Patent Description:
A conventional loudspeaker includes a single suspension region. The single suspension region places a voice coil in an unbalanced state. The unbalanced state occurs because the single suspension region acts on one side of the voice coil. Additionally, the conventional loudspeaker includes an asymmetric motor region. In the asymmetric motor region, the motor geometry around the voice coil is not symmetric. The unbalanced state and the asymmetric motor region lead to significant asymmetrical motor force (BL), significant asymmetrical suspension stiffness (K), and significant asymmetrical inductance (Le). The aforementioned, thus, makes the conventional loudspeaker prone to non-linear distortion, instability, and other acoustical performance issues.

Publication <CIT> discloses a double-dangling-edge loudspeaker, comprising a frame body, a voice coil, a voice diaphragm, an upper dangling edge and a lower dangling edge. The frame body is provided with an accommodation space, the voice coil is disposed in the accommodation space, a first magnet, a first washer and a second magnet are disposed at the bottom end of a hollow portion in the voice coil sequentially in a direction toward the top end, the bottom end of the first magnet is provided with round iron locked at the bottom of the frame body, the voice diaphragm covers the top of the voice coil, the upper dangling edge is disposed at the top end of the frame body and connected to the voice diaphragm, and the lower dangling edge is disposed at the bottom end of the frame body and connected to the voice coil.

Document <CIT> discloses a voice coil motor assembly comprising a voice coil, first and second magnets, the poles of the first and second magnets providing aligned, opposing lines of force in first and second opposite directions, a first spacer having a first face adjacent a pole of the first magnet and a second opposite face, a second spacer having a first face adjacent the like pole of the second magnet and a second opposite face, a third magnet oriented between the second faces of the first and second spacers, and means for mounting the voice coil in close proximity to the third magnet, the third magnet providing lines of force extending in a third direction generally transverse to both the first and second directions, and the voice coil having a direction of motion extending generally perpendicular to the third direction.

In one embodiment, a loudspeaker is provided with a magnet assembly that is aligned along a longitudinal axis. A frame encircles the magnet assembly. The frame includes an outer wall. The magnet assembly and the outer wall form a voice coil gap. A voice coil is disposed in the voice coil gap. The voice coil includes a first side longitudinally spaced from a second side. The voice coil is aligned with the magnet assembly to yield: a substantially symmetric motor force, a substantially symmetric suspension stiffness, and a substantially symmetric inductance. The loudspeaker further comprises a first suspension element attached to the frame and adapted to apply a first stiffness to the first side of the voice coil, and a second suspension element attached to the frame and adapted to apply a second stiffness to the second side of the voice coil. The voice coil is symmetrically aligned with the magnet assembly such that the magnet assembly includes an overall length along the longitudinal axis and the voice coil includes an overall length along the longitudinal axis, wherein a halfway point of the overall length of the magnet assembly coincides with a halfway point of the overall length of the voice coil when the voice coil is at rest. The outer wall includes an overall length along the longitudinal axis, wherein a halfway point of the overall length of the outer wall coincides with the halfway point of the overall length of the voice coil when the voice coil is at rest.

As such, compared to the conventional loudspeaker, the embodiments herein allow for balanced voice coils, as well as substantially symmetric motor force, substantially symmetric suspension stiffness, and substantially symmetric inductance.

<FIG> illustrates a partial section view of a conventional loudspeaker, which is in accordance with the prior-art and is generally referenced by numeral <NUM>. The conventional loudspeaker <NUM> includes a single suspension region <NUM>. The single suspension region <NUM> includes a first suspension element <NUM> and a second suspension element <NUM>. The single suspension region <NUM> places a voice coil <NUM> of the conventional loudspeaker <NUM> in an unbalanced state.

In the unbalanced state, the single suspension region <NUM> acts on a first side <NUM> of the voice coil <NUM>. More specifically, the first suspension element <NUM> and the second suspension element <NUM> act on the first side <NUM> of the voice coil <NUM>. Alternatively stated, the first suspension element <NUM> and the second suspension element <NUM> support the first side <NUM> of the voice coil <NUM>. The voice coil <NUM> includes a second side <NUM> that is longitudinally spaced from the first side <NUM>. Because of the single suspension region <NUM>, though, the application of stiffness/support is one-sided. The one-sided application of stiffness/support occurs because the first suspension element <NUM> and the second suspension element <NUM> both act on the first side <NUM> of the voice coil <NUM>. In the conventional loudspeaker <NUM>, there is not an additional suspension element that acts on the second side <NUM> of the voice coil <NUM> to complement the stiffness/support effects of the first suspension element <NUM> and the second suspension element <NUM>. Because of that, the voice coil <NUM> is in the unbalanced state.

In the conventional loudspeaker <NUM>, the unbalanced state is acoustically undesirable. For example, the unbalanced state is likely to cause rocking, midband rubs, extraneous noise, permanent damage, or outright failure.

The conventional loudspeaker <NUM> includes an asymmetric motor region <NUM>. In the asymmetric motor region <NUM>, the voice coil <NUM> asymmetrically aligns with a magnet assembly <NUM>. Moreover, in the asymmetric motor region, the conventional loudspeaker <NUM> includes a motor geometry <NUM> around the voice coil <NUM> that is not symmetric. The motor geometry <NUM> is such that there is more material (e.g., low carbon steel) around the second side <NUM> of the voice coil <NUM> than the first side <NUM>. The motor geometry results in significant acoustical parameter asymmetry for motor force (BL), suspension stiffness (K), and inductance (Le). Therefore, in the conventional loudspeaker <NUM>, the motor force, the suspension stiffness, and the inductance are not substantially symmetric.

In the conventional loudspeaker <NUM>, the significantly asymmetric motor force, suspension stiffness, and inductance are acoustically undesirable. For example, the significantly asymmetric motor force, suspension stiffness, and inductance are likely to cause nonlinear distortion, instability, etc..

The conventional loudspeaker <NUM> aligns along a longitudinal axis <NUM>. Therefore, the magnet assembly <NUM> aligns along the longitudinal axis <NUM>. The magnet assembly <NUM> includes a first magnet <NUM> and a second magnet <NUM>. A spacer <NUM> separates the first magnet <NUM> from the second magnet <NUM>. In addition to the spacer <NUM>, the first magnet <NUM> attaches to an end cap <NUM>.

In addition to the spacer <NUM>, the second magnet <NUM> attaches to a back cover <NUM>. The back cover <NUM> attaches to a basket <NUM>. The basket <NUM> extends from the back cover into the single suspension region <NUM>. The single suspension region <NUM> extends longitudinally from the first side <NUM> of the voice coil <NUM> and transversely from the longitudinal axis <NUM>. Additionally, the back cover <NUM> and the magnet assembly <NUM> form a voice coil gap <NUM>. The voice coil <NUM> resides in the voice coil gap <NUM>. , the voice coil <NUM> is disposed in the voice coil gap <NUM>. ) The voice coil <NUM> attaches to a voice coil former <NUM>. The voice coil former <NUM> attaches to a diaphragm <NUM>. A dust cap <NUM> attaches to the diaphragm <NUM>. Furthermore, in the conventional loudspeaker <NUM>, the first suspension element <NUM> attaches to the basket <NUM> and the diaphragm <NUM>. And the second suspension element <NUM> attaches to the basket <NUM> and the voice coil former <NUM>.

Because of the unbalanced state, the voice coil <NUM> is prone to misalignment issues in the voice coil gap <NUM>. For example, transversely to the longitudinal axis, the spacing between the back cover <NUM> and the voice coil <NUM> at the first side <NUM> in the voice coil gap <NUM> may be significantly different than the spacing between the back cover <NUM> and the voice coil <NUM> at the second side <NUM> in the voice coil gap <NUM>. Because of the unbalanced state, the voice coil <NUM> is particularly vulnerable to varying the transverse spacing at the second side <NUM>. Alternatively stated, because of the unbalanced state, the second side <NUM> is more prone to movement in a direction that is transverse to the longitudinal axis <NUM>. This may be exacerbated when the voice coil <NUM> translates along the longitudinal axis <NUM>. While translation along the longitudinal axis <NUM> is expected during normal operation, significant movement in the transverse direction (which the voice coil <NUM> is prone to) yields undesirable consequences, such as the aforementioned rocking, midband rubs, extraneous noise, etc..

In the conventional loudspeaker <NUM>, the asymmetric motor region <NUM> includes the magnet assembly <NUM>, the back cover <NUM>, and the voice coil <NUM>. Additionally, the asymmetric motor region <NUM> includes at least a portion of the basket <NUM>. The magnet assembly <NUM>, the back cover <NUM>, and the portion of the basket <NUM> define the motor geometry <NUM> around the voice coil <NUM>. In the conventional loudspeaker <NUM>, the back cover <NUM> forms part of a magnetic flux flow loop through the voice coil <NUM>. This is because the back cover <NUM> is made out of low carbon steel or a comparable material. The spacer <NUM>, the end cap <NUM>, and the basket <NUM> may be made out of the same material as the back cover <NUM>.

Additionally, the conventional loudspeaker <NUM> includes an overall length L along the longitudinal axis <NUM>. The overall length L runs from a backside <NUM> of the back cover <NUM> to a point <NUM> that is distally located in the single suspension region <NUM>. The point122 corresponds to the dust cap <NUM>, the first suspension element <NUM>, or the basket <NUM>-whichever is most distally located from the backside <NUM> along the longitudinal axis <NUM>. Along the longitudinal axis <NUM>, the point <NUM> is farthest from the backside <NUM> of the back cover <NUM>.

In order to increase the overall motor force of the conventional loudspeaker <NUM>, the overall length L generally needs to increase. In general, to increase the overall motor force, the length of the magnet assembly <NUM> needs to be increased (by the introduction of longer and/or additional magnets or other components therein), the length of the voice coil <NUM> needs to be increased (such as by increasing the number of turns along the longitudinal axis) or at least one or more additional voice coils needs to be introduced, or a combination of the aforementioned needs to occur. Often, through the aforementioned, the overall length L of the conventional loudspeaker <NUM> needs to be increased. That is often the case when there is not enough room in the conventional loudspeaker <NUM> to increase the length of the magnet assembly <NUM>, increase the length of the voice coil <NUM>, or add additional voice coils.

Increasing the overall length L of the conventional loudspeaker <NUM> may be impractical in a shallow-depth environment, such as between two walls of a listening room, between a first surface and a second surface of an automobile door, under a seat bottom and a floor pan of an automobile, etc. The shallow-depth environment may include a design constraint such that the overall length L of the conventional loudspeaker <NUM> must be less than or equal to a shallow-depth. If the overall length is equal to the shallow-depth, the overall motor force of the conventional loudspeaker <NUM> may be maxed out.

<FIG> and <FIG> illustrate partial section views of a loudspeaker <NUM>, which is in accordance with one or more embodiments of the present invention. The loudspeaker <NUM> includes a first suspension region <NUM> and a second suspension region <NUM>. The first suspension region <NUM> includes a first suspension element <NUM>. The second suspension region <NUM> includes a second suspension element <NUM>.

The first suspension region <NUM> and the second suspension region <NUM> place a voice coil <NUM> in a balanced state. More specifically, the first suspension element <NUM> acts on a first side <NUM> of the voice coil <NUM>. The first side <NUM> is longitudinally spaced from a second side <NUM> of the voice coil <NUM>. The second suspension element <NUM> acts on the second side <NUM> of the voice coil <NUM>. Alternatively stated, the first suspension element <NUM> supports the first side <NUM> of the voice coil <NUM>, and the second suspension element <NUM> supports the second side <NUM> of the voice coil <NUM>. Because of the way that the first suspension element <NUM> and the second suspension element <NUM> act on the first side <NUM> and the second side <NUM>, the voice coil <NUM> is in the balanced state. The balanced state is thus achieved because at least one suspension element (i.e., the first suspension element <NUM>) acts on the first side <NUM> of the voice coil <NUM>, and at least one other suspension element (i.e., the second suspension element <NUM>) acts on the second side <NUM> of the voice coil <NUM>.

In the balanced state, the first suspension element <NUM> applies a first stiffness that acts on the first side <NUM> of the voice coil <NUM>, and the second suspension element <NUM> applies a second stiffness that acts on the second side <NUM> of the voice coil <NUM>. In an ideal case, the first stiffness is equal to the second stiffness. However, alternative cases for the first stiffness and the second stiffness may be utilized. Alternatively stated, the balanced state includes a two-sided application of stiffness/support. The two-sided application of stiffness/support occurs because the first suspension element <NUM> acts on the first side <NUM> of the voice coil <NUM>, and the second suspension element <NUM> complementarily acts on the second side <NUM> of the voice coil <NUM>. The two-sided application of stiffness/support provides for greater voice coil stability.

The first stiffness and the second stiffness may be desirably obtained by material selection and dimensioning for the first suspension element and the second suspension element (and any additional suspension elements). The first suspension element may be made of the same material as the second suspension element (and any additional suspension elements). Alternatively, the suspension elements may be made out of different materials. Some examples of materials for the suspension elements include rubbers (such as nitrile butadiene rubber), nonwoven fabrics, woven fabrics, foams, and other materials known in the art, such as other polymers and elastomeric materials.

Placing the voice coil <NUM> in the balanced state is acoustically desirable. For example, in the loudspeaker <NUM>, placing the voice coil <NUM> in the balanced state reduces rocking, midband rubs, extraneous noise, permanent damage, and outright failure-at least compared to the conventional loudspeaker <NUM>.

The loudspeaker <NUM> aligns along a longitudinal axis <NUM>. The loudspeaker <NUM> includes a magnet assembly <NUM>. The magnet assembly <NUM> attaches to a back plate <NUM>. The back plate <NUM> attaches to a frame <NUM>. The frame <NUM> encircles the magnet assembly <NUM> about the longitudinal axis <NUM>. Moreover, the frame <NUM> and the magnet assembly <NUM> form a voice coil gap <NUM>. The voice coil <NUM> is attached to a voice coil former <NUM>, such as by winding therearound. Additionally, the voice coil <NUM> resides in the voice coil gap <NUM>. The voice coil former <NUM> attaches to a diaphragm <NUM>, such as through an adhesive or other ways known in the art. The first suspension element <NUM> attaches to the diaphragm <NUM> and the frame <NUM>, such as through an adhesive or other ways known in the art. The second suspension element <NUM> attaches to the voice coil former <NUM> and the frame <NUM>, such as through an adhesive or other ways known in the art. And a dust cap <NUM> attaches to the diaphragm <NUM>, such as through an adhesive or other ways known in the art.

Along the longitudinal axis <NUM>, the loudspeaker <NUM> includes an overall length L'. The overall length L' is defined by a first point <NUM> and a second point <NUM>. The first point <NUM> is located in the first suspension region <NUM>, and the second point <NUM> is located in the second suspension region <NUM>. Along the longitudinal axis <NUM>, the first point <NUM> corresponds to the dust cap <NUM>, the diaphragm <NUM>, the frame <NUM>, or the first suspension element <NUM>-whichever is most distally located from the second point <NUM> along the longitudinal axis <NUM>. And along the longitudinal axis <NUM>, the second point <NUM> corresponds to a location on the back plate <NUM> that is most distally located from the first point <NUM>.

The first suspension region <NUM> extends in a first longitudinal direction <NUM>, which is parallel to the longitudinal axis <NUM>. The first longitudinal direction <NUM> extends from the first side <NUM> of the voice coil <NUM> toward the dust cap <NUM>. The second suspension region <NUM> extends in a second longitudinal direction <NUM>, which is parallel to the longitudinal axis <NUM>. The second longitudinal direction <NUM> is opposite to the first longitudinal direction <NUM>. Moreover, the second longitudinal direction <NUM> extends from the second side <NUM> of the voice coil <NUM> toward the back plate <NUM>. Additionally, both the first suspension region <NUM> and the second suspension region <NUM> extend transversely from the longitudinal axis <NUM>.

The magnet assembly <NUM> and the voice coil <NUM> align along the longitudinal axis <NUM>. The magnet assembly <NUM> includes a first inner magnet <NUM>. The first inner magnet <NUM> attaches to a transitional spacer <NUM>. The transitional spacer <NUM> longitudinally separates the first inner magnet <NUM> from a second inner magnet <NUM>. The second inner magnet <NUM> attaches to the transitional spacer <NUM>. The magnet assembly <NUM> further includes a first intermediate spacer <NUM> that attaches to the first inner magnet <NUM>. The first intermediate spacer <NUM> longitudinally separates the first inner magnet <NUM> from a first outer magnet <NUM>. The first outer magnet <NUM> attaches to the first intermediate spacer <NUM> and a first end cap <NUM>. A second intermediate spacer <NUM> attaches to the second inner magnet <NUM>. The second intermediate spacer <NUM> longitudinally separates the second inner magnet <NUM> from a second outer magnet <NUM>. The second outer magnet <NUM> attaches to the second intermediate spacer <NUM> and a second end cap <NUM>. And the second end cap <NUM> attaches to the back plate <NUM>. The attachments in the magnet assembly <NUM> and the magnet assembly <NUM> to the back plate <NUM> may occur via fasteners, adhesives, or other ways known in the art.

Along the longitudinal axis <NUM>, the magnet assembly <NUM> includes a length M'. The length M' is less than the overall length L'. Additionally, the length M' is defined by a third point <NUM> and a fourth point <NUM>. The fourth point <NUM> corresponds to the side of the second end cap <NUM> that rests on the back plate <NUM>. And the third point <NUM> corresponds to the first end cap <NUM> at a location most distal to the fourth point <NUM>. The magnet assembly <NUM> includes a halfway point <NUM> that is defined as the half the length of M'. The magnet assembly <NUM> from the halfway point <NUM> to the third point <NUM> is symmetrical to the magnet assembly <NUM> from the halfway point <NUM> to the fourth point <NUM>. The halfway point <NUM> of the magnet assembly <NUM> corresponds to a halfway point <NUM> of the voice coil <NUM>.

Along the longitudinal axis <NUM>, the voice coil <NUM> includes a length O'. The length O' is defined by the first side <NUM> and the second side <NUM> of the voice coil <NUM>. The halfway point <NUM> of the voice coil <NUM> is defined as half of the length of O'. On the longitudinal axis <NUM>, at rest, the halfway point <NUM> of the voice coil <NUM> is at the same location as the halfway point <NUM> of the magnet assembly <NUM>. Because of that, at rest, the voice coil <NUM> is symmetrically aligned with the magnet assembly <NUM>.

The symmetrical alignment between the voice coil <NUM> and the magnet assembly <NUM> is acoustically desirable. For example, compared to an asymmetrical alignment (such as in the conventional loudspeaker <NUM>), the symmetrical alignment yields substantially symmetric motor force (BL), suspension stiffness (K), and inductance (Le), which helps reduce nonlinear distortion, instability, etc..

Mathematically, the substantially symmetric motor force is determined from a motor force versus excursion plot for the loudspeaker <NUM>. Based on the motor force versus excursion plot, an asymmetry motor force curve is determined for the loudspeaker <NUM>. An asymmetry motor force value is determined by averaging the absolute value of the asymmetry motor force curve. The asymmetry value is less than <NUM>%, which means that for motor force the loudspeaker <NUM> is at least <NUM>% symmetric. Therefore, substantially symmetric motor force means that for motor force the loudspeaker <NUM> is at least <NUM>% symmetric.

Mathematically, the substantially symmetric suspension stiffness is determined from a suspension stiffness versus excursion plot for the loudspeaker <NUM>. Based on the suspension stiffness versus excursion plot, an asymmetry suspension stiffness curve is determined for the loudspeaker <NUM>. An asymmetry suspension stiffness value is determined by averaging the absolute value of the asymmetry suspension stiffness curve. The asymmetry value is less than <NUM>%, which means that for suspension stiffness the loudspeaker <NUM> is at least <NUM>% symmetric. Therefore, substantially symmetric suspension stiffness means that for suspension stiffness the loudspeaker <NUM> is at least <NUM>% symmetric.

Mathematically, the substantially symmetric inductance is determined from an inductance versus excursion plot for the loudspeaker <NUM>. Based on the inductance versus excursion plot, an asymmetry inductance curve is determined for the loudspeaker <NUM>. An asymmetry inductance value is determined by averaging the absolute value of the asymmetry inductance curve. The asymmetry value is less than <NUM>%, which means that for inductance the loudspeaker <NUM> is at least <NUM>% symmetric. Therefore, substantially symmetric inductance means that for inductance the loudspeaker <NUM> is at least <NUM>% symmetric.

Along the longitudinal axis <NUM>, in an ideal case, in the magnet assembly <NUM>, the length of the first inner magnet <NUM> is equal to the length of the second inner magnet <NUM>. Additionally, along the longitudinal axis <NUM>, the length of the first outer magnet <NUM> is equal to the length of the second outer magnet <NUM>. Furthermore, along the longitudinal axis <NUM>, the length of the first intermediate spacer <NUM> is equal to the length of the second intermediate spacer <NUM>. And along the longitudinal axis <NUM>, the length of the first end cap <NUM> is equal to the length of the second end cap <NUM>. The length of the first inner magnet <NUM> is greater than the length of the first outer magnet <NUM>. And, therefore, the length of the second inner magnet <NUM> is greater than the length of the second outer magnet <NUM>.

In the magnet assembly <NUM>, the first inner magnet <NUM> includes a first permanence coefficient, and the second inner magnet <NUM> includes a second permanence coefficient. In an ideal case, the first permanence coefficient is equal to the second permanence coefficient. Additionally, the first outer magnet <NUM> includes a third permanence coefficient, and the second outer magnet <NUM> includes a fourth permanence coefficient. In an ideal case, the third permanence coefficient is equal to the fourth permanence coefficient. The first permanence coefficient and the second permanence coefficient are equal to or greater than the third permanence coefficient and the fourth permanence coefficient. This arrangement of the permanence coefficients creates a desirable magnetic flux flow through the voice coil <NUM>. In this arrangement, the magnetic flux flow is at a maximum at half the length of the voice coil, which is desirable.

Additionally, in the magnet assembly <NUM>, the permanence coefficients are within a target value range of one to two. At a value of one, a permanence coefficient provides a maximum magnetic energy (efficiency). And at a value of two, a permanence coefficient provides robustness against demagnetization.

In the magnet assembly <NUM>, the first inner magnet <NUM>, the second inner magnet <NUM>, the first outer magnet <NUM>, and the second outer magnet <NUM> may be made out of the same magnetic material. More specifically, each magnet (e.g., first inner magnet <NUM>, first outer magnet <NUM>, etc.) may be a neodymium magnet. Additionally, in the magnet assembly <NUM>, the first intermediate spacer <NUM>, the second intermediate spacer <NUM>, the transitional spacer <NUM>, the first end cap <NUM>, and the second end cap <NUM> may be made out the same material. More specifically, each spacer (e.g., first intermediate spacer <NUM>, etc.) and each end cap (e.g., first end cap <NUM>, etc.) may be made out of low carbon steel. The voice coil <NUM> may be made out of copper or a number of different materials known in the art.

The magnet assembly <NUM> includes a first magnetic flux flow loop <NUM>. The first magnetic flux flow loop <NUM> travels opposite to a second magnetic flux flow loop <NUM>. For example, as shown in <FIG>, the first magnetic flux flow loop <NUM> travels in a counter-clockwise direction, whereas the second magnetic flux flow loop <NUM> travels in a clockwise direction. Because of that, the first magnetic flux flow loop <NUM> constructively combines with the second magnetic flux flow loop <NUM> when entering the voice coil <NUM>. At rest, the constructive combination is at a maximum at half the length O' of the voice coil <NUM>. When transitioning out of the voice coil <NUM>, the constructive combination deconstructs into the first magnetic flux flow loop <NUM> and the second magnetic flux flow loop <NUM>.

In general, the first magnetic flux flow loop <NUM> travels from the first inner magnet <NUM>, through the transitional spacer <NUM>, into the voice coil <NUM>, into the frame <NUM>, into the first end cap <NUM>, through the first outer magnet <NUM>, into the first intermediate spacer <NUM>, and back into the first inner magnet <NUM>. And in general, the second magnetic flux flow loop <NUM> travels from the second inner magnet <NUM>, through the transitional spacer <NUM>, into the voice coil <NUM>, into the frame <NUM>, into the back plate <NUM>, into the second end cap <NUM>, into the second outer magnet <NUM>, into the second intermediate spacer <NUM>, and back into the second inner magnet <NUM>.

To create the first magnetic flux flow loop <NUM> and the second magnetic flux flow loop <NUM>, the magnets (e.g., the first inner magnet, the first outer magnet, etc.) are axially polarized. When aligned along the longitudinal axis <NUM>, the first inner magnet <NUM> and the first outer magnet <NUM> have their axial polarities appropriately oriented to create the first magnetic flux flow loop <NUM>. And the second inner magnet <NUM> and the second outer magnet <NUM> have their axial polarities appropriately oriented to create the second magnetic flux flow loop <NUM>.

In the magnet assembly <NUM>, the first inner magnet <NUM>, the second inner magnet <NUM>, the first outer magnet <NUM>, and the second outer magnet <NUM> may be disks, rectangular plates, or other similar shapes. Additionally, the first intermediate spacer <NUM>, the second intermediate spacer <NUM>, the transitional spacer <NUM>, the first end cap <NUM>, and the second end cap <NUM> may be disks, rectangular plates, or other similar shapes.

In the loudspeaker <NUM>, the back plate <NUM> may be made out of plastic, aluminum, or a number of different non-ferrous materials known in the art. Using a non-ferrous material for the back plate <NUM> helps maintain magnetic symmetry in the loudspeaker <NUM>. More specifically, because the non-ferrous material does not influence the second magnetic flux flow loop <NUM>, at rest, the second magnetic flux flow loop <NUM> may be a mirror image of the first magnetic flux flow loop <NUM>. Additionally, the diaphragm <NUM> may be made out of carbon fiber, fiberglass, paper, or a number of different materials known in the art. Furthermore, the frame <NUM> may be made out of low carbon steel or a number of different ferrous materials known in the art.

In the loudspeaker <NUM>, the frame <NUM> includes an outer wall <NUM> that forms the voice coil gap <NUM> with the magnet assembly <NUM>. Extending from the outer wall <NUM> to the first suspension element <NUM>, the frame <NUM> includes a first basket <NUM>. In relation to the longitudinal axis <NUM>, the first basket <NUM> generally extends angularly outward from the outer wall <NUM>. In the first basket <NUM>, the angular extension from the outer wall <NUM> terminates at a distal first portion <NUM>. The first suspension element <NUM> attaches to the first portion <NUM>. The first portion <NUM> is located in the first suspension region <NUM> and is transversely spaced from the longitudinal axis <NUM>.

In the loudspeaker <NUM>, extending from the outer wall <NUM> to the second suspension element <NUM>, the frame <NUM> includes a second basket <NUM>. In relation to the longitudinal axis <NUM>, the second basket <NUM> generally extends angularly outward from the outer wall <NUM>. In the second basket <NUM>, the angular extension from the outer wall <NUM> terminates at a distal second portion <NUM>. The second suspension element <NUM> attaches to the second portion <NUM>. The second portion <NUM> is located in the second suspension region <NUM> and is transversely spaced from the longitudinal axis <NUM>. Therefore, the first portion <NUM> is spaced apart from the second portion <NUM>. The outer wall <NUM>, the first basket <NUM>, and the second basket <NUM> may be integrally formed or may be modularly attached, such as through fasteners.

Along the longitudinal axis <NUM>, the outer wall includes a length P'. The length P' of the outer wall <NUM> may be less than, equal to, or greater than the length O' of the voice coil <NUM>. Along the longitudinal axis <NUM>, the outer wall <NUM> includes a halfway point <NUM> that is defined as half of the length of P'. When the voice coil <NUM> is at rest, the halfway point <NUM> of the outer wall <NUM> is at the same location as the halfway point <NUM> of the voice coil <NUM>.

In a shallow-depth environment, the length P' of the outer wall <NUM> may be maximized based on a shallow depth of the shallow-depth environment. One reason for doing so is that the length P' of the outer wall <NUM> directly impacts the motor force of the loudspeaker <NUM>. In a scenario where the overall length L' is equal to the shallow depth, and is therefore maximally constrained, the largest value for P' may be selected such that the overall Length L' does not increase. Alternatively, a value smaller than the largest value for P' may be selected, but the overall length L' could remain the same. Therefore, to influence motor force, the shallow-depth environment may only require altering the length P', as opposed to having to also alter the magnet assembly <NUM>, the voice coil <NUM>, the overall length L', etc. For any alteration, though, the loudspeaker <NUM> maintains the balanced state, the substantially symmetrical motor force, the substantially symmetrical suspension stiffness, and the substantially symmetrical inductance.

Often, increasing the length P' of the outer wall <NUM> results in a greater motor force. For example, if the length P' of the outer wall <NUM> is less than the length M' of the magnet assembly <NUM>, then increasing the length P' to equal the length M' yields an increase in motor force. One reason for that is due to the relationship between the outer wall <NUM> and the magnet assembly <NUM>. More specifically, increasing the length P', as described in the example, influences the first magnetic flux flow loop <NUM> and the second magnetic flux flow loop <NUM>. In particular, that influence affects the return paths (e.g., from the voice coil, through the frame, and back into the magnet assembly) of the first magnetic flux flow loop <NUM> and the second magnetic flux flow loop <NUM>. Because of that, if the length M' of the magnet assembly <NUM> is held constant, then the length P' of the outer wall <NUM> may be adjusted to obtain the maximum motor force.

In some instances, increasing the length P' does not result in increasing the overall length L'. While in other instances increasing the length P' of the outer wall <NUM> may result in increasing the overall length L' of the loudspeaker <NUM>. The fact that no additional magnets, voice coils, etc., need to be added, though, may make the loudspeaker <NUM> desirable. Two reasons for that are complexity of such a change is low and financial cost remains largely unchanged.

During operation of the loudspeaker <NUM>, the voice coil <NUM> may translate longitudinally along the longitudinal axis <NUM>. More specifically, during operation of the loudspeaker <NUM>, the voice coil <NUM> may cause the voice coil former <NUM> to translate longitudinally along the longitudinal axis <NUM>.

Additionally, because of the balanced state, the voice coil <NUM> may be able to maintain an ideal alignment in the voice coil gap <NUM>. For example, transversely to the longitudinal axis <NUM>, the spacing between the outer wall <NUM> and the voice coil <NUM> would be consistent along the voice coil length O'. Similarly, transversely to the longitudinal axis <NUM>, the spacing between the magnet assembly <NUM> and the voice coil <NUM> would be consistent along the voice coil length O'. Additionally, the transverse spacing between the magnet assembly <NUM> and the voice coil <NUM> (along length O'), and the transverse spacing between the outer wall <NUM> and the voice coil <NUM> (along length O'), would stay constant during translation of the voice coil <NUM> along the longitudinal axis <NUM>.

At the very least, because of the balanced state, the voice coil <NUM> is able to maintain a desirable alignment in the voice coil gap <NUM>. In the desirable alignment, the risk of rocking, midband rubs, extraneous noise, etc., is low-especially when compared against the risks in the conventional loudspeaker. Moreover, unlike the conventional loudspeaker <NUM>, in the event that the voice coil <NUM> were to move in a direction transverse to the longitudinal axis <NUM>, that movement would be insignificant and essentially uniform (if not entirely uniform) along the length O'.

<FIG> and <FIG> illustrate partial views of a loudspeaker <NUM>, which is in accordance with one or more embodiments of the present invention. The loudspeaker <NUM> includes a first suspension region <NUM>. The first suspension region <NUM> is longitudinally separated from a second suspension region <NUM>. The first suspension region <NUM> includes a first suspension element <NUM>. The second suspension region <NUM> includes a second suspension element <NUM>. Furthermore, the first suspension region <NUM> includes a third suspension element <NUM>. The first suspension element <NUM> may be a surround, the third suspension element <NUM> may be a first spider, and the second suspension element <NUM> may be a second spider.

The first suspension region <NUM> and the second suspension region <NUM> place a voice coil <NUM> in a balanced state. More specifically, the first suspension region <NUM> includes at least one suspension element (e.g., the first suspension element <NUM>) that acts on a first side <NUM> of the voice coil <NUM>, and the second suspension region <NUM> includes at least one other suspension element (i.e., the second suspension element <NUM>) that acts on a second side <NUM> of the voice coil <NUM>.

In the loudspeaker <NUM>, the first suspension element <NUM> acts on the first side <NUM> of the voice coil <NUM>. Additionally, the second suspension element <NUM> acts on the second side <NUM> of the voice coil <NUM>. And the third suspension element <NUM> acts on the first side <NUM> of the voice coil <NUM>. Alternatively stated, the first suspension element <NUM> and the third suspension element <NUM> support the first side <NUM> of the voice coil <NUM>, and the second suspension element <NUM> supports the second side <NUM> of the voice coil <NUM>. In doing so, the first suspension element <NUM> applies a first stiffness to the first side <NUM> of the voice coil <NUM>, the second suspension element <NUM> applies a second stiffness to the second side <NUM> of the voice coil <NUM>, and the third suspension element <NUM> applies a third stiffness to the first side <NUM> of the voice coil <NUM>. In an ideal case, the first stiffness and the third stiffness total to equal the second stiffness. However, alternative cases for the first stiffness, the second stiffness, and the third stiffness may be utilized.

This combination of the three suspension elements <NUM>, <NUM>, <NUM>, as oriented in the two suspension regions <NUM>, <NUM>, is particularly desirable for heavier weighted voice coils. Additionally, the combination of the three suspension elements <NUM>, <NUM>, <NUM>, as oriented in the two suspensions regions <NUM>, <NUM>, is particularly desirable for voice coils that operate at high excursions. In such scenarios, the three suspension elements <NUM>, <NUM>, <NUM>, as oriented in the two suspension regions <NUM>, <NUM>, should provide greater voice coil stability and life.

The loudspeaker <NUM> aligns along a longitudinal axis <NUM>. Therefore, the voice coil <NUM> and a magnet assembly <NUM> align along the longitudinal axis <NUM>. The magnet assembly <NUM> attaches to a back plate <NUM>. The back plate attaches to a frame <NUM>. The frame <NUM> and the magnet assembly <NUM> form a voice coil gap <NUM>. The voice coil <NUM> is wound around a voice coil former <NUM> and resides in the voice coil gap <NUM>. The voice coil former <NUM> attaches to a diaphragm <NUM>. In the first suspension region <NUM>, the first suspension element <NUM> attaches to the diaphragm <NUM> and the frame <NUM>. In the second suspension region <NUM>, the second suspension element <NUM> attaches to the voice coil former <NUM> and the frame <NUM>. In the first suspension region <NUM>, the third suspension element <NUM> attaches to the voice coil former <NUM> and the frame <NUM>, such as through an adhesive or other ways known in the art. And a dust cap <NUM> attaches to the diaphragm.

Along the longitudinal axis <NUM>, the first suspension region <NUM> extends from the first side <NUM> of the voice coil <NUM> toward the dust cap <NUM>. And along the longitudinal axis <NUM>, the second suspension region <NUM> extends from the second side <NUM> of the voice coil <NUM> toward the back plate <NUM>. The first suspension region <NUM> and the second suspension region <NUM> further extend transversely from the longitudinal axis <NUM>.

The magnet assembly <NUM> includes a first inner magnet <NUM>. The first inner magnet <NUM> attaches to a transitional spacer <NUM>. The transitional spacer <NUM> attaches to a second inner magnet <NUM>. The magnet assembly <NUM> further includes a first intermediate spacer <NUM> that attaches to the first inner magnet <NUM>. A first outer magnet <NUM> attaches to the first intermediate spacer <NUM>. And a first end cap <NUM> attaches to the first outer magnet <NUM>. Additionally, the magnet assembly <NUM> includes a second intermediate spacer <NUM> that attaches to the second inner magnet <NUM>. A second outer magnet <NUM> attaches to the second intermediate spacer <NUM>. And a second end cap <NUM> attaches to the first outer magnet <NUM> and the back plate <NUM>.

Along the longitudinal axis <NUM>, the magnet assembly <NUM> includes a length M". The length M" is defined by the first end cap <NUM> and the second end cap <NUM>. The magnet assembly <NUM> includes a halfway point <NUM> that is defined as half of the length M". The magnet assembly <NUM> from the halfway point <NUM> to the first end cap <NUM> is symmetrical to the halfway point <NUM> to the second end cap <NUM>. The halfway point <NUM> of the magnet assembly <NUM> corresponds to a halfway point <NUM> of the voice coil <NUM>.

Along the longitudinal axis <NUM>, the voice coil <NUM> includes a length O". The length O" is defined by the first side <NUM> and the second side <NUM> of the voice coil <NUM>. The halfway point <NUM> of the voice coil is defined as half of the length of O". On the longitudinal axis <NUM>, at rest, the halfway point <NUM> of the voice coil <NUM> is at the same location as the halfway point <NUM> of the magnet assembly <NUM>. Because of that, at rest, the voice coil <NUM> is symmetrically aligned with the magnet assembly <NUM>. The symmetrical alignment yields substantially symmetric motor force and inductance for the loudspeaker <NUM>.

The magnet assembly <NUM> includes a first magnetic flux flow loop <NUM>. The first magnetic flux flow loop <NUM> travels opposite to a second magnetic flux flow loop <NUM>. For example, if the first magnetic flux flow loop <NUM> travels in a counter-clockwise direction, then the second magnetic flux flow loop <NUM> travels in a clockwise direction. Because of that, the first magnetic flux flow loop <NUM> constructively combines with the second magnetic flux flow loop <NUM> when entering the voice coil <NUM>. At rest, the constructive combination is at a maximum at half the length O" of the voice coil <NUM>. When transitioning out of the voice coil <NUM>, the constructive combination deconstructs into the first magnetic flux flow loop <NUM> and the second magnetic flux flow loop <NUM>.

In the loudspeaker <NUM>, the frame <NUM> includes an outer wall <NUM> that forms the voice coil gap <NUM> with the magnet assembly <NUM>. Extending from the outer wall <NUM> to the first suspension element <NUM>, the frame <NUM> includes a first basket <NUM>. Extending from the outer wall <NUM> to the second suspension element <NUM>, the frame <NUM> includes a second basket <NUM>.

Along the longitudinal axis <NUM>, the outer wall includes a length P". The length P" of the outer wall <NUM> is equal to the length M" of the magnet assembly <NUM>. Along the longitudinal axis <NUM>, the outer wall <NUM> includes a halfway point <NUM> that is defined as half of the length of P". When the voice coil <NUM> is at rest, the halfway point <NUM> of the outer wall <NUM> is at the same location as the halfway point <NUM> of the voice coil <NUM>.

The outer wall <NUM> includes a first projection <NUM>. The first projection <NUM> forms a first end of the outer wall <NUM>. Additionally, the outer wall <NUM> includes a second projection <NUM>. The second projection <NUM> forms a second end of the outer wall <NUM>. The first projection <NUM> is, therefore, longitudinally spaced from the second projection <NUM>. And therefore, the length P" of the outer wall <NUM> is defined by the first projection <NUM> and the second projection <NUM>.

Between the first projection <NUM> and the second projection <NUM>, but not including the first projection <NUM> or the second projection <NUM>, the voice coil gap <NUM> includes a major width <NUM>. At rest, the major width <NUM> is measured transversely to the longitudinal axis <NUM>.

The voice coil gap <NUM> further includes a first minor width <NUM>. At rest, the first minor width <NUM> is measured transversely to the longitudinal axis <NUM>. In doing so, the first minor width <NUM> is measured from the magnet assembly <NUM> (e.g., from the first end cap <NUM>) to the first projection <NUM>. The first minor width <NUM> is less than the major width <NUM>.

The voice coil gap <NUM> further includes a second minor width <NUM>. At rest, the second minor width <NUM> is measured transversely to the longitudinal axis <NUM>. In doing so, the second minor width <NUM> is measured from the magnet assembly <NUM> (e.g., from the second end cap <NUM>) to the second projection <NUM>. The second minor width <NUM> is less than the major width <NUM>. The second minor width <NUM> may be equal to the first minor width <NUM>.

Through the first minor width <NUM> and the second minor width <NUM>, the first projection <NUM> and the second projection <NUM> increase the motor force of the loudspeaker <NUM>. Without the first projection <NUM> and the second projection <NUM>, the motor force of the loudspeaker <NUM> would be noticeably less.

Along the longitudinal axis <NUM>, the second suspension element <NUM> is spaced from the third suspension element <NUM> by a distance Q". The distance Q" includes a halfway point <NUM>. The halfway point <NUM> of the distance Q" may correspond to the halfway point <NUM> of the magnet assembly <NUM>. Additionally, along the longitudinal axis <NUM>, the second suspension element <NUM> is longitudinally spaced from the first suspension element <NUM> by a distance R". The distance R" is greater than the distance Q".

The third suspension element <NUM> attaches to the frame <NUM> at an intermediate location <NUM> on the first basket <NUM>. On the first basket <NUM>, the intermediate location <NUM> is located between the initial extension from the outer wall <NUM> and a distal first portion <NUM>. The first suspension element <NUM> attaches to the frame <NUM> at the first portion <NUM>. Similarly, the second basket <NUM> extends from the outer wall <NUM> to a distal second portion <NUM>. The second suspension element <NUM> attaches to the frame <NUM> at the second portion <NUM>.

<FIG> illustrates a partial view of a loudspeaker <NUM>, which is in accordance with one or more embodiments of the present invention. The loudspeaker <NUM> includes a first suspension region <NUM>. The first suspension region <NUM> is longitudinally separated from a second suspension region <NUM>. The first suspension region <NUM> includes a first suspension element <NUM>. The second suspension region <NUM> includes a second suspension element <NUM>. Furthermore, the first suspension region <NUM> includes a third suspension element <NUM>. The first suspension region <NUM> and the second suspension region <NUM> place a voice coil <NUM> of the loudspeaker <NUM> in a balanced state.

The loudspeaker <NUM> aligns along a longitudinal axis <NUM>. Therefore, the voice coil <NUM> and a magnet assembly <NUM> align along the longitudinal axis <NUM>. The magnet assembly <NUM> attaches to a back plate <NUM>. The back plate attaches to a frame <NUM>. The frame <NUM> and the magnet assembly <NUM> form a voice coil gap <NUM>. The voice coil <NUM> is wound around a voice coil former <NUM> and resides in the voice coil gap <NUM>. The voice coil former <NUM> attaches to a diaphragm <NUM>. In the first suspension region <NUM>, the first suspension element <NUM> attaches to the diaphragm <NUM> and the frame <NUM>. In the second suspension region <NUM>, the second suspension element <NUM> attaches to the voice coil former <NUM> and the frame <NUM>. In the first suspension region <NUM>, the third suspension element <NUM> attaches to the voice coil former <NUM> and the frame <NUM>. And a dust cap <NUM> attaches to the diaphragm.

The magnet assembly <NUM> includes a first inner magnet <NUM>. The first inner magnet <NUM> attaches to a transitional spacer <NUM>. The transitional spacer <NUM> attaches to a second inner magnet <NUM>. The magnet assembly <NUM> further includes a first intermediate spacer <NUM> that attaches to the first inner magnet <NUM>. A first outer magnet <NUM> attaches to the first intermediate spacer <NUM>. And a first end cap <NUM> attaches to the first outer magnet <NUM>. Additionally, the magnet assembly <NUM> includes a second intermediate spacer <NUM> that attaches to the second inner magnet <NUM>. A second outer magnet <NUM> attaches to the second intermediate spacer <NUM>. And a second end cap <NUM> attaches to the second outer magnet <NUM> and the back plate <NUM>.

At rest, the voice coil <NUM> is symmetrically aligned with the magnet assembly <NUM>. The symmetrical alignment yields substantially symmetric motor force and inductance for the loudspeaker <NUM>.

In the loudspeaker <NUM>, the frame <NUM> includes an outer wall <NUM> that forms the voice coil gap <NUM> with the magnet assembly <NUM>. Extending from the outer wall <NUM> to the first suspension element <NUM>, the frame <NUM> includes a first basket <NUM>. Extending from the outer wall <NUM> to the second suspension element <NUM>, the frame <NUM> includes a second basket <NUM>. The length of the outer wall <NUM> is less than the length of the voice coil <NUM>.

<FIG>, and 14B illustrate results from laboratory testing a loudspeaker based on the loudspeaker <NUM> of <FIG> (hereinafter referred to as "Sym-Bal Loudspeaker"). Additionally, <FIG>, and 14A illustrate results from laboratory testing a loudspeaker based on the conventional loudspeaker <NUM> of <FIG> (hereinafter referred to as "Reference Loudspeaker"). For the laboratory testing, the Sym-Bal Loudspeaker and the Reference Loudspeaker were designed to carry out a fair comparison. Because of that, extensive thought was given to dimensioning and material selection.

<FIG> illustrates a motor force versus excursion curve for the Sym-Bal Loudspeaker <NUM>. Additionally, <FIG> illustrates a motor force versus excursion curve for the Reference Loudspeaker <NUM>. The motor force versus excursion curve for the Sym-Bal Loudspeaker <NUM> indicates a great deal of symmetry, whereas the motor force versus excursion curve for the Reference Loudspeaker <NUM> does not. The motor force symmetry for the Sym-Bal Loudspeaker, and the lack of motor force symmetry for the Reference Loudspeaker, is further illustrated in <FIG>.

<FIG> illustrates an asymmetry motor force curve for the Sym-Bal Loudspeaker <NUM>, which is based on the motor force versus excursion curve for the Sym-Bal Loudspeaker <NUM>. Additionally, <FIG> illustrates an asymmetry motor force curve for the Reference Loudspeaker <NUM>, which is based on the motor force versus excursion curve for the Reference Loudspeaker <NUM>. The asymmetry motor force curve for the Sym-Bal Loudspeaker is nearly flat, which also indicates the great deal of symmetry. And as expected, the asymmetry motor force curve for the Reference Loudspeaker indicates lack of symmetry.

Averaging the absolute values of the asymmetry motor force curve for the Sym-Bal Loudspeaker <NUM> returns an asymmetry motor force value of <NUM>%. Therefore, the Sym-Bal Loudspeaker includes a substantially symmetric motor force. And averaging the absolute values of the asymmetry motor force curve for the Reference Loudspeaker <NUM> returns an asymmetry motor force value of <NUM>%. Therefore, the Reference Loudspeaker does not include a substantially symmetric motor force; instead, the motor force for the Reference Loudspeaker is significantly asymmetric.

<FIG> illustrates an inductance versus excursion curve for the Sym-Bal Loudspeaker <NUM>. Additionally, <FIG> illustrates an inductance versus excursion curve for the Reference Loudspeaker <NUM>. The inductance versus excursion curve for the Sym-Bal Loudspeaker <NUM> indicates a great deal of symmetry, whereas the inductance versus excursion curve for the Reference Loudspeaker <NUM> does not. The inductance symmetry for the Sym-Bal Loudspeaker, and the lack of inductance symmetry for the Reference Loudspeaker, is further illustrated in <FIG>.

<FIG> illustrates an asymmetry inductance curve for the Sym-Bal Loudspeaker <NUM>, which is based on the inductance versus excursion curve for the Sym-Bal Loudspeaker <NUM>. Additionally, <FIG> illustrates an asymmetry inductance curve for the Reference Loudspeaker <NUM>, which is based on the inductance versus excursion curve for the Reference Loudspeaker <NUM>. The asymmetry inductance curve for the Sym-Bal Loudspeaker is nearly flat, which also indicates the great deal of symmetry. And as expected, the asymmetry inductance curve for the Reference Loudspeaker indicates lack of symmetry.

Averaging the absolute values of the asymmetry inductance curve for the Sym-Bal Loudspeaker <NUM> returns an asymmetry inductance value of <NUM>%. Therefore, the Sym-Bal Loudspeaker includes a substantially symmetric inductance. And averaging the absolute values of the asymmetry inductance curve for the Reference Loudspeaker <NUM> returns an asymmetry inductance value of <NUM>%. Therefore, the Reference Loudspeaker does not include a substantially symmetric inductance; instead, the inductance for the Reference Loudspeaker is significantly asymmetric.

<FIG> illustrates a suspension stiffness versus excursion curve for the Sym-Bal Loudspeaker <NUM>. Additionally, <FIG> illustrates a suspension stiffness versus excursion curve for the Reference Loudspeaker <NUM>. The suspension stiffness versus excursion curve for the Sym-Bal Loudspeaker <NUM> indicates a great deal of symmetry, whereas the suspension stiffness versus excursion curve for the Reference Loudspeaker <NUM> does not. The suspension stiffness symmetry for the Sym-Bal Loudspeaker, and the lack of suspension stiffness symmetry for the Reference Loudspeaker, is further illustrated in <FIG>.

<FIG> illustrates an asymmetry suspension stiffness curve for the Sym-Bal Loudspeaker <NUM>, which is based on the suspension stiffness versus excursion curve for the Sym-Bal Loudspeaker <NUM>. Additionally, <FIG> illustrates an asymmetry suspension stiffness curve for the Reference Loudspeaker <NUM>, which is based on the suspension stiffness versus excursion curve for the Reference Loudspeaker <NUM>. The asymmetry suspension stiffness curve for the Sym-Bal Loudspeaker is nearly flat, which also indicates the great deal of symmetry. And as expected, the asymmetry suspension stiffness curve for the Reference Loudspeaker indicates lack of symmetry.

Averaging the absolute values of the asymmetry suspension stiffness curve for the Sym-Bal Loudspeaker <NUM> returns an asymmetry suspension stiffness value of <NUM>%. Therefore, the Sym-Bal Loudspeaker includes a substantially symmetric suspension stiffness. And averaging the absolute values of the asymmetry suspension stiffness curve for the Reference Loudspeaker <NUM> returns an asymmetry suspension stiffness value of <NUM>%. Therefore, the Reference Loudspeaker does not include a substantially symmetric suspension stiffness.

<FIG> illustrates sound pressure level (SPL) frequency responses between <NUM> and <NUM>,<NUM> for the Sym-Bal Loudspeaker at four different drive voltages: <NUM>. 8V, and 17V (respectively identified as <NUM>, <NUM>, <NUM>, and <NUM>). Additionally, <FIG> illustrates total harmonic distortion (THD) frequency responses between <NUM> and <NUM>,<NUM> for the Sym-Bal Loudspeaker at four different drive voltages: <NUM>. 8V, and 17V (respectively identified as <NUM>, <NUM>, <NUM>, and <NUM>). Therefore, the SPL response at <NUM>. 7V <NUM> corresponds to the THD response at <NUM>. 7V <NUM> for the Sym-Bal Loudspeaker, as do the <NUM>. 5V SPL <NUM> and the <NUM>. 5V THD <NUM>, the <NUM>. 8V SPL <NUM> and the <NUM>. 8V THD <NUM>, and the 17V SPL <NUM> and the 17V THD <NUM>.

Claim 1:
A loudspeaker (<NUM>; <NUM>; <NUM>) comprising:
a magnet assembly (<NUM>; <NUM>; <NUM>) aligned along a longitudinal axis (<NUM>; <NUM>; <NUM>);
a frame (<NUM>; <NUM>; <NUM>) encircled around the magnet assembly (<NUM>; <NUM>; <NUM>), wherein the frame (<NUM>; <NUM>; <NUM>) includes an outer wall (<NUM>; <NUM>; <NUM>), wherein the magnet assembly (<NUM>; <NUM>; <NUM>) and the outer wall (<NUM>; <NUM>; <NUM>) form a voice coil gap (<NUM>; <NUM>; <NUM>);
a voice coil (<NUM>; <NUM>; <NUM>) disposed in the voice coil gap (<NUM>; <NUM>; <NUM>), wherein the voice coil (<NUM>; <NUM>; <NUM>) includes a first side (<NUM>; <NUM>) longitudinally spaced from a second side (<NUM>; <NUM>), and wherein the voice coil (<NUM>; <NUM>; <NUM>) is aligned with the magnet assembly (<NUM>; <NUM>; <NUM>) to yield:
a substantially symmetric motor force,
a substantially symmetric suspension stiffness, and
a substantially symmetric inductance;
a first suspension element (<NUM>; <NUM>; <NUM>) attached to the frame (<NUM>; <NUM>; <NUM>) and adapted to apply a first stiffness to the first side (<NUM>; <NUM>) of the voice coil (<NUM>; <NUM>; <NUM>); and
a second suspension element (<NUM>; <NUM>; <NUM>) attached to the frame (<NUM>; <NUM>; <NUM>) and adapted to apply a second stiffness to the second side (<NUM>; <NUM>) of the voice coil (<NUM>; <NUM>; <NUM>),
wherein the voice coil (<NUM>; <NUM>; <NUM>) is symmetrically aligned with the magnet assembly (<NUM>; <NUM>; <NUM>) such that the magnet assembly (<NUM>; <NUM>; <NUM>) includes an overall length (M') along the longitudinal axis (<NUM>; <NUM>; <NUM>) and the voice coil (<NUM>; <NUM>; <NUM>) includes an overall length (O') along the longitudinal axis (<NUM>; <NUM>; <NUM>), wherein a halfway point (<NUM>; <NUM>) of the overall length (M') of the magnet assembly (<NUM>; <NUM>; <NUM>) coincides with a halfway point (<NUM>; <NUM>) of the overall length (O') of the voice coil (<NUM>; <NUM>; <NUM>) when the voice coil (<NUM>; <NUM>; <NUM>) is at rest,
wherein the outer wall (<NUM>; <NUM>; <NUM>) includes an overall length (P') along the longitudinal axis (<NUM>; <NUM>; <NUM>), wherein a halfway point (<NUM>; <NUM>) of the overall length (P') of the outer wall (<NUM>; <NUM>; <NUM>) coincides with the halfway point (<NUM>; <NUM>) of the overall length (O') of the voice coil (<NUM>; <NUM>; <NUM>) when the voice coil (<NUM>; <NUM>; <NUM>) is at rest.