GB2222744A - Improvements in and relating to loudspeaker enclosures - Google Patents
Improvements in and relating to loudspeaker enclosures Download PDFInfo
- Publication number
- GB2222744A GB2222744A GB8821451A GB8821451A GB2222744A GB 2222744 A GB2222744 A GB 2222744A GB 8821451 A GB8821451 A GB 8821451A GB 8821451 A GB8821451 A GB 8821451A GB 2222744 A GB2222744 A GB 2222744A
- Authority
- GB
- United Kingdom
- Prior art keywords
- enclosure
- walls
- loudspeaker
- open
- loudspeaker enclosure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
- 239000006261 foam material Substances 0.000 claims abstract description 59
- 239000000463 material Substances 0.000 claims description 64
- 239000006260 foam Substances 0.000 claims description 46
- 239000011148 porous material Substances 0.000 claims description 37
- 229920005613 synthetic organic polymer Polymers 0.000 claims description 8
- 239000000853 adhesive Substances 0.000 claims description 6
- 230000001070 adhesive effect Effects 0.000 claims description 6
- 238000005187 foaming Methods 0.000 claims description 4
- -1 polyethylene Polymers 0.000 claims description 4
- 238000005266 casting Methods 0.000 claims description 3
- 238000000465 moulding Methods 0.000 claims description 3
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical group [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 2
- 239000004593 Epoxy Substances 0.000 claims description 2
- 239000004698 Polyethylene Substances 0.000 claims description 2
- 239000004743 Polypropylene Substances 0.000 claims description 2
- 229920003180 amino resin Polymers 0.000 claims description 2
- 238000011065 in-situ storage Methods 0.000 claims description 2
- 229920001568 phenolic resin Polymers 0.000 claims description 2
- 239000005011 phenolic resin Substances 0.000 claims description 2
- 229920000573 polyethylene Polymers 0.000 claims description 2
- 229920001155 polypropylene Polymers 0.000 claims description 2
- 229920005990 polystyrene resin Polymers 0.000 claims description 2
- 229920005749 polyurethane resin Polymers 0.000 claims description 2
- 238000010276 construction Methods 0.000 abstract description 5
- 239000007789 gas Substances 0.000 description 15
- 229920003319 Araldite® Polymers 0.000 description 12
- 210000004027 cell Anatomy 0.000 description 11
- 230000000694 effects Effects 0.000 description 5
- 241001453445 Acalypha rhomboidea Species 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 230000003247 decreasing effect Effects 0.000 description 4
- 230000005294 ferromagnetic effect Effects 0.000 description 4
- 229920005989 resin Polymers 0.000 description 4
- 239000011347 resin Substances 0.000 description 4
- 230000009471 action Effects 0.000 description 3
- 239000003822 epoxy resin Substances 0.000 description 3
- 229920000647 polyepoxide Polymers 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 239000011152 fibreglass Substances 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229920003002 synthetic resin Polymers 0.000 description 2
- 239000000057 synthetic resin Substances 0.000 description 2
- 241000239290 Araneae Species 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- 229920001651 Cyanoacrylate Polymers 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 239000004830 Super Glue Substances 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 210000002421 cell wall Anatomy 0.000 description 1
- 230000001413 cellular effect Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000004567 concrete Substances 0.000 description 1
- 239000002178 crystalline material Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
- 210000002268 wool Anatomy 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only
- H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
- H04R1/2869—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself
- H04R1/2884—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of the enclosure structure, i.e. strengthening or shape of the enclosure
- H04R1/2888—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of the enclosure structure, i.e. strengthening or shape of the enclosure for loudspeaker transducers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only
- H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
- H04R1/2869—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself
- H04R1/2876—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding
- H04R1/288—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding for loudspeaker transducers
Landscapes
- Health & Medical Sciences (AREA)
- Otolaryngology (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Details Of Audible-Bandwidth Transducers (AREA)
Abstract
In order to provide a loudspeaker enclosure of which the coloration arising from vibration of the walls is low, but the construction of which is suitable for loudspeaker enclosures of a wide variety of both sizes and shapes, at least a substantial part of the interior of the enclosure 1 is filled with a rigid open-cell foam material 2 that extends between walls of the enclosure to impart a substantial measure of rigidity to them, the foam material having a Young's modulus of at least 1x10<7> Newtons per square metre. <IMAGE>
Description
Improvements in and relating to loudspeaker
enclosures
The invention relates to loudspeaker enclosures.
The sound output from a loudspeaker system includes, in addition to the sound from the loudspeaker drive unit or units, sound resulting from vibration of the walls of the enclosure. The enclosure will inevitably have resonance frequencies, with the result that the intensity of the sound resulting from vibration of the walls of the enclosure will be greater at some frequencies than at others, thus causing coloration of the sound output.
The problems involved in decreasing the coloration that results from the vibration of the walls of the enclosure are discussed in European Patent Application 0191595, which proposes the provision of a hollow stiffening structure located within the housing, the structure comprising a first set of spaced-apart stiffening panels extending substantially parallel to each other and to the walls of a pair of opposed housing walls, a second set of such panels which intersect the panels of the first set substantially orthogonally and are secured to the panels of the first set. The panels extend from the top wall of the enclosure to the bottom wall, from one side wall to the other, and from the front wall to the rear wall, dividina the interior of the enclosure into a multiplicity of rectangular parallelepipedal cells.
Communication between adjacent cells, at least some of which may contain acoustically absorbent material, is provided by holes in the stiffening partitions.
The arrangement described in European Patent
Application 0191595 gives very good results, but it is of course desirable that the stiffening panels should be closely spaced, and that both increases the cost of the enclosure and significantly decreases the volume of air within the enclosure. Accordingly, the arrangement is most suitable for loudspeakers of high quality and relatively large size.
It is an object of this invention to provide a loudspeaker enclosure of which the coloration arising from vibration of the walls is low, but the construction of which is suitable for loudspeaker enclosures of a wide variety of both sizes and shapes.
The invention provides a loudspeaker enclosure of which at least a substantial part of the interior is filled with a rigid open-cell foam material that extends between walls of the enclosure to impart a substantial measure of rigidity to them, the foam material having a Young's modulus of at least lxlO7 Newtons per square metre and being bonded to or integral with the walls of the enclosure.
The term foamy as used throughout this specification includes not only material in a cellular form produced by foaming but also material in that form produced by a moulding or casting process.
The bonding of the foam material to the walls of the enclosure may, where the material of which the foam is made will bond to the walls of the enclosure, be achieved as a result of in situ foaming, moulding or casting of the foam within the walls of the enclosure, or it may be achieved by the use of an adhesive material between the foam material and the walls of the enclosure. Suitable adhesive materials are, for example, those used conventionally in loudspeaker enclosure construction, such as epoxy resin adhesives, cyano acrylate adhesives (so-called "super glues") and P.V.A. adhesives.
It has been found that the use of such a rigid open-cell foam material within a loudspeaker enclosure has a number of very important advantages. Firstly, the rigidity imparted by the material is so great that the walls of the enclosure can be made light, and consequently thin. That is because, even if conventional, relatively thick walls are used, their stiffness adds only insignificantly to the rigidity imparted to the enclosure by the foam. If the walls are thinner than conventional walls, then (neglecting other factors and for a given external volume) the internal volume of the enclosure is increased, and the increase, because it has the effect of lowering the fundamental resonance frequency, may be used to permit an increase in the sensitivity of the system and/or to lower the bass cut-off frequency of the system.
Secondly, it has been found experimentally that the velocity of sound waves within the enclosure is close to what would be expected if sound waves were isothermal rather than adiabatic, with the result that the linear dimensions of the enclosure are, for acoustic purposes, effectively increased by a factor that is only a little less than (the ratio of the specific heat of gas at constant pressure to that at constant volume, which for air is equal to approximately 1.4). The acoustic compliance (the reciprocal of the acoustic stiffness) of a loudspeaker enclosure is the factor that determines the fundamental resonance of the loudspeaker enclosure and drive unit combination. The acoustic compliance is proportional to the internal volume of the enclosure divided by the product of the density of the gas within the enclosure and the square of the sound velocity.Thus, the acoustic compliance is inversely proportional to the square of the velocity of sound within the enclosure and so, assuming the interior of the enclosure to be completely filled with the foam and the gas in the enclosure to be air, it is possible approximately to double the acoustic compliance of the enclosure by the use of the foam. That means that, for acoustic purposes, the volume of the enclosure is (neglecting the volume of the material of which the foam is composed) approximately doubled. Even when the volume of that material is taken into account, the effective volume of the enclosure for acoustic purposes is considerably increased. Thus, the resonance frequency of the loudspeaker system is reduced by a factor approaching 1.4, because the resonance frequency is proportional to the square root of the volume.Whilst the fundamental resonance of a loudspeaker enclosure and drive unit combination is most significant in terms of acoustic performance of the combination, the harmonic modes above the fundamental resonance also affect acoustic performance. The frequency of each mode will also be reduced by the use of the foam by a factor of roughly 1.4.
Thirdly, as is explained below, the presence within the loudspeaker enclosure of the rigid open-cell foam can be used to simplify the mounting of the loudspeaker drive unit or units.
In order to ensure that the requirement that the foam material must have a Youngs modulus of at least lox107 Newtons per square metre is met with a foam material having an acceptably high porosity, the material of which the open-cell foam material is composed advantageously has a Young's modulus of at least low Newtons per square metre.
Whilst it is essential that the open-cell foam material be very rigid, its other properties can vary widely and the foam can be made from a wide variety of materials.
The diameters of the pores in the open-cell foam material may be within the range of from 0.1 millimetres to 1/30 of the largest linear dimension of the interior of the enclosure.
The average diameter of the pores in the open-cell foam material may be not greater than 10 millimetres.
Advantageously, the said average diameter of the pores does not exceed 5 millimetres. Preferably, the said average diameter of the pores is within the range of from 0.5 millimetre to 2 millimetres.
The proportion of the volume of the material of which the foam is composed to the volume of the opencell foam itself may be within the range of from 0.2% (corresponding to a porosity of 99.8%) to 25% (corresponding to a porosity of 75%).
The ratio of the diameter of the vents that interconnect adjacent cells or pores (and so render the foam open-cell rather than closed-cell) to the diameter of the cells or pores may be within the range of from 0.1:1 to 1.0:1. Thus, the cells or pores may, at one extreme, be bounded by walls that are generally continuous, but are perforated by relatively widely spaced fine holes. At the other extreme, the material of which the foam is composed is largely of filamentary habit, so that the voids in the material are not in the form of well-defined cells or pores bounded by solid walls.
Provided that it has à sufficiently high Young's modulus, the material of which the foam is composed may be any of a wide variety of materials, including plastics materials, metals, concrete, wood, composite materials and crystalline materials.
Advantageously, the open-cell foam material is a polymeric material.
Preferably, the polymeric material is an organic polymeric material.
Preferably, the organic polymeric material is as synthetic organic polymer.
Advantageously, the synthetic organic polymer is epoxy-based.
Instead, the synthetic organic polymer may be a phenolic resin or an aminoplast.
Instead, the synthetic organic polymer may be a polystyrene resin, a polyurethane resin, polyethylene or polypropylene.
Other properties of the material that can vary widely include specific heat and thermal conductivity.
Thus, the specific heat and thermal conductivity of the material may be as low as the values of those qualities that are found for an insulating polymer, for example, wool, or as high as the values found for'a metal having a high electrical conductivity, for example, silver (which has a much higher specific heat than an insulating polymer and a very high thermal conductivity).
It has been explained above that the walls of the loudspeaker enclosure can be thinner than conventional walls, because the rigidity of the open-cell foam is sufficiently high to render the provision of stiff walls superfluous, but it is essential that the enclosure actually be an enclosure, that is to say, that it be sealed except for an aperture or apertures to receive one or more drive units and perhaps also, depending on the design of the loudspeaker, to provide a vent.
The walls of the enclosure may be formed of the same material as the open-cell foam material and may be integral with that material.
Depending on the nature of the material of which the foam is made and on the way in which the foam is made, it is possible to arrange that a foaming action that leads to the formation of the open-cell foam material causes the formation of a skin that seals the material externally except at an aperture or apertures provided to receive a drive unit or drive units, or to enable the enclosure to be vented.
For radiation from the walls of the enclosure to be kept down to an acceptably low level, the walls must be adequately stiff. The minimum stiffness of the walls depends on the intervals at which they are supported, which may be taken to be equal to the pore diameter of the foam material.
When the walls are made of a material having a
Young's modulus equal to that of the material of which the foam is made (irrespective of whether the two materials are the same, and of whether, if they are the same, the walls are formed with a skin that is integral with the foam material) , the walls may have a thickness equal to at least 0.5 times the pore diameter of the foam material.
Advantageously, (when the materials have the same
Young's modulus), the walls have a thickness not less than the pore diameter of the foam material.
Preferably, when the two materials have the same
Young's modulus, the thickness of the walls does not exceed 2 times the pore diameter of the foam material, because it will commonly be found that the performance of a loudspeaker system, which includes a loudspeaker enclosure according to the invention and having a given external volume, will benefit more from the increased volume of the enclosure that will result from restricting the thickness of the walls in that way than it would from increasing the thickness of the walls to more than twice the pore diameter of the foam material.
In fact, when the two materials have the same Young's modulus, it will usually be preferable for the wall thickness to be substantially equal to the pore diameter of the foam material.
As an example of typical dimensions, if the foam material has a pore diameter of 1.5 millimetres, the walls (when made of a material having the same Young's modulus as the material of which the foam is made) may also have a thickness of 1.5 millimetres, which is to be compared with a typical thickness of 1 to 2 centimetres for the walls of conventional loudspeaker enclosures.
When the material of which the walls are made does not have the same Young's modulus as the material of which the foam is made, the figures given above for the thickness of the walls, expressed as a multiple or submultiple of the pore diameter of the foam material should be multiplied by the ratio of the Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made.
Where the ready commercial availability of material for the walls of the enclosure has to be taken into account, it can be advantageous for the thickness of the walls of the enclosure not to exceed 11, multiplied by the ratio of the Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made, times the pore diameter of the foam material.
It is in principle possible for the gas within the enclosure to be a gas other than air, and the use of such a gas will, if it is a gas in which the velocity of sound is lower than it is in air, have the effect of increasing the effective volume of the chamber still more. Such a gas other than air can, however, be used only with a sealed enclosure and not with a vented one, so that a restriction is placed on the design of the loudspeaker. Further, when some gases are used, especial care has to be taken with the sealing of the enclosure because an escape of gas could have adverse consequences extending beyond a loss of performance of the loudspeakers.An example of such a gas is a fluorinated hydrocarbon gas, in which the velocity of sound could be approximately 1/3 of the velocity of sound in air so that the volume of the enclosure would be effectively increased for acoustic purposes by a factor of approximately 9, and the acoustic stiffness of the enclosure would be increased by a factor of approximately 6, if such a gas were used instead of air.
It has been explained above that, within the open-cell foam, the velocity of sound is reduced, because the compressions and rarefactions that constitute the sound waves tend to become isothermal rather than adiabatic, and there are a number of factors that determine the extent of that tendency.
They include the thermal conductivity (which is desirably high) and the specific heat (which is desirably high) of the material of which the open-cell foam is composed, and the pore size (which is desirably small, but not so small as to give rise to serious viscous losses resulting from the effects of viscous drag within the pores).
It will be apparent from what has been stated above that, if the maximum advantage is to be derived from the provision of the open-cell foam material within the enclosure, it should fill the interior of the enclosure as nearly as possible. In that way, for a given type of foam material, it makes the greatest possible contribution to the overall rigidity of the enclosure, manifested as the apparent stiffness of the "walls" of the enclosure (whether separate from the foam material or not), and will also effect the greatest possible increase in the apparent internal volume of the enclosure by the effect it has in reducing the velocity of sound.Other things being equal, a small pore size and a high porosity are to be preferred, but it will not in general be possible to combine a pore size as small as 0.1 millimetre with a porosity as high as 99.8% when using a given foam material, and then some form of compromise will be necessary. Similarly, a material having a higher
Young's modulus is to be preferred but such materials may prove to be more expensive and may, in some cases, have other disadvantages, for example, lower thermal conductivity or lower specific heat. The size of the apertures between adjacent pores is desirably large but should not in any case be so small as to give rise to serious viscous losses.
It has been found that very satisfactory results are obtained if the material of which the open-cell foam is composed is a rigid epoxy resin. A suitable epoxy resin is the synthetic resin sold under the name
Araldite CY219 (the name Araldite is a Registered Trade
Mark), and the foam has a pore size within the range of from 200 micrometres to 3 millimetres and a porosity within the range of from 70% to 90% . Hereinafter, the word "Araldite" is used to mean the synthetic resin sold under the name "Araldite CY219". Araldite has a
Young's modulus of 3x109 Newtons per square metre and, the precise value depending on the pore size and porosity, the open-cell foam has a Young's modulus of at least lox10 Newtons per square metre.Thus, not only is such open-cell foam material sufficiently rigid to enable light enclosure walls to be used, the walls being made either of Araldite or of a different material, but it also gives (despite its relatively low thermal conductivity) a decrease in sound velocity through the gas within it that is approaching the theoretical maximum. Thus, measurements have shown that, when the gas in the enclosure is air, the velocity of sound in the air is decreased by a factor of approximately 1.3.
The invention also provides a loudspeaker system which comprises a loudspeaker enclosure according to the invention fitted with at least one drive unit.
Advantageously, the drive unit, or at least one of the drive units, comprises a magnet which is mounted directly on the open-cell foam material and a diaphragm of which the surround is mounted directly on the open cell foam material
The use of the open-cell foam as a filling for the enclosure makes it possible for both the surround of the diaphragm and the magnet of a drive unit of the loudspeaker to be mounted directly on the foam. In that way the conventional drive unit chassis can be dispensed with since the surround of the diaphragm is mounted directly on the foam, resulting in a simplified construction at the possible expense (dependent on the material of which the open-cell foam is composed) of reduced conduction of heat away from the voice coil and magnet.
One form of loudspeaker system constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing, which is a diagrammatic vertical axial section through the loudspeaker system.
Referring to the accompanying drawing, the loudspeaker system comprises an enclosure of which the walls are indicated generally by the reference numeral 1, which is substantially filled with a mass of a rigid open-cell foam material 2, and a single drive unit which is indicated generally by the reference numeral 3.
The walls 1 of the enclosure are made of thin fibre glass board (having a thickness of 1.6 mm and a
Young's modulus of 6.5 X lO9 Newtons per square metre so bonded to the outer surfaces of the mass of open cell foam 2 as to ensure, in conjunction with the drive unit 3, that the enclosure is air-tight. Such fibre glass board is thicker than the acoustic considerations require but has the merit of being readily available commercially. As one continues to increase the thickness of the walls of the enclosure beyond what is necessary on acoustic grounds, the additional benefit in acoustic terms becomes more and more insubstantial.
The drive unit 1 comprises a magnet assembly 4 and a cone 5 and is essentially of conventional construction except that the cone 5 and magnet assembly 4 are not mounted on a chassis member of the drive unit but are instead mounted directly on parts of the enclosure.
The cone 5 is mounted at its inner end by an apertured mounting ring 6 of the type usually called a "spider" and at its outer end by an annular surround 7. The mounting ring 6 is bonded to an annular face provided on the foam material 2 and the outer periphery of the surround 7 is bonded to the front wall of the enclosure. A dust cap 8 is provided in the centre of the cone 5.
The magnet assembly 4 comprises an annular magnet 9, a ferro-magnetic backing plate 10, a central ferro-magnetic pole piece 11 of circular cross-section carried by the backing plate, and an annular ferromagnetic flux plate 12 mounted on the front face of the magnet and surrounding the pole piece. The ferro-magnetic backing plate 10 is bonded to the foam material 2.
The cone 2 is attached to a speech coil 13 surrounding the pole piece 11. The speech coil 13 is arranged to lie in the annular space between the pole piece 11 and the flux plate 12 and is electrically connected to leads 14, of the type sometimes called "tinsels", which in turn are connected to solid core lead-in wires 15 connected to terminals 16 mounted at the rear of the enclosure 1.
The open-cell foam material was composed of
Araldite and was made by the process described below.
A vessel containing wax and having an inlet for compressed air and an outlet provided with a nozzle was heated, and molten wax issuing from the nozzle under the action of compressed air applied to the inlet fell into a bath of water. In that way, numerous small balls of wax (the diameter of the balls being equal to the desired diameter of the cells or pores in the open-cell foam material to be produced) were produced.
A cylindrical (not in this instance right circular cylindrical but in fact prismatic) container of which the interior had the size and shape of the interior of the loudspeaker enclosure, and of which the top was closed by a wall which was removable to open the top and which could slide within the container in the manner of a piston, was filled through the open top with wax balls. By pressing the top wall of the container down, the mass of wax balls was compressed with deformation of the wax balls so that adjacent wax balls were in contact with one another over circular areas of the required size.
A resin (Araldite) was then poured onto the balls in the container and, the resin having too high a viscosity for it to fill the interstices between the balls under the action of gravity alone, a suction pump fitted to an outlet in the bottom of the container was brought into operation. In that way, an even distribution of the resin throughout the interior of the container was achieved. When the resin had set, a major part of the wax was removed by melting, the remainder being removed by a solvent.
The walls of the enclosure were bonded to the mass of open-cell foam material so made by means of more Araldite applied as an adhesive.
The cells or pores in the open-cell foam material produced in that way had diameters of approximately 0.75 to 1.5 millimetres and the apertures in cell walls that provided communication between adjacent cells, had diameters of approximately 0.5 millimetres. The porosity of the foam material was 83%.
Young's modulus for the open-cell foam was found to be 2.5x107 Newtons per square metre. Araldite has a thermal conductivity of 0.1 Watts metre 1 Kelvin-1 and a specific heat of 2 Joules gram-1 Kelvin-1.
Measurements made on the loudspeaker system indicated that the velocity of sound within the foam was decreased by a factor of 1.27. After allowing for the fact that the Araldite occupied 17% of the interior of the enclosure, the effective volume of the enclosure was 34% greater than it would have been without the presence of the foam.
To that increase there has to be added the increase that stems from the use of very thin walls.
Had it been necessary to use conventional, stiff walls having a thickness of, say, 15 millimetres, then for given external dimensions, the internal volume of the enclosure would have been decreased by 30%.
To achieve the performance of an enclosure filled with such rigid open-cell Araldite foam, having very thin walls and an external volume of approximately 8 litres, it would have been necessary, using a conventional enclosure not containing the rigid opencell foam and having conventional walls, 15 millimetres thick, for the enclosure to have an external volume of approximately 14 litres.
Claims (27)
1. A loudspeaker enclosure of which at least a substantial part of the interior is filled with a rigid open-cell foam material that extends between walls of the enclosure to impart a substantial measure of rigidity to them, the foam material having a Young's modulus of at least lox107 Newtons per square metre and being bonded to or integral with the walls of the enclosure.
2. A loudspeaker enclosure as claimed in claim 1, wherein the open-cell foam material is a polymeric material.
3. A loudspeaker enclosure as claimed in claim 2, wherein the polymeric material is an organic polymeric material.
4. A loudspeaker enclosure as claimed in claim 3, wherein the organic polymeric material is a synthetic organic polymer.
5. A loudspeaker enclosure as claimed in claim 4, wherein the synthetic organic polymer is epoxy-based.
6. A loudspeaker enclosure as claimed in claim 4, wherein the synthetic organic polymer is a phenolic resin or an aminoplast.
7. A loudspeaker enclosure as claimed in claim 4, wherein the synthetic organic polymer is a polystyrene resin, a polyurethane resin, polyethylene or polypropylene.
8. A loudspeaker enclosure as claimed in any one of claims 1 to 7, wherein the diameters of the pores in the open-cell foam material are within the range of from 0.1 millimetre to 1/30 of the largest linear dimension of the interior of the enclosure.
9. A loudspeaker enclosure as claimed in any one of claims 1 to 8, wherein the average diameter of the pores in the open-cell foam material does not exceed 10 millimetres.
10. A loudspeaker enclosure as claimed in claim 9, wherein the said average diameter of the pores does not exceed 5 millimetres.
11. A loudspeaker enclosure as claimed in claim 10, wherein the said average diameter of the pores is within the range of from 0.5 millimetre to 2 millimetres.
12. A loudspeaker enclosure as claimed in any one of claims 1 to 11, wherein the ratio of the diameter of the vents that interconnect adjacent pores (and so render the foam open-cell rather than closed cell) to the diameter of the pores is within the range of from 0.1:1 to 1.0:1.
13. A loudspeaker enclosure as claimed in any one of claims 1 to 12, wherein the proportion of the volume of the material of which the foam is composed to the volume of the open-cell foam itself is within the range of from 0.2% to 25%.
14. A loudspeaker enclosure as claimed any one of claims 1 to 13, wherein the walls of the enclosure are formed of the same material as the open-cell foam material.
15. A loudspeaker enclosure as claimed in claim 14, wherein the walls of the enclosure are integral with the open-cell foam material.
16. A loudspeaker enclosure as claimed in any one of claims 1 to 14, wherein the walls of the enclosure are bonded to the open-cell foam material.
17. A loudspeaker enclosure as claimed in claim 16, wherein the bond between the walls of the enclosure and the open-cell foam material is the result of in
situ foaming, moulding or casting of the foam within the walls of the enclosure.
18. A loudspeaker enclosure as claimed in claim 16, wherein the bond between the walls of the enclosure and the open-cell foam material results from the application of an adhesive between the foam material and the walls of the enclosure.
19. A loudspeaker enclosure as claimed in any one of claims 1 to 18, wherein the thickness of the walls of the enclosure is at least 0.5, multiplied by the ratio of the Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made, times the pore diameter of the foam material.
20. A loudspeaker enclosure as claimed in claim 19, wherein the thickness of the walls of the enclosure is at least unity, multiplied by the ratio of the
Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made, times the pore diameter of the foam material.
21. A loudspeaker enclosure as claimed in claim 19 or claim 20 , wherein the thickness of the walls of the enclosure does not exceed 2, multiplied by the ratio of the Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made, times the pore diameter of the foam material.
22. A loudspeaker enclosure as claimed in claim 19 or claim 20 , wherein the thickness of the walls of the enclosure does not exceed 11, multiplied by the ratio of the Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made, times the pore diameter of the foam material.
23. A loudspeaker enclosure as claimed in claim 19, wherein the foam material has a pore diameter of substantially 1.5 millimetres, and the walls have a thickness of substantially 1.5, multiplied by the ratio of the Young's modulus of the material of which the foam is made to the Young's modulus of the material of which the walls are made, millimetres.
24. A loudspeaker system which comprises a loudspeaker enclosure as claimed in any one of claims 1 to 23, the loudspeaker enclosure being fitted with at least one drive unit.
25. A loudspeaker system as claimed in claim 24, wherein the drive unit, or at least one of the drive units, comprises a magnet which is mounted directly on the open-cell foam material and a diaphragm of which the surround is mounted directly on the open-cell foam material
26. A loudspeaker enclosure substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.
27. A loudspeaker system substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8821451A GB2222744A (en) | 1988-09-13 | 1988-09-13 | Improvements in and relating to loudspeaker enclosures |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8821451A GB2222744A (en) | 1988-09-13 | 1988-09-13 | Improvements in and relating to loudspeaker enclosures |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8821451D0 GB8821451D0 (en) | 1988-10-12 |
| GB2222744A true GB2222744A (en) | 1990-03-14 |
Family
ID=10643515
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8821451A Withdrawn GB2222744A (en) | 1988-09-13 | 1988-09-13 | Improvements in and relating to loudspeaker enclosures |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2222744A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2290919A (en) * | 1994-06-21 | 1996-01-10 | Jonathan Gregory Michael White | A filling for loudspeakers and loudspeaker stands |
| US20200332518A1 (en) * | 2017-11-21 | 2020-10-22 | Nitto Denko Corporation | Sound reducing system |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115109410A (en) * | 2022-06-30 | 2022-09-27 | 歌尔股份有限公司 | Shell of sound generating device, sound generating device and electronic equipment thereof |
| CN115209257B (en) * | 2022-09-14 | 2023-02-03 | 歌尔股份有限公司 | Casing of sound generating device, sound generating device and electronic equipment |
| CN115460518B (en) * | 2022-09-14 | 2024-05-14 | 歌尔股份有限公司 | Shell of sound generating device, sound generating device and electronic equipment |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1229451A (en) * | 1968-01-18 | 1971-04-21 | ||
| US4057689A (en) * | 1973-07-09 | 1977-11-08 | Roy H. Smith, Jr. | High fidelity sound reproduction system and modules thereof |
| GB2002200A (en) * | 1977-08-06 | 1979-02-14 | Nissan Motor | Acoustic apparatus |
| EP0111408A1 (en) * | 1982-12-02 | 1984-06-20 | Celestion International Limited | Loudspeaker cabinets |
-
1988
- 1988-09-13 GB GB8821451A patent/GB2222744A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1229451A (en) * | 1968-01-18 | 1971-04-21 | ||
| US4057689A (en) * | 1973-07-09 | 1977-11-08 | Roy H. Smith, Jr. | High fidelity sound reproduction system and modules thereof |
| GB2002200A (en) * | 1977-08-06 | 1979-02-14 | Nissan Motor | Acoustic apparatus |
| EP0111408A1 (en) * | 1982-12-02 | 1984-06-20 | Celestion International Limited | Loudspeaker cabinets |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2290919A (en) * | 1994-06-21 | 1996-01-10 | Jonathan Gregory Michael White | A filling for loudspeakers and loudspeaker stands |
| GB2290919B (en) * | 1994-06-21 | 1998-08-19 | Jonathan Gregory Michael White | Loudspeakers |
| US20200332518A1 (en) * | 2017-11-21 | 2020-10-22 | Nitto Denko Corporation | Sound reducing system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8821451D0 (en) | 1988-10-12 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4127751A (en) | Loudspeaker with rigid foamed back-cavity | |
| US4410768A (en) | Electro-acoustic transducer | |
| US4517416A (en) | Electro-acoustic transducer having a diaphragm comprising a layer of polymethacrylimide foam | |
| US3720285A (en) | Loudspeakers | |
| US3801943A (en) | Electoacoustic transducers and electromagnetic assembly therefor | |
| CN209390306U (en) | Loudspeaker | |
| CN207612403U (en) | Loudspeaker enclosure | |
| US7096995B2 (en) | Polyurethane foam cabinets | |
| RO119046B1 (en) | Panel-shaped speaker | |
| EA000860B1 (en) | Packaging | |
| US3033945A (en) | Voice coil and diaphragm support for high frequency loud-speaker | |
| CN111739500A (en) | Underwater broadband sound absorption structure of perforated sandwich plate modified by damping layer | |
| GB2222744A (en) | Improvements in and relating to loudspeaker enclosures | |
| CN206908837U (en) | A kind of sound-producing device module | |
| CN208657071U (en) | Vibrating diaphragm and acoustical generator including the vibrating diaphragm | |
| US4624338A (en) | Loudspeaker enclosure for a vibrating diaphragm loudspeaker | |
| US9743190B2 (en) | Acoustic diaphragm | |
| US9769570B2 (en) | Acoustic diaphragm | |
| CN111601221A (en) | High-pitch sound production device | |
| JP5442728B2 (en) | Voice coil support device with coil type converter motor structure | |
| WO2021120915A1 (en) | Sound absorbing material encapsulation structure for sound production device, and sound production device | |
| US5895896A (en) | Fluid coupled subwoofer acoustic enclosure system with port chamber | |
| CN208806977U (en) | A kind of vibrating diaphragm and the loudspeaker enclosure using the vibrating diaphragm | |
| US5281777A (en) | Fluid damped acoustic enclosure system | |
| CN208806976U (en) | A kind of vibrating diaphragm and the loudspeaker enclosure using the vibrating diaphragm |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |