Speaker with frequency directed dual drivers

This application claims priority to U.S. provisional patent application Ser. No. 60/573,050, filed on May 21, 2004.

The present invention relates to a control system for independently modulating the activation of broad frequency, dual, in-plane drivers in a speaker based on the commanded frequency to be output by the drivers.

A typical broadband loudspeaker system usually includes separate loudspeakers for providing the different frequency components of the broadband acoustic signal. These separate loudspeakers are coupled together by a suitable crossover network for applying the appropriate frequency component of the electrical input drive signal to each of the loudspeakers.

Usually, these types of speaker systems have more than one driver (i.e. a midrange and tweeter) that operate within at least a portion of the same frequency range. When two of these drivers operate within that range, destructive interference, which is also often referred to as phase discontinuity, in the axial response can arise caused by the cancellation of the spaced-apart like sound waves generated by each component.

Because of the finite distance between the two drivers, the sound waves will have a phase discontinuity. At points in space located axially about the speaker system, the two sound waves will sum or subtract from each other causing the net audio signal at that frequency to be muted or accentuated. This is commonly referred to as lobing and is shown schematically in prior art FIG. 5B .

More recently, speakers having dual, spaced-apart, in plane, drivers that operate within the same frequency range are gaining in popularity, particularly for use as auxiliary computer speakers. However, one side effect of having dual, spaced-apart, in-plane drivers is that they will acoustically interfere with each other over a much broader frequency range when operated together.

Efforts to reduce or prevent this interference have had limited success. For example, U.S. Pat. No. 4,233,472 to Kleis, the disclosure of which is hereby incorporated by reference, disclosures connecting more than two in-plane drivers together in series with some of the drivers being mutable at defined frequencies as a result of low pass filtering. While such structures reduce some interference, it relies on more than two drivers with at least two of the drivers being positioned at an angle with respect to each other. Such a configuration is not desirable in many speaker applications, including use as auxiliary computer speakers, which favor having only two, spaced apart, in-plane drivers in each speaker.

Accordingly, despite the available improvements offered by available interference control systems, there remains a need for a cost effective control system that modulates the activation of broad frequency drivers of a speaker having dual, in-plane, drivers based on the commanded frequency to be output by those drivers.

The present invention is a speaker that includes a pair of spaced-apart, in-plane mounted drivers connected in series to a network for applying the appropriate frequency component of the electrical input drive signal to each of the drivers. A frequency dependent shunting network is applied to one of the drivers so as to gradually mute the one driver as a desired frequency is approached. The frequency dependent shunting network also serves to gradually increase the power provided to the other driver. Accordingly, this power increase is proportional to the amount of muting on the other driver, thereby preventing the muting of the first driver and related power increase on the second driver from being discernable to a listener.

The result is an aesthetically pleasing speaker that has dual in-plane drivers and that produces superior sound quality throughout the entire frequency range of the speaker, including those ranges in which dual, in-plane, drivers tend to interfere with each other.

FIG. 1 is a front view of a speaker having dual, spaced-apart, in-plane drivers in accordance with an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the speaker of FIG. 1 taken along line 2 - 2 of FIG. 1 .

FIG. 3 is a schematic diagram of a preferred control system for modulating the activation of the drivers of FIG. 1 based on the commanded frequency of the drivers.

FIG. 4 details a preferred activation response for each driver of the drivers of FIG. 1 based on an increased commanded frequency of the drivers.

FIG. 5A is a schematic diagram displaying the acoustic benefits of the present invention on a dual, spaced-apart, in-plan driver speaker.

FIG. 5B (PRIOR ART) is a schematic diagram displaying the acoustic characteristic of a dual, spaced-apart, in-plane driver speaker of FIG. 5A without the present invention activated thereon.

FIGS. 6 & 7 are schematic polar maps comparing the same dual-driver, in-plane, speaker performance at two different frequencies (approximately 4000 Hz for FIG. 6 and approximately 8000 Hz for FIG. 7 ) with the present invention activated and again without it activated.

A dual-driver speaker 20 having a driver activation control system 22 for modulating the activation of the drivers 24 , 26 based on their commanded frequency is disclosed in FIGS. 1-4 , with comparison information showing exemplar benefits of the present invention over the prior art shown in FIGS. 5A-7 .

The speaker 20 preferably includes a case 28 operably securing a first driver 24 and a second driver 26 , to define a pair of drivers, therein. Each driver of the pair of drivers is preferably spaced apart from the other driver by a defined distance 34 and positioned so as to be substantially in the same plane 36 with each other as best shown in FIG. 2 . The speaker 20 includes conventional electronics and related circuitry to receive an electrical input drive signal and apply an appropriate frequency component of the electrical input drive signal to each of the drivers. Preferably, the drivers 24 , 26 are substantially identical and configured to operate within substantially the same range of frequencies.

An exemplar driver activation control system 22 for modulating the activation of the drivers 24 , 26 based on their commanded frequencies is shown in FIG. 3 . Both of the drivers 24 , 26 are preferably connected together in series as shown. A capacitor 40 with a defined capacitance is connected across one of the drivers (here driver 24 is shown) so that the defined capacitance of the capacitor 40 and resistance 42 of the driver 24 thereby operate as a low pass filter 50 .

Preferably and as shown in FIG. 4 , the defined capacitance is selected so as to allow the driver 24 to gradually mute as a defined frequency is achieved. The low pass filter 50 also serves to gradually increase the amplitude of the second driver 26 . This amplitude increase is proportional to the amount of muting on the first driver 24 , thereby preventing the activation of the low pass filter 50 from being discernable to a listener.

The desired frequency cut-off for the low pass filter 50 is a function of the speaker components and the distance the drivers are spaced apart from each other. For example, in cases where the speaker is to be used as a computer speaker, and the drivers are spaced apart from each other by about 2.5 inches. Particular success at reducing interference was achieved by selecting a capacitance of the capacitor so that the cutout frequency was about 5600 Hz or above.

The result is an aesthetically pleasing, dual-driver speaker 20 that has superior sound quality through the entire frequency range of the speaker 20 , including those ranges in which dual, in-plane, drivers tend to interfere with each other.

Having described and illustrated the principles of our invention with reference to a preferred embodiment thereof, it will be apparent that the invention can be modified in arrangement and detail without departing from such principles. In view of the many possible embodiments to which the principles may be put, it should be recognized that the detailed embodiment is illustrative only and should not be taken as limiting the scope of our invention. Accordingly, we claim as our invention all such modifications as may come within the scope and spirit of the following claims and equivalents thereto.