Closed loop embedded audio transmission line technology for loudspeaker enclosures and systems

An acoustic impedance matching enclosure is provided having a driver loaded into a chamber buffering the throat/mouth of a closed loop transmission line. Transmission line consists of a termination member, outer and inner enclosure walls, high-density lining and throat/mouth area. Transmission line eliminates internal random standing waves while providing variable-frequency standing waves that through superposition of the waves compensates for mass-acceleration loss of the high-end of the driver output while damping the resonance of the driver. Alternative application of the acoustic impedance matching enclosure is that of compression loading the driver directly into the closed loop transmission line and using an acoustic low pass filter to translate the output into low frequencies only through a port. Both applications of the acoustic impedance matching enclosure are to insure that the drivers' diaphragm is clear of disruptive internal standing waves, properly loaded at all frequencies and not easily affected by room reflections.

BACKGROUND OF INVENTION

Loudspeakers are a part of everyday life and used for consumer, commercial, military and research applications. The typical loudspeaker is an electro-dynamic transducer and has a diaphragm of some depth and diameter or shape. Electro-dynamic describes a transducer that moves in a positive and negative direction in response to a alternating voltage source to stimulate adjacent air molecules. At this point in time loudspeakers of this type are considered a commodity and are cheap and plentiful in supply. They are typically always 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 form of specialized enclosure is utilized to enhance the bass performance. There are other types of electro-mechanical transducers in use generally exotic but most of which will benefit from the use of the Embedded Transmission Line Technology.

One of the greatest problems is the inherent nature of the driver to favor an acoustic impedance over a narrow range of frequencies relative to 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 others it reacts 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 are much 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 only. The industry has recognized the problem as one associated more with the mid-range speaker and has produced units with a solid basket behind the diaphragm. This may prevent random standing waves from the other drivers but it creates extreme backpressure for the range of frequencies produced by the midrange driver. This causes the driver to see a distinct acoustic impedance differential for all of its' operating range and not produce a natural sound.

Loudspeaker driver dimensions favor a certain range of frequencies thus making a single size for all frequencies an impossible task if wide axis listening is desired. It is a design goal to produce loudspeakers of the smallest dimensions necessary and maintain the proper loudness level while retaining the sonic presentation of full frequency range, low distortion, wide-constant dispersion and low cost. If one were to examine the situation it would appear to be a paradox requiring a compromise solution and the use of multiple drivers operating for a common acoustic purpose. This is reflected in the current loudspeaker design with theory compromised by art in an effort to produce subjectively accepted loudspeakers when the goal should be objectivity.

The requirement to use a single driver places a compromise solution favoring the 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 necessary evil or an opportunity to profit from the furniture created however the use of the enclosure as explained in the pending application provides a positive operating environment exposing the true quality of the driver. The result is elimination of the idiosyncratic behavior, objective sonic acceptance, simplified loudspeaker design and predictable results for varying acoustic situations.

SUMMARY OF INVENTION

This application relates to 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. Its relation to an earlier application is that of a radial expansive transmission line created when a sound wave traverses a path of a different dynamic acoustic density. The pending application was directed to sub-bass frequencies and included direct radiation of upper bass frequencies but suggested an open line. There was no suggestion for use with full range speakers. It has been determined that an open line although somewhat beneficial would only allow for limited and ambiguous sound output. Although the earlier application defined the transmission line as radial the invention described within introduces the embedded line whose function is consistent with a shorted termination transmission line radial or otherwise and not required to be symmetrical in its' relation to the driver to perform its' function. Radial implementation of this device defines symmetry and is considered the most logical path if possible. This type of line is defined as a Closed Loop Embedded Acoustic Transmission Line (EATL) and does not provide an exit path into the ambient 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 must provide a distinct path for a wave of energy that results in the complete wave being present at some physically distant point. Any panels spaced sufficiently apart will cease to be a wave-guide and not contain the wave. The panel spacing would in actuality depend on the volume of air involved with the wave energy. Within the loudspeaker industry an acoustic transmission line will convey 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 and not to interfere with the radiated output of the driver. The terminus is the terminology used to described the wave energy exit and can be at the front, rear or bottom of the typically large TL enclosure. Large dimensions are required for existing TL designs to have any effect on other than midrange frequencies. The goals of today's audio industry is for things to work better and be smaller unless for commercial applications when better can be almost any size. The rather larger dimensions typically required don't providing loading of the driver to sub-bass frequencies. It is argued in some enthusiasts circles that a transmission line for loudspeakers have infinitely dissipative loading and not assisting the main driver in any way to add or subtract from the output at the diaphragm. The EATL is proving a more effective implementation of the transmission line with more achievable and definitive goals for a speaker designer for the full range of loudspeaker applications.

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. Although this applications' focus is on smaller speaker units this technique applies to large-scale bass, full range or sub-bass sound reproduction applications to enhance the larger drivers performance as well. Focus on operation in the sub-bass range generally involves using a port or horn to reduce the motion of the diaphragm near the maximum low frequency output range. Larger drivers will produce more low bass with less diaphragm motion but will be less favorable for direct radiating full range operation because of limited high frequency capabilities. Low frequencies can be directly radiated or radiated through a port or horn coupling for larger drivers. The EAL maintains a constant enclosure pressure over the full frequency range and any volume displacement that can't occupy the line results in greater displacement of the drivers' diaphragm. This results when long wavelength signals stimulate the EATL creating beneficial standing waves to load the driver diaphragm. All wavelengths exist at some finite length within the line as partial or complete as dictated by the variable dynamic air density. Any pressure stimuli will cause a dynamic molecular disturbance within the EATL that creates desirable standing waves that displace the diaphragm with greater ease and accuracy than the signal alone. This enhanced physical displacement is both created by and is the result of the drivers' stimulation by the electrical source plus the dynamic standing wave pattern established within the EATL. This predictable internal loading pattern takes precedent over all other external driver diaphragm stimuli providing critical damping, optimal loading and resistance to room reflections.

Furthermore this technology allows a small single driver type and dimension to be optimized for full range and sub-bass operation using small drivers normally efficient only in the higher frequency ranges. The enclosures developed using the pending application determine the acoustic impedance favored by the identical drivers.

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 ('s) and abbreviation may appear subsequently to refresh the memory. Some important statements may be underscored for recognition purposes. 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. 1represents a preferred embodiment of the subject invention.FIG. 1AandFIG. 1Brepresent 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 simply 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)3must 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. 1Aillustrates a side cross sectional view of the DRE29enclosure with the Indirect coupled (IDC) Embedded Acoustic Transmission Line (EATL5) structured to receive air pressure through its' throat/mouth6behind the driver41mounted on baffle board7but buffered by the air chamber10ofFIG. 1A. The EATL5unlike conventional trans-mission lines has its throat and mouth at the same point through superposition. IDC means that the wave that enters the EATL5does so through an air chamber10of some relative volume so its' influence on the DD3will be indirect yet influential. The EATL5is constructed of the wave-guide20of the outer cabinet1and the wave-guide21of the Inner enclosure2separated by spacers9. The EATL5can be extended by using the side cabinet walls wave-guide21that are inherent in construction of the inner box in conjunction with extensions of wave-guide20. These extensions of the EATL5are20A and21A and will allow the EATL5to operate to a lower frequency than the20and21alone but are generally relative to driver41size. The EATL5is sealed by the termination member13that contains the wave at one end of the EATL5reverses it and creates Dynamic Standing Waves (DSW) at the throat/mouth6located in the center (from each corner) as seen inFIG. 1B. The term throat/mouth defining6results 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 EATL5is always small relative to the operating volume of chamber10ofFIG. 1or19ofFIG. 6and is not to be confused with any type of closed band-pass box closed. 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 EATL5may be repeatedly folded to increase its' length as needed if20A and21A are not adequate in length.

The EATL5is lined with an Alternate Density Transmission Medium (ADTM4), which in the preferred 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. 10Avs.FIG. 10BwhereasFIG. 10Ais the curve of the preferred 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/mouth6of the EATL5has only to be within inches of the driver diaphragm3to reach its wavelength in normal air density. The standard enclosure inFIG. 2example here is only a few inches deep meaning that any wave below 10 kHz would experience enclosure reflections almost immediately.FIG. 2represents an enclosure of air volume11with identical dimensions as that ofFIG. 1but without2and4of that structure. The waves traveling the stream lines15will enter the mouth6of the EATL5and travel through the EATL5barely interacting with the surface cells of the ADTM4expanding almost immediately until it reaches the termination point13, which then reflects the wave back toward the driver diaphragm3. The throat/mouth6at the entrance of the EATL5will experience nodes and anti-nodes (DSW), which overlap and influence the pressure in chamber10behind the driver41and are considered a positive pressure relative to the atmosphere. As the frequencies go lower from that first influenced, the EATL5will maintain a constant positive pressure on the driver diaphragm3due to the DSW condition of the air space8and the DSW condition caused by depth migration indicated by streamlines14. As varying wavelengths/intensities occupy deeper depths of the ADTM4cell structure they create individual DSW and therefore dynamically enhance motion of the driver diaphragm3. The individual DSW produced will integrate their pressures and produce a composite DSW in the presence of multiple frequencies simultaneously (superposition). Wave-guides20,21must remain within a close spacing so as to contain the wave energy while directing it to the termination member13. [In the preferred example here20,20A,21,21A are at 12 mm and 9 mm spacing respectively and will vary somewhat depending on driver diameter and purpose for system.] The driver41will 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 ADTM4material to the sound energy entering its' cells. The resulting interaction of the three variables maintains the chamber10pressure constant as the frequency changes while the drivers velocity remains linear. Internal pressure at chamber10would be a composite DSW resulting from the voice coil28signal input and the initial motion of the DD3, the static pressure of10and the positive pressure created in the EATL5. This resultant composite pressure is constant and is relative to intensity and wavelength in the EATL5and determines DD3motions.

The length of the EATL5is directly associated with its' low frequency limit of influence as is clearly indicated by the curves ofFIGS. 12B and 13A. InFIG. 12Bthe impedance plot of the speaker system ofFIG. 1is 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 the EATL5¼ wave impedance peak ofFIG. 1.FIG. 13Arepresents the frequency response if the enclosure ofFIG. 1is lengthened by 2 cm to become the enclosureFIG. 3. The 2 cm increase in enclosure depth26FIG. 3can be interpreted inFIG. 13Aby the new EATL5peak E at 400 Hz to cause a 100 Hz shift downward in ¼ wave frequency at the EATL5throat/mouth for processing into DSW. The main driver resonance frequency ofFIG. 3does not change appreciably when chamber10is increased as seen in40FIG. 13A. It can also be seen in the frequency response plot Q ofFIG. 14EofFIG. 3to 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. 2with the same driver) but without a properly damped (controlled) impedance peak A or an EATL5peak BasFIG. 1orFIG. 3. The change in volume10did little to affect the drivers' resonance frequency A of the driver41, which indicates the effectiveness of the EATL5in delaying the wave in such a short distance. The damping of the DD3improves acoustic impedance for bass frequencies lessening cut-off slope for deeper bass extension and better overall transient performance. The 500 Hz EATL5peak B ofFIG. 12Brepresents the lowest frequency that will be lifted by the EATL5ofFIG. 1to correct the sagging output (FIG. 12Avs.12C) of the DD3that normally occurs above the driver resonance frequency A and the point in which the EATL5will begin to dampen oscillatory conditions near, at and below the drivers' resonance frequency AFIG. 12B.

The impedance curveFIG. 12DofFIG. 2shows the same location for the drivers' resonance frequency C as that ofFIG. 12BofFIG. 1andFIG. 13AofFIG. 3. The curve inFIG. 12D, clearly shows this peak C occurring at 150 Hz and if followed closely above this point shows no EATL5peak B as inFIG. 12B,FIG. 13AandFIG. 13B. If the curve U ofFIG. 12AofFIG. 1is observed it will show an increase in output be-ginning at 500 Hz or the same point as the EATL5peak 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 in efficiency 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 DD3velocity as frequency changes. This process does not change the specifics of a driver41sound signature only the effects mass and random internal standing waves have on its' operation. The frequency peak UU, @500 HzFIG. 12AofFIG. 1does not exist in the graphFIG. 12CofFIG. 2nor does the increase at 10 kHz. At point TT@500 HzFIG. 12Cthere 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 the DD3as needed at higher frequencies) while the DSW in the EATL5are directly related to frequency and increase pressure to counter the loss and maintain pressure constant (DD3in motion). The DSW generated internally at the mouth of the EATL5provides positive pressure in real time buffered through volume of chamber10as 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. 2disturb the dispersion pattern by producing random pressures on various parts of the DD3to generate noisy sound. [Loudspeaker driver engineers in determining parameters for their products cannot predict the effects of field usage. 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 the DD3radiation pattern. This is one of the main reasons that engineers seek various types of suspension27and DD3materials as a solution to resist DD3breakup caused by these unknown sources. These breakup patterns are caused by random standing waves, which are dynamic and linked to the enclosure1, 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 the driver41to 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 the voice coil28is stimulated. Initial stimulation at28results in DD3motions, flexing of all materials and a physical transfer of acoustical-mechanical energy towards the edges of the DD3as waves. At the outer edges of the DD3exist some type of flexible material27that surrounds and anchors the diaphragm to allow general motion of the entire moving assembly when the voice coil28stimulates it. It is desired to have the energy that travels these paths dissipate in the diaphragm material and as kinetic energy into the surround material27and that does occur in most cases. The diaphragm and surround material27do 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 the DD3material causing regions of positive and negative standing waves to exist on the DD3surface that alter the dispersion pattern. These types of patterns can be observed and countered during engineering design phases and perhaps will result in a better driver41. The EATL5will minimize audibility of these types of breakup modes but not eliminate them.

The Drawing ofFIG. 4represents the enclosure ofFIG. 1orFIG. 3with the inclusion of a port17to enhance bass frequencies. The addition of a port17does not affect the DSW at the throat/mouth6and the maintenance of acceleration of higher frequencies by the EATL5whose primary purpose in this embodiment is to counter the mass that results in signal loss above the resonance frequency of the driver41. The EATL5provides critical damping for the DD3to improve stability at lower frequencies as indicated inFIG. 12BofFIG. 1andFIG. 12DofFIG. 2. These impedance plots indicate that the resonance frequency remains near the same for both enclosures however the peak A ofFIG. 12Bindicates 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. 12Dindicates that the driver41has a high sharp resonance peak C [to indicate a sharp loose resonate sound]. This highly damped condition is maintained inFIG. 13BofFIG. 4with a port17included to extend the response of bass. The impedance plotFIG. 13Bhas 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-damped driver41that is simultaneously having its' upper frequencies lifted beginning at 400 Hz. When compared with the driver inFIG. 2with the impedance curveFIG. 12Dthe driver41ofFIG. 4has three peaksFIG. 13Bindicating 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 EATL5positive pressures it can clearly be seen that the ported enclosure ofFIG. 4is the 9 mm enclosure discussed earlier with a 400 Hz peak position on the graph. This peak H and EATL5peak I of impedance curveFIG. 12at 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. 10is a simple illustration using a suitable passive radiator30substituted for the port to work in conjunction with the driver41to extended the bass to lower frequencies. The use of a passive radiator30would maintain the sealed condition of the acoustic system however all configurations would not benefit from this type of resonate system. Passive radiators30generally require more mounting area and would be suitable for larger systems with more available baffle board7area. The passive radiator30EATL5configuration 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 the driver41to an acoustic low pass filter as inFIG. 11. A port17or passive radiator30is capable of acting as an acoustic low pass filter in conjunction with air mass31. Here the EATL5provides for constant pressure loading, damping and enhanced upper bass output and control while the port17establishes box loading with air volume31reducing DD3excursion allowing for a sealed air chamber10and better damping. The design will have three impedance peaks as that of the other ported EATL5designs one ahead and behind the DRF. Again as in the earlier example a passive radiator30can exist to resonate the new air mass31existing in front of the driver41when mounted in at least one wall of the additional enclosure32. The IDC EATL5acts 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 DD3can be loaded into an acoustic low pass filter to focus on a range of bass frequencies.

Any 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 one driver41over the range of 20 Hz to 20,000 Hz especially at higher power levels. Individual EATL5optimized enclosures DRE29can 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 EATL5enclosures or it may be for the purpose of increasing the sound level in a single rangeFIG. 10B29A,29B,29C,29D using multiple EATL5enclosures operating in the same frequency range or for both applications simultaneously. These types of operation are enhanced because of the positive pressure behind each driver and the resistance therefore from interfering with each other” diaphragm. 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 of EATL5enclosures 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 housing16can be used to adjust the DRE29units properly for the application.

The EATL5can 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. 7is a simple illustration indicating the important reference parts for EATL5use with these flat panel type loudspeakers. The EATL5would consist of the same basic parts as illustrated as the dynamic driver41version only larger panels would be involved and adjustments of certain other parameters involved with EATL5construction. Certain types of exotic drivers qualify and can only benefit from IDC of the EATL5and this is the case for the planar speaker DD3. Illustrated inFIG. 9is the use of a horn apparatus to IDC the EATL5for 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 the unaided DD3of the horn produces intense reflections back into the DD3. Typically a horn coupled driver41suffers chronically from breakup because these reflected features are acoustically amplified so the DD3suffers from competing horn bell type reflections at its' surface. A phase plug25may be necessary to maximize pressure transfer depending on the diaphragm type. The driver41operating with the positive pressure of the EATL5assisted environment will not be as affected by these reflections producing a much clearer output from a well designed horn coupling.

DIRECT COUPLED LOW FREQUENCY ONLY 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. The DC EATL5mode 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. 5represents the application of the EATL5in conjunction with a dynamic driver41for the purpose of generating very low frequencies only and is called the Direct Coupled DC EATL5. The EATL construction is very similar to the IDC with the exception of a larger throat/mouth opening6equal to the driver diameter and compression plug12located immediately in front of the driver41. The EATL5is Directly Coupled (DC) to the driver41with minimum area air volume in chamber10between the driver and the throat/mouth6of the EATL5. The driver is mounted with front facing the EATL5mouth6so as to create a high compression chamber10for driver loading. In this mode the driver41is compression loaded so a compression plug12is used to help direct wave motion into the EATL5and to minimize air turbulence at the throat/mouth6of the EATL5and to establish the correct throat/mouth6area for the EATL5. DC coupling places the driver41completely under the influence of the EATL5and it will follow the frequency pattern it establishes. The ADTM4establishes delay of the waves through depth migration thus allowing a wide DSW bandwidth. The higher low frequencies above driver41resonance are not effected as readily by the cellular structure and will sustain constant pressure in the EATL5before depth migration. This can be seen inFIGS. 13C and 14D. The frequency response curveFIG. 13Crepresents the driver41output of a DC driver and EATL5only and it can be seen that the frequency response shows a 12 db/oct falling output from the driver41resonance frequency and frequency irregularities above driver resonance. This represents a constant high positive pressure on the DD3relative 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 DD3is 40 db greater than that at the mouth of the port17when it is added. This output curve represents the actual output that the driver41will deliver with the positive pressure applied to the DD3from the EATL5. 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 reduce DD3motion in the power bass frequency range (30 Hz–60 Hz) and not have a subsonic distortion problem after the EATL5peak. An acoustic low pass filter18connected to the driver41/EATL5inFIG. 5would favor the lowest frequencies even though these frequencies are falling in curve SFIG. 13C. The 12 db/oct falling output ofFIG. 13Care transformed into the curve R ofFIG. 13DforFIG. 6which shows 6 db/oct rising output from 70 Hz. The curve inFIG. 13Cis generated with the driver41in 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 with acoustic volume19at 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 any similar diameter driver41used if its compliance is not to stiff will generate the curves ofFIG. 13CandFIG. 13D. The ¼ wave positive pressure is a real-time mass component acoustically applied to the DD3to produce the enhanced low pass performance from the driver41as indicated inFIG. 13DforFIG. 6. The drivers'41mass 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 through driver41choice. The efficiency of this type of bass system is still related to actual DD3area and it increases with a larger driver41as would be normal since more air molecules would be moved. Typically the low frequency output of large drivers41increase relative to mid-band output because of diaphragm area as mass deters output at higher frequencies. The DCEATL5low 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. 14Crepresents 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. 14Crelative to adjacent frequencies.FIG. 14Aindicates the impedance ofFIG. 5andFIG. 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 the EATL5dominates the drivers' impedance with little effect on the driver41/EATL5operating parameters from the addition of the acoustic low pass filter. InFIG. 14Athe large peak K represents the impedance of the driver inFIG. 5. The small peak J trailing the driver peak L inFIG. 14Awould 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 the same EATL5peak that was observed in the impedance peak ofFIG. 12B,FIG. 13A,FIG. 13Bexcept 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 EATL5will lower the EATL5peak, 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. It is also observed as shown inFIG. 13Dthat the output will fall after the main EATL5peak but the close coupling will load the driver to the EATL5cut-off frequency of near 15 Hz. If it is observed carefully the output curve R ofFIG. 13Dof the sub-bass enclosureFIG. 6has its' highest output at the EATL5peak of 35 Hz which is an extraordinary feature. The reason for this can be seen if the curves ofFIG. 14Dare observed.FIG. 14Drepresents 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 its' surface boundary area24where it will show the curve of the EATL5. Curve N is indicating the output at the port17of the same sub-bass speaker ofFIG. 6and it can clearly be seen a large shift in phase beginning at 55 Hz which is near the box tuning frequency. The outputs of the DD3and the port17are remarkably similar until the phase begins to shift at the box frequency G ofFIG. 14Aproducing the initial rise in output as seen in curve RFIG. 13Dat G. The phase curve MFIG. 14Dof 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 DD3is 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 EATL5feedback 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-loaded driver41is 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.

Of course as with the EATL5DRE29D enclosures multiple units of the IRE29I may be configured to increase the output as a combined coherent source as inFIG. 8Athe 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. 8Bto have the EATL5peak 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 preferred example of an extreme application of the IDC and DC systems used concurrently for a single sound system is illustrated by the graph ofFIG. 14B. The curve inFIG. 14Brepresents 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. 1andFIG. 6. They are the left speakerFIG. 1, the right speakerFIG. 1and the subwooferFIG. 6that reproduces the lower bass from both channels. The 3-inch driver41as inFIG. 1is 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 EATL5to 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. 14Bis 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 been involving the validation of the effectiveness of a very simple process. Only a few drawings are needed to express this basic technology that improves the quality of sound so effectively. 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 EATL5to the atmospheric pressure including in some ways the basic principles of the EATL5. Any use of the principles discussed within this document is an infringement even if these changes or modifications are not expressed explicitly here. Once a person skilled in the art realizes the immediacy of the problem sees the drawings and experiences the sonic differences it will be very easy to duplicate and enhance the process without understanding the theory to a great degree. Any devices deriving their basic purpose for the same reasons that the EATL5derives its' purpose are in violation of this technology if the same basic elements coupling the driver41for the same purpose are physically connected to the enclosure in the same manner. This means that relocating certain features to various locations will not allow a violation to be overcome as all research on the depth of features and implementation has not been investigated and will be a continuing effort of the inventor.