EP0040281A1

EP0040281A1 - Loudspeaker and enclosure system with digital encoding phase shifted crossover network and self contained digital power drive system, and a modular method of utilizing moulded inserts

Info

Publication number: EP0040281A1
Application number: EP80400691A
Authority: EP
Inventors: Walter Carl Thomas; Wayne William Thomas
Original assignee: LADY BEA ENTERPRISES Inc
Current assignee: LADY BEA ENTERPRISES Inc
Priority date: 1980-05-20
Filing date: 1980-05-20
Publication date: 1981-11-25
Also published as: WO1981003595A1

Abstract

A loud speaker and enclosure system that has improved acoustical properties, comprises a cubical frame (12) composed of two sidewalls (21, 22), a top (18) and a bottom (20), having an open front and back. The frame (12) is made of substantially rigid material. The backwall is closed by means of a panel (23) of styro-foam. An acoustical horn (14) in the form of a truncated square pyramid is molded from foamed plastic and is of such size as to be fitted into the inner space of the frame with the wide end of the pyramid atthe front end of the frame. Means are (42, 44) provided at the corners of the pyramid, forattachmentto the frame (12). Along the walls (36) of the horn (14) there is a space (29) between the walls (36) of the horn (14) and the walls (18,20,21,22) of the frame (12), of selected dimension. At the small end of the horn (14) is a transverse wall (40), which has a circular opening (38). A low frequency, large diameter, cone type speaker (52) is fastened to this wall (40), mounted inside of the horn (14), with the cone facing toward the back of the frame. A structure (60), is mounted to the loud speaker (52) and supports one or more higher frequency, smaller speakers (66, 68A, 688), which are faced toward the front of the frame.

Description

This invention lies in the field of acoustical loud-speakers. More particularly it concerns a construction for a loud speaker enclosure system which has superior acoustical properties.
In the prior art there are many types of loud-speaker enclosures that have been designed, many of which utilize a horn, or a folded horn. However, in all those instances known to the inventors, the horn is not truncated, and the sound enters the horn from the small end and is directed downwardly inside of the horn to the large end. In this design the reverse is true, and the sound from the principal low frequency speaker is directed into the space surrounding the horn between the horn and the enclosure, with means for sound emergence around the circumference of the horn.
Prior art in time delay echo systems for speaker enclosures had realized limitations to the fact that the time delay was adjustable only manually to a specified amount and usually left at the same duration for a particular listening performance. The soft passages had the same amount of time delay treatment as the loud passages. This introduced distortion and unrealistic reproduction of the original sound as recorded.
On the premise that loud sounds echo longer than soft sounds; there a need realized for realistic reproduction of time delay simulation with separate automatic time delay control. Further, separate treatment is needed in different band-width zones.
These and other disadvantages of the prior art are overcome by the automatic variable time delay features of this circuit, causing the loud passages of the recorded sound to delay the louder segments of sound longer on an independant basis even in different specified band- width zones. Thus, a clearer more concise reproduction combination of the original sound and echo variations are achieved automatically throughout succeeding sound passages with less distortion. Digital power boosting was added to reproduce the final separately delayed bandwidth audio zones more accurately.
The combination of these automatic time delay controls for the various bass, midrange, and tweeter (high frequency) bandwidth audio zones, with separate digital booster powering of each bandwidth zone overcomes to a much greater degree of accuracy the distortion and echo time delay problems of the prior art.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components. It is understood that the invention is not to be limited to the specific embodiments set forth herein by way of exemplifying the invention, but the invention is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element or step thereof is entitled.
It is a primary object of this invention to provide a loud speaker and enclosure system, having superior acoustical properties.
It is a further object of this invention, to provide a loud speaker enclosure system that provides for flexible walls in the enclosure, and in the speaker mounting system, so that low frequency acoustic energy, can be transmitted through the walls and high frequency noises can be absorbed.
These and other objects are realized and the limitation of the prior art are overcome in this invention, by providing a rigid three dimensional structure, or frame, that serves as an enclosure for the speaker system and also provides a framework to support the various parts of the loud speaker system.
In one embodiment the enclosure, or frame, is in the form of a cube with side walls, top and bottom, but with no front or back wall. A back wall is provided of a planar sheet of foamed plastic, such as styrofoam, which is attached to form a back closure of the frame.
A truncated pyramidal horn is provided of selected dimensions such that it will fit within the inner walls of the frame, with the wide portion of the horn at the front end of the frame. The angle of the walls with respect to the axis of the horn is a selected angle. The horn is truncated, and provided with a closure wall at the small end, such that the plane of the closure wall is substantially halfway between the front and back planes of the frame.
A circular opening is provided in the transverse wall closing the small end of the horn, and a low frequency loud-speaker of the cone type, is mounted to that closure wall with the speaker inside of the horn and the cone facing outwardly toward the rear wall of the frame. Means are provided for mounting the horn to the frame at the front end thereof.
A suitable structure, preferably made of foamed plastic, is provided for support of one or more higher frequency, small, loud-speakers attachable to the low frequency speaker. The small speaker, or speakers, are directed toward the front of the frame. The front may be covered with a porous cloth or screen, such as is well-known in the art.
While this invention has been described in terms of a frame of square cross-section, it is possible also to provide an assembly which is rectangular in shape at the front of the frame. Such a rectangular frame would include a horn having two parallel, opposed walls, and two sloping walls. Again, as in the square design, the sloping walls of the horn are spaced from the wall at the front, to form slots of selected width at top and bottom of the frame.
In another embodiment, the frame is made in a cylindrical form, and the horn to which the speaker assembly is mounted, is a conical horn, of diameter at its wide end, which is smaller than the interior diameter of the frame, by a selected dimension. Thus when the horn is positioned inside of the frame, there will be an annular gap between the horn, and the inner surface of the frame. As in the first embodiment the cone is made of foamed plastic of a selected material and wall thickness.
These and other objects and advantages of this invention and a better understanding of the principles and details of the invention will be evident from the following description, taken in conjunction with the appended drawings in which:

Figure 1 and 2 show front view and side view in section, of one embodiment of this invention.
Figure 3 is a front elevationalviewof a second embodiment of this invention.
Figure 4 is a front elevational view of a third embodiment of this invention.
Figure 5 is the basic block drawing of the electronic circuit of the above embodiments.
Figure 6 is a detailed block diagram of the digital amplifiers shown in 7a, 7b, and 7c of Figure 5.
Figure 7 is an additional embodiment of this invention; an expanded use of the above embodiments.

Referring now to the drawings and in particular to Figures 1 and 2, there are shown two views of one embodiment of this invention. Figure 1 illustrates a front view of the invention, indicated generally by the numeral 10. Figure 2 illustrates a side view, in section, of the same embodiment, taken along the plane 2-2 of Figure 1.
The enclosing structure of the assembly, or system, is a frame of approximately cubical shape, indicated generally by numeral 12. This includes a top 18 and a bottom 20, with two sidewalls 2l and 22, fastened together to form a rigid enclosure. The frame has no front or back walls.
As seen in Figure 2, the back is closed off by means of a panel 28 of foamed plastic, such as styrofoam, which is supported inside of the frame 12, and attached to strips 30 which are supported to the frame 12 by means of screws 31, and so on, as is well-known in the art. The styrofoam panel 28 closing off the back end of the frame 13 can be of thickness in the range of 3/4" to 1". This provides sufficient strength and rigidity of the panel, but also because of the plastic properties of the material provides the ability to vibrate and transmit acoustical waves impinging on the inner surface and transmitting them outwardly from the back surface.
The principal structure that holds the speakers, is a horn indicated generally by the numeral 14. In Figures 1 and 2 this is a truncated pyramidal horn of square cross-sections, of selected angles 34 with respect to the axis of the horn. This horn can be molded in one piece from suitable foamed plastic, and would have 4 tapering walls 36, and a transverse wall 40 closing off the small end of the horn. The wall 40 has a central circular opening 38 of such a size as to approximately equal the diameter of a speaker 52 of the cone type, which is fastened by conventional means to the transverse wall 40. The fastening can be by support ring 54 and screws 56.
At the large end of the horn 14 there are fixture- -.2 molded into the corners, such as will adapt for the tapered horn to fit snuggly into the corners of the frame 12. The horn can be fastened to the frame 12 by means such as screws 44, or other suitable fasteners. As seen in Figure 1, the walls 36 are spaced from the inner surface of the frame 12 by gaps 29, which are of width, a selected dimension 46.
The sound generated by the speaker 52, facing backward into the space 70 behind and outside of the horn, is transmitted outwardly partially by vibration of the back wall panel 28, and also by transmission of sound outside of the horn, and through the apertures, or slots, 29 and out to the front of the enclosure. There will be transmission of sound from the back surface of the cone of the speaker 52. There will also be lateral vibration, of the walls 36 of the horn, all of which together provides a flat response of considerable breadth, from very low to high frequencies.
The speaker 52 has an enclosure 58 around the magnet. A support member 60 is molded of styrofoam, or other suitable foam plastic, with a cylindrical opening 62, adapted to fit over the magnet structure 58 of the speaker. This fixture 60 can be clamped around the cylindrical surface 64, so as to be held tightly to the magnet 58 of the speaker 52.
This foamed plastic structure 60 serves to support, in any selected manner, one or more higher frequency loud-speakers, such as a tweeter 66, which is mounted facing to the front, and one or more mid-range speakers 68A, 68B. These intermediate range speakers would complete the full range of frequency from the high tweeter frequencies down to the low frequencies of the woofer speaker 52.
While we have shown in Figure 1 that the horn 14 is a symmetrical pyramid, and is fitted symmetrically into the square frame 12 to provide four openings 29 symmetrically positioned, it is possible also to provide other shapes of horns and enclosures. For example, in Figure 3 there is shown a variation of Figure 1, in which the horn is comprised of a structure which has two parallel walls 76, and two sloping walls 36A, of slope angles similar to those of Figure 1. This could be fitted into a rectangular frame 12A, to provide two slots or openings 29A at top and bottom, similar to those of Figure 1. The transverse wall 40 of the horn 14A in Figure 3, would be substantially identical to that of Figure 1, as would be the speaker assembly 16 for the two embodiments.
In Figure 4 is shown a third embodiment, which has a circular symmetry. Here the frame 12B is a cylindrical, substantially rigid frame. As in the case of Figure 2, the back wall is closed with a circular styrofoam panel, not shown. The front is partially closed by a conical horn 14B, which is fastened at a plurality of points to the interior surface of the frame, by means of cast members 42B, made of the same foam plastic of which the horn 14B is cast. In this case the transverse wall across the small end of the horn, would be circular in shape and in the form of an annular wall, just sufficiently wide to support the loud speaker assembly 16 in a manner similar to that shown in Figure 2.
Here again the horn is shown assembled symmetrically within the circular frame, providing an annular opening 29B between the outer perimeter of the horn and the inner wall of the frame.
In both Figures 3 and 4, the speaker assemblies 16 are identical, and are supported from the transverse wall 40 by conventional means, such as support rings 52 and screws 56 for example.
In all three embodiments, the slope angle of the walls of the horn are substantially the same, namely at an angle 34 to the axis of the horn 14, or to the walls of the enclosure 12. This angle 34 of the wall of the horn 14 can be in the range of 15° - 30°. More preferably it can be in the range of 20° - 25^0. The optimum angle has been found to be 23°.
The wall thickness of the styrofoam horn 14, like that of the back panel 28 is in the range of 3/4" to 1".
The position of the transverse wall 40 is substantially in the midplane 46 between the front face 24 of the frame, and the back closure panel 28. Thus, as in Figure 2 dimensions 47 and 48 are substantially equal, and half of the dimension 50.
One characteristic of this invention is that low frequency energy is directed into the space surrounding the horn, where part of the enclosing walls are made of flexible foamed plastic, whereas the high frequency energy is directed directly to the front of the enclosure, from inside of the horn.
In Figures 8 and 10 are embodiments, utilizing the concept of polystyrene foam molded speaker inserts. Figure 9 is a rigid outer housing for the inserts of Figures 8 and 10. The outer housing 1 of Fig. 9 can be made of aluminum, plexiglass, or laminated wood, molded fibre glass (blown), or any material of rigid density. The base 2 of Figure 9 can be of any suitable material to support the speaker. The grill-cloth can be wrapped and glued to the polystyrene insert of Figures 8, 10, or 11 before being inserted from the back and slid to the front. Optionally a rigid grill cloth (frame mounted) can be slid into an aluminum "L" shaped mounting ring 3 mounted on the end or inside of the outer housing 1.
In the one piece molded insert of Figure 8 the molded horn portion is the same inside as horn 14 in Figure 2. The circular horn of Figure 9 is dimensionally identical to the circular horn of Fig. 4. The circular holes 8 - Figure 8 - are for small mid-range speakers. The tweeter mouth 7 of Fig. 8 is also dimensional as in Fig. 3. Also a small tweeter opening 7 of Figure 10 is dimensional as shown in Figure 3. The bass vents 11 of Figures 8 and 10 are dimensional as shown in Figure 1.
In Figure 11 is shown an embodiment to accommodate many inserts of the configuration of Figures 8 and 10, which when.the holes 10 are filled with speaker inserts combine to make a large auditorium type speaker conducive to the multi-speaker digital power booster multiplexing system whose circuit is described in Figure 7. This multi-speaker can be made of any semi-rigid material such as polystyrene, and inserted into a rigid frame.
In Figure 5 is shown the electrical circuit for the enclosure system. In this embodiment, three bandwidth zones for the bass, midrange, and tweeter sections are utilized. However, one or more can be utilized separately.
For this description only the mid-range B treatment of frequencies shall be traced; the others are the same with only the initial bandwidth filters differing in their specific frequency ranges (i.e. bass bandwidth, and tweeter high frequency bandwidth zonesi.
The audio signal attenuated to pre-amp level by variable resistor 11 is fed to filter 2, which by known and standard methods filter the audio signal to include only the mid-range frequencies. (Nominally in the range of 250 Hz to 3 or 4 thousand Hz.).
The filtered audio signal emerges at 2a and is taken off at 15b where it is rectified by standard and known procedures and the negative going output of rectifier 15b fed into voltage controlled oscillator 4b. Variable resistor 15c allows the VCO 4b to be positively biased to set the oscillation of VCO 4b in the proper frequency range with the negative going output of 15b decreasing the speed of VCO 4b as loud or more powerful fluctuations of 2a are passed by filter 2. This has the effect of slowing down the frequency sensitive control input l6b of Delay 5b. (This is a 512 stage serial analog delay-SAD-lines type such as the SAD-1024A chip) which normally utilize an external clock to set the delay times - but in this case VCO 4b automatically sets the drive time oscillation speed which determines the length of delay at various precise moments.
The automatically delayed analog audio signal is then fed to analog to digital converter 6b where (this can be' a 4 bit, 8 bit, 16 bit, or any size bit configuration depending on the amount of accuracy decoding desired - in this case, nominally an 8 bit word or byte is considered sufficient) via 14b the 8 bit word byte digital signal is fed to digital power booster amplified 7b which ultimately powers the mid-range speakers 9a and 9b.
The digital power booster amplifier will be described in Figure 6 and the following text. The analog to digital converter 6b and digital amplified 7b will be synhronized by control clock 5 of Figure 6 to connection 11 of Figure 6, via line 22b of Figure 5.
In Figure 6 the digital power amplifier section is shown. The heart of this power amplifier is the SCR line 3, which overcomes the prior arts in-ability to digitally generate enough power to drive high power speakers. SCR's are readily available in practically any power or amperage rating desirable. However they have one drawback which has eliminated them in the past for high power digital sound reproduction; namely when they are gated on by the control pulse they stay on until sufficiently reverse biased or their main source of power disconnected; turned off. This tended to eliminate the on and off requirements of digital audio reproduction for SCR's because audio frequencies do turn on and off at a relative high speed.
This objection in prior art has been overcome by powering the SCR line 3 (eight SCR's in this case to accept the incoming 8 bit word bus 1) with a high amperage, high frequency A.C. power supply 4(only this power supply oscillates at nominally 50,000 Hz instead of the usual D.C. or 60 Hz). Further the H.F. A.C. power supply is controlled or synchronized with the 8 bit shift register 2 by the same control clock 5 which clocks the digital information coming in on bus 1 from analog tot digital converter 6b of Fig. 5 via line 7.
An out of phase negative pulse on line 6 is simultaneously fed to the H.F. A.C. power supply 4 while it simultaneously feeds a positive pulse via line 7 to the eight clock inputs of the 8 bit shift register 2; causing the new information to be loaded on the right side of the shift register 2a'b'c'd'e'f'g'h', while the SCR line 3 is turned off. Conversely while the clock 5 is loading the shift register 2abcdefgh (while its square wave is negative going to line 7) it is simultaneously exiting the positive going edge of its positive swing, via line 6, to the H.F. A.C. power supply 4 to send a powerful power pulse to read and execute the digital word byte present at the gates of the 8 SCR line 3, as read from 2 a'b'c'd'e'f'g'h'.
Via line connection 11, the digital to analog converters of Figure 5 are clocked in step or synchronization to keep the whole system in sync, or step with itself.
So the whole process continues at 50,000 Hz (or at least two times the highest frequency of the bandwidth to be amplified) to continuously analyze, convert (at A/D converters of Figure 5), read and clock the digital audio word byte (at the shift register 2 abcdefgh and a'b'c'd'e'f'g'h'), assume its digital power state at SCR line 3, and recombine through the 8 bit resistor ladder 12, exiting a clean accurate digitally boosted analog signal at 10 to power the respective speaker.
The resistor ladder 12 is made up of 8 resistors of proper wattage and resistance to handle the power amperage rating selected for the H.F. A.C. power supply 4 (this determined by the power requirements of the speakers). Once the value for R has been selected it is binarily multiplied according to the ~ ± procedures (i.e. α X R, 6X R, C X R, α X R, h X R, g X R, f X R, e X R), and inserted into the resistor ladder network to correctly convert the power digital signal back to analog for connection to the respective speaker assemblies 58, 68B, 66, and 68A of Figure 1; with zero potential between d+ h.
digital booster power line A of Figure 5 being fed to bass speaker 8 of Figure 5 (58 of Figure 1) via line 23 of Figure 5,
digital booster power line B of Figure 5 being fed to mid-range speakers 9a & 9b of Figure 5 (68B & 68A of Figure 1) via lines 24a & 24b of Figure 5, and
digital booster power line C of Figure 5 being fed to tweeter speaker 10 of Figure 5 (66 of Figure 1) via line 25.
The digital booster power lines A,B & C of Figure 5 can optionally draw their power and synchronizing clock pulses from a single clock and H.F. A.C. power supply; in which case H.F. A.C. power supply 4 of Figure 6 would set or designed at the maximum power requirements to handle the amperage drain of all the digital booster power lines, and clock 5 of Figure 5 set at maximum speed (i.e. at least 50,000 Hz to give a 25 kHz frequency response for the system. In this case filtering of the bandwidth zones would rely entirely upon the conventional filters 1,2 & 3 of Figure 5.
However limitations of the prior art in filtering these band- width zones are further overcome by introducing digital filtering by utilizing separate E.F. A.C. power supplies and control clocks for each digital booster power line A,B & C of Figure 5.
In the case of digital booster power line A of Figure 5, which powers the bass speaker 8, the maximum frequency allowed to be amplified is held to 250 Hz by setting the control clock 4 of Figure 6 at 500 Hz (using the rule of thumb 2X factor any frequencies over approximately 250 Hz simply would not be decoded). Additionally by specifying a high volt/amp H.F. A.C. power supply the bass frequencies decoded would be attenuated. (The H.F. A.C. power supply in this configuration oscillating at 500 Hz in sync with clock 5 of Figure 5).
In the case of digital booster power line B of Figure 5 which powers the mid-range speakers, 9a & 9b, the maximum frequency allowed to be amplified is held to approximately 3500 Hz setting the control clock 4 of Figure 6 at 7000 Hz. (Again, using the rule of thumb 2X factor any frequencies over 3500 Hz would not be decoded.) Conversely the lower bass frequencies would be held down to a minimum by not using as much volt/amp power in the H.F. A.C. power supply. Power line C would use a 50 kHz clock.
In Figure 7 is shown a multi-speaker enclosure installation in a large auditorium or system. The digital audio words of line A,B & C can be taken off at data busses l4a, 14b & 14c of Figure 5 and fed to any number of the above described speaker systems 1 containing, individually, only the digital amplifiers of Figure 6. (The clock sync pulse output of 11 Figure 6 and H.F. A.C. power supply output 14 of Figure 6 being supplied to all the speakers or systems externally.) These "slave" speaker enclosures would physically be the same as in Figure 1 but would only have the electronics as shown from the right of dotted line 18 of Figure 5, with external encoding via data busses 14a, 14b, and 14c, and sync from output 11 of Figure 6 and H.F. A.C. power supply output 14 of Figure 6. (Again optionally, one feed of sync and H.F. A.C. could power any number of speakers or systems as long as clock 5 of Figure 6 speed was approximately 50 kHz, or two times the frequency response desired, and H.F. A.C. power supply 4 of Figure 6 was of sufficient amperage to meet the requirenents of the additional slave units or systems.)
The above arrangement would cut the cost of amplifiers in a large installation and overcome the disadvantage and problems of impedance matching and power loss in large systems, plus have the accuracy of digital amplification uniformally.

Claims

1. A loud-speaker assembly and enclosure system, comprising:

(a) A three dimensional frame enclosing a volume of selected shape, and having an open front and back; said frame, made of substantially rigid material;

(b) Means to enclose said back of said frame with a planar sheet of foamed material of selected composition and thickness, attached to said frame;

(c) A truncated tapering horn, of overall dimension across the large end, a selected dimension less than the internal dimension of said frame; said horn made of foamed material of selected composition and wall thickness; the small end of said horn closed with a wall of said foamed material; and means to support said horn to said frame at a plurality of points around the perimeter of said horn, near the front end of said frame, such that when said horn is positioned inside said frame, the space between said horn and said back closure communicates with the front of said frame through openings of selected width over at least a portion of its perimeter;

(d) A circular opening in the transverse wall across the small end of said horn, and means to mount a large diameter cone speaker, inside said horn across said circular opening, facing to the back of said frame; and

(e) Means to mount at least one high frequency speaker, inside said horn, facing toward the front of said frame.

2. The assembly as in claim 1 in which said frame and said horn are rectangular in cross-section, and said horn is supported in said frame at the four corners.

3. The assembly as in claim 2 in which said horn is positioned inside said frame, including at least one opening along at least one wall of said horn, said at least one opening of selected width.

4. The assembly as in claim 1 including also at least one intermediate frequency speaker mounted inside said horn facing toward the front of said frame.

5. The assembly as in claim 1 in which said frame and said horn are circular in cross-section and said horn is supported in said frame at a plurality of points around its perimeter.

6. The assembly as in claim 5 in which said horn is positioned inside said frame including at least one opening along at least a portion of its perimeter, said opening of selected width.

7. The assembly as in claim 5 in which said horn is symmetrically positioned in said frame, providing an annular opening between the perimeter of said horn and the inner surface of said frame.

8. The assembly as in claim 1 in which the slope of the wall of said horn makes an angle with the axis of said horn in the range of the 15° to ₂₅ ⁰.

9. The assembly as in claim 8 in which said angle is in the range of 20° to 25°.

10. The assembly as in claim 8 in which said angle is 23°.

11. The assembly as in claim 1 in which said opening between the perimeter of said horn and the inner surface of said frame is of width in the range of 1/4" to- 3/4".

12. The assembly as in claim 11 in which said width is in the range of 3/8" to 1/2".

13. The assembly as in claim 1 in which the mounting plane of said large diameter cone speaker is approximately midway between the planes of the front and back of said frame.

14. The assembly as in claim 1 in which said planar sheet of foamed material is of thickness in the range of 3/4" to 1".

15. The assembly in claim 1 in which said truncated tapering horn is of wall thickness in the range of 3/4" tot 1".

16. An electronic digital circuit mounted inside of the speaker enclosure of said claims 1,2 and 5, comprising;

(a) means to conventionally filter one or more separate bandwidths from the output of an analog pre-amp or amplifier (i.e. bass midrange, or high frequency range bandwidths);

(b) means to rectify separately, part of said audio signals to a D.C. negative voltage which varies with the strength of the said filtered audio signal;

(c) means to bias a voltage controlled oscillator (VCO) with a positive D.C. voltage to its control input thereby setting its oscillation at a desired frequency range, by means of a variable resistor connected to a positive D.C. power source.

(d) means to connect output of said negative D.C. rectifier of said claim l6b to the control input of said VCO of claim 16c, to automatically decrease the frequency of said VCO when audio level of said bandwidth of claim l6a increases;

(e) means to connect the output of said VCO of claim 16c, to the control input of a (SAD) type delay chip.(such as the SAD1024+A which is a 512 stage serial analog delay which is frequency controlled, i.e., lower frequencies delaying longer than higher frequencies);

(f) means to connect the output of bandwidth filters of claim l6a individually to (SAD) type delay of claim l6e, with a manually adjusted trimming potentiometer;

(g) means to directly connect the output of bandwidth filters of claim 16a, individually bridging to the outputs of the (SAD) type delays of claim 16e, to combine the direct portion of the said filtered audio to the echo portion of the said automatically delayed audio signal.

17. Additional electronic circuits to power amplify either the filtered bandwidth audio outputs individually of claim l6a; and the echo delay portions of claim l6f; or to individually amplify the combined direct and echo portion of audio of claim 16g; either through conventional power amplifiers or by a digital power amplification system comprising:

(a) means to connect the bandwidth filtered, automatic delayed echo, or combined direct and delayed audio signals of claim 16 individually to analog to digital converters of appropriate bit size configuration for conversion to a digital format;

(b) means to control the conversion rate or frequency response of the said analog to digital converter (ADC) of claim 17a with one of the outputs of a dual out of phase digital clock generator (one of the_' said outputs being out of phase with the other 180 degrees);

(c) means to bus the output of said ADC of claim 17b to the the inputs of 8 (or more) bit ;

(d) shift register whose clock shift control input is connected to the in-phase output of said dual clock generator of claim 17b, synchronizing them;

(e) means to connect the output or right side of the shift register of claim 17c to the gate inputs of the silican controlled rectifier (SCR) line of the digital power amplifier;

(f) means to connect the output of the high frequency A.C. power supply to the positive voltage inputs of the SCR's;

(g) means to control and synchronize the speed of the alternating current of the said high frequency A.C. power supply of claim 17f, by control out of phase clock pulse of said dual clock of claim 17b, causing the said H.F. A.C. power supply to turn off and on synchronously with the A.D.C. of claim 17a, making the SCR's of claim 17e to turn off and on synchronously as gated by the digital word dyte present at the output of the said shift register of claim ^17c;

(h) means to connect the respective outputs of the SCR's of claim 17e to a digital resistor ladder network consisting of consecutive resistors each being of the same amperage but twice the resistance of the in series resistors in the network, as shown in Figure 6;

(i) -means to tie the ends of the resistors of claim 17h to a common bus to power the respective analog speaker, thus summing the digital outputs of the SCR line of claim 17e, as shown in Figure 6;

18. A digital power booster multiplexing system comprising:

(a) means to transmit the bass filtered and processed digital word byte by digital bus from the outputs of said shift registers of claim 17e to the respective said SCR gate input lines of SCR line of claim 17e, digital power booster as in Figure 6, slave amplifiers connected to bass speakers, in a system of one or more speakers;

(b) means to transmit the mid-range filtered and processed digital word byte by digital bus from the outputs of said shift registers of claim 17e to the respective said SCR gate input lines of (SCR line of claim 17e) all digital power booster as in Figure 6, slave amplifiers connected to mid-range speakers, in a system of one or more speakers;

(c) means to transmit the high frequency filtered and processed digital word byte by digital bus from the outputs of said shift registers of claim 17e to the respective said SCR gate input lines of (SCR line of claim 17e) all digital power booster as in Figure 6, slave amplifiers connected to high frequency tweeters in a system of one or more speakers.

(e) means to transmit a control sync pulse from said dual clock of claim 17b to the shift registers clock inputs (said shift register of daim 17c) of all the digital power booster salve. amplifiers of claims 18a,b & c;

(f) means to connect the high frequency A.C. power supply of claim 17f to the SCR positive voltage inputs (said claim of 17f) of all the SCR lines in the multiplexing system of said claim 18.

19. A modular method of utilyzing mass produced polystyrene molded inserts comprizing:

(a) means to insert a modularly molded polystyrene insert with dimensionally formed as in said claim lc & ld, but of the design characteristics of Figure 8;

(b) means to insert a modularly molded polystyrene insert being dimensionally formed as in said claim 5, but of the design characteristics of Figure 10;

(c) means to insert the said molded insert of said claims 19a and 19b into a rigid square or rectangular housing of wrapped aluminum, plexiglass, laminated wood, or blown fibre glass;

(d) means to wrap and glue a grill-cloth around the said molded insert of claims 19a & 19b before inserting said mold into said housing claim 19c;

(e) means optionally to mount an "L" shaped acceptance ring inside of the front of said rigid housing of said claim 19c to accommodate a grill-cloth mounted on a frame;

(f) means to form a multi modularly molded polystyrene insert molded with two or more openings of the same design of the molded configurations of any combination of the above said inserts of said claims 19a & 19b.