Hydrodynamically pressure regulated loudspeaker systems

The invention is a low frequency ported loudspeaker system comprising a hollow rectangular enclosure, the enclosure having a woofer driver airtight mounted to an aperature of the enclosure, changes in air pressure of the invention's enclosure's interior air mass are reduced by the coaction of a liquid mass contained within an open-ended manometer type structure, inlet of open-ended manometer type structure being attached to the enclosure and is in pressure conveyance with the invention's interior air mass.

SUMMARY OF THE INVENTION 
The invention is an improved low frequency loudspeaker system. The 
invention provides a means of extending the low frequency range and 
improves the loudspeaker's performance throughout the low frequency range. 
The invention is able to accomplish these improvements by utilizing the 
physical structure of the enclosure which includes the utilization of an 
open-ended manometer type device. The invention possesses a structure 
which is relatively easy to construct. 
Historically, the function of a low frequency loudspeaker enclosure is to 
control the compressional energy waves produced by the oscillating 
diaphragm of an electrical low frequency loudspeaker (i.e. "a woofer" or a 
low frequency driver). These compressional air waves generated by the 
front and back surfaces of the low frequency driver's diaphragm are 
phasically destructive to one another. To prevent these waves from 
physically meeting, the compressional air waves produced by the back 
surface of the low frequency driver's diaphragm are collected in an 
airtight box (i.e. the loudspeaker enclosure). To facilitate the 
collection of this energy, the low frequency driver is securely mounted in 
an airtight fashion to an aperature located on the loudspeaker enclosure. 
There are basically three design types of low frequency enclosures, the 
acoustical suspension system, the transmission line system, and the ported 
system. These three systems treat the compressional air energy within the 
enclosure differently. It is the common intent of these systems to prevent 
the phasic destruction of the produced air waves. In the acoustical 
suspension system there is a force on the low frequency driver's diaphragm 
caused by the difference in the kinetic energy content of the air inside 
the enclosure and that of the air exterior to the enclosure. 
This force can be qualitatively thought of as an "air spring force". It can 
be used as a damping force to control speaker excursion. The disadvantages 
of this force is that it can prevent the lower portion of the low 
frequency range from being reproduced and can reduce the efficiency of the 
low frequency driver's performance. The magnitude of the "air spring 
force" can be reduced or increased by changing the interior volume of the 
enclosure. 
Another performance reducing feature of the "air spring force" is the 
promotion of excessive loudspeaker diaphragm excursion, causing an 
increase in distortion. The "air spring force" can act as a controlling 
force until the internal air pressure within the enclosure builds up, this 
pressure increase causes an excessive "air spring force" creating excess 
loudspeaker excursion. 
A transmission system is not significantly different from an acoustical 
suspension system. Its interior enclosure volume contains a labyrinth for 
channeling the compressional energy produced by the back surface of the 
low frequency driver's diaphragm. The purpose of the labyrinth is to 
attenuate this energy and in doing so, achieves a reduction of the 
interior's "air spring force". The transmission system in reducing the 
"air spring force" is able to mimic the internal pressure response of a 
much larger loudspeaker enclosure. 
The ported system makes use of its enclosure's interior air compressional 
energy by creating the "air spring force", and also by creating an 
oscillating mass of air (i.e. an "air piston") in its port which acts as a 
passive radiator (i.e. a clone speaker) of low frequency sound. A port is 
a conduit connecting an enclosure's interior air volume with the air 
exterior of the enclosure. Ported systems typically require a medium or 
large size enclosures. Bass waves are relatively large (eg. 11 feet long 
@100 Hz) and the compressional energy associated with these waves makes 
designing a ported system for small enclosure a difficult task. The "air 
spring force" acts on the driver's diaphragm and, in addition, it acts on 
the air mass residing in the portal volume producing it oscillating piston 
motion. Should this force be too large, the portal air will cease to act 
as an oscillating piston and will turn to "wind" which is turbulent and 
acoustically not valued. To avoid this turbulent portal wind, a designer 
may select a larger interior air volume. 
In the three types of low frequency systems described here, the interior 
air volume of the enclosure must be considered in the system's design. To 
change the enclosure's volume is to change its "air spring force" or the 
change in pressure (change from ambient within the enclosure). 
To have the ability to physically simulate the internal pressure response 
of a larger enclosure using a smaller enclosure may be desirable from a 
logistical consideration (i.e. taking up less space in the listener's 
room). In engineering terms, having the ability to simulate the interior 
air pressure behavior of a larger enclosure using a smaller enclosure 
provides a means of lowering the system Q for a smaller enclosure. 
The invention provides a means for reducing the average change in the air 
pressure occuring within its interior's air volume and, in doing so, is 
able to physically simulate the average interior air pressure behavior of 
a larger enclosure. 
It is the ability of the invention to perform this reduction of its changes 
in its interior air pressure which is the main inventive concept of the 
invention. The invention, in its ability to physically simulate the 
average pressure behavior of a larger enclosure volume, is able to extend 
the operational range of the low frequency range and is able to improve 
the operational efficiency of the loudspeaker system throughout this 
range. The invention accomplishes this pressure regulation feature in a 
manner which will be described in written form referencing the 
accompanying figures. 
The following written description of the invention and the accompanying 
figures serve to define the invention and its merits. The following is a 
summary of the accompanying figures;

DETAILED DESCRIPTION OF THE INVENTION 
The structure of the invention is a hollow rectangular enclosure, FIG. 1, 
comprised of six plane sides, elements 1, 2, 3, 4, 5, 6 of FIG. 1, these 
sides are to be composed of sheets of a rigid, high density material 
having uniform thickness, these sides to be joined to one another in a 
rigid, airtight fashion. The purposes of invention's sides are to confine 
an air mass within the invention, and to act as a supporting structure. 
A low frequency driver is rigidly mounted in an airtight fashion upon the 
periphery of a primary aperature, element 7 of FIG. 1, the center of the 
primary aperature, element 7 located on the horizontal center axis of the 
front side, element 1. 
A rectangular front side, element 1 of FIG. 2, with width, element 8, and 
heighth, element 9, possessing as a minimum values such as to accommodate 
the dimensions of the chassis of the low frequency driver and the 
perpendicular, external flush, airtight mounting of a circular port 
conduit, element 10, to a second aperature, element 11 of the front side, 
element 1, the second aperature, element 11, to lie above the center 
horizontal axis, element 12, of the front side, element 1. The port 
conduit, element 10, to be dimensionally selected to achieve a 
pre-selected Helmholtz resonance of the enclosure. 
The back side, element 3 of FIG. 3, possesses the same heighth and width as 
front side, element 1, and is exactly parallel with the front side, 
element 1, separated by the width, elements 13 and 14, of the 
perpendicular lateral sides, elements 2 and 4, these widths, elements 13 
and 14 possess, at a minimum, dimensional values equal to the diameter of 
the loudspeaker driver's chassis. The heighth elements 15 and 16 of 
lateral sides, elements 2 and 4 possess at a minimum values equal to their 
respective widths, elements 13 and 14. The lower portion of elements 15 
and 16, of the lateral sides, elements 2 and 4, serving to elevate and 
support the enclosure box a distance, element 16a, of sufficient dimension 
such as the accommodate heighth element 17, plus clearance dimension 
element 18. 
The top side, element 5, perpendicularly intersecting the planes of the 
front side, element 1, back side, element 3, and lateral sides, elements 2 
and 4, element 5 acting as a top boundary for the enclosure, FIG. 1. 
The bottom side, element 6, is exactly parallel with top side, element 5, 
separated by a distance element 15, element 6 is dimensionally equal to 
the top side, element 5, with the exception that element 6 possesses an 
aperature, element 19, the area of element 19, to provide an air pressure 
diffusion area possessing at a minimum a dimensional area equal to the 
effective loudspeaker diaphragm area located at the geometric center of 
bottom side, element 6, a waterproof conduit element 20, is 
perpendicularly extending from the bottom side, element 6, and is rigidly 
mounted to the periphery of aperature, element 19; in an airtight fashion, 
the exterior length of the conduit, element 20, to possess at a minimum a 
value such as to accommodate twice the volumetric displacement, Vd, of the 
low frequency driver's diaphragm's excursion, the bottom portion, element 
21 of element 20, to be immersed in liquid contained within element 22, 
the liquid, element 23, possessing as a minimum a depth such as to 
accommodate the volumetric displacement, Vd, of the low frequency driver's 
diaphragm's excursion, a waterproof cup-type structure element 22 
possesses a heighth element 17, element 22 possessing sufficient dimension 
such as to permit the liquid surface cross sectional area, element 23a, 
(i.e. the liquid surface area existing between the inner dimension of 
element 22 and the outer dimension of conduit, element 20), to possess at 
a minimum, an area equal to the area of element 19. The liquid, element 
23, filling element 22, is to have a density of 2 gm/cc (+/--gm/cc. The 
heighth element 17 of element 22 of dimension such as to accommodate at 
least three times the volumetric displacement, Vd, Vd associated with the 
maximum linear excursion of the loudspeaker's diaphragm. 
An aperature, element 24, on the back side, element 3, element 24 is of 
sufficient dimension to facilitate the passing of two electrical wires. 
These wires are used to supply the transmission of electrical power to the 
low frequency driver's motor. Element 24 is sealed in an airtight fashion 
about the electrical wires. 
The chief merit of the invention is its ability to emulate the change in 
pressure behavior of the interior air of a larger enclosure's volume. To 
illustrate how the invention is able to accomplish this, a qualitative 
analysis of the energy content of the invention possessing a volume V is 
presented in conjunction with an analysis for a conventional loudspeaker 
enclosure possessing the same volume V, qualitative comparison's for the 
maximum interior enclosure pressure are made for both the invention and a 
conventional low frequency enclosure as follows, (heat flow through the 
enclosure sides and air leaks in the systems are ignored). The following 
description refers to FIG. 5. The nomenclature used for the analysis is 
defined here. 
______________________________________ 
let: Eo = initial, ambient kinetic energy content of the air 
within a volume V. 
(Ef)INV = final kinetic energy content of the interior air 
within the invention, of volume V, after 
energy, Q, has been added to the interior 
air of the invention. 
(Ef)w/o = final kinetic energy content of the interior air 
within a conventional loudspeaker's enclosure 
of volume V, after energy, Q, has been added 
to the interior air of the conventional 
loudspeaker's enclosure. 
Q = kinetic energy created by low frequence 
driver's diaphragm during its air com- 
pression excursion. 
Pa = pressure, atmospheric 
(Pf)INV = final average pressure of the interior air of 
the invention after energy, Q, has been added 
to the interior air of the invention. 
(Pf)w/o = final average pressure of the interior air of a 
conventional low frequency loudspeaker's 
enclosure after energy, Q, has been added 
to the interior air of the enclosure. 
V = interior air volume of an enclosure, 
constant. 
g = acceleration of gravity 
m = mass of liquid continued by element 25 of 
FIG. 5 within the height, h, element 26 
of FIG. 5. 
h = height element 26 is the distance between 
the liquid levels within the invention's 
structure after the addition of energy, Q. 
mc = moving mass of woofer driver's diaphragm. 
v = velocity of woofer driver's diaphragm. 
Eo = Pa V 
(Ef)INV = Eo + Q 
(Ef)INV = Pa V + Q 
______________________________________ 
At hydrostatic equilibrium of the fluid column, element 26, 50% of the 
energy added, Q, is stored in the form of potential energy in the form of 
a fluid column, element 26, with the remaining 50% of the energy added, Q, 
being responsible for supplying the incremental kinetic energy to the 
interior air of the invention, serving to sustain fluid column heighth, h, 
element 26. The product of (m g h) represents the potential energy of 
fluid column, element 26, thus Q, the energy added to the invention is 
responsible for the change in kinetic energy level of the air within the 
invention and the potential energy of the fluid column, element 26. 
Q=mgh+((P.sub.f).sub.INV -Pa)(V), at hydrostatic equilibrium, 
mgh=((Pf)INV-Pa)(V) now, ps 
EQU (Ef)INV=Pa V+Q 1) 
EQU (Ef)INV=Pa V+mgh+((Pf).sub.INV -Pa)(V) 2) 
EQU (Ef)INV=Pa V+2((Pf).sub.INV -Pa)(V) 3) 
equating equations 1 and 3, and rearranging, it is shown that for the 
invention the qualitative pressure change within volume V (change from 
ambient atmospheric pressure) is; 
EQU ((Pf)INV-Pa)=1/2 (1/V)(Q), 4) 
Performing an analysis of the qualitative change in pressure (change from 
atmospheric air pressure) for a conventional low frequency loudspeaker 
enclosure, of interior air volume, V, with the addition of energy Q is the 
following: 
##EQU1## 
The addition of energy, Q, will increase the kinetic energy of the 
interior air of said conventional low frequency loudspeaker by the amount 
Q, as follows: 
EQU Q=[(Pf).sub.w/o -(Pa)] (V), 8) 
substituting the above equation into equation 6, equating equations 6 and 
7, and rearranging, the qualitative pressure change (change from ambient 
atmospheric pressure) for a conventional loudspeaker enclosure is 
determined to be: 
EQU [(P.sub.f).sub.w/o -(Pa)]=(1/V)(Q), 9) 
comparing the above equation with that of the interior air pressure change 
of that of the invention is the following: 
EQU [(Pf).sub.INV -Pa]=1/2 (1/V)(Q), (the invention), 10) 
EQU [(Pf).sub.w/o -Pa]=(1) (1/V)(Q), (conventional enclosure), 11) 
It is seen from the above qualitative expressions for pressure changes, 
equations 10 and 11, that the invention possesses the ability to possess 
an average change in pressure which is half of that of a conventional 
enclosure. The invention is able to mimic the average change in interior 
air pressure behavior of a larger conventional enclosure, qualitatively 
the invention's average interior air pressure will be equal to that of a 
conventional enclosure possessing twice the interior air volume of that of 
the invention. This can be qualitatively seen by substituting a value of 
(2 V) for the V value in equation 11 and then comparing equation 10 with 
equation 11. 
Curves "A" and "B" of FIG. 4 qualitatively represent the change in pressure 
(Pd) versus enclosure volume (Vb). 
Referring to FIG. 4, curve "A" represents the pressure response of a 
loudspeaker enclosure volume, Vb, utilizing invention's structure elements 
19, 20, 22, and 23; Curve "B" represents the pressure response of a 
conventional loudspeaker enclosure volume Vb without the invention's 
elements 19, 20, 22, and 23. 
The slope of curve "B" is twice that of curve "A". Examining these curves 
"A" and "B" for a particular average pressure change, Pd, shows that curve 
"A", is able to possess a P.sub.d representative of a larger volume (i.e. 
a larger conventional enclosure volume). The change in pressure, P.sub.d 
of FIG. 4, is caused by the volumetric air displacement created by the 
loudspeaker's diaphragm's movement. 
The "air spring force", previously mentioned, is caused by the pressure 
differential existing between the two surfaces of the loudspeaker's 
diaphragm. During the operation of a low frequency loudspeaker system an 
average pressure increase occurs within an enclosure, this pressure change 
is caused by air displacement created by the loudspeaker's diaphragm's 
movement. 
Examining curves "A" and "B" of FIG. 4 it is seen that for a given pressure 
change, Pd*, the invention (curve "A") represents a volume of 2 units, the 
conventional enclosure (curve "B") undergoing the same pressure drop, Pd*, 
represents a volume of 1 unit. In addition to the individual change in air 
pressure caused by the movement during an individual cycle of the 
loudspeaker diaphragm, there is an incremental "build-up" in average 
interior air pressure caused by the continuous cyclic movement of the 
loudspeaker diaphragm. This operational incremental "build-up" of pressure 
within the loudspeaker's enclosure serves to create an incremental 
increase in the "air spring force" causing excessive loudspeaker diaphragm 
excursion, this causes distortion in the sound reproduction. The 
invention's elements 19, 20, 22 and 23 serve to relieve one half of this 
incremental "build up" pressure within loudspeaker's air volume, thus, in 
doing so, reduces the incremental increase in the "air spring force", thus 
reducing excessive loudspeaker excursion (i.e. distortion). The following 
equation qualitatively illustrates the relationship between the kinetic 
energy delivered by the movement of the diaphragm of the loudspeaker (i.e. 
1/2 mcv.sup.2) and the associated change in the interior air pressure, 
(dP), of the loudspeaker enclosure (of volume V). 
EQU VdP=1/2 mcv.sup.2 =Q 12) 
It is seen from equation (12) that if a finite energy is added, Q, to a 
closed volume that increasing the volume will result in a decrease in the 
pressure change and the associated "air spring force". The "air spring 
force" multipled by a loudspeaker's diaphragm's linear excursion yields 
the value of the energy opposing the loudspeaker's diaphragm's motion, 
this opposing compressional air energy serves to impair the efficiency of 
the loudspeaker system. The elements 19, 20, 22, and 23 serve to reduce 
changes in the enclosure's interior air pressure and in doing so reduces 
the opposing energy of the enclosure interior air and improves the 
operational efficiency of the loudspeaker system. The compressional energy 
increase can serve to retard the loudspeaker's diaphragm's motion in the 
lower portion of the low frequency range, a reduction of this 
compressional energy will lessen the energy opposing the loudspeaker's 
diaphragm's motion and thus will permit a lowering of the operational 
limits of the low frequency range, the elements 19, 20, 22, and 23 
facilitate a reduction is this compressional energy and hence, extends the 
lower operating limit of the low frequency range of a low frequency 
loudspeaker system. It is obvious that various physical configurations of 
the invention's elements 19, 20, 22, and 23 are possible and the inventive 
concept represented by the functionality of the invention's elements 19, 
20, 22 and 23 (in their ability to reduce the interior air pressure of a 
loudspeaker enclosure) is the inventive uniqueness of the invention. 
Elements 19, 20, 22, and 23 have the ability to be used in beneficial 
conjunction with either a ported, an acoustical suspension or transmission 
system. The invention uses a ported system in an attempt to utilize a port 
as passive radiator, making a beneficial use of the enclosure's 
compressional air. A prototype of the invention was constructed and 
performed satisfactorily. 
The dimensions of the port, element 10, are selected to achieve a specified 
Helmholtz bass resonance for the low frequency loudspeaker system; at this 
resonance the compressional air energy of the loudspeaker enclosure's 
volume is reduced (i.e. it is transformed into the oscillating movement of 
the air mass residing within the portal volume); this reduction in this 
energy serves to reduce excessive loudspeaker diaphragm excursion. It has 
been described, a means of improving the performance of a low frequency 
loudspeaker system by the usage of the inventive concept of the invention. 
The invention improves the operational performance efficiency of a low 
frequency loudspeaker system, the invention extends the extension of the 
operational low frequency range, and the invention reduces speaker 
diaphragm excess excursion. The invention here is to serve as a low 
frequency loudspeaker system when equipped with a woofer driver. The 
invention, when used in conjunction with higher frequency driver and 
appropriate electronic frequency cross over provides a broadband frequency 
loudspeaker system. 
This disclosure of the invention described herein represents the preferred 
embodiment of the invention. It is obvious that those who are skilled in 
the art can now make numerous designs which are variations of the 
methodologies and apparatus herein described and the modified application 
of the invention are possible without departing from the spirit and scope 
of the appended claims.