Flat loudspeaker with enhanced low frequency

[57] ABSTRACT

Flat loudspeaker diaphragm with means for enhancing the low frequencies, wherein the diaphragm has a marginal vibration damping portion surrounding a sound producing figure portion and at least a portion of said marginal vibration damping portion is connected to a plate-like member adapted to vibrate only in the low frequency range.

Claims, 4 Drawing Figures

<img file="US3767005A_D0001.tif" />

ΡΑΤΕΝΤΕ00Π231973

3,767,005

<img file="US3767005A_D0002.tif" />

3,767,005

FLAT LOUDSPEAKER WITH ENHANCED LOW FREQUENCY

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a diaphragm for flat loudspeakers, where the low frequencies are enhanced to change the shade and colour of the sound.

The tastes in relationship to musical reproductions are not equal throughout the world; thus some people prefer that in a musical song the human voice be clearly distinguishable from the musical background, while others prefer that the human voice merge into the music.

In this latter case it is advisable to increase the low frequencies of the sound reproduction; such an emphasis may be obtained by providing suitable means which increase the range of the low frequency vibrations.

2. Description of the Prior Art

In conventional loudspeakers, this effect is achieved by housing the loudspeakers in large wood casings which act as resonance boxes or baffles. In many cases these casings are several times larger in surface and volume than that actually required for the installation of the loudspeakers and in a good number of embodiments it is necessary to provide these casings with heavy weights to avoid that due to the low frequencies the casings start to move along the floor. From the foregoing it is apparent that the known embodiments are large in volume and rather expensive.

As to the resulting sound, its colour and shade, this depends on the type of material (usually wood) used for manufacturing the casing.

SUMMARY OF THE INVENTION

Bearing in mind the foregoing, a diaphragm has been conceived for loudspeakers which enables to emphazing the low frequencies and changing the colour and shade of the sound without requiring excessively large surfaces or volumes and without requiring special weights to immobilize the assembly. At the same time, such diaphragms are extremely simple to manufacture and of much lower cost than those of the known systems. The present invention is applied to the so called “flat loudspeakers” which have generally a flat front face and a rear face to which is connected a driving unit, that is, electromagnetic assembly, which includes a vibratory coil. All these flat loudspeakers have a zone to vibrate and this zone is surrounded by a vibration damping marginal portion. As a typical example the diaphragm described in my U.S. Pat. No. 3,596,733 may be cited, as well as the earlier known flat diaphragms some of which are described in the introductory portion of said patent.

The present invention consists in connecting to said marginal vibration damping portion a plate adapted to vibrate in the low frequency range, to emphasize said frequencies. Said plate may project beyond the member defining the diaphragm and which is preferably made of a foamed plastic. More particularly, the present invention refers to a diaphragm for flat loudspeakers which emphasize the low frequencies and changes the shade and colour of the sound and which comprises a first plate-like member preferably made of foamed plastics and which has a substantially flat front face and a rear face defining a marginal vibration damping portion which substantially circumscribes a figure portion including a zone for collecting vibrations arranged out of the geometric center of said figure portion and wherein at least one part of the rear face, in the zone corresponding to the marginal vibration damping portion, is connected to a second plate like member, which projects beyond said marginal vibration damping portion, said second plate-like member being capable of collecting low frequency vibrations which are capable of entering in said marginal vibration damping portion.

It may be stated that within the concept of the present invention it is also conceivable to arrange, within said marginal damping vibration portion a tweeter for reproducing high frequency vibrations or the first plate-like member may include an additional portion defining a second loudspeaker for reproducing high frequencies and in this event the second-plate like member projects beyond the first plate-like member corresponding to the first loudspeaker and may cover the zone corresponding to the second loudspeaker intended for reproducing high frequency vibrations, without changing the behaviour of the second platelike member and thus it is not necessary that the second plate-like member projects beyond the second loudspeaker since the behaviour of one does not interfere with the other. In this latter embodiment it is advisable that the first plate-like member has a dividing zone formed by means of a channelled portion in said first plate-like member which separates the two loudspeakers. Conveniently this channelled member is filled with a resilient material, such as a silicone rubber, which is capable of maintaining its resiliency and will not attack the material from which the first plate-like member is manufactured, when the latter is made of foamed plastics, such as polystyrene or polyurethane.

Another concept which falls within the scope of the present invention is that the second plate-like member, to collect the sounds corresponding to the low frequencies, is replaced by a resonance casing (of the type of a violin casing) the shape of which may vary so that it may be adjusted to define any particular shade and colour of tone.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate the comprehension of the present invention reference will now be made to the drawings wherein, by way of example, three structural embodiments are shown, in which:

FIG. 1 is a perspective view of the front portion of the diaphragm of the present invention.

FIG. 2 is a perspective view of the rear portion of the diaphragm shown in FIG. 1.

FIG. 3 is a longitudinal section through a diaphragm which is to form part of two loudspeakers of which the portion corresponding to the smaller loudspeaker is to act as a tweeter.

FIG. 4 is a longitudinal section through an arrangement of a diaphragm including a resonance casing to emphasize the low frequencies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As may be appreciated from FIG. 1, the diaphragm of the present invention consists of a first plate-like member 1, preferably manufactured of foamed plastics, such as polystyrene or polyurethane. The platelike member 1 has a substantially flat front face 2 and side faces 3 which link the front face 2 to a rear face

3,767,005 (FIG. 2). To this rear face 4, as will be later explained, a second plate-like member 5 is connected in a particular manner and which projects beyond the first plate-like member 1, (with regard to the side faces 3). The second plate-like member 5 may be manufactured of any suitable material which is capable of vibrating in the low frequency range. A material which has proven excellent for the purpose above specified is conglomerated or compensated wood which exists on the markets in the shape of plates. The side faces 6 do not prevent atmospheric agents from undesirably entering such a plate like member. Therefore it is convenient to submit such a second plate-like member to a previous drying process and then to seal the side faces 6 with a sealant 6' such as a synthetic resin of the vinyl type, for example, which exist on the market.

Referring now to FIG. 2, it may be appreciated that the rear face 4 of the first plate-like member 1 defines a marginal portion 7 which circumscribes a figure portion 8 of particular shape, similarly to the pinna of a human ear. This figure portion 8 is dome shaped-as may be better seen in FIG. 3— and a portion of maximum height 9 is at a zone out of the geometric center of said figure portion 8. The portion of maximum height 9 includes preferably a recess 10 to which the electromagnetic or driving unit 11 (FIG. 2) is to be connected and which is mounted on a bridge 12 the ends of which are supported by the marginal zone of the first plate-like member 1 —actually this bridge is mounted on a frame which is not shown, since the bridge and the electromagnetic assembly do not form part of the present invention and are merely described for informative purpose.

It will be understood that upon vibrating the electromagnetic assembly 11, vibrations will be transmitted to the recess 10 and thereby to the figure portion 8. The zone of maximum height or thickness 9 therefore receives the vibrations from the electromagnetic assembly. Conveniently the marginal portion 7 is flat and defines a plane parallel to the front face 2 and the zone of maximum height 9 of the figure portion 9 is tangential to said plane. The marginal portion 7 forms a marginal vibration damping portion and is capable of damping the majority of the vibrations which are transmitted through the electromagnetic assembly 11 to the figure portion 8. However the low frequency range vibrations have the tendency to propagate through the marginal portion 7.

It may also be appreciated from FIGS. 2 and 3 that the figure portion 8 forms with the marginal portion 7 an endless side wall 13.

The second plate-like member 5 has a cut-out portion in its center portion, the shape of which is substantially equal to that of the figure portion 8, so that the endless lateral wall 14 becomes coplanar with the side wall 13. It is advisable that said lateral wall 14 is subjected to the same sealing process by means of the synthetic resin as the side faces 6.

The second plate-like member 5 is adhesively connected, for instance by means of a synthetic adhesive of the vinyl type, to the rear face 4 which defines the marginal portion 7 of the first plate-like member 1 and in this embodiment the plate 5 projects beyond the side faces 3 of the first plate-like member 1. Since the object is to enhance the low frequencies by using the theory that the low frequencies are transmitted by the first plate-like member 1 in the vectorial channels (see my above cited patentjwhich start from the electromagnetic assembly 11 towards those portions of the side wall 13 which are the remotest ones from the electromagnetic assembly 11, it will presumably be sufficient that the second plate-like member 5 projects beyond the first plate-like member 1, in the pertinent vectorial zone.

Eventually it will be possible to insert through the second plate-like member 5 in the zone corresponding to one of the marginal portion 7, preferably a zone having a large surface, a tweeter (not shown ) specially useful for obtaining particular stereophonic effects.

With regard to the example shown in FIG. 3, it may be appreciated that the plate-like member 1' includes a portion 1 of smaller size, but which is similar to the plate-like member 1' and which may be used for producing the tweeter device. In this embodiment the marginal zone 7 is provided in the rear face with a channel member 15 which insulates vibrations and which is conveniently filled with a resilient material 16, which does not attack the material of which the member 1', 1 is manufactured. If the last mentioned member is manufactured of polystyrene or polyurethane then a silicone rubber, may be used such as the one known by the trade name SILASTIC produced by Dow Corning. Portion 1. defines likewise a side wall 17 and the pertinent marginal vibration damping portion 18, as well as a figure portion 19. In this embodiment the second plate-like member 5 has a second opening formed by an internal endless lateral wall 20. Apart from that, the second plate-like member 5 covers also the marginal portion 18, although it is not necessary that it is adhesively adhered thereto. Thus the portion of the second plate-like member 5 corresponding to the portion 1'', performs the role of the portion of the plate-like member 5 which projects beyond the plate-like member 1 in the example corresponding to FIGS. 1 and 2. In this embodiment it is not necessary that the plate-like member 5 projects beyond the side walls defined by body 1', 1''.

Finally reference has to be made to FIG. 4, wherein a first plate-like member 1 is shown, having also the marginal vibration damping portion 7 and the figure portion 8 provided with the recess 10. On the marginal portion 7 a resonance box 21 is arranged consisting of a first plate member 22 the peripheral portion of which is linked through a perimetrical cross band member 23 with a second plate member 24. First plate member 22 has a cutout portion 22' whose size and shape are substantially equal to that of the figure portion 8, the relationship and positioning of plate member 22 relative to figure portion 8 being substantially the same as that of plate-like member 5 described in connection with FIGS. 1 and 2. Second plate member 24 is also provided with a cutout portion or mouth 26 aligned with cutout portion 22', the area of cutout portion 26 being less than that of cutout portion 22'. In this manner, the internal free edge portion 24' of second plate member 24 overhangs the figure portion 8. In the illustrated embodiment internal free edge portion 24' overhangs the entire periphery of figure portion 8 between the members 22, 23 and 24 a chamber 25 is formed. By varying the size of the projecting portion of the first plate member 22 with regard to the marginal portion 7, the volume of chamber 25 may be changed. Another way of changing said volume is by varying the size of the perimetrical cross band member 23.

3,767,005

Upon transmitting vibrations to the first plate-like member 1 through the electromagnetic assembly (such as assembly 11 of FIG. 2) part of these vibrations of the low frequency range are transmitted through the figure portion 8 into the marginal portion 7 and therefrom by contact to the first plate member 22.

The mass of air which vibrates behind the rear face corresponding to the figure portion 8 is in part forced to enter chamber 25, because the second plate member 24 faces a portion of the rear face of the first plate-like member 1. When the electromagnetic assembly 11 starts to transmit high frequency vibrations corresponding to the high tones, these may freely project through the mouth 26 defined by the free edge 24' of the second plate member 24 and therefore substantially do not enter the chamber 25.

Thus the chamber 25 operates as a resonance casing for low frequencies and a special colour and shade is achieved for these low frequencies.

If desired the mouth 26 may be covered by a lid 27. Obviously the members 22, 23 and 24 may be made of many kinds of materials, but are preferably made of wood of the type used for producing violins and other musical string instruments. In some cases it may be interesting to replace the wood by other materials such as plastics.

It is not necessary that the resonance casing 21 defines a mouth 26 of similar shape but of smaller area than the shape of the figure portion 8. In some cases it may become even interesting that the resonance casing is only provided in the vector zone corresponding to the low frequencies.

It is also possible to make holes 27' ( of any shape) in the second plate member 24, and/or in the cross band member 23 (see hole 28) in order to connect the chamber 25 with the outside atmosphere to thus vary the sound characteristics.

It will be obvious that modifications may be introduced in this invention upon carrying it out into practice as far as certain structural details are concerned, but always without departing from the fundamental principles which are clearly specified in the following claims.