US2766839A - Loudspeaker system - Google Patents

Description

Oct. 16, 1956 J. J BRUCH ET AL 2,766,839

LOUDSPEAKER SYSTEM Filed March 16, 1955 2 Sheets-Sheet 1 14j Fig. 2 /e &PY/Mi WAV JORDAN J. BARUCH Fi 4 HENRY c. LANG ,WWW

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ATTORNEYS 1955 J. J. BARUCH ET AL 2,766,839

' LOUDSPEAKER SYSTEM Filed March 16, 1953 2 Sheets-Sheet 2 MS MAB us ms us RAS RAE W a 4 a Fg. 5 ua P T ua R MAS MAS ms I l l -W-II--NNW 'vvvw 'vvvx as ms RAS e R F q. 6 MR M I C un un TCMR SOUND POWER LEVEL RESPONSE IN DB 2 3 4 I 5 3 IOO FREQklJENCY IOOO I 7 CYCLES SEC.

- INVENTORS JORDAN J. BARUCH HENRY C. LANG BY/ I I ATTORNEYS LOUDSPEAKER SYSTEM Jordan J. Baruch and Henry C. Lang, Watertown, Mass., assignors to Research Corporation, York, N. Y., a corporation of New Yor-h t Application March 16, 1953, Serial No. 342554' 3 Clainas. (Ci. 131--31) The present invention relates to loudspeaker systems, and is concerned primarily withthe provision of loud- Speaker systems of simple and compact Construction which permit a Wide frequency response to be obtained from' relatively low cost Speaker driving units. More specifically, the invention is directed to Speaker enclosures of novel Construction and arrangement which, when suitably correlated with the parameters of the driving units, permit a substantial reduction in cabinet size as compared with conventional designs while providing a Wide frequency response.

The problem of obtaining adequate bass response in radio equipment and other forms of sound reproducing apparatus has received the attention of many investigators. Because of the decrease in efiectve coupling between the usual loudspeaker cone diaphragm and the air mass as the frequency is lowered, the bass response generally falls at a rate of 12 to 18 db per octave, beginning at a frequency corresponding approximately to the resonant frequency of the Speaker in free air. Thus, a loudspeaker mounted in a wall or in a large box so that one side only of the Speaker cone may radiate to the listener, shows a drop of 12 db per octave, while a Speaker mounted in an open back enclosure, on' a small battle, or in a ported or vented type enclosure will show an 18 db fall-oli? per octave.

Because of the requirement that the so-called total enclosure or closed box type have a very considerable Volume if the resonant frequency of the Speaker is not to be unduly raised by the stiness of the enclosed Volume at the rear of the Speaker, the ported or vented form of enclosure has been extensively employed. The usual type of such enclosure is cne which consists of a simple box having, adjacent the Speaker opening, a single port communicating between the inside and the outside of the box. The port introduces a mass which resonates with the box compliance, the box Volume and port size being selected to cause the resonance to occur in the vicinity of the Speaker resonant frequency. As a result, a response curve of the system shows a double peak, With a relatively high peak, Compared to Speaker mid-range output, occurring somewhat above the original resonant frequency of the Speaker and another peak, of lesser magnitude than the mid-range plateau, occurrng below Speaker resonance. The separation of the peaks above and below the tuned frequency of the enclosure is a function of box Volume, the peak separation increasing with decrease in enclosure Volume.

While it might appear that the response below Speaker resonance might be somewhat improved, as Compared with infinite baffle or total enclosure response, by moving the lower peak downwardly through use of a small Volume enclosure, it has been recognized that this leads to generally unsatisfactory results, since the upper peak is correspondingly increased in frequency and also undergoes a substantial increase in amplitude, so as to introduce a very noticeable and highly objectionable resonance. A further objection to increasing the separarates Patent ice QA tion of the peaks is that the lower peak becomes relatively less significant, since the port size, and therefore its radiation eectiveness, must be made smaller as the box Volume is decreased, in order that the box may still be tuned to the Speaker resonant frequency.

It has therefore been the practice, in vented enclosures, to employ enclosures having a Volume generally in excess of live or sh; cubic feet to provide a relatively small peai; separation, and to employ driving units that have a fairly low resonant frequency. Even in cases where large driving units having heavy magnet structure and highly compliant, large diameter cones are employed, the bass response below Speaker resonance is generally unsatisfactory since the port area is inadequate to provide appreciable radiation in the frequency range from Speaker resonance down to the lower peak, while below this peak the phase relation betwen the radiation from the front of the cone and from the port is such as to give rise to substantial cancellation, accounting for the 13 db per octave fall-oti that is characteristic of Speaker systems of this type.

With a view to providing a satisfactory wide range response characterstic in a relatively low cost unit that may be small in size compared to conventional enclosures, the present invention has as an object the provision of load Speaker systems employing enclosures of novel Construction and embodying novel principles, wherein appreciable radiation may be caused to take place at frequencies well below the normal resonant frequency of the drivi-ng unit or units.

More specifically, it is an object of the inventic-n to provide a loudspealer system wherein relatively small loudspeaker units may be utilized, such units being sufficiently small and lightweight to serve as effective radiators of high frequencies, thereby permitting the same unit or units to serve both as the low frequency and high frequency radiating elements with consequent saving in cost.

Still another object of the invention is the provision of a loudspeaker system wherein the resonant peaks that are characteristic of a ported or vented enclosure may be widely spaced above and below the nominal resonant frequency of the Speaker without involving an excessive and objectionable upper resonance peak and without depressing unduly the lower pealr. More specically, the invention contemplates a novel form of porting means for communication between the interier and the exterior of the enclosure whereby enhanced low frequency radiation from the port means may be obtained, in part through control of the phase relations and coupling characteristics between the port region and the front of the cone, in the desired frequency range.

To this end, the invention has as a feature a lendspeaker system of relatively small enclosed Volume so as to provide a snbstantial separation of the resonance peaks, the system embodying means within the enclosure to minimize the upper resonance peak, and porting means comprising a plurality of spaced apertures to provide an enhanced response in the region of the lower resonance peak. The plurality of small spaced apertures makes it possible to provide, in both the porting means and in the internal means for controlling the upper resonance peak, appropriate mass and resistance values for the proper operation of the system, and in the case of the port or vent, an enhanced radiation of the lower frequencies as Compared with conventional single port Construction.

In the drawings illnstrating the invention in its several embodiments and its theoretical aspects,

Fig. 1 is a front oblique View of one form of loudspeaker system embodying the invention.

Fig'. 2 is a vertical sectional elevation thereof.

Fig. 3 is an oblique View of an alternative embodiment of the invention.

Fig. 4- is a vertical sectonal View thereof.

Fig. 5 is a representative equivalent circuit dagram of a loudspeaker system employing a loudspeaker mounted in a vented enclosure.

Fig. 6 is a representative equivalent circuit diagram of a loudspeaker system including additional internal means for the control of the upper resonance peak.

Fig. 7 is a plot of curves illustrating the improved low frequency performance of a typical loudspeaker system embodying the invention, in comparison with systems of the same size but not utilizing the features of the invention. i

As has been indicated, the invention is primarily concerned With providing a loudspeaker system characterized by exceptionally small box Volume yet with satisfactory low requency response even where relatively small Speaker units are employed that do not possess a particularly low resonance frequency. As a result, a system having acceptably Wide frequency response may be provided at low cost, since the same driving unit or units may also be made to provide appreciable response in the region of 10 kc./s. and above, if desired.

The embodiment shown in Figs. l and 2 makes use of a plurality of small loudspeaker units Hi arranged on the front wall 12 of a generally triangular enclosure of small dimensione. By way of example, a representative system may employ' an enclosure having a Volume of only about one-half cubic foot. The structure must be rigidly constructed, With adequate wall thickness to resist vibration under the considerable pressures generated during operation. The porting or venting of the enclosure is provided by a plurality of spaced apertures 14 in the triangular top wall 16. The diameter and depth of these apertures are determined by suitable calculations based on the characteristics of the Speaker units and the Volume of the enclosure, as hereinafter fully set forth and described.

By reason of the fact that the Speaker system will preferably be utilized by mounting in a corner of a room or, still better in the intersection of Walls and floor or ceiling, the ported top wall 16 of the enclosure (or bottom, if the Speaker is inverted for mounting adjacent ceiling level) will be normal to two extended surfaces of the room. This serves to enhance the efectiveness of the low frequency radiation from the ported area of the Speaker system.

The Speaker system likewise embodies an internal ported member comprising an inclined partition 20 having spaced apertures 22 providing communication between the two chambers into which the enclosure is divided. Damping means 24 in the form of thin brous material or of other suitable composition is employed in association with the apertured partition to control the acoustic transmission therethrough. The purpose of this internal partition is to minmize the amplitude of the upper resonance peak so as to permit the use of a small Volume enclosure in the desired manner.

An alternative embodiment of the invention is illustrated in Figs. 3 and 4, wherein a single loudspeaker unit, for example a single 10" or 12" unit, may be employed in a small Volume enclosure. In this embodiment, of reetangular configuration, the Speaker 30 is mounted on one of the smaller walls in order that the ported area may utilize a relatively large wall 32, While still permitting the enclosure Volume to remain small, generally less than two cubic feet.

It is to be understood that the illustrated embodments are merely representative of possible constructions utilizng the principles of the invention, and that other forms and arrangements may be employed, constructed in accordance With the novel design principles of the invention and providing the improved response characteristics afforded thereby.

The effective utilization of the invention to provide the desired response requires that the characteristics of the enclosure, and particularly the porting, be properly correlated with the loudspeaker unit or units. While some degree of correlation of these factors has been recognized as desirable in conventional ported enclosures, the utilization in the present invention of novel elements in the system and the extension of the performance into regions beyond that heretofore atternped makes it desirable to carry out the correlation of Speaker and enclosure characteristics to a greater degree than has generally been done heretofore.

For an Understanding of the design principles involved and the mode of operation of the invention, the system Will first be described in terms of the equivalent electrical circuit of Fig. 5 which represents a loudspeaker mounted in a ported enclosure. In this equivalent circuit, current U is analogous to Volume velocity in cm. /sec., while voltage P is analogous to pressure, in dynes/cm?. The symbols are defined as follows:

MMS represents the mass associated with the coil assembly and cone assembly of the loudspeaker (in grns./cm.

CMS represents the complance of the Speaker (in cm.

sec. gm.)

RMs represents the mechanical dissipation in the speaker system (in gms./cm. sec.)

MAS represents the mass of the air load on the Speaker (same units as MMS) RAs represents the mechanical dissipation involved in the air load (same unts as RMs) MMB, CMB and RM-B represent respectvely the mass, compliance and dissipation of the enclosure MAB and RAB represent respectively the mass and dissipation (or radiation resistance) associated with the port in the enclosure.

In providing a system embodying the invention, it is first necessary to determine the Speaker characteristics, namely, the parameters MMS, CMS, Rvs, RAs and MAS. These are derived by a combination or" measurement and calculation, as hereinafter illustrated by typical examples. From the Speaker characteristics, the enclosure parameters CMB and MMB may be determined to properly match the Speaker unit or units, while providing the desired substantial separation of the peaks. The box complianee CMB defines the box Volume required, while the box mass (provided by the inductance of the port) provides one of the parameters inuencing the port design.

In general, RAs and MAS Will be derived by calculaton, while MMS, CMS and RMs are determined from a frequency response curve and measurement of either the compliance of the Speaker suspension, or of the mass of the coil and cone assembly. A frequency run of the Speaker in an infinite baffle will reveal the resonant frequency w and the Q. For a Speaker having an efiective piston area Sr in cm?, the resistive Component of the air load, RAS, is given by 1.4pc SD and MAS, the air mass load on one side of the Speaker cone, by

E in gruan/emi see.

MAs=RAs in gms./cm.

mass of coil and cone assembly The compliance CMS of the Speaker may then be found y bstituting the values for wN, MAS and MMS in the expression (assuming purely reactive impedances at the frequencies involved) Note that in this equation, the value of MAS must be doubled, since the Speaker compliance CMS is being determined on the basis of Speaker characteristics` in an infinite bafl'le, where there is an air load otr-both sides of the cone.

The value of Rvrs may be calculated from the Speaker Q or may be obtained by measurement of the Speaker characteristics in an exacuated chamber to eliminate the air load.

In correlating the enclosure with the Speaker unit or units, the enclosure is preferably tuned to the resonant frequency of the Speaker when mounted in the enclosure. This resonant frequency w will be higher than the'infinte bafile resonant frequency wN, due to elimination of the back mass load on the Speaker cone.

The resonant frequency w of the system is given by ,=oMsMTs o for the case of relatively small enclosures such as employed in the present invention.

For the tuned condition,

CMS (MMS+MAS) :Cms (MMB-i-MAB) which is Conveniently rewritten as i M TB C MB M Ts where M Ts=total mass of the Speaker mesh and (k 1 CM s k CMB while the enclosure compliance in terms of box Volume is given by VB C Accordingly, the box Volume for a given peak separation factor may be determined, and hence the required port mass MTB, since rs CMS rs CMB The mass of the enclosure MTB (for a properly rigid Construction) is provided solely by the port, and for a circular port is given approximately by where d port diameter in cm. S =port area in cm. t=thickness or depth of port in cm.

For frequences above the upper resonance peak kw the radiation from the Speaker unit or units is almost entirely from the front of the cone, the Speaker cone serving as a direct radiator substantially unaffected by the enclosure characteristics, assuming that adequate acoustically-absorptive material is employed to line the interior of the enclosure. The present invention is therefore concerned almost exclusively with the response chao acteristics in the range of frequencies kal down to Lo Also, the invention is particularly directed to providing peak separations substantially in excess of those normally attained in conventional ported enclosures. By way of example, the invention is particularly applicable to peak sepa tion factors Wherein k has a value in excess of approximately 1.5, as compared with values of k of the order of 1.1 to 1.2 in ported or vented enclosures of conventional design.

The problem, as has long been recognized, is to provide effective radiation from the port so that the low frequency peak occurring at tu makes a useful contribution to the low frequency response, and at the sane time to prevent the peak at ku from being excessive. The larger the peak separation factor k, the greater the difficulty with both these aspects, hence the use heretofore of relatively small peak separations.

For a given speaker -compliance, the box Volume is prOpOtiOnal to kZ l while the port mass varies as k -l 2 ?c Thus, increasing k requires that Mrs be made larger, corresponding to a decrease in port area, it a single aperture is to be used. As a result, for small box volumes, (k greater than about 1.5) the port diameter may be substantially smaller than the effective pisten area of the Speaker unit or units. Corsequently the radiation from the port is relatively insiginficant and the performance of the system resembles that oi an unported enclosure of inadequate Volume.

Instead, therefore, or" the usual single port or opening, the present invention makes use of a plurality of spaced apertures or holes which together provide the required MTB and Q for the proper operation of the enclosure with the selected Speaker or speakers. While the precise mechanisn by which the holes, in the aggregate, provide an enhanced radiation effectiveness as Compared With a single port, is not yet completely understood, it is believed that a mutual coupling effect exists which causes the array of holes to function at least to some extent as if the entire region of the array Were the port. It is distinctly no "ceable in the operation of systems embodying the invention that appreciable aspirating action occurs in the vicinity of the holes due to the velocity of the air therethrough, and it is thought that this action may provide effective coupling to the air mass in the region of the array of apertures so that the radiation etfectiveness is greater than that of a single opening of the same MTH as the array.

The holes or apertures comprising the port likewise permit effective control of the Q of the enclosure,

moll I RTK since the diameter and number of the holes may be varied to provide the desired resistance. Alternatively, fibrous material of appropriate flow resistance may be used over the holes to provide the correct ow resistance for optimun port clamping.

In constructing the port comprising an array of spaced apertures, there are a number of variables that influence the design. The several factors include hole diameter, length, number and spacing. By reason of the fact that the holes are in parallel, the total mass of N holes is 1/N times the mass of a single hole.

7 As has been indicated above, the expression for the mass of a single round hole is given by in c. g. s. units. i

Accordingly, the mass of an array of N holes is given y The above relationship of hole diameter, wall thickness and mass reveals that a considerahle choice exists in the number of holes, their diameter and length to give the same MTI-I.

The Q of the holes (the Q of one hole is the same as that of the array) s given approximately by where d is the diameter in cm. and f is the resonant frequency to which the enclosure is tuned.

It will be noted that the Q of the holes may be controlled by the diameter so that even if no resistive material is used, the required Q and the MTI-I of the holes may be obtained with a considerable degree of independence since the Q of the hole is independent of depth. For values of Q requiring considerable diameters the Wall thickness may be increased or, alternatively, inserts such as tubes or the like may be utilized to provide the required mass. If resistive material is employed over the holes, the small hole diameter that might be required under certain conditions may be rendered unnecessary, the added flow resistance being obtained from the fabric or fibrous material over the holes.

If a supplementary flow resistance is required, over that provided by the holes alone, then the required flow resistance R in Rayls is given by where t=hole length in inches d=hole diameter in inches f =resonant frequency In order to show the improvement in low frequency response that results from the use of the plurality of small apertures as compared with a single opening ofconventional practice, expressions have been derived to show the relation, in a conventionally-ported enclosure, of output response at the three frequeneies of particular interest in the low frequency region, to the average output in the mid-range of the Speaker, at frequencies appreciably above the frequency ku The response in this latter region is hereinafter referred to as the plateau or flat portion of the frequency response characteristic.

If ;9 is dened as the ratio of the response at a critical frequency to the plateau response, and ,G is the response ratio for the critical frequency Lo /k, ,G for the frequency w and [S for kw then acteristic is a function of the Speaker Q (Q), the box Volume (by reason of the peak separation factor k), and

the Q (Qa) of the port. In general, Qz will be larger than Q, and k will be greater than 1 but generally not over 2. It will be seen that increasing k to values of the order of 1.5 and above has a marked efiect in lowering B and in raising B though not significantly altering B To illustrate by typical examples, take the case of a conventionally-ported system wherein k has a value of 1.9, Q=1.1 and Q2:28. The values of B are As another example, consider the case Where k=2, Q1=3 and Q2=l3.

Here

Bar -7 db fin -l- 11.5 db

In both examples, the response characteristic is obviously extremely poor, due to the severe fall-oli in response below w and the excessive peak at kw By way of comparison, a Speaker system having the same Speaker units and box Volume as in the first example, when provided with an array of holes as the port, shows a response represented by Note that ;S has been raised 6 db, ,S has been brought up 2 db, and the upper peak left unchanged. The control of this objectionable resonance is eected by means hereinafter described. This increase at B and B is due to the increased radiation atforded by the array of holes, as compared with a conventional single aperture of correct dimensions for the enclosure Volume.

The improvement in low frequency response due to the increased radiation is defined by a factor y, and the magnitude of the improvement may be expressed in terms of 'y and k as follows:

'for large values of Qz, then if the response ratio ,G becomes unity and the actual response at w is the same as the reference or plateau level.

In the same fashion, the new value of ,S may be found by introducing the value of into the expression for B If B is to equal 1, then At kam the increase is 1+( Thus the condition on fi sets the value of 'y while the condition on /S and the derived 'y sets the value of Q2.

While the values of 7 that may be obtained by employing an array of holes as the port, for embodiments in which radiation is occurring both from the front of the Speaker cone and from the holes, are probably limited to less than about 1.5, as presently understood, nevertheless appreciable improvement is possible over the usual single port, for values of k in excess of 1.62. Thus, in the case of the first example given, a 'y of 1.26 results in the attained improvement of 6 db in f and 2 db in fi The provision of a suitable array of holes preferably involves correlating the hole diameter, number of holes, and depth so as to provide, with a hole spacing of the order of Sd to lOd, an array of appreoiabie over-all area, While still meeting the requirements for M and Qz. The holes-may be arranged in various confi urations, including triangular, circular and rectangular arrays, depending on the shape of available wall or surface of the enclosure. For speaker systems wherein the array, though occupying an entire surface of the enclosure, is still relativeiy small in total area because of the small size of the enclosure, as in the embodiment of Fig. l where the top wall in a typical system may be only about /2 square foot in area, it is preferable to utilize for the array a surface that may occupy a position normal to and adjacent at least one and preferably two walls of the room when the speaker system is installed.

To control the ampl itude of the upper resonance peal: ocourring at kcu and represen-ted by B which has heretofore been one of the factors preventing the satisfactory use of small enclosures, the partition 20 is employed to divide the interior of the box into separate chambers. This partition is provided with a plurality of spaced apertures 22 which provide communication between the two chambers. Damping means 2.4 is employed to increase the flow resistance between chambers. Referring to the equivalent circuit diagram, Fig. 6, it will 'oe seen that this partition serves to introduce a shunt path across the cabinet compliance C the eifect being that of a damped Helmholtz resonator within the chanber. f the resonator is series tuned to w then it acts as a shunt path at w reducing the peak resonance. As a result, instead of a single high peak at kw two new peaks of lesser magnitude will appear, above and below kto In practice, it has been found possible to reduce a single 15 db peak to two peaks each approxim ately 3 db high.

Through the use of a plurality of spaced apertures, plus appropriate damping means, the resonator mass M and its clamping R may read-ily be controlled to provide, with substantal independence, the proper values to minimize the effect of the upper resonance peak. The calculation of the hole diameter, the number of holes, and the clamping required rnay utilize the same formulae as given above for the porting means of the enclosure.

To consider in detail a specific example of a Speaker system embodying the invention, the embodiment of Figs. 1 and 2 may be referred to. This system makes use of four small size Speaker units nominally referred to as five inch speakers. By measurement of the voice coil and cone mass, the value of M was found to be 1.49 gms. for each Speaker. The resonant frequency of the speakers, air load on one side, was found to be approximately 120 cycles. Q Was determined to be 1.1.

To provide a highly compact system, a Volume of onehalf cubic foot was selected, having a compliance of 0.1 l* cm. secP/gm. The required mass for the holes is then 0.133X* gms/cmfi. Using a spacing of slightly over two inches, an array of fifteen holes will provide the required M and a Qz of 28 if the hole length is /2", corresponding to the Wall thickness. The internal resonator or third mesh comprises a partition of /2" material having 15 holes of diameter, with a covering of a fibrous material of 13 Rayls in flow resistance.

The performance of such a system is: illustrated in Fig; 7, for the range of frequencies with which the present invention is concerned. The curve in solid line 42 is a typical response of the Speaker taken in free field With the speaker mounted at the intersection of three mutually perpendicular surfaces and with the sound pressure level integrated over the surface of that portion of a sphere subtended by the three bounding surfaces. The dot and dash line 4-4 shows the response obtained with an unported enclosure of the same size and with no internal resonator, while the dashed line curve 46 shows the response with the plurality of ports but without the internal resonator means.

It is readily apparent that the porting means provides a substantial contribution to the low frequency response in the region below about cycles, a 6 db gain being obtained in the vicinity of 60 cycles. At the same time, the internal resonator provides satisfactory control of the upper resonance peak, reducing the 9 db maximum above the plateau region %E to about 4 db. While the frequency response curve is not shown as fully extended into the high frequency region, it may be remarked that the response of the system, using the same small units that are relied upon for the low frequency response, extends efectively to the region of 10 kc. and above so as to provide a satisfactory balance between the low frequency and the high frequency response.

The present invention accordngly makes possible an extremely compact, low cost loudspeaker system` which provides an appreciabiy extended frequency response as Compared with conventional Speaker systems normally employed in small radio receiving sets. Since the eiiiciency of systems embodying the present invention may be made reiativeiy high, it is found that when such systems are attaehed to existing receivers, the available Volume is markedly increased, in addition to the improvement in quality of response.

While the invention has been specically illustrated in terms of a particular embodiment employing a plurality of transducer units and an alternative form employing a single transducer, it will be understood that the invention is not so limited, but comprehends other forms and constructions embodying the principles and mode of operation of the invention, within the scope of the appended claims. lt is also to be understood that the term loudspealter means or transducer means comprehends one or more loudspealter units or driving units, since the invention is applicable to both the single and the multiple unit systems.

We claim:

1. A loudspeaker system comprising an enclosure, transducer means mounted therein with one side of said means in communication with the interior of the enclosure, porting means communicating With the exterior of the enclosure, said porting means conprising a plurality of spaced apertures disposed in an array, the enclosure having a Volume corresponding to a peak separation factor in excess of approximately 1.5, and partition means within the enclosure for separating the interior into chambers, the partition means having a plurality of spaced apertures and clamping means for restricting fiow communication through said apertures between the chambers to minimize the upper resonance peal 2. A loudspeaker system comprising an enclosure in the shape of a ri ht triangular prism, transducing means comprising a plurality of loudspeaker driving units mounted on a wall of the enclosure, the Volume of the enclosure being related to the compliance of the transducer means to provide a peal( separation factor approximately equal to 2, porting means in a triangular wall of said enclosure, said portin" means comprising an array of apertures disposed in a spacing approximately 5 to 10 times the aperture cross-sectional dimension, the area and the depth of each aperture in the wall providing an equivalent acoustic mass substantially l/N times the mass required to tune the enclosure substantially to the resonant frequency of the transducer means in the enclosure, where N is the number of apertures in the array, and means within the enclosure for controliing the amplitude of the upper resonance peak, comprising a parti tion separating the interier into chambers, the partition having a plurality of spaced apertures disposed in an array, the array of apertures in the partition corresponding approximately in number, spacing and depth to the apertures of the porting array, and damping means associated with said apertures of the partition.

3. A loudspeaker system comprising an renciosure in the shape of a right triangular prism of approximateiy one-half cubic foot Volume, transducing means comprising four loudspeaker units mounted on a rectanglar wall of the enclosure, the Ioudspeakers having a freespace resonant frequeney higher than approximately one hundred cycles, porting means in a triangular Wall of the enclosure, said porting means comprising an array of approximately fifteen holes of the order of one-half inch in diameter spaced approxmately two inches apart, and means within the enclosure comprising a partition separating the interier into chambers, the partition having an array of apertures comparable to said porting means, and damping means for minimizing flow through said apertures of the partition.

References Cited in the file of this patent UNITED STATES PATENTS 1,841,101 Fianders et al Jan. 12, 1932 1,861,178 Thuras July 26, 1932 1,901,388 Wolf Mar. 14, 1933 2,065,751 Scheldorf Dec. 29, 1936 2,217,279 Karns Oct. 8, 1940 2,295,483 Knowles Sept. 8, 1942 2,337,213 Topping Dec. 21, 1943 FOREIGN PATENTS 557,850 Germany Sept. 1, 1932 4%,619 Great Britain Dec. 2, 1938 OTHER REFERENCES Publication, Popular Science, September 1952, page 171.

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