voice coil.

1 . A high pressure, high back emf, small volume subwoofer for processing an input audio signal and comprising, in combination: 
 a) a cabinet having front, rear, left, right, top and bottom walls defining a sealed box enclosing a volume of space of less than 1 ft 3  with coaxial openings formed in said left and right walls;    b) first and second basket-like frames mounted within said cabinet coaxial with said openings on respective different ones of said left and right walls;    c) a mass weighing approximately 2 lbs.;    d) a first circular flexible surround secured at its midpoint to said mass and having its outer periphery secured to said first basket-like frame at said frame's junction with one of said left and right walls;    e) a speaker cone having a large diameter outer end and a small diameter inner end;    f) a second circular flexible surround secured to said large diameter end of said speaker cone and extending radially outward from the periphery thereof with the outer peripheral edge of said second surround being secured to said second basket-like frame at said frame's junction with the other of said left and right walls;    g) means defining an annular magnet weighing approximately 225 oz. fixedly mounted within said cabinet;    h) a cylindrical pole piece fixedly mounted within said cabinet, said pole piece extending through said annular magnet and being spaced therefrom with said space defining an annular magnetic gap;    i) a cylindrical voice coil former having an inside diameter slightly greater than the outside diameter of said cylindrical pole piece and extending into said magnetic gap, the outboard end of said cylindrical voice coil former being affixed to said small diameter end of said speaker cone;    j) a voice coil wound about said voice coil former and positioned thereon so as to be located within said annular magnetic gap in spaced relation to said magnet;    k) said first and second flexible circular surrounds each having a uniform thickness at least equal to 0.1″ and an edgeroll having a diameter of at least 1.5″ with said edgeroll on said first surround located outboard of said mass and inboard of the outer peripheral edge of said first basket-like frame, and said edgeroll on said second surround located outboard of said large diameter end of said speaker cone and inboard of the outer peripheral end of said second basket-like frame, said first and second flexible surrounds having sufficient strength and rigidity to stand off internal box pressure within said cabinet in the range of from about 1.5 lbs./in 2  to about 3 lbs./in 2 ;    l) a first annular flexible spider secured at its outer periphery to said first basket-like frame and at its inner periphery to said mass;    m) a second annular flexible spider secured at its outer periphery to said second basket-like frame and at its inner periphery to said voice coil former;    n) said first surround and said first spider defining the sole suspension means within said cabinet for said mass, and said second surround and said second spider defining the sole suspension means within said cabinet for said voice coil former, voice coil and speaker cone, and being capable of accommodating peak-to-peak coaxial strokes of about 2.5″ for each of: i) said mass; and ii), said voice coil former, voice coil and speaker cone, without significant wobble;    o) a tracking downconvertor drive amplifier mounted in said cabinet for generating (+)-v and (−)-v audio output signals and alternately delivering said signals to said voice coil, said amplifier characterized by its ability to deliver 2,700 watts rms and to swing 104 volts rms;    p) said tracking downconvertor drive amplifier including: i) a (+) Tracking Downconvertor Power Supply for generating (+)-v audio signals; ii) a (−) Tracking Downconvertor Power Supply for generating (−)-v audio signals; and iii), a Driver Amplifier coupled to the outputs of said (+) and (−) Tracking Downconvertor Power Supplies for receipt of said (+)-v and (−)-v audio signals and for delivering said signals alternately to said voice coil for establishing an alternating magnetic flux field thereabout;    q) means including tinsel leads for coupling said voice coil to said Driver Amplifier;    r) means for maintaining said tinsel leads under tension during reciprocation of said voice coil driven driver through its peak-to-peak stroke of about 2.5″;    s) means for inputting the left and right channels of audio signal information to be processed to said subwoofer cabinet and for summing the left and right channel audio signal information at different acoustic dB levels so as to produce one of two composite audio signals (L+R)+α(L−R) and α(L+R)+(L−R) where the (L−R) component of the input audio signal representing the stereo sound field is retained;    t) means for feeding said composite audio signal in parallel to first and second signal processing channels wherein said first signal processing channel includes first and second inverting amplifier means spaced apart by a first opto-coupler and said second signal processing channel includes first and second unity gain buffers spaced apart by a second opto-coupler;    u) means for summing the twice inverted audio signals output from said second inverting amplifier means in said first signal processing channel with said audio signal output from said second unity gain buffer in said second signal processing channel to produce a composite audio output signal to be processed and wherein said first and second opto-couplers provide breaks which prevent any continuous ground loop between input and output grounds; and, any hum signal generated at said first opto-coupler is inverted by said second inverting amplifier means in said first signal processing channel and summed with any hum signal generated at said second opto-coupler and output from said second unity gain buffer in said second signal processing channel so as to cancel and effectively eliminate any ground loop induced 60 Hz hum signal;    v) a Diode Steering Network for separating the composite audio signal output from said first and second signal processing channels into its positive-going and negative-going portions and for steering: i) said positive-going portions of said audio signal to said (+) Tracking Downconvertor Power Supply; ii) said negative-going portions of said audio signal to said (−) Tracking Downconvertor Power Supply; and iii), both said positive-going and said negative-going portions of said composite audio signal to said Driver Amplifier for enabling said Driver Amplifier to alternately deliver said (+)-v and (−)-v signals input from said (+) and (−) Tracking Downconvertor Power Supplies to said voice coil; whereby said voice coil former is axially reciprocated within said magnetic gap through a peak-to-peak stroke of about 2.5″ as a result of interaction between the first magnetic flux field generated by said magnet and the second magnetic flux field generated by said voice coil with said voice coil therefore cutting many lines of flux within said interacting magnetic flux fields and thereby generating a large back emf which acts in opposition to the emf applied to said voice coil by said tracking downconvertor drive amplifier and, thereby preventing the flow of damaging stall mode currents in said voice coil and minimizing heat dissipation requirements; and, wherein the force applied to said voice coil driven subwoofer given by Bli is equal and opposite to the force applied to said mass driven subwoofer Mdv/dt, the air contained within said cabinet is alternately: i) pressurized to pressures in the range of from about 1.5 lbs./in 2  to about 3 lbs./in 2 ; and ii), rarefied, during inward and outward movement respectively of said voice coil, voice coil former and speaker cone so that said mass driven subwoofer and said voice coil driven subwoofer simultaneously move outward and simultaneously move inward with PUSH/PULL strokes of about 2.5″ and at a frequency determined by the acoustic signal being processed through said tracking downconvertor drive amplifier.    
     
     
         2 . A voice coil driven woofer comprising, in combination: 
 a) a cabinet having front, rear, left, right, top and bottom walls defining a sealed box enclosing a volume of space of less than 1 ft 3  with an opening formed in one of said walls;    b) a basket-like frame mounted within said cabinet on said one wall coaxial with said opening;    c) a speaker cone having a large diameter outer end and a small diameter inner end;    d) a flexible surround secured to said large diameter end of said speaker cone and extending radially outward from the periphery thereof with the outer peripheral edge of said surround being secured to said basket-like frame at said frame's juncture with said wall;    e) means defining an annular magnet weighing approximately 225 oz. fixedly mounted within said cabinet;    f) a cylindrical pole piece fixedly mounted within said cabinet, said pole piece extending through said annular magnet and being spaced therefrom with said space defining an annular magnetic gap;    g) a cylindrical voice coil former having an inside diameter slightly greater than the outside diameter of said pole piece extending into said magnetic gap, the outer end of said cylindrical voice coil former being affixed to said small diameter end of said speaker cone;    h) a voice coil wound about said voice coil former and positioned thereon so as to be located within said annular magnetic gap in spaced relation to said magnet;    i) said flexible circular surround having a uniform thickness at least equal to 0.1″ and an edgeroll having a diameter of at least 1.5″ with said edgeroll located outboard of said large diameter end of said speaker cone and inboard of the outer peripheral end of said basket-like frame, said surround having sufficient strength and rigidity to stand off internal box pressures within said cabinet in the range of from about 1.5 lbs./in 2  to about 3 lbs./in 2 ;    j) an annular flexible spider secured at its outer periphery to said basket-like frame and at its inner periphery to said voice coil former;    k) said surround and said spider defining the sole suspension means within said cabinet for said voice coil former, voice coil and speaker cone and being capable of accommodating peak-to-peak strokes of about 2.5″ for said voice coil former, voice coil and speaker cone without significant wobble;    1) a tracking downconvertor drive amplifier mounted in said cabinet for generating (+)-v and (−)-v audio output signals and alternately delivering said signals to said voice coil, said amplifier characterized by its ability to deliver 2,700 watts rms and to swing 104 volts rms;    m) said tracking downconvertor drive amplifier including: i) a (+) Tracking Downconvertor Power Supply for generating (+)-v audio signals; ii) a (−) Tracking Downconvertor Power Supply for generating (−)-v audio signals; and iii), a Driver Amplifier coupled to the outputs of said (+) and (−) Tracking Downconvertor Power Supplies for receipt of said (+)-v and (−)-v audio signals and for delivering said signals alternately to said voice coil for establishing an alternating magnetic flux field thereabout;    n) means for inputting a composite audio signal to be processed to said subwoofer;    o) a Diode Steering Network for separating the composite audio signal input to said subwoofer into its positive-going and negative-going portions and for steering: i) said positive-going portions of said audio signal to said (+) Tracking Downconvertor Power Supply; ii) said negativegoing portions of said audio signal to said (−) Tracking Downconvertor Power Supply; and iii), both said positive-going and said negative-going portions of said composite audio signal to said Driver Amplifier for enabling said Driver Amplifier to alternately deliver said (+)-v and (−)-v audio signals input from said (+) and (−) Tracking Downconvertor Power Supplies to said voice coil;    whereby said voice coil former is axially reciprocated within said magnetic gap through a peak-to-peak stroke of about 2.5″ as a result of interaction between the magnetic flux field generated by said magnet and the magnetic flux field generated by said voice coil with said voice coil therefore cutting many lines of flux within said interacting magnetic flux fields and thereby generating a large back emf which acts in opposition to the emf applied to said voice coil by said tracking downconvertor drive amplifier so as to prevent flow of damaging stall mode current in said voice coil and thereby minimize heat dissipation requirements; wherein the air contained within said cabinet is pressurized to pressures in the range of from 1.5 lbs./in 2  to about 3 lbs./in 2  and alternately rarefied so that said voice coil former, voice coil and speaker cone move outwardly and inwardly with PUSH/PULL strokes of about 2.5″ and at a frequency determined by the acoustic signal being processed through said tracking downconvertor drive amplifier.    
     
     
         3 . A resilient suspension system for supporting movable driver components within stationary driver components in a driven driver mounted in a subwoofer cabinet, said resilient suspension system comprising, in combination: 
 a) an annular flexible spider adapted to be coupled at its inner periphery to the movable components of said driver and at its outer periphery to the stationary components of said driver; and,    b) a circular surround formed of compressible surround foam, said circular surround having an edgeroll adjacent its outer periphery, said circular surround adapted to be attached to the movable driver components inboard of said edgeroll and to the stationary driver components at the outer periphery of said surround, said surround: i) having a uniform compressed thickness of at least 0.1″; ii) having an edgeroll diameter of at least 1.5″; and iii), being capable of standing off internal box pressures generated within the subwoofer in the range of from about 1.5 lbs./in 2  to about 3 lbs./in 2 .    
     
     
         4 . A resilient suspension system as set forth in  claim 3  wherein said surround is formed of n laminations of surround foam having an initial aggregate thickness of at least 2{fraction (3/16)}″ compressed to a uniform thickness of at least 0.1″.  
     
     
         5 . A resilient suspension system as set forth in  claim 4  wherein said n laminations is equal to five laminations, each having an initial thickness of about {fraction (7/16)}″.  
     
     
         6 . A resilient suspension system as set forth in  claim 4  wherein said n laminations of surround foam have an initial aggregate thickness of at least {fraction (3/16)}″ compressed to a uniform thickness of at least 0.14″.  
     
     
         7 . A resilient suspension system as set forth in  claim 6  wherein said n laminations is equal to seven laminations, each having an initial thickness of about {fraction (7/16)}″.  
     
     
         8 . A flexible, resilient surround for use in suspending the movable driver components of a subwoofer driver from the stationary driver components of a subwoofer driver comprising a circular surround formed of compressible surround foam, said circular surround having an edgeroll adjacent its outer periphery, said circular surround adapted to be attached to the movable driver components inboard of said edgeroll and to the stationary driver components at the outer periphery of said surround, said surround: i) having a uniform compressed thickness of at least 0.1″; ii) having an edgeroll diameter of at least 1.5″; and iii), being capable of standing off internal box pressures generated within the subwoofer in the range of from about 1.5 lbs./in 2  to about 3 lbs./in 2 .  
     
     
         9 . A flexible resilient surround as set forth in  claim 8  wherein said surround is formed of n laminations of surround foam having an initial thickness of at least 2{fraction (3/16)}″ compressed to a uniform thickness of at least 0.1″.  
     
     
         10 . A flexible resilient surround as set forth in  claim 9  wherein said n laminations is equal to five laminations, each having an initial thickness of about {fraction (7/16)}″.  
     
     
         11 . A flexible resilient surround as set forth in  claim 9  wherein said n laminations of surround foam have an initial aggregate thickness of at least 3{fraction (1/16)}″ compressed to a uniform thickness of at least 0.14″.  
     
     
         12 . A flexible resilient surround as set forth in  claim 11  wherein said n laminations is equal to seven laminations each having an initial thickness of about {fraction (7/16)}″.  
     
     
         13 . The method of making a surround capable of standing off internal subwoofer box pressures of from about 1.5 lbs./in 2  to about 3 lbs./in 2  while stably supporting the subwoofer driver substantially without wobble as it moves through a peak-to-peak stroke of about 2.5″, said method comprising the steps of: 
 a) placing cellular surround foam having an aggregate thickness of at least 2{fraction (3/16)}″ intermediate complementary male and female dies; and    b) closing the male and female dies relative to one another for a period of time T at a pressure P and at a temperature F sufficient to form a surround having a uniform thickness of from about 0.1″ to about 0.14″, and an edgeroll having a diameter of at least 1.5″.    
     
     
         14 . The method as set forth in  claim 13  wherein the cellular surround foam aggregating at least 2{fraction (3/16)}″ comprises at least five layers of cellular surround foam each approximately {fraction (7/16)}″ thick.  
     
     
         15 . The method as set forth in  claim 13  wherein T is in the range of 40 to 90 seconds, P is in the range of 60 to 100 psi, and F is in the range of 420° F. to 450° F.  
     
     
         16 . The method as set forth in  claim 13  wherein T is approximately 45 seconds, P is approximately 80 psi, and F is approximately 430° F.  
     
     
         17 . The method as set forth in  claim 13  wherein the cellular surround foam aggregates an initial thickness of at least 3{fraction (1/16)}″ and comprises seven layers of cellular surround foam, each approximately {fraction (7/16)}″ thick compressed to a uniform thickness of at least 0.14″.  
     
     
         18 . Subwoofer apparatus including circuitry for converting the left and right channels of audio signal information input to a subwoofer into one of two composite audio signals (L+R)+α(L−R) and α(L+R)+(L−R) where the (L−R) components of the audio signal representing the stereo sound field are retained, said subwoofer apparatus comprising, in combination: 
 a) left and right channel inputs for the audio signal; and,    b) means for summing the left channel audio signal input and the right channel audio signal input at different acoustic dB levels so as to deliver one of the two following output composite audio signals: 
 i) (L+R)+α(L−R); and,  
 ii) α((L+R)+(L−R)  
   wherein said left and right channel inputs comprise first and second unity gain buffers for respectively receiving and outputting the left and right channel components of the audio signal; and, said means for summing the left channel audio signal input and the right channel audio signal input at different acoustic dB levels constitutes first and second parallel resistors R 1  and R 2  respectively coupled to the outputs of said first and second unity gain buffers whereby said composite audio output signal is derived from the sum of the left and right channel signal information at the junction of said two resistors and said resistors R 1  and R 2  have substantially different resistor values.    
     
     
         19 . Subwoofer apparatus as set forth in  claim 18  wherein one of said resistors R 1  and R 2  is approximately 680 ohms and the other of said resistors R 1  and R 2  is approximately 1600 ohms.  
     
     
         20 . Subwoofer apparatus including circuitry for eliminating undesirable ground loops and ground loop induced 60 Hz hum from a composite audio signal to be processed, said apparatus comprising, in combination: 
 a) means for feeding the composite audio signal in parallel to first and second signal processing channels wherein said first signal processing channel includes first and second inverting amplifier means spaced apart by a first opto-coupler and said second signal processing channel includes first and second unity gain buffers spaced apart by a second opto-coupler; and    b) means for summing the twice inverted audio signal output from said second inverting amplifier means in said first signal processing channel with said audio signal output from said second unity gain buffer in said second signal processing channel to produce a composite audio output signal to be processed and wherein said first and second opto-couplers provide breaks which prevent any completed ground loop between input and output grounds and any hum signal generated at said first output coupler is inverted by said second inverting amplifier means in said first signal processing channel and summed with a non-inverted hum signal output from said second unity gain buffer in said second signal processing channel so as to cancel and effectively eliminate the ground loop induced 60 Hz hum signal.    
     
     
         21 . Subwoofer apparatus of the type including a voice coil driven driver comprising, in combination: 
 a) stationary driver components including:    i) a basket-like frame;    ii) an annular magnet weighing approximately 225 oz.; and,    iii) a pole piece extending through said annular magnet and defining a magnetic gap therebetween;    b) movable driver components including:    iv) a cylindrical voice coil former adapted to reciprocate in said magnetic gap through a peak-to-peak stroke of about 2.5″;    v) a voice coil wound about said former and positioned thereon so as to be located within said magnetic gap and spaced from said annular magnet;    vi) a speaker cone having a large diameter end and a small diameter end wherein said small diameter end is attached to one end of said voice coil former;    vii) a flexible circular surround having an edgeroll adjacent its outer periphery, said surround being attached to said large diameter end of said speaker cone inboard of said edgeroll and being attached outboard of said edgeroll to said basket-like frame; and,    viii) an annular flexible spider attached at its inner periphery to said cylindrical voice coil former and at its outer periphery to said basket-like frame;    c) electrical leads extending from said voice coil to said speaker cone;    d) tinsel leads coupled to said electrical leads at said speaker cone and extending to said basket-like frame, said tinsel leads adapted to be coupled to the drive amplifier of a subwoofer; and,    e) means for maintaining said tinsel leads under tension in the span between said speaker cone and said basket-like frame at all positions of said movable driver components; whereby, as said movable driver components move inwardly and outwardly through peak-to-peak strokes of about 2.5″, said tinsel leads are prevented from flapping and striking said speaker cone and, therefore, undesirable noise resulting from said tinsel leads striking said speaker cone during axial reciprocation of said speaker cone is eliminated.