US20070256888A1 - Speaker System With Improved Frequency Response - Google Patents

Abstract

A speaker enclosure includes a first set of walls defining a first box, a second set of walls defining a second box disposed within the first box to define an enclosed compartment between the first set of walls and the second set of walls, an aperture located at least one of the second set of walls defining an opening between the internal volume of the second box and the enclosed compartment, and an alternative density transmission medium affixed to one or more surfaces of the first set of walls and/or the second set of walls in the enclosed compartment.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This utility patent application is a continuation of U.S. patent application Ser. No. 10/709,538 filed on May 12, 2004.
BACKGROUND OF THE INVENTION
• A typical loudspeaker is an electro-dynamic transducer attached to a diaphragm of some depth, diameter and shape. Electro-dynamic describes a transducer that moves back and forth in response to an alternating voltage source to stimulate adjacent air molecules. Some of these types of loudspeakers may be considered a commodity and are inexpensive. They are typically mounted on a baffle as part of an existing product or structure; in some form of housing for practical containment or in some cases a specialized enclosure is utilized to enhance the bass performance.
• One problem with these types of loudspeakers is that the driver may have a favorable acoustic impedance only over a narrow range of frequencies depending on its size. The smaller driver generally has unfavorable acoustical impedance for lower frequencies and vise versa for larger ones. The enclosure also favors a narrow range of frequencies and for other frequencies it may react violently creating a plethora of incoherent internal standing waves that modulate the diaphragm with nonsymmetrical vibration patterns. These random internal modulations disturb the natural dispersion pattern of the driver and cause electrical feedback (reactance) to the amplifying source. Brute force power and heavy gauge wiring are current attempts to minimize this problem for the amplifier and the effects on sound quality.
• Another problem is the general acoustic impedance differential that exists on either side of the driver diaphragm. The diaphragm must work simultaneously in two different acoustic environments as the enclosure creates standing waves that constantly modify the drivers' acoustic impedance in most of its frequency range. Reflected waves from the room cause additional modifications of the drivers' acoustic impedance more as the frequencies go lower towards that of the rooms' dimensions. Smaller enclosures can be worse because of the even higher frequencies that are reflected internally and the lack of low frequency capabilities.
• Two identical drivers will sound different due to their operating enclosure. One solution with mid-range speakers is to produce units with a solid basket behind the diaphragm. This may prevent random standing waves from interfering with the other drivers but it may create extreme backpressure for the range of frequencies produced by the midrange driver. This causes the driver to see a distinct acoustic impedance differential throughout its operating range thereby preventing it from producing a natural sound.
• Loudspeaker driver dimensions favor a certain range of frequencies thus making a single size for all frequencies difficult if wide axis listening is desired. It is a design goal to produce loudspeakers of the smallest dimensions necessary at minimum cost while maintaining the proper loudness level while retaining the sonic presentation of full frequency range, low distortion and wide-constant dispersion. A solution is the use of multiple drivers operating for a common acoustic purpose. This is reflected current loudspeaker designs in an effort to produce subjectively accepted loudspeakers.
• When a single driver is used, it is typically designed to favor lower or higher end frequencies while attempting to maintain quality in the middle ranges. The human ear tends to more sensitive to the higher frequencies but the human ear-brain combination prefers to hear all of the frequencies in the spectrum without phase or frequency aberrations to interrupt the flow of energy of the event otherwise it will appear to be artificial. The reproduction of sound is typically for either of two purposes and that is communication and entertainment. The latter requires unencumbered sonic balance and dispersion to balance the energy in the listening environment.
• The continued efforts to perfect sound reproduction with predictable field results depend greatly on a solution to solve the dilemma of the enclosure. Engineers recognize the drivers' enclosure as a design challenge. The use of the apparatus as explained in the pending application can improve sound quality.
SUMMARY
• Application of the device improves the reproduction of the full range of audio frequencies using a specific technique that allows for the delay of sound waves in a very short distance within a defined space to create beneficial standing waves over a wide frequency range.
• The device utilizes a closed loop embedded acoustic transmission line (EATL) and does not provide an exit path for the wave into the ambient environment for the wave. Dynamically the internal enclosure volume varies due to the EATL construction acting with a constant pressure relative to frequency.
• Normally a transmission line is used to carry energy in one direction from an originating point to a consumption or load point. An audio transmission line provides a path wave of energy to deliver the wave to a physically distant point. Any panels spaced too far apart will cease to be a wave-guide. The optimal panel spacing depends on the volume of air involved with the wave energy.
• The typical acoustic transmission line conveys acoustic energy away from the rear of the driver to the terminus in an attempt to prevent the back wave energy from reflecting back on the driver thereby interfering with the radiated output of the driver. The terminus describes the wave energy exit and can be at the front, rear or bottom of the TL enclosure. Large dimensions are required for existing TL designs to have any effect on other than midrange frequencies.
• The proposed invention relates to loudspeakers and in particular methods of improving the quality of reproduction for very low, low, middle and higher frequencies, reducing the relative enclosure dimensions, reducing the costs and dependency on the rooms' acoustics for consistent results. The improvements reflect on a manner of enclosing the driver that frees it from dependence on its general ambient acoustic environment and allows small drivers of essentially the same diameter to function as full range units or subwoofer units that operate with full range units primarily to extend the response into the lowest registers of the frequency spectrum.
• In one general aspect, a speaker enclosure includes a first set of walls defining a first box, a second set of walls defining a second box disposed within the first box to define an enclosed compartment between the first set of walls and the second set of walls, an aperture located at least one of the second set of walls defining an opening between the internal volume of the second box and the enclosed compartment, and an alternative density transmission medium affixed to one or more surfaces of the first set of walls and/or the second set of walls in the enclosed compartment.
• Embodiments may include one or more of the following features. For example, the surfaces of the first and second set of walls that define boundaries of the enclosed compartment may be first and second wave-guides. As another example, a termination member may be positioned at ends of the pair of wave-guides, the termination member having a surface defining a third wave-guide. In this embodiment, the first, second and third wave-guides are configured as an embedded acoustic transmission line.
• The alternative density transmission medium may have a first alternative density transmission medium attached to outer surfaces of the first set of walls and/or a second alternative density transmission medium attached to inner surfaces of the second set of walls to define a channel in the enclosed compartment. As another feature, the alternative density transmission medium includes open cell urethane foam.
• The enclosed compartment may be a sealed compartment with a single opening provided by the aperture. As another feature, a port may be installed in one of the first set of walls.
• A front wall common to the first and second set of walls may include an opening to receive a loudspeaker. As another feature, at least three of the second set of walls may be attached to a front wall of the first box.
• In still another general aspect, a speaker system includes a first cabinet, a second cabinet disposed within the first cabinet to define an enclosed compartment between inner surfaces of the first cabinet and outer surfaces of the second cabinet, an aperture in the first cabinet to define an opening that connects the internal volume of the first cabinet with the volume of the enclosed compartment, an alternative density transmission medium affixed to one or more of the inner surfaces of the first cabinet and/or outer surfaces of the second cabinet and a loudspeaker mounted on a wall of the first cabinet.
• Embodiments may include one or more of the above or following features. For example, the loudspeaker may be center mounted along a radial axis of the aperture.
• As another feature, the alternative density transmission medium may include open cell foam attached to inner surfaces of the first cabinet and/or outer surfaces of the second cabinet. In addition, inner surfaces of the first cabinet and the outer surfaces of the second cabinet that define boundaries of the enclosed compartment may be first and second wave-guides configured as an embedded acoustic transmission line.
• In a further general aspect, a method of moderating a bias pressure caused by a reflected sound wave in a speaker cabinet includes producing a sound wave with a speaker in a first chamber, directing the sound wave through an aperture from a first chamber to a second chamber of the speaker enclosure, compressing an alternative density transmission medium in the second chamber with the directed sound wave, the amount of compression varying according to the frequency and the intensity of the sound wave, and reflecting the sound wave back into the first chamber to moderate the bias pressure in the speaker enclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1A andFIG. 1B are side and front cross section views of a speaker enclosure in accordance with this invention.
• FIG. 2 is a cross section view of a speaker enclosure without the EATL features.
• FIG. 3 is a cross section view of a speaker enclosure.
• FIGS. 4A andFIG. 4B are cross section front and side views of the speaker enclosure with a reflex port added.
• FIG. 5 is a cross section view of the Direct Coupled (DC) EATL in accordance with this invention.
• FIG. 6 is a cross section view of the DC EATL physically combined with a standard non-damped bass reflex enclosure.
• FIG. 7 is a drawing highlighting features of the EATL technology with planar speakers.
• FIG. 8A illustrates a multi-way frequency divided IDC EATL system.
• FIG. 8B is illustrates a cluster of DRE or IRE EATL enclosures to increase SPL in a single range.
• FIG. 9 illustrates the use of the EATL technology with horn coupling devices.
• FIG. 10 is a side cross-sectional view of the speaker system ofFIG. 1 wherein the port has been replaced with a passive radiator mounted on the baffle board with the driver.
• FIG. 11 illustrates a band-pass mode of operation of the system ofFIG. 1 showing an acoustic low pass filter coupled to the front of the driver using a port to radiate the sound.
• FIG. 12A,FIG. 12B,FIG. 12C, andFIG. 12D are graphical representations of performance characteristics.
• FIG. 13A,FIG. 13B,FIG. 13C, andFIG. 13D are graphical representations of performance characteristics.
• FIG. 14A,FIG. 14B,FIG. 14C,FIG. 14D, andFIG. 14E are graphical representations of performance characteristics.
DETAILED DESCRIPTION
• Throughout this document there will be references to particular items, figures, names, phrases and notable words. The items will appear written once with a bold capital introductory letter and then abbreviated in the bold letters representing the name in text following. The capitalized bold first letter and abbreviation may appear subsequently to refresh the memory. Certain terms that may also have an importance in this document but are not pertaining directly to a feature of the document and will not be highlighted or underscored in this mode.
• FIG. 1 represents an embodiment of the invention.FIG. 1A andFIG. 1B represent a complete Direct Radiator Enclosure (DRE)29D speaker assembly constructed according to this invention. Bernoulli's theorem for the flow of liquid plainly states that a pressure differential must exist for a fluid to flow from a container through a discharge opening into a pressure region the same as that of the container. This means that if a sound (a fluid) of high quality is to be produced by a loudspeaker that a pressure differential must exists between its diaphragm and the atmospheric pressure and it must be consistent for all frequencies and acoustic conditions. All drivers of concern with this invention are bi-directional meaning that they radiate sound from both sides of the diaphragm. One side of the Driver Diaphragm (DD)3 must be dynamically isolated from the Atmospheric Pressure at all frequencies within its range without concern for reflections from within or external. Dynamic isolation refers to isolation from atmospheric pressure when in motion not static isolation.
• FIG. 1A illustrates a side cross sectional view of the DRE29 enclosure with the Indirect coupled (IDC) Embedded Acoustic Transmission Line (EATL5) structured to receive air pressure through its throat/mouth6 behind thedriver41 mounted onbaffle board7 but buffered by theair chamber10 ofFIG. 1A. TheEATL5 unlike conventional trans-mission lines has its throat and mouth at the same point through superposition. IDC means that the wave that enters the EATL5 does so through anair chamber10 of some relative volume so its influence on theDD3 will be indirect yet influential. The EATL5 is constructed of the wave-guide20 of theouter cabinet1 and the wave-guide21 of theInner enclosure2 separated by spacers9. The EATL5 can be extended by using the side cabinet walls wave-guide21 that are inherent in construction of the inner box in conjunction with extensions of wave-guide20. These extensions of the EATL5 are20A and21A and will allow the EATL5 to operate to a lower frequency than the20 and21 alone but are generally relative todriver41 size.
• The EATL5 is sealed by thetermination member13 that contains the wave at one end of the EATL5 reverses it and creates Dynamic Standing Waves (DSW) at the throat/mouth6 located in the center (from each corner) as seen inFIG. 1B. The term throat/mouth defining6 results from the reflected wave having its point of exit at the same point as the waves point of entry. The fact that the in/out waves can be superimposed on each other accounts for this unique pressure feedback principle. The air volume within the EATL5 is always small relative to the operating volume ofchamber10 ofFIG. 1 or19 ofFIG. 6 and is not a closed band-pass box. The overall dimensions may be further reduced using miniature construction techniques to enhance the output of smaller drivers in small spaces as well as OEM tweeter construction where the rear wave will be collected and returned as beneficial standing waves. The spacing dimensions can be reduced or increased as needed and the EATL5 may be repeatedly folded to increase its length as needed if20A and21A are not adequate in length.
• The EATL5 is lined with an Alternate Density Transmission Medium (ADTM4), which in the embodiment is open cell urethane foam that under normal air density and higher frequencies is inert, randomly accepting new air particles, yet at lower frequencies when pressurized allows additional air molecules to expand to within its cell structure in search of volume but instead are lost in heat dissipation. This is a lossy process hence the DSW and damping of the Driver Resonance Peak (DRP) as shown inFIG. 10A vs.FIG. 10B whereasFIG. 10A is the curve of the embodiment. Damping is a term referring to ability of a vibrating body to cease motion immediately when stimulus is removed.
• A relatively high frequency wave entering the throat/mouth6 of the EATL5 has only to be within inches of thedriver diaphragm3 to reach its wavelength in normal air density. The enclosure inFIG. 2 is only a few inches deep meaning that any wave below 10 kHz would experience enclosure reflections almost immediately.FIG. 2 represents an enclosure ofair volume11 with identical dimensions as that ofFIG. 1 but without2 and4 of that structure.
• The waves traveling the stream lines15 will enter themouth6 of the EATL5 and travel through the EATL5 barely interacting with the surface cells of the ADTM4 expanding almost immediately until it reaches thetermination point13, which then reflects the wave back toward thedriver diaphragm3. The throat/mouth6 at the entrance of the EATL5 will experience nodes and anti-nodes (DSW), which overlap and influence the pressure inchamber10 behind thedriver41 and are considered a positive pressure relative to the atmosphere.
• As the frequencies go lower from that first influenced, the EATL5 will maintain a constant positive pressure on thedriver diaphragm3 due to the DSW condition of the air space8 and the DSW condition caused by depth migration indicated by streamlines14. As varying wavelengths/intensities occupy deeper depths of the ADTM4 cell structure they create individual DSW and therefore dynamically enhance motion of thedriver diaphragm3. The individual DSW produced will integrate their pressures and produce a composite DSW in the presence of multiple frequencies simultaneously (superposition).
• Wave-guides20,21 must remain within a close spacing so as to contain the wave energy while directing it to thetermination member13. In the example,20,20A,21,21A are at 12 mm and 9 mm spacing respectively and will vary somewhat depending on driver diameter and purpose for system. Thedriver41 will see these DSW influence its acoustic impedance because the pressure-differential with that of the atmosphere is maintained with frequency. The DSW are the result of changing frequencies, driver compliance and resistance by the ADTM4 material to the sound energy entering its cells.
• The resulting interaction of the three variables maintains thechamber10 pressure constant as the frequency changes while the drivers velocity remains linear. Internal pressure atchamber10 would be a composite DSW resulting from thevoice coil28 signal input and the initial motion of theDD3, the static pressure of 10 and the positive pressure created in the EATL5. This resultant composite pressure is constant and is relative to intensity and wavelength in the EATL5 and determinesDD3 motions.
• The length of the EATL5 is directly associated with its low frequency limit of influence as is clearly indicated by the curves ofFIGS. 12B and 13A. InFIG. 12B the impedance plot of the speaker system ofFIG. 1 is indicated. There are two peaks associated with this impedance plot; the large one A is the DRP that occurs at 150 Hz and the other peak B that occurs at 500 Hz represents theEATL5 ¼ wave impedance peak ofFIG. 1.FIG. 13A represents the frequency response if the enclosure ofFIG. 1 is lengthened by 2 cm to become the enclosureFIG. 3. The 2 cm increase inenclosure depth26FIG. 3 can be interpreted inFIG. 13A by thenew EATL5 peak E at 400 Hz to cause a 100 Hz shift downward in ¼ wave frequency at the EATL5 throat/mouth for processing into DSW.
• The main driver resonance frequency ofFIG. 3 does not change appreciably whenchamber10 is increased as seen in40FIG. 13A. It can also be seen in the frequency response plot Q ofFIG. 14E ofFIG. 3 to show the lifting of output to begin at 400 Hz instead of the 500 Hz of the shallow enclosure ofFIG. 1. A large peak C can be seen inFIG. 12D (which is the standard closed type enclosureFIG. 2 with the same driver) but without a properly damped (controlled) impedance peak A or anEATL5 peak BasFIG. 1 orFIG. 3. The change involume10 did little to affect the drivers' resonance frequency A of thedriver41, which indicates the effectiveness of the EATL5 in delaying the wave in such a short distance. The damping of theDD3 improves acoustic impedance for bass frequencies lessening cut-off slope for deeper bass extension and better overall transient performance. The 500 Hz EATL5 peak B ofFIG. 12B represents the lowest frequency that will be lifted by the EATL5 ofFIG. 1 to correct the sagging output (FIG. 12A vs.12C) of the DD3 that normally occurs above the driver resonance frequency A and the point in which the EATL5 will begin to dampen oscillatory conditions near, at and below the drivers' resonance frequency AFIG. 12B.
• The impedance curveFIG. 12D ofFIG. 2 shows the same location for the drivers' resonance frequency C as that ofFIG. 12B ofFIG. 1 andFIG. 13A ofFIG. 3. The curve inFIG. 12D, clearly shows this peak C occurring at 150 Hz and if followed closely above this point shows no EATL5 peak B as inFIG. 12B,FIG. 13A andFIG. 13B. If the curve U ofFIG. 12A ofFIG. 1 is observed it will show an increase in output be-ginning at 500 Hz or the same point as the EATL5 peak B ofFIG. 12B. All frequencies above this peak will show an increase in output developing a gain to increase and maintain a flat response. The gain inefficiency averages 6 db for this particular example when averaging several points from 500 Hz and above. The only way for this to occur is for a constant pressure from within the enclosure to maintain the proper DD3 velocity as frequency changes. This process does not change the specifics of adriver41 sound signature only the effects mass and random internal standing waves have on its operation. The frequency peak UU, @500 HzFIG. 12A ofFIG. 1 does not exist in the graphFIG. 12C ofFIG. 2 nor does the increase at 10 kHz. At point TT@500 HzFIG. 12C there is a dip and only a small insignificant peak then falling response.
• A vibrating body will experience its greatest motion at resonance with less movement above and below that frequency for the same stimuli. The output (motion) falls much faster below resonance because of compliance while above it falls at a slower rate due to mass. The loss of output above resonance is directly related to mass (as it is affects the acceleration of theDD3 as needed at higher frequencies) while the DSW in the EATL5 are directly related to frequency and increase pressure to counter the loss and maintain pressure constant (DD3 in motion). The DSW generated internally at the mouth of the EATL5 provides positive pressure in real time buffered through volume ofchamber10 as each frequency may require in a composite wave maintaining maximum signal transfer relative to atmospheric pressure. The random standing waves existing in the enclosure ofFIG. 2 disturb the dispersion pattern by producing random pressures on various parts of the DD3 to generate noisy sound.
• It is difficult to determine parameters for certain products since the effects of field usage are hard to predict. Specifications developed to predict the vibration characteristics and dispersion of any given driver diameter are not useful if the enclosures SW are allowed to affect theDD3 radiation pattern. This is one of the main reasons that engineers seek various types of suspension27 andDD3 materials as a solution to resistDD3 breakup caused by these unknown sources. These breakup patterns are caused by random standing waves, which are dynamic and linked to theenclosure1, amplifying source and signal. Random standing waves must be transformed into beneficial ones not resisted as in existing enclosure design if a neutral expression of a driver is to be observed. The elimination of random internal standing waves and the production of useful coherent ones allow thedriver41 to operate as specifications describe for the materials, diameter and construction.
• A further result of this acoustically derived internal positive pressure is to further reduce diaphragm breakup as the pressure is applied to the entire surface to reduce the effects of solid transfer breakup modes. These are breakup modes that are generated when thevoice coil28 is stimulated.
• Initial stimulation at28 results in DD3 motions, flexing of all materials and a physical transfer of acoustical-mechanical energy towards the edges of theDD3 as waves. At the outer edges of theDD3 exist some type of flexible material27 that surrounds and anchors the diaphragm to allow general motion of the entire moving assembly when thevoice coil28 stimulates it.
• It is desired to have the energy that travels these paths dissipate in the diaphragm material and as kinetic energy into the surround material27 and that does occur in most cases. The diaphragm and surrounding material27 do not absorb all frequencies and some are reflected back toward the center or point of origin. In doing so waves, coherent and non-coherent, physically collide in theDD3 material causing regions of positive and negative standing waves to exist on the DD3 surface that alter the dispersion pattern. These types of patterns can be observed and countered during engineering design phases and perhaps will result in abetter driver41. The EATL5 will minimize audibility of these types of breakup modes but not eliminate them.
• FIG. 4 represents the enclosure ofFIG. 1 orFIG. 3 with the inclusion of aport17 to enhance bass frequencies. The addition of aport17 does not affect the DSW at the throat/mouth6 and the maintenance of acceleration of higher frequencies by the EATL5 whose primary purpose in this embodiment is to counter the mass that results in signal loss above the resonance frequency of thedriver41. The EATL5 provides critical damping for the DD3 to improve stability at lower frequencies as indicated inFIG. 12B ofFIG. 1 andFIG. 12D ofFIG. 2. These impedance plots indicate that the resonance frequency remains near the same for both enclosures however the peak A ofFIG. 12B indicates proper damping of the DD3 (as a controlled peak ratio is achieved for a smooth extended bass response and character) whereas the impedance plot ofFIG. 12D indicates that thedriver41 has a high sharp resonance peak C (to indicate a sharp loose resonate sound).
• This highly damped condition is maintained inFIG. 13B ofFIG. 4 with aport17 included to extend the response of bass. The impedance plotFIG. 13B has three distinguished peaks with the port peak F and saddle G (box resonance frequency) before the driver resonance peak H indicating reflex operation is occurring with a well-dampeddriver41 that is simultaneously having its upper frequencies lifted beginning at 400 Hz. When compared with the driver inFIG. 2 with the impedance curveFIG. 12D thedriver41 ofFIG. 4 has three peaksFIG. 13B indicating an increase in output both above and below the driver resonance peak H due to controlled resonance.
• In observing the frequency location of the peak I caused by the EATL5 positive pressures it can clearly be seen that the ported enclosure ofFIG. 4 is the 9 mm enclosure discussed earlier with a 400 Hz peak position on the graph. This peak H and EATL5 peak I of impedance curveFIG. 12 at 400 Hz remained in the same position indicating a well loaded speaker system that has enhanced (properly damped and extended) lower frequencies and (properly accelerated) upper frequencies.
• Shown inFIG. 10 is a simple illustration using a suitablepassive radiator30 substituted for the port to work in conjunction with thedriver41 to extended the bass to lower frequencies. The use of apassive radiator30 would maintain the sealed condition of the acoustic system however all configurations would not benefit from this type of resonate system.Passive radiators30 generally require more mounting area and would be suitable for larger systems with moreavailable baffle board7 area. Thepassive radiator30 EATL5 configuration would maintain the same general characteristics as the ported system if it is aligned properly and have a curve similar to that ofFIG. 13B.
• Another alignment for the DRE29I is that of coupling the front of thedriver41 to an acoustic low pass filter as inFIG. 11. Aport17 orpassive radiator30 is capable of acting as an acoustic low pass filter in conjunction withair mass31. Here the EATL5 provides for constant pressure loading, damping and enhanced upper bass output and control while theport17 establishes box loading withair volume31 reducingDD3 excursion allowing for a sealedair chamber10 and better damping. The design will have three impedance peaks as that of the other portedEATL5 designs one ahead and behind the DRF.
• As in the earlier example, apassive radiator30 can exist to resonate thenew air mass31 existing in front of thedriver41 when mounted in at least one wall of theadditional enclosure32. The IDC EATL5 acts as an ideal impedance matching device for virtually any conventional type of driver and loading method. It creates two ranges of increased pressure to benefit the frequencies above and below a drivers' resonance. Frequencies above resonance can be directly radiated as for the full range or the DD3 can be loaded into an acoustic low pass filter to focus on a range of bass frequencies.
• A driver will have an optimum frequency range of operation that it is most suited to reproduce. It would be very difficult if not impossible to obtain perfect operation for onedriver41 over the range of 20 Hz to 20,000 Hz especially at higher power levels. Individual EATL5 optimized enclosures DRE29 can focus their advantages on narrow sound ranges to assist the driver in its optimal range.
• This may be for the purpose of dividing the sound ranges to use optimal drivers for each rangeFIG. 10A29H,29M,29L,29VL using individually optimized EATL5 enclosures or it may be for the purpose of increasing the sound level in a single rangeFIG.10B29A,29B,29C,29D using multiple EATL5 enclosures operating in the same frequency range or for both applications simultaneously. This type of operation is enhanced because of the positive pressure behind each driver and the resistance therefore from interfering with other diaphragms.
• Conventional close spacing of drivers' results in many unpredictable effects because the random nature of the individual internal standing waves further alters the dispersion pattern. The coherent output ofEATL5 enclosures will combine in multi-way speakers to make the crossover from one driver to another smoother and more lobe free. The coherent output from grouped reinforcement drivers whether cluster or line will perform according to their intended theory. A special housing16 can be used to adjust the DRE29 units properly for the application.
• The EATL5 can also be used in conjunction with exotic acoustic transducers (driver41) such as with electrostatic and dynamic planar type diaphragms. Typically the flat panel loudspeakers radiate bi-directionally because of the negative effect an enclosure or close wall placement has to one side of the sensitive diaphragm. The random reflected standing waves are of even greater harm because of the large diaphragm surface area required to generate meaningful sound levels with these types.
• FIG. 7 is a simple illustration indicating the important reference parts for EATL5 use with these flat panel type loudspeakers. The EATL5 would consist of the same basic parts as illustrated as thedynamic driver41 version only larger panels would be involved and adjustments of certain other parameters involved with EATL5 construction. Certain types of exotic drivers qualify and can only benefit from IDC of the EATL5 and this is the case for the planar speaker DD3.
• Illustrated inFIG. 9 is the use of a horn apparatus to IDC the EATL5 for further transmission benefit. Horns are generally used to increase the level, distance and some times coverage in a specific area while shadowing others. The close coupling of the horn extension to theunaided DD3 of the horn produces intense reflections back into theDD3. Typically a horn coupleddriver41 suffers chronically from breakup because these reflected features are acoustically amplified so theDD3 suffers from competing horn bell type reflections at its surface.
• A phase plug25 may be necessary to maximize pressure transfer depending on the diaphragm type. Thedriver41 operating with the positive pressure of the EATL5 assisted environment will not be as affected by these reflections producing a much clearer output from a well designed horn coupling.
• Direct Coupled Low Frequency Applications
• Conventional loudspeakers need large diaphragm areas and/or high mass to produce low frequencies while attaining high efficiency in the process. The current processes for bass reproduction are inherently efficient because they operate the driver at and near its resonant frequency but this is also the Achilles' heel for sound quality. Resonance is the number one enemy of a finished sound system although the parameter is involved with the execution of any speaker system. TheDC EATL5 mode of operation will allow a very small driver to produce low bass frequencies at low to moderate efficiencies. When a 3″ driver is made capable of producing very low frequencies at a useful level then efficiency isn't a proper term to characterize its performance.
• FIG. 5 represents the application of the EATL5 in conjunction with adynamic driver41 for the purpose of generating very low frequencies only and is called the Direct CoupledDC EATL5. The EATL construction is very similar to the IDC with the exception of a larger throat/mouth opening6 equal to the driver diameter and compression plug12 located immediately in front of thedriver41. TheEATL5 is Directly Coupled (DC) to thedriver41 with minimum area air volume inchamber10 between the driver and the throat/mouth6 of theEATL5. The driver is mounted with front facing theEATL5 mouth6 so as to create ahigh compression chamber10 for driver loading. In this mode thedriver41 is compression loaded so a compression plug12 is used to help direct wave motion into theEATL5 and to minimize air turbulence at the throat/mouth6 of the EATL5 and to establish the correct throat/mouth6 area for the EATL5.
• DC coupling places thedriver41 completely under the influence of the EATL5 and it will follow the frequency pattern it establishes. TheADTM4 establishes delay of the waves through depth migration thus allowing a wide DSW bandwidth. The higher low frequencies abovedriver41 resonance are not effected as readily by the cellular structure and will sustain constant pressure in theEATL5 before depth migration.
• This can be seen inFIGS. 13C and 14D. The frequency response curveFIG. 13C represents thedriver41 output of a DC driver and EATL5 only and it can be seen that the frequency response shows a 12 db/oct falling output from thedriver41 resonance frequency and frequency irregularities above driver resonance. This represents a constant high positive pressure on theDD3 relative to frequency and a dynamic pressure much greater than atmospheric pressure for all frequencies in the systems bandwidth. When measured at 100 Hz this signal at the DD3 is 40 db greater than that at the mouth of theport17 when it is added. This output curve represents the actual output that thedriver41 will deliver with the positive pressure applied to theDD3 from theEATL5.
• In free air a similar pattern would be generated except the 12 db/oct slope would begin at the drivers' free air resonance frequency. Under these conditions the frequency would shift if the acoustic impedance of the driver is altered. Curve S is a reference high-pressure curve with a predictable 12 db/oct rate of fall and is easy to shape with an acoustic low pass filter. This curve also reflects a predictable falling diaphragm excursion relative to lower frequencies.
• A reflex enclosure would further reduceDD3 motion in the power bass frequency range (30 Hz-60 Hz) and not have a subsonic distortion problem after the EATL5 peak. An acoustic low pass filter18 connected to thedriver41/EATL5 inFIG. 5 would favor the lowest frequencies even though these frequencies are falling in curve SFIG. 13C. The 12 db/oct falling output ofFIG. 13C are transformed into the curve R ofFIG. 13D forFIG. 6 which shows 6 db/oct rising output from 70 Hz. The curve inFIG. 13C is generated with thedriver41 in high-pressure environment that will resonate the box with little effect on the constant pressure loading of the driver. The positive pressure allows the output from the rear of the driver to resonate a reflex enclosure withacoustic volume19 at frequencies within the 12 db/oct slope. The efficiency in the range of the transformation is moderate relative to the driver mid-band efficiency yet it allows a small low mass driver to use its fast responding diaphragm to produce usable bass at frequencies determined by the EATL5.
• Almost anysimilar diameter driver41 may be used to generate the curves ofFIG. 13C andFIG. 13D. The ¼ wave positive pressure is a real-time mass component acoustically applied to theDD3 to produce the enhanced low pass performance from thedriver41 as indicated inFIG. 13D forFIG. 6. The drivers'41 mass and other parameters will affect distortion, efficiency and to some degree extreme frequency cut-off so optimum performance from a certain EATL/Reflex enclosure can be had throughdriver41 choice. The efficiency of this type of bass system is still related toactual DD3 area and it increases with alarger driver41 as would be normal since more air molecules would be moved. Typically the low frequency output oflarge drivers41 increase relative to mid-band output because of diaphragm area as mass deters output at higher frequencies.
• TheDCEATL5 low frequency system develops output from diaphragm area not geometry. The listening room, typically being an acoustic space with dimensional gain, also favors lower frequencies if they are present. The curve ofFIG. 14C represents distant microphone placement when measuring the sub-bass system ofFIG. 6. The room acts similar to the reflex enclosure in lifting the output at the lower bass frequencies as is seen in curve O by the big increase in gain in the 15 Hz octave inFIG. 14C relative to adjacent frequencies.FIG. 14A indicates the impedance ofFIG. 5 andFIG. 6. The curves are overlaid to show how little the reflex box alters the resonant frequency and Q of the driver when it is connected. This indicates that the positive pressure within theEATL5 dominates the drivers' impedance with little effect on thedriver41/EATL5 operating parameters from the addition of the acoustic low pass filter.
• InFIG. 14A the large peak K represents the impedance of the driver inFIG. 5. The small peak J trailing the driver peak L inFIG. 14A would be considered the ports peak with a conventional reflex enclosure and the output would fall off rapidly as the frequency approaches this peak. This peak represents thesame EATL5 peak that was observed in the impedance peak ofFIG. 12B,FIG. 13A,FIG. 13B except that it has been pushed below the driver resonance due to the close coupling of the EATL5. It has been shown that increasing the length of the EATL5 will lower the EATL5 peak, as close coupling will also cause. Depth migration is greater under high pressure causing the ¼ wave signal to appear at the driver diaphragm below box tuning.
• As shown inFIG. 13D, the output will fall after themain EATL5 peak but the close coupling will load the driver to the EATL5 cut-off frequency of near 15 Hz. If it is observed carefully the output curve R ofFIG. 13D of the sub-bass enclosureFIG. 6 has its highest output at theEATL5 peak of 35 Hz which is an extraordinary feature. The reason for this can be seen if the curves ofFIG. 14D are observed.FIG. 14D represents the phase curves of the subwoofer inFIG. 6. The curves are overlaid to show their relationships. Curve M represents the microphone placement very close to the driver diaphragm at itssurface boundary area24 where it will show the curve of the EATL5. Curve N is indicating the output at theport17 of the same sub-bass speaker ofFIG. 6 and it can clearly be seen a large shift in phase beginning at 55 Hz which is near the box tuning frequency. The outputs of theDD3 and theport17 are remarkably similar until the phase begins to shift at the box frequency G ofFIG. 14A producing the initial rise in output as seen in curve RFIG. 13D at G. The phase curve MFIG. 14D of the driver indicates a reverse change beginning at near the same point 55 Hz with a small depression indicated throughout the remainder of the phase curve at the driver. This depression represents the high pressure being applied to the diaphragm to produce the phase change at the port and the corresponding increase in output. This pressure is applied at the time when the DD3 is under box loading for maximum effectiveness. The pressure on the diaphragm remains constant as viewed by the flat phase curve to 55 Hz and doesn't change even when the EATL Speak further loads the diaphragm to cause the increased output. The result of the EATL5 feedback and the box loading establishes an effective acoustic low pass system that will allow any practical driver diameter to produce very low frequencies at efficiencies relative to the driver diameter even if the resonance frequency is much higher.
• Horn loading of the driver for low frequency reproduction while in the DC compression mode of operation can be effective if physical space isn't a real consideration. The well-loadeddriver41 is a good candidate for horn coupling to the ambient but large surface expansion areas are required to support launching of the long waves. In some cases embedded applications in buildings or large structures will allow portions of the structure to act as horn wave-guides. In some cases folding of the required waveguides will allow implementation of a low frequency horn even an enclosure version.
• With the EATL5 DRE29D enclosures multiple units of the IRE29I may be configured to increase the output as a combined coherent source as inFIG. 8A the sound will more approach the theoretical 6 db per doubling of units. This and the excellent immunity to the rooms' reflections will maintain the integrity of the source. The IRE29I may also be combined as inFIG. 8B to have theEATL5 peak to occur in different ranges to maximize the output in each range. This will allow for maximum low frequency output over a wider range.
• An example of an application of the IDC and DC systems used concurrently for a single sound system is illustrated by the graph ofFIG. 14B. The curve inFIG. 14B represents coverage of the audio range from below 35 Hz to 20 kHz using 3 identical 3-inch diameter drivers operating in almost identically sized miniature (<0.06 cu. ft.) DRE and IRE enclosures as depicted inFIG. 1 andFIG. 6. They are the left speakerFIG. 1, the right speakerFIG. 1 and the subwooferFIG. 6 that reproduces the lower bass from both channels. The 3-inch driver41 as inFIG. 1 is the only candidate for a system of this type because it retains the dispersion properties required of a tweeter or high frequency driver but has enough diaphragm area making it capable of having its impedance matched by both the DC or IDC coupled EATL5 to cover the entire frequency range. The free-air resonance of the driver is 100 Hz normally much to high for subwoofer operation yet the DC EATL/Reflexenclosure29D covers the range from below 35 Hz to 125 Hz where it mates with an IDCEATLenclosure29I, which covers the range from 125 Hz to 20 kHz. The DC EATL/Reflexlow frequency system has its upper frequency range adjusted electronically and is powered by a separate amplifier so that it can be set to properly blend with the IDC EATLenclosure29I in any field environment. This system achieves near perfect vertical and horizontal off-axis response and requires no additional parts within the enclosures. The system output illustrated inFIG. 14B is capable of achieving in excess of 90 db output at the listening position in an average size room for the indicated frequency range. This system including 2 speakers, subwoofer, amplifier, tripod stands and all connecting accessories fits neatly in a standard executive sized briefcase and exists today.
• Most of this document has described particular embodiments of the invention, however, there will be many ways to use the general principles of this technology because of the generic nature of the improvements involved. For example one may develop a new product with a different shape or discover new ways to couple the EATL5 to the atmospheric pressure including in some ways the basic principles of theEATL5. As such, other embodiments fall within the scope of the following claims.

Claims (14)

1. A speaker enclosure, comprising:

a first set of walls defining a first box;

a second set of walls defining a second box disposed within the first box to define an enclosed compartment between the first set of walls and the second set of walls;

an aperture located at least one of the second set of walls defining an opening between the internal volume of the second box and the enclosed compartment; and

an alternative density transmission medium affixed to one or more surfaces of the first set of walls and/or the second set of walls in the enclosed compartment.

2. The apparatus ofclaim 1, wherein surfaces of the first and second set of walls that define boundaries of the enclosed compartment comprise first and second wave-guides.

3. The apparatus ofclaim 2, further comprising:

a termination member at ends of the pair of wave-guides, the termination member having a surface defining a third wave-guide;

wherein the first, second and third wave-guides comprise an embedded acoustic transmission line.

4. The apparatus ofclaim 1, wherein the alternative density transmission medium comprises a first alternative density transmission medium attached to outer surfaces of the first set of walls and/or a second alternative density transmission medium attached to inner surfaces of the second set of walls to define a channel in the enclosed compartment.

5. The apparatus ofclaim 1, wherein the enclosed compartment is a sealed compartment with a single opening provided by the aperture.

6. The apparatus ofclaim 1, wherein the alternative density transmission medium comprises open cell urethane foam.

7. The apparatus ofclaim 1, further comprising:

a port in one of the first set of walls.

8. The apparatus ofclaim 1, wherein a front wall common to the first and second set of walls includes an opening to receive a loudspeaker.

9. The apparatus ofclaim 1, wherein at least three of the second set of walls are attached to a front wall of the first box.

10. A speaker system, comprising:

a first cabinet;

a second cabinet disposed within the first cabinet to define an enclosed compartment between inner surfaces of the first cabinet and outer surfaces of the second cabinet;

an aperture in the first cabinet to define an opening that connects the internal volume of the first cabinet with the volume of the enclosed compartment;

an alternative density transmission medium affixed to one or more of the inner surfaces of the first cabinet and/or outer surfaces of the second cabinet; and

a loudspeaker mounted on a wall of the first cabinet.

11. The system ofclaim 10, wherein the loudspeaker is center mounted along a radial axis of the aperture.

12. The system ofclaim 10, wherein the alternative density transmission medium comprises open cell foam attached to inner surfaces of the first cabinet and/or outer surfaces of the second cabinet.

13. The method ofclaim 10, wherein the inner surfaces of the first cabinet and the outer surfaces of the second cabinet that define boundaries of the enclosed compartment comprise first and second wave-guides configured as an embedded acoustic transmission line.

14. A method of moderating a bias pressure caused by a reflected sound wave in a speaker cabinet, the method comprising:

producing a sound wave with a speaker in a first chamber;

directing the sound wave through an aperture from a first chamber to a second chamber of the speaker enclosure;

compressing an alternative density transmission medium in the second chamber with the directed sound wave, the amount of compression varying according to the frequency and the intensity of the sound wave; and

reflecting the sound wave back into the first chamber to moderate the bias pressure in the speaker enclosure.

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