The road to the Trapagons
a brief look at some earlier designs

The Original Trapezoids 1981 to 1984

The original waveguide experiments started with a 5" 2-way system on a standard enclosure, which was refined over a period of time until it became obvious that any further efforts would require a significant reduction in the diffraction effects caused by the rectangular enclosure shape, and the standing wave energy inside of the enclosure also caused by the rectangular shape. The actual driver/filter combination from a pair of those early 502s was removed and placed in the original 502R enclosure, which was a refinement of the rectangular enclosure that had radiused edges to reduce diffraction. This did have the expected effect, and prompted further experimentation. The next step was to build a trapezoidal enclosure to test both the waveguide effects and a non-rectangular interior. This 4" 2-way experiment ended up being sold as a prototype to Seifert-May along with the original Slot-loaded subwoofer, and became the Seifert-May Trapezoid. The next experiment added the top wing and resulted in the bottom-right speaker in the picture above right, the 502 Trapezoid. This was very successful in reducing the diffraction effects and increasing control over the wave as it left the speaker, plus it reduced the standing waves inside of the enclosure quite a bit. Further experiments were conducted with this waveguide shape, resulting in several products shown above. The three-way system above left, the Electro-Magnetic Induction Trapezoid, was shown along with a Slot-loaded subwoofer at the 1984 CES show, illustrating the results of the work to date (a fair amount of which was funded by the modification of Infinity Reference systems, hence the availability of the EMIM and EMIT drivers). Further work in 1985 resulted in the speakers shown below, the 803S and the original Trapagon.

803S
(slot-loaded subwoofer)

The 803S to the left was the first of the RR Audio speakers released to production with a slot-loaded subwoofer. It also used the wide, radiused edge to reduce edge-diffraction, as well as separate enclosures to reduce the effects of vibration (esp. on the HF driver). The next speaker to be completed during this period was the original Trapagon and the 1201S slot-loaded subwoofer. This speaker was the first to use a fully non-parallel enclosure and tapered walls to combat not only the standing wave resonances in the enclosure, but the panel resonances themselves.

1201S Slot-loaded Subwoofer and Filter

The next refinement in the Trapagon line was the creation of the Trapagon 2, a 7" 2-way design with a fully non-parallel enclosure similar in shape to that of the Trapagon, but with a wider wing structure for greater support of the HF waves leaving the enclosure. This system led directly to the Nearfield monitors, and later to the 702R/R1. There were also refinements to the 1201S subwoofer, with the inclusion of a far more powerful LF driver and a 3rd-order Transitional Gaussian filter with tremendous 10ga. coils and high-grade capacitors, as shown to the left.

Trapagon 2

The turntable above is a design that was undertaken with Robert Bergner in 1986, a year or so before the CD revolution began. The mass-loaded platform was suspended on gas shocks, and the belt-driven, vacuum platter was suspended on an air bearing. To the left are 501F monitors, an extremely accurate limited bandwidth monitor with the -3dB points at 60Hz and 13kHz. To the right is the Tri-Obelisk, a 360-radiating triple 2-way reflex-tuned cross-eyed monitor.

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RR Audio Laboratory
636 E. Harvard Rd. unit B
Burbank, CA  91501  USA
Telephone : (818) 843-8212
Facsimile : (818) 563-9372
E-mail : 
rr@trapagon.com