Bandpass type woofers have come to be generally well accepted, and have become somewhat popular as a means for producing reasonable amounts of bass from relatively small enclosures with good efficiency. However, it has taken a long time for this type of woofer to receive serious consideration.
The basic idea for a bandpass woofer has been known since the first part of this century. Even double vented bandpass enclosures (such as the original AM-5 produced by Bose Corporation) are discussed in the 1934 U.S. Pat. No. 1,969,704, issued to A. D'Alton. But it was really not until the 1970's, after the work of Thiele and Small, that any serious attention was paid to bandpass type woofers. A summary of their work is set forth in "Loudspeakers in Vented Boxes" by A. N. Thiele, a multipart series which appeared in the Journal of the Audio Engineering Society, Vol. 19, pp. 382-392 (May 1971) and "Vented-Box Loudspeaker Systems" by Richard H. Small also a multipart series which appeared in the Journal of The Audio Engineering Society. Thereafter a paper presented to the Audio Engineering Society Convention in Los Angeles, May 15-18, 1979 by Louise Fincham, entitled A Bandpass Loudspeaker Enclosure, set forth a good basis for analyzing bandpass system response. Since then numerous papers and articles have appeared discussing the subject in greater or less depth. Notable among the various papers is the very thorough paper by Earl Geddes and David Fawcett presented at the Audio Engineering Society Convention in Los Angeles in November 12-16, 1986, entitled Bandpass Loudspeaker Enclosures. The Geddes and Fawcett paper discusses solutions for 4th through 8th order bandpass systems.
With the theoretical tools in place, as discussed above, the availability of powerful personal computers and workstations has made it possible to analyze and specify complicated bandpass woofer designs. However, the inherent higher cost and narrow bandwidth of these systems as compared to standard ported or acoustic suspension designs limited their appeal until 3-piece or sub-woofer satellite systems became popular in the late 1980's. The appeal of these new sub-woofer satellite systems lies mainly in the small size and utility of the satellites. A bandpass sub-woofer offers the perfect complement to these small satellites in that it is a relatively compact sub-woofer with a sharp high-frequency cut-off which desirably minimizes localizability of the sub-woofer. Due in part to the popularity of 3-piece systems, recent years have seen a multitude of variations on the basic bandpass scheme. These include double-vented systems, where both cavities are vented directly to the outside air; internally double-vented systems, where the second cavity is vented into the first which is, in turn, vented to the outside; triple cavity systems where two cavities share a drive unit which is vented into a third cavity which is, in turn, vented to the outside; and so on.
Although these new variations are interesting and offer potential, recent research and experimentation has revealed that the potential of the basic single vented bandpass woofer has not been fully exploited. Additionally, the single-ended acoustic nature of a single vented bandpass system gives it a significant advantage over double-vented bandpass and normal vented woofer systems in both its ability to benefit from room gain and in reduced sensitivity to room placement. Additionally, the growing popularity of home theater systems has made self-powered sub-woofers a virtual requirement for high quality home systems. However, market research has shown that virtually all consumers who have brought self-powered sub-woofers would like them to be smaller. The opportunity to design the amplifier and woofer system together offers interesting possibilities, and allows reevaluating the question of size versus efficiency in sub-woofers. In particular, the cost differential to obtain a slightly more powerful amplifier may be offset entirely by the cost savings of a smaller enclosure.
USPTO Backgrounds
USPTO Backgrounds