Self Damping Speaker Matching Device

The invention relates to loudspeakers, and in particular to a damping circuit for use in association with loudspeakers and, in particular, to a self-damping crossover circuit for use in multi-speaker audio systems.

The problem of sound distortion in loudspeakers is well known. Generally it is detectable especially in the bass regions of sound reproduction as a form of "rumble", which muffles or masks the full purity of the bass tones. The problem also occur in the mid-range and upper ranges of audio frequency reproduction, but is less noticeable to an untrained ear. This distortion is apparent in coil-driven loudspeaker systems having a single coil-driven loudspeaker, as well as those having a plurality of coil-driven loudspeakers. High fidelity audio loudspeaker systems usually comprise at least two and more often, three or more separate coil-driven speakers. These speakers will include a speaker to cover the high frequency high notes (tweeter) and a speaker to cover the low frequency bass notes (woofer), and in most cases, a speaker to cover the mid-range frequency notes (mid-range). In some cases there may be multiple speakers for each range. It is customary in such multi-speaker systems to provide one or more filter circuits known as "crossovers" in which the signals for the various ranges are separated so that they are reproduced in the appropriate speakers in the system. Such crossovers incorporate one or more crossover coils as part of the filter circuit. The precise causes of the type of distortion described above are not entirely clear. However, it seems reasonable to assume that one source is the collapsing of the magnetic fields created around the crossover coil during the passage of audio signals. As the magnetic fields collapse, they induce, within the coil, a secondary transient signal related to, but not part of, the primary audio signal. Some evidence is available for this theory in the well-known relationship between the strength of the primary signal and the strength of the distortion signal. Various attempts have been made to deal with the problem.

One recent proposal is shown in U.S. Pat. No. 4,160,133. In this patent, the speaker itself is manufactured with an additional damping coil mounted directly on the speaker. The degree of effectiveness of this solution has not been evaluated, but it is certain that the cost of manufacturing speakers incorporating this proposal would be considerably higher than the manufacture of conventional speakers, and the efficiency of the speaker is adversely affected. Thus such a solution would be less than optimal for the consumer. Consequently, this proposal has not achieved wide acceptance.

In general terms, the present invention finds its application both to single speakers and to such crossover circuits for multiple speakers so that a damping effect is provided over a part of the frequency ranges or indeed all of the frequency ranges to damp out distortion.

It is believed that a major cause of speaker distortion is in the design of the crossover circuits themselves. Such crossover circuits inherently incorporate some form of coils, of varying inductances, whereby signals may be divided up into groups or bands of selected wavelengths for reproduction in the different speakers. It is, of course, well known that the passing of electrical current wave forms through a coil will result in the development of transient electromagnetic fields around the coil itself. As the current fluctuates, so also does the induced electromagnetic field. The fluctuation of the induced electromagnetic field is believed to induce, in turn, a fluctuating voltage across the coil which is passed through the speaker coil producing a further unwanted movement and hence sound waves from the speaker. It is believed that this is a major cause of the distortions or so-called "rumble" which can be heard in speaker systems and this distortion is generally considered to be undesirable by the great majority of listeners. While this explanation has not been scientifically proved it does seem to be a reasonable explanation for the phenomenon of sound distortion in speakers.

It will of course be understood that in most of the speaker systems to which the invention relates, the speakers will be of the moving coil type. Such speakers inherently incorporate their own integral coil means. Such speaker coils will in themselves develop a back EMF, induced as the voice coil moves through the magnetic field of the permanent magnet which surrounds the voice coil. This factor is a "given" in almost all speaker systems, and may also be, in itself, a cause of distortion.

With a view to providing a damping circuit for improved performance of speaker systems of the type containing at least one speaker means having input and output connection means, of the type subject to interference by unwanted circuited generated noise signals the invention comprises a damping circuit means comprising matching coil means defining matching coil input and output connection means, with said matching coil output connection means connectable with said speaker input connection means, damping coil means defining damping coil input and output connection means, with said damping coil input connection means connectable to said speaker output connection means, and said matching and damping coil means being wound together, with their said input connection means adjacent one another and their said output connection means adjacent one another whereby currents will flow through said matching and damping coil means in the same direction and whereby to reduce in strength, or damp, the unwanted noise signals.

The invention further comprises a method of damping audio signals in a speaker system, by passing the same through a damping circuit means, said damping circuit means comprising: matching coil means and damping coil means; said matching and damping coil means each having a first coil end and a second coil end, and having respective input and output connection means; said matching coil means and damping coil means being wound together about a common core and having respective input connection means at a coincident first coil end, and having respective output connection means at a respective coincident second coil end; said matching coil means and damping coil means being wound in a manner to provide unity coefficient of coupling between said matching and damping coil means; said matching coil connected in series with a coil driven speaker having input connection means and output connection means, with matching coil output connection means connected to the input connection means of the loudspeaker; said damping coil means connected in series with the same coil driven loudspeaker and having speaker output connection means connected to damping coil input connection means in such a manner as to provide a continuous circuit between the matching coil input connection means and the damping coil output connection means; whereby currents will flow through said matching and damping coil means in the same direction whereby to reduce in strength, or damp, the unwanted noise signals.

The invention further provides that said matching coil means may be of a first predetermined inductance and said damping coil means may be of a second predetermined inductance different from said matching coil means.

The invention further provides that variable means may be provided for varying the inductance of one of said matching and damping coil means relative to the other.

The invention further provides such a speaker system wherein there are at least, high frequency speaker means and low frequency speaker means, and incorporating first high frequency damping circuit means for said high frequency speaker means and further low frequency damping circuit means for said low frequency speaker means.

The invention further comprises such a system wherein there are at least three separate speakers in each speaker system, and there being respective damping circuit means said speakers in said speaker system.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention .

FIG. 1 is an electrical circuit diagram showing a single damping circuit illustrating the use of the invention for application to a single speaker;

FIG. 1A is a detail of the bifilar winding of the matching coil and the damping coil;

FIG. 2 is an electrical circuit diagram illustrating a typical audio loudspeaker system comprising a plurality of speakers and damping circuits;

FIG. 3 is an electrical circuit diagram illustrating damping circuit provided with a variable tapping on the windings of the damping coil means whereby the inductance of that coil may be changed; and,

FIG. 4 is a diagram illustrating another preferred embodiment.

Referring first to all of FIG. 1, it will be seen that the invention is there illustrated in connection with a speaker system comprising a single speaker 10 having an integral voice coil 12 and speaker input connection means 14 and speaker output connection means 16. The invention 18 provides matching coil 20 and a damping coil 22 each having respective input connection means 24, 26 and having respective output connection means 28, 30. Matching coil 20 and damping coil 22 are wound in a mode known as "unity coefficient of coupling", in bifilar style i.e. two conductors of the same or very nearly the same thickness placed adjacent one another and wound on a common support means 36 in the same rotational direction as illustrated in FIG. 1A. In this form of winding as shown in FIG. 1A, each wire loop of matching coil 20 alternates with and is separated by a respective wire loop of damping coil 22.

In operation, it will be appreciated that the driving circuit i.e., the audio signal source will supply power via the input 32 which is connected to matching coil input connection means 24. Matching coil output connection means 28 is connected to speaker input connection means 14 and power passes through integral voice coil 12 to speaker output connection means 16. Power then flows from speaker output connection means 16 to damping coil input connection means 26, through damping coil 22 to damping coil output connection means 30 from whence it passes to the negative side of the driving circuit 34.

As FIG. 1 indicates, matching and damping coils 20, 22 are wrapped in the same rotational direction about a common support means such as core 36. Common core 36 may be formed of iron-steel, nickel-steel, or any other support means which may be advantageous in a given situation.

It is believed that the damping circuit as herein described relies on induced currents to function. As a audio signal is fed into the circuit is passed first through the matching coil, then the speaker coil, and then the damping coil.

The presence of the loudspeaker coil in the circuit provides a phase shift in the current flowing through the circuit. It is believed that this phase shift allows the damping circuit means to perform its job of damping unwanted circuit generated noise signals which greatly improves the performance of the loudspeaker.

There are three different electrical signals which are easily identified and flow within the standard speaker circuit as a given instant. First is the primary signal or applied voltage, second is the "back EMF" produced in the voice coil of the loudspeaker, and third is the induced current created by the passage of the primary current through the matching coil. It is believed that the design of the damping circuit provides, for the back EMF in the circuit, a very nearly equally strong signal which is out of phase with the original.

More frequently, the invention will be used in a speaker system employing a plurality of loudspeakers interconnected through a matching circuit. By way of illustration, FIG. 2 shows the invention in a system having three separate speakers; namely, a low frequency speaker 38, a mid-range frequency speaker 40, and a high range frequency speaker 42. Each of the speakers is of the moving coil type, and the speakers are together intended to handle the entire audible range of sound waves, with, in most cases, a certain degree of overlap between the adjacent speakers, in a manner well known in the art and requiring no description. Low range frequency speaker 38 has an input 44 and an output 46, indicated respectively as positive and negative. The mid range speaker 40 has an input connection 48 and an output connection 50 indicated respectively as positive and negative. The high range frequency speaker 42 has an input connection 52 and an output connection 54 indicated respectively as positive and negative.

It is assumed that the speaker system comprising the three speakers 38, 40, and 42 is intended to be connected to a source of audio frequency signals, coming from a suitable source such as some form of sound reproduction device either a disc or tape type device, or for example from a radio receiver, or directly for example from a microphone or series of microphones with amplifiers and other equipment as needed (not shown). All of these different systems are very well known in the art and require no further description.

The connections for such systems are indicated generally as 56 and 58 being indicated respectively as positive and negative. As is well known in the art, in the normal speaker system, there would be, between the main connections 56 and 58, and the speakers 38, 40, and 50 a series of what are known as "crossover" circuits. The purpose of the crossover circuits is to filter out or separate the high-frequency mid-range and low-frequency signals, so that they are directed to the appropriate speakers for reproduction therein, and are excluded from the other speakers. As mentioned, in most crossover circuits and speaker systems, some small degree of overlap is provided, the exact degree being dependent upon the design of the speakers and the requirements of the system, all as is well known in the art. It will be appreciated that in FIG. 2 no such typical prior art crossover circuits are illustrated.

In place of the conventional crossover circuits, there are provided low range matching and damping coils 60 and 62, and high range matching and damping coils 64 and 66. Low range matching coil 60 has an input 68 and an output 70 and low range damping coil 62 has an input 72 and an output 74. High range matching coil 64 has an input 76 and an output 78. High range damping coil 66 has an input 80 and an output 82. Each of the respective pairs of coils 60-62 and 64-66 are wound in a bifilar manner in the same rotational direction concentrically together about respective common support means as shown and as described above (FIGS. 1 and 1a), providing unity coefficient of coupling, with their inputs adjacent one another at respective first coil ends, and with their outputs adjacent one another at respective second coil ends. Preferably, they are wound about their support means indicated generally as 84 and 86. Low range matching coil 60 is connected with its input 68 connected to the input side of the driving circuit 56. The output 70 of low range matching coil 60 is connected to the input side 44 low range speaker 38. The input 72 of low range damping coil 62 is connected to the output 46 of low range speaker 38. The output 74 of low range damping coil 62 is connected to the negative side 58 of the driving circuit. A suitable condenser 88 is incorporated where necessary, in the connection between the output 50 of mid range speaker 40, and the input 44 of low range speaker 38. In addition, a further connection, together with a condenser 90, extends between the output 50 of mid range speaker 40, and the negative side 58 of the driving circuit.

In the high range matching and damping coils 64 and 66, the input 76 of high range matching coil 64 is connected to the positive side 56 of the driving circuit through condenser 94a.

The output 78 of high range matching coil 64 is connected to the input 52 of the high range speaker 42. The input 80 of high range damping coil 66 is connected to the output 54 of the high range speaker 42. The output 82 of the high range damping coil 66 is connected through a condenser 94b to the negative side 58 of the driving circuit. Suitable auxiliary coils 92, and condenser 94c are provided to filter super-sonic transients.

FIG. 3 is an example of a variant of the damping circuit. It may be desirable for the user to control the inductance of the damping coil, thereby altering the performance of the damping circuit. In order to vary the inductance of the damping coil, a series of tappings 11, 13, 15, 17, and 19 are provided along the damping coil. These tappings are connected into multi-position selector switch 21. Selector switch 21 provides a convenient method of altering the connection point of the outlet side 34 of the driving circuit and damping coil 22, thereby altering the number of effective windings of damping coil 22 and hence its inductance. It can be appreciated that damping circuits having variable tappings may be utilised in multi-speaker systems such as those shown in FIG. 2 and FIG. 4.

FIG. 4 is a diagram of a further preferred embodiment of the inventive circuit in a loudspeaker system having a high frequency speaker 100, a middle range frequency speaker 102, and a low range frequency speaker 104. The benefits of providing different speakers for the reproduction of different frequency ranges are well known in the art and therefore will not be described here. Each speaker is provided with a damping circuit, indicated generally as 106, 108, 110. In the circuit of FIG. 4, capacitors 112, 114 are connected in the circuit to filter unwanted frequencies from respective speakers.

The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only. The invention is not to be taken as limited to any of the specific features as described but comprehends all such variations thereof as come within the scope of the appended claims.