Throughout the history of speaker system development the desire to create a compact speaker system that can reproduce low frequencies can easily be considered one of the highest goals of speaker manufacturers. The following is a brief description of current loudspeaker technology, describing the various types of speaker technologies that are related to this disclosure as well as the limitations of these technologies. Typically a driver of a speaker system is mounted in an enclosure, or cabinet. A major role of the enclosure is to prevent out-of-phase sound waves from the rear of the speaker from combining with positive phase sound waves from the front of the speaker, which result in cancellation. Cancellation causes the efficiency of the speaker to be compromised and produces interference particularly in low frequencies where the wavelengths are large enough that interference will affect the entire listening area. Enclosures also play a significant role in sound production, adding resonances, diffraction, and other unwanted effects. Increasing enclosure rigidity, adding internal damping and increasing the enclosure's mass are current approaches for reducing problems with resonance. Diffraction problems are addressed in the shape of the enclosure for example, without limitation, avoiding sharp corners on the front of the enclosure.
The ideal mount for a loudspeaker driver, or transducer, is a flat board of infinite size with infinite space behind it. Thus, the rear sound waves, or rarefaction, cannot cancel the front sound waves, or excursion. An “open baffle” loudspeaker is an approximation of this. In an open baffle loudspeaker, the transducer is mounted on a simple board of size comparable to the lowest wavelength to be reproduced. However, for many purposes this is impractical and the enclosure must use other techniques to maximize the output of the loudspeaker, also called loading. For example, without limitation, a wavelength of 20 Hz is approximately 56 ft long and is too large to be maximized with an open baffle loudspeaker.
FIGS. 1 and 2 illustrate an exemplary conventional art single driver open baffle system utilizing a large baffle to maximize low frequency reproduction. FIG. 1 shows a front view, and FIG. 2 shows a rear perspective view. In the present system a large baffle 20 is required to accommodate a single driver 21. In many applications the size of baffle 20 is too large for reasons such as, but not limited to, size constraints and aesthetics. For example, without limitation, most listeners would not want a speaker system with a large baffle in their home.
FIGS. 3 and 4 illustrate an exemplary conventional art multiple drive open baffle speaker system utilizing a narrow baffle 25 but compensating by employing more than one low frequency drivers 26. FIG. 3 shows a front view, and FIG. 4 shows a rear perspective view. In the present system and other systems where a narrow baffle is utilized, larger diameter low frequency drivers may be employed to compensate for the lack of baffle area.
Another prior art system is an “infinite baffle” system. FIGS. 5 and 6 illustrate an exemplary conventional art infinite baffle speaker system. FIG. 5 shows a front perspective view and FIG. 6 shows a rear perspective view. An infinite baffle speaker system is a variation on the open baffle system and is made by placing a loudspeaker 27 in a large sealed box 28. Sealed box 28 is typically filled with acoustic absorbing material such as, but not limited to, foam, pillow stuffing, fiberglass, or other wadding. This enables loudspeaker 27 to behave as if loudspeaker 27 has a larger cabinet behind it.
Other types of conventional enclosures attempt to improve the low frequency response or overall efficiency of the loudspeaker by using various combinations of reflex or passive radiating elements to transmit the energy from the rear of the speaker to the listener; these enclosures may also be referred to as vented or ported enclosures, bass reflex, or transmission lines. FIG. 7 illustrates an exemplary conventional art vented enclosure 29. Vented enclosure 29 comprises a vent 30. The interiors of such enclosures are also often lined with fiberglass matting for absorption. Reflex ports are tuned by the amount of mass within the vent, using appropriate diameter and length to reach this point. This enclosure is the most common conventional enclosure as it lends itself to small size and reasonable bass.
As shown by way of example in FIGS. 1 through 7, conventional enclosures are large, bulky, and some of them require multiple speaker drivers. In view of the foregoing, there is a need for an improved speaker system for maximizing low frequency reproduction that is small and efficient.
Unless otherwise indicated illustrations in the figures are not necessarily drawn to scale.