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Issue link: https://www.relevantize.com/i/160815
Reviewer Comments PRECISION TRANSDUCERS THE ART OF DETAIL sound culture www.rcf.it ND 940 COMPRESSION DRIVER The ND940 is a ultra compact size, high performance, high power handling 4.0-inch diaphragm compression driver with a 1.4 inch exit throat. The high power neodymium magnet guarantee the perfect control of the dome assembly's moving mass. * 280 Watt continuos power handling * 4.0 inch, Kapton former, edge wound aluminium voice coil * Neodymium magnet 12 VOICE COIL The trend and intense desire on the part of speaker engineers is to design smaller loudspeakers that can effectively deliver at low frequencies. Ultimately, a bass reflex enclosure architecture can realize a lower cut-off frequency for a given enclosure size than an acoustic suspension. But, as a loudspeaker size is reduced, there is a point where a port of large enough diameter to minimize losses and turbulence-based noise must be extended in length and no longer fits within the enclosure's longest dimension. In this case, a passive cone radiator is typically used as a vent replacement. But, this substitution is not without compromise. Due to the passive radiator's output being greater than that of the active transducer, the passive radiator's surface area is usually required to be at least twice that of the active woofer. Also, due to a noninfinite compliance, the passive radiator often exhibits a notch in the response near the cut-off frequency. To address these issues, the invention discloses a form of folded, coaxial vent construction that includes smaller diameter tubes placed concentrically within larger diameter tubes, creating a vent that can have an effective length of three to four times the vent structure's actual depth. This solution can be handy in realizing long effective vent lengths with a large cross-sectional area, but are not without shortcomings. By implementing this approach, greater turbulence can be created due to the multiple folds throughout the vent's length. That said, the approach is useful and effective in many applications. The patent office granted this patent without a comprehensive awareness of prior art. Besides easily discoverable previous patent applications (e.g., Japanese JP5-183976 and US 7,450,733 to Susimin Suprapmo at Creative Technology). Dr. Po Ser Hsu at Hsu Research developed some of the earliest products with this approach. He also applied for a patent on the folded vent in the 1990s, but it was not granted (some patent examiners are more thorough than others). So, while the inventors have developed a clever and functional vent structure for effective use in shallow enclosures, it is possible the device resides in the public domain, available to anyone with the need for a low-frequency Helmholtz tuning in shallow enclosure. VC