Variable alignment loudspeaker system

A loudspeaker system has a primary driver and an active radiator sealed in an enclosure where the active radiator is adapted to vary its operating characteristics to tune the sound pressure level and resultant frequency response generated by a primary driver. The primary driver and the active radiator share the same acoustic volume of the enclosure, i.e., the primary driver and the active radiator share a common acoustic compliance of the internal enclosure volume. The primary driver has electromagnetic components designed to oscillate a flexible cone or diaphragm along the longitudinal axis of the primary driver. The active radiator has electromagnetic components adapted to couple to a number of electrical configuration settings. Each electrical configuration setting may affect the operating characteristics of the diaphragm of the active radiator and is reflected back electro-acoustically, through the shared volume, to the primary driver. This electro-acoustical coupling, in turn provides the tuning mechanism for the primary driver.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention provides a loudspeaker system having a primary driver and an active radiator sealed within an enclosure where the sound pressure level generated by the primary driver is tunable by adjusting the operational characteristics of the active radiator.

2. Related Art

A loudspeaker system, also known as an audio transducer, converts electrical energy into acoustical energy to generate sound. A loudspeaker system includes at least one “primary” transducer or driver that is mounted into an enclosure. The term “primary” generally indicates that the driver is connected to a signal source such as an amplifier or a crossover network.FIG. 1shows a cutout view of a typical driver100illustrating some of its electromagnetic components. The driver100includes a magnet102and a voice coil104with two leads106. The voice coil104is wound cylindrically around a tube like cylinder108and placed within an air gap110. The tube like cylinder108is coupled to a diaphragm112that is supported by a suspension114and a spider116. A dust cap118may be provided over the cylinder108. The outer ends of the suspension114and the spider116may be coupled to a basket120to ensure that the voice coil104moves back and forth substantially along the axial direction. The two leads106from the voice coil104, for example, may be connected to an audio amplifier that provides current through the voice coil104that is a function of the electrical signal to be transformed by the driver100into an audible, sub-audible or subsonic pressure variation. As the electrical signal from the amplifier passes through the voice coil104, the interaction between the current passing through the voice coil104and the magnetic field produced by the permanent magnet102causes the voice coil104to oscillate in accordance with the electrical signal and, in turn, drives the diaphragm112and produces sound. As such, the driver100converts the electrical signal source into acoustical energy to produce sound.

A loudspeaker system typically has a driver housed in a ported enclosure or a sealed enclosure. The ported enclosure has an opening to allow sound waves to push in and out of the enclosure as the diaphragm of the driver oscillates back and forth. With the sealed enclosure, however, air inside the sealed enclosure compresses and expands as the diaphragm of the driver oscillates back and forth. In some instances, the sealed enclosure may be provided with a primary driver and a passive radiator. As discussed above, the primary driver has electromagnetic components to convert the electrical signal source into acoustical energy to produce sound. In contrast, the passive radiator has a diaphragm but no other electromagnetic components. This allows the diaphragm of the passive radiator to freely vibrate based on the pressure differential inside the sealed enclosure imparted by the primary driver. As the diaphragm of the passive radiator expands the net internal volume of the sealed enclosure increases to ease the pressure differential inside the sealed enclosure. The passive radiator may be incorporated in the sealed enclosure to improve the low frequency extension of the primary driver. This allows the diaphragm of the primary driver to extend further to increase the low frequency response.

With a sealed enclosure, the passive radiator and the primary driver share the same enclosure or the same acoustic-internal volume of the enclosure. The air compression and rarefaction caused by the primary driver push and pull on the diaphragm that is freely coupled to the passive radiator. Operating characteristics (excursion properties) of the passive radiator indicate how much force may be needed to push and pull on the diaphragm of the passive radiator. Many factors may define the operating characteristics of the passive radiator such as mass of the diaphragm, surface area of the diaphragm, material, etc. The operating characteristics of the passive radiator may partly determine the characteristics of the pressure changes within the enclosure and may have an effect on the overall performance of the primary driver. In other words, the passive radiator's resistance to push and pull movement may affect the overall performance of the primary driver. For example, if the passive radiator is very massive, then there may be greater resistance. If such is the case, the enclosure may be subject to a higher pressure, thereby affecting the overall performance of the primary driver.

One of the problems with a passive radiator is that its operating characteristics are fixed. In other words, once the loudspeaker system is constructed with a passive radiator, the operating characteristics of the passive radiator may not be changed without changing the mechanical properties of the passive radiator. Put differently, in the design phase of the loudspeaker system, appropriate design parameters are selected for a desired operating characteristic, such as mass, surface area, compliance of suspension, and material for the passive radiator. Once the design parameters of the passive radiator have been selected, however, they cannot be later changed.

Accordingly, there is a need for a loudspeaker system that may vary the operating characteristics of a passive radiator without altering mechanical properties of the passive radiator. This way, by varying the operating characteristics of the passive radiator, the overall output of the primary driver may be varied as well to improve the performance of the loudspeaker system.

SUMMARY

This invention provides a loudspeaker system having an active radiator that can vary its operating characteristics to tune the sound pressure level generated by a primary driver. The loudspeaker system includes a primary driver and an active radiator sealed within an enclosure so that the primary driver and the active radiator share the same acoustic volume of the enclosure. In other words, the primary driver and the active radiator share a common acoustic compliance of the enclosure. The primary driver has electromagnetic components designed to oscillate a flexible cone or diaphragm along the longitudinal axis of the primary driver. The primary driver is provided with an audio signal from an audio signal source such as an amplifier. The primary driver converts the audio signal source to sound waves by rapidly oscillating the flexible cone or diaphragm forwards and backwards along the longitudinal axis corresponding to the audio signal. As the diaphragm of the primary driver oscillates back and forth, the active radiator may also radiate as a result of sharing the same acoustic volume with the primary driver.

The active radiator has electromagnetic components that may be controlled by a number of electrical configuration settings. Each electrical configuration setting may affect the operating characteristics (excursion properties) of a diaphragm of the active radiator. With the primary driver and the active radiator sharing the same acoustic volume or compliance, varying the excursion properties of the diaphragm for the active radiator in turn affects the excursion properties of the diaphragm for the primary driver. As such, the sound pressure level generated by the primary driver can be tuned by varying the configuration setting provided to the active radiator. This allows a user or processor to tune the operating characteristics of the loudspeaker system by varying the electrical configuration setting provided to the active radiator rather than through altering the mechanical properties of the active radiator.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2is a cross-sectional view of a loudspeaker system200having an active radiator208designed to tune the operational characteristics of a primary driver204housed within a sealed enclosure202. The primary driver204converts audio signal to corresponding audible sound. The primary driver204has electromagnetic components adapted to convert electrical audio signal to acoustical energy to produce sound. The electromagnetic components of the primary driver204include a voice coil disposed within a voice coil gap. Two leads from the voice coil may be communicably coupled to input terminals206of the primary driver204. Audio signals from an amplifier or a crossover network (not shown) may be provided to the input terminals206to drive the primary driver204to produce sound. The active radiator208has electromagnetic components with input terminals210. The input terminals210are adapted to communicably couple to a configuration unit212having a number of electrical configuration settings such as: (1) an active network214; (2) a wire216that bridges the two input terminals to short the two input terminals210; (3) an open terminal217, and (4) passive network218. Each of the electrical configurations can vary the performance of the loudspeaker system200depending on the application of the loudspeaker200as further explained below.

FIG. 3illustrates a circuitry300that substantially represents the operational characteristics of a loudspeaker system having one driver housed in a sealed enclosure. The circuitry300divides the electromagnetic components of the primary driver into three equivalent circuits: (1) an electrical equivalent302; (2) a mechanical equivalent304; and (3) an acoustical equivalent306. An audio electrical signal may be provided to the input side of the electrical equivalent302. The electrical equivalent302factors in electrical resistance (Re), inductance (Le), and capacitance (Ce) of the loudspeaker system. For instance, Re and Le may factor in the resistance and inductance in the voice coil of the driver, respectively. The mechanical equivalent304may factor in mechanical resistance (Rm), mass (Lm), and compliance (Cm) of the loudspeaker system. For instance, Rm may factor in the inherent resistance to vibration of the diaphragm due to the spider and suspension. The acoustical equivalent306may factor in the acoustical resistance (Ra), acoustical mass (La), and acoustical compliance (Ca) of the loudspeaker system. The Ra may factor in the resistance to vibrating the diaphragm due to the size of the diaphragm, and the Ca may factor in the acoustical compliance due to the space within the enclosure. The transfer function F(Sd) between the acoustical equivalent306and the mechanical equivalent304may represent a function of the surface area of the diaphragm (Sd). The transfer function F(BL, Sd) between the mechanical equivalent the electrical equivalent may represent a function of Sd and magnetic field strength defined as the (BL) product.

FIG. 4illustrates a circuitry400that substantially represents the operational characteristics of a loudspeaker system200having a primary driver204and an active radiator208, both sealed within the enclosure202. The primary driver204may be represented by an electrical equivalent402, mechanical equivalent404, and acoustical equivalent406. The active radiator208may be represented by an electrical equivalent408, mechanical equivalent410, and acoustical equivalent412. The acoustical compliance (Ca)414may be common to the primary acoustical equivalent406and the active acoustical equivalent412. That is, the Ca414is an equivalent circuit element representing acoustical compliance of the enclosure volume shared by both primary and active radiators204and208, respectively. The electrical equivalent circuit408of the active radiator208has input terminals210that are adapted to communicably couple to the configuration unit212.

The function F(Nr)416corresponds to the setting in the configuration unit212such as the active circuit214, short circuit216, open circuit217, and passive circuit218, where each setting may vary the operating characteristics of the primary driver204. The electrical equivalent408of the active radiator208is represented by capacitor Cer, the inductor Ler, and the resistor Rer. The function F(BLr, Nr)418represents the product of the electrical equivalent408and the function F(Nr)416corresponds to the setting in the configuration unit212. If the configuration unit212is set to an open circuit217, then the active radiator208operates as a passive radiator, such that there is an acoustical contribution from the active radiator. In other words, with the open circuit217, other than the additional mass due to the voice coil and the compliance of the spider in the active radiator208, the active radiator208may perform more like a traditional passive radiator without the electromagnetic components and which shares the same acoustic volume with the primary driver204.

The configuration unit212may provide an option of selecting a short circuit216so that the input terminals210can be closed, thereby closing the electrical equivalent circuit408. The function F(BLr, Nr)418is a function of F(Nr) and the electrical equivalent circuit408of the active radiator208. With the configuration unit212set to the short circuit216, or zero resistance, F(BLr, Nr)418=the electrical equivalent circuit408of the active radiator208. Likewise, the function F(Sdr, BLr, Nr)420is a function of F(BLr, Nr)418and the mechanical equivalent440of the active radiator208. In general, the mechanical equivalent440of the active radiator208may be associated with the surface area of the diaphragm (Sdr) of the active radiator208. As such, the function F(Sdr, BLr, Nr)420is a function of F(BLr, Nr)418and Sdr of the active radiator208. That is, the combined electrical equivalent408and the mechanical equivalent410of the active radiator208is represented by the equivalent function F(Sdr, BLr, Nr)420. Likewise, the combined electrical and mechanical equivalent F(BLr, Nr)418and the acoustical equivalent412of the active radiator208and the acoustical equivalent406of the primary driver204may be represented by the equivalent function F(Sdp, Sdr, BLr, Nr)422. Note that Sdp represents the surface area of the primary driver204. The function F(BLp, Sdp, Sdr, BLr, Nr)424may be represented by combination of F(Sdp, Sdr, BLr, Nr)422and the mechanical equivalent404of the primary driver204. The function424can be combined with the overall output of the loudspeaker system200. Note that the Ca414representing the acoustical compliance of the enclosure volume shared between the primary driver202and the active radiator204is a variable of the overall function424. A user and/or designer may selectively choose a circuit from the configuration unit212to tune the performance of the primary driver204contained in the enclosure202.

As illustrated inFIG. 2, the configuration unit212includes a number of circuit configurations such as an active network212, short circuit216, open circuit217, and passive network218. With the active radiator208having electromagnetic components, the input terminals210of the active radiator208may be connected to the variable configuration unit212to provide an active circuit214, short circuit216, open circuit217, and/or passive circuit218to the active radiator208to vary the operating characteristics of the active radiator208. For example, the active circuit214may provide an electrical signal to the active radiator208to adjust the excursion range of its diaphragm. Adjusting the operating characteristics of the active radiator208in turn influences the overall output of the primary driver204because the primary driver204and the active radiator208share a common enclosure202or Ca414. For instance, as the primary driver204radiates back and forth, compression and rarefaction occur inside of the enclosure202. The pressure variations inside of the enclosure202cause the active radiator208to vibrate back and forth as well. The excursion properties of the active radiator208, however, depend on the circuit configuration that is provided to the input terminals210of the active radiator208. Accordingly, varying the circuit configuration provided to the input terminals210of the active radiator208can influence the performance of the primary driver204.

The configuration unit212may also provide the short circuit216to the input terminals210of the active radiator210to complete the circuit in the active radiator208such that the oscillation of the voice coil in the magnetic gap of the active radiator208induces current through its voice coil. The induced current through the voice coil of the active radiator208in turn generates an opposing magnetic flux in the magnetic components of the active radiator208to resist the oscillating movement of the voice coil of the active radiator208. As such, the configuration unit212includes a number of circuits to allow a user or processor to select a desired circuit provided to the active radiator208to change its operating characteristics in order to tune the operating characteristics of the primary driver204.

The loudspeaker system200may include one or more primary drivers204arranged in a variety of ways with respect to the active radiator208. Likewise, two or more active radiators208may be incorporated into the enclosure202. For instance,FIG. 5illustrates a primary driver204and an active radiator208facing away from each other within the sealed enclosure202.FIG. 6illustrates two primary drivers204facing the same direction but in opposite direction of the active radiator208within the sealed enclosure202. As such, more than one primary driver and active radiator may be positioned in a variety of ways within a sealed enclosure.

FIGS. 7 through 12illustrate two sound pressure level (SPL) plots generated by a loudspeaker200based on two different settings in the configuration unit212for comparison purposes. The SPLs were measured using a loudspeaker system200having one primary driver204and one active radiator208facing in opposite directions within a sealed enclosure202, as illustrated inFIG. 5. A microphone was placed perpendicular to the primary driver204to measure the SPL generated by the primary driver204.FIGS. 7 through 12illustrate a plot line702representing the measured SPL from the primary driver204, when the setting for the configuration unit212was left opened, i.e., the input terminals210to the active-radiator208was provided with the open circuit217. With the input terminals210being open, the active radiator208behaved more like a traditional passive radiator without the electromagnetic component. For comparison purposes, a second plot line is provided inFIGS. 7 through 12to analyze the differences between the plot line702and other plot lines when the configuration unit212provides different type of passive circuits to the input terminals210of the active radiator208.

FIG. 7illustrates a plot line704representing the measured SPL from the primary driver204when the configuration unit212was set to the short circuit216. In other words, a wire was provided between the input terminals210to close the circuit. The two plot lines702and704indicate that below about 35 Hz, the plot line704(short circuit) has a higher SPL than the plot line702(open circuit) and cross-over takes place at about 35 Hz. Between about 35 Hz and about 80 Hz, the plot line704(short circuit) has lower SPL than the plot line702(open circuit). That is, when the configuration unit212was set at the short circuit216, the plot line704indicates that below about 35 Hz—the SPL from the primary driver204is boosted, while dampening the SPL between 35 Hz and 80 Hz as compared to the plot line702. Such boosting of SPL below about 35 Hz may be used in a variety of applications. For example, in some instances when a loudspeaker is placed near a wall, the wall may reflect back additional energy to the listener's position in a frequency range of 40 Hz to 70 Hz. In such instances, a loudspeaker system200capable of generating SPL corresponding to the plot line704may be utilized to boost the SPL below about 35 Hz, while dampening between 35 Hz and 80 Hz to even out the response in the listening room.

FIGS. 8 through 12show plot lines based on the configuration unit212providing a variety of passive circuits218to the input terminals210of the active radiator208. For instance,FIG. 8shows a plot line804representing the measured SPL from the primary driver204with a resistor R1provided at the input terminals210of the active radiator208. The plot line804illustrate that the SPL generated by the primary driver204appears substantially similar to the plot line704ofFIG. 7. That is, providing a resistor R1or a short circuit216across the input terminals210of the active radiator208generates a substantially similar SPL from the primary driver204.

FIG. 9illustrates a plot line904representing the measured SPL from the primary driver204when the passive circuit218having a resistor R1in series with a capacitor C1is provided to the input terminals210of the active radiator208. Comparing the two plot lines702and904, the plot line904indicates that by adding a simple passive circuit218such as R1and C1to the input terminals210of the active radiator208, the primary driver204generates additional SPL below about 40 Hz a, while SPL is dampened above 40 Hz. In applications where boost in SPL would be desirable below 40 Hz with nominal dampening above 40 Hz, a passive circuit218having a resistor R1in series with a capacitor C1may be provided at the input terminals210of the active radiator208.

FIG. 10illustrates a plot line1004representing the measured SPL from the primary driver204when the passive circuit218having a resistor R1, C2, and L1in series is provided at the input terminals210of the active radiator208. Comparing the two plots702and2004, the plot line2004indicates that by providing a simple passive circuit218with R1, C2, and L1in series to the input terminals210of the active radiator208, the primary driver204generates additional SPL below about 35 Hz, while generating substantially similar SPL, as the plot line702, above 35 Hz. As such, by providing a simple passive circuit having R1, C2, and L1in series to the input terminals210of the active radiators208, additional boost can be obtained below 35 Hz without losing SPL above 35 Hz. In other words, the plot line1004indicates that the loudspeaker system200would produce a deeper bass sound without dampening the mid and high end of the bass sound.

FIG. 11illustrates a plot line1104representing the measured SPL from the primary driver204when the passive circuit218having a resistor R1, C3, and L1in series is provided at the input terminals210of the active radiator208. Comparing the two plots702and,1104the plot line1104indicates that providing a simple passive circuit having R1, C3, and L1in series to the input terminals210of the active radiators208, additional boost can be obtained below 35 Hz without losing SPL above 35 Hz. In addition, comparing the two plot lines1104and1004indicates that using C3in the active circuit218in place of C2generates additional SPL from the primary driver204below about 30 Hz.

FIG. 12illustrates a plot line1204representing the measured SPL from the primary driver204when the passive circuit218having C3and L1in series is provided at the input terminals210of the active radiator208. The plot line1204is substantially similar to the plot lines704and804indicating that a resistor and a capacitor may be needed to minimize the dampening that may occur above 35 Hz.

FIGS. 7 through 12illustrate that by providing simple passive circuits to the input terminals210of the active radiator208, the performance of the loudspeaker system200may be tuned, dampened, or boosted along the low, mid, and high frequency range of the bass. This allows a user to tune the operating characteristics of the loudspeaker system200by varying the electrical configuration setting provided to the active radiator208rather than through changing the mechanical properties of the active radiator208. The SPL generated by the primary driver204may vary depending on the type of primary driver204, active radiator208, and the circuit provided to the input terminals210of the active radiator208. In addition, a number of different types of active and/or passive circuits may be provided through the configuration unit212. For example, active circuits such as operational amplifiers or a series of tuning circuits that require an external power supply may be provided to the input terminals210of the active radiator208. As another example, when coupling the active radiator208to an active circuit214such as a partition of an excursion limiting circuit, the active radiator208may be used as a mechanical servomechanism to limit the excursion of the primary driver204. In addition, a variable active notch filter may be provided at the input terminals210of the active radiator208to tune the loudspeaker system200at one or more frequencies.

FIG. 13shows a flow chart1300illustrating a process that may be used to tune the loudspeaker system200. In block1302, a loudspeaker system200may be provided with a common acoustical compliance between the acoustical equivalent406of the primary driver204and the acoustical equivalent412of the active radiator208. In a decision block1304, a decision may be made as to whether the operational characteristics of the primary driver204should be tuned. If no tuning is required, then in block1306, an open circuit217may be provided to the electrical equivalent408of the active radiator208. On the other hand, if tuning is required, then in block1308, at least a portion of the resistance, capacitance, and/or inductance to the electrical equivalent408of the active radiator208may be adjusted to tune the SPL generated by the primary driver204. The tuning may be accomplished by selecting the active circuit214, short circuit216, or passive circuit218from the configuration unit212, for example.

The flow chart1300also illustrates that a feed back system may be incorporated into the process. In block1310, the SPL generated by the primary driver204may be measured. In the decision block1312, the measured SPL from the primary driver204may be compared to a desired SPL range. The desired SPL range may be established by an operator. The desired SPL range may be also stored in a look-up-table for comparison. If the measured SPL is within the desired SPL range, then the process may stop. On the other hand, if the measured SPL is not within the desired SPL range, then the process may go back to the block1308to readjust the resistance, capacitance, and/or inductance provided to the electrical equivalent408of the active radiator208until the measured SPL is within the desired range.