Home     Frugel-Horn Spawn Family   Plans Ron's Horns Daleks Metronome     Acknowledgments, etc Use of Designs Builders & Kit Links Mail Us		24_march_08 Note: a substantial rewrite of this page underway. Inspired by the Frugel-Horn project, we decided to pursue a new family of frugal enclosures. For these cabinets, rather than using corner-loading, we wanted to utilise the double mouth layout pioneered by Terry Cain in his beautiful Double BEN (Big ENough) horns.* The result was the Spawn series of cabinets depicted on these pages. These are split into two distinct subsets, the BVRs, and the Olson-Nagaoka designs respectively, which are considered separately below. All of these cabinets were designed, refined and modelled from scratch in the latest editions of Martin J. King's seminal MathCAD worksheets. Firstly why double-horns? The simple reason, leaving aside the aesthetic appeal, is that the split over-under MDM (Mouth-Driver-Mouth) layout potentially can offer some significant acoustic benefits over the more usually seen single horn types. A considerably larger mouth size for a given footprint is instantly attainable, while imaging can be spectacular thanks to the near-cylindrical wavefront launched over the horn's passband, a la a line array. Less obviously, the upper and mid-bass also greatly benefit from this arrangement, subjectively providing greater punch and scale. The BVRs -- Harvey, Iris & Bruce (& Loreena) The first of the two subsets of enclosures you will find on these pages took further inspiration from the Replikon horn, the Jensen Imperial, and other cabinets of this type. Once commonly seen in PA circles (until the recent development of cheap high-power SS amps) this style of horn is comparatively rare in the hifi scene. Strictly speaking, such cabinets are not horns at all, but Big Vent Reflex (BVR) enclosures. Unlike the more usually seen designs, such enclosures feature a large chamber to the rear of the driver, coupled to a short, rapidly flaring waveguide. As the name suggests they are effectively bass-reflex cabinets with extremely large vents, the expansion being chosen to minimise distortion. Compared to their small-vent cousins, they couple to a far greater quantity of air (like any bass-horn) while maintaining the classic attributes of low ripple and impressive extension characteristic of reflex enclosures. An extensive discussion at diyAudio.com. Harvey had his coming out at Fostex Fest in september 2006. Some comments can be found in the event coverage.       This family of cabinets initially began with a design for the Fostex FE126E which could be adapted to accept other drive-units of similar dimensions; the same objective of flexibility being applied to the larger cabinet designs. In ascending order of size, the BVRs are (note: Full Plans) Harvey (named for diminutive English rock-singer Polly Jean Harvey): intended for drivers in the 4-5" range (100-125mm) Iris: intended for drivers in the 6 1/2" (165mm) range Bruce: intended for drivers in the 8" (200mm) range. (More BVR cabinets are under development, and a revision to Harvey (1v1), Iris (1v1), Bruce (1v2) and Loreena (1v1)(Lyeco LY802F / Visaton B200) are immenient. These revisions will allow broader driver range. Fostex F120A & CSS FR125SR will now work in Harvey, Loreena will accept both the Lyeco & Visaton, but Bruce is no longer suggested for the Lowthers. Not quite publishable, but useable versions of the new Harvey & Bruce are available on request. Also a full range of ProBVRs is under development -- 1st out the gat will likely be Maria for 12" Pro FRs & Co-axes). Nagaoka-Style -- Mikasa, Hiro & Sachiko (& Aiko) The second of the two subsets of double-horn enclosures are the Olson-Nagaoka designs. These designs are also somewhat different to those more frequently seen in that they feature stepped, rather than constant, expansion. This design method is most commonly associated with the late Mr. Tetsuo Nagaoka, one of the great pundits of Japanese speaker cabinet design, and also many of the designs Fostex suggest for their drive-units. However, it was first suggested by Harry Olson, in his 1937 patent application (granted 1940). Although not discussed in particular detail in the application, which focused upon the marrying of a low-pass filter (chamber) to a horn rather than the expansion of the horn itself, the diagrams clearly illustrate the first known instance of this stepped expansion method, and references are to be found in the text, hence our respectful name-checking of both men. Such stepped designs operate as an expanding QWR, the expansion created by a cascade of straight half-wave resonators, which roughly follow a known horn flare-profile (exponential, hyperbolic etc). Cabinets of this type are exceptionally easy to build, as there are no complex angles involved, and also allow a longer path-length for a given cabinet size due to the efficient use of space and volume. The internal Œsteps‚ also operate like reflectors, and help disperse unwanted HF leakage in the horn. Such cabinets typically offer impressive extension and smoothness in their bass response. Again, in ascending order of size, the Olson-Nagaoka cabinets are: Mikasa: intended for drivers in the 4-5" range (100-125mm) Saburo: intended for drivers in the 4-5" range (100-125mm) Hiro: intended for drivers in the 6 1/2" (165mm) range Sachiko: intended for drivers in the 8" (200mm) range.   Review   Review Like the BVRs, these enclosures were designed to have flexibility built-in, and they will accept a wide range of units. 2Moose BVR -- Calhoun & Shadow & the Chang Family The love child of Harvey & Hiro, Calhoun is the result of a request for a Nagaoka-style box for 2 CSS WR125s. The long-path horn didn't work, so the two concepts were used for somthing unique. In only 10 days they went from plans to playing music. You can read about them in this diyAudio thread. Following Calhoun is his trusy woof Shadow for a pair of Extremis extended range Woofers.       Interest in Calhoun for other drivers has led to the Chang family... too many to mention. The Chang family really exemplifies previously unexplored space that has been opened up to exploration by Martin King's software and a confluence of ideas from all over. The original BVR idea from GM, its implementation in the Replikons, Terry Cain's double mouth horns, the Frugel-Horn inspiring Scott to explore double mouth concepts that lead to Harvey, Bruce & Iris. The work to discover how the BIB works leading to openess to explore the Nagaoka-style horns (Mikasa, Hiro, & Sachiko), the Fonken (the contributor of the high aspect slots*), and chance... all this sitting as a back-ground for a quest from left-field to find a home for some WR125s which lead to the 1st Changs, the Calhoun, then Shadow. Scott has taken the concept far enuff into unexplored territory that i'm now calling the cabinet style Moose BVRs in honour of the ground-breaking work Scott has done. Ron's contribution also has to be noted... the curved mouth 1st seen on the Austins and then the Frugel-horn have found application in the tall ones, hopefully he will find enuff time to optimize this for the boxes that can take advantage (Chang, Chili Chang, Maria Chang...) Not much harder than a typical BR, but without most of its drawbacks (ie tuning changes as you turn up the wick) and the cosmetics of a horn.       Like the Frugel Horn, the Spawn family of BVR and Nagaoka cabinets is an open source project, and feedback from builders will help us improve the designs, and drive future modifications. Thanks must be given in particular to Greg Monfort and Martin J. King for their advice, and MathCAD worksheets, without which these enclosures would not have come to fruition. *Sadly, our friend Terry Cain died just before midnight on Sunday 10th December 2006 after a battle with both Lyme Disease and Lou Gerhig's Disease. He will be sadly missed by the DIY and the general audio community. He was always helpful, a great inspiration to others, and he designed and built many superb speakers. These double-mouth horns are dedicated to his memory.