This is a brief guide to the Ohm Walsh series of speakers, a popular speaker manufactured in the early 80's to late 90's (and still offered factory direct through Ohm Acoustics).
The Ohm Walsh is a unique speaker that uses the infamous Walsh driver. Unlike a typical dynamic speaker, which uses a cone firing directly into the room, the Walsh driver works by exciting (or energizing) the surface of the driver itself. Lincoln Walsh theorized that a dynamic speaker could never behave like a true "piston", so instead designed his driver to radiate sound by exciting the driver's suface. The lower the frequency, the more of the driver's surface is utilized to radiate the sound into the room. The Walsh driver, most visible in the Model "A" and "F", appears similar to a cone driver firing directly into the cabinet, though both the "F" and extremely-rare "A" are considerably larger than most conventional drivers. The "A" and "F" drivers are manufactured using varying materials along the drivers length.
The Walsh driver results in an omnidirectional, phase-coherent soundstage that is unique relative to more conventional speakers. Later-generation (as opposed to the original "A" and "F" drivers) Ohm speakers with the Walsh driver used a conventional tweeter with a simple crossover to supplement the high frequencies; this radiates into the center of the room when facing the speaker (nominally 45 degrees off center when facing the speaker). They also utilize acoustic shielding in the "cans" to reduce the sensitivity of the speaker to room placement and, by design, are not truly omnidirectional speakers. The cans also protect the Walsh driver from dust, damage and, alas, visible operation.
Later, Ohm Acoustics switched from trapezoidal wood cabinets using real wood veneers to what are referred to as "sound cylinders", which are essentially cardboard tubes with a contact paper overlay. These reduced manufacturing and selling costs, essentially making these speakers cost competitive with mass-market speakers. Modern Walsh speakers sold by Ohm Acoustics have (thankfully) returned to using wood cabinets with real wood veneers, and continue to receive good reviews.
Why such a loyal following on E-bay for the Ohm Walsh? Several. First, these speakers are very unique, both in terms of appearance and sound, relative to "conventional" dynamic speakers. While Ohm is no longer the only manufacturer to make speakers using the Walsh driver, the others doing so now are esoteric, small volume (read: expensive to outlandishly expensive) producers.
Second, Ohm is rather unique in that they still support their entire product line, including crediting a portion of the original retail price (typically 25%) towards purchase of a new one. Replacement parts and upgrades are available for their entire product line through their website. How many speaker manufacturers today provide that level of service and support?!
Third, the soundstage provides what Ohm refers to as "full stage stereo"; unlike conventional speakers, the soundstage is very wide and largely independent of the user's position relative to the location of the speakers (in large part because of the omnidirectional driver coupled with the controlled directivity of the tweeter on later models). Personally, I find the effect very appealing. They even work well in a home theater set-up without a center channel, operating with a "phantom" center channel...try that with conventional speakers! It will not work effectively with most traditional speakers...the soundstage will simply collapse to the speaker you are sitting closest to!
Issues to look for include the speaker cabinet (the wood veneers used on these models is prone to chipping, as they have sharp, exposed edges, particularly on the lower edge of the cabinet), "foam rot" of the surround (buzzing present, particularly at low frequencies), dented "cans", and improperly repaired or inoperable drivers. Ohm claims that the original Model "F" driver, extremely complex in terms of materials and construction, cannot be properly repaired (Ohm does offer other, more modern Walsh drivers that can be utilized in the original cabinets). The grills are often damaged and discolored, though Ohm does offer replacements. Finally, the speakers are rather large and heavy, requiring careful handling and packaging to avoid damage in shipment (Ohm recommends removing the drivers, packing and shipping them separately from the cabinets to reduce risk of damage).
Please note that this article is intended only to provide general information on the Ohm Walsh; I am not affiliated with Ohm Acoustics. For specific information about their products, and comprehensive information about any of their models, please refer to Ohm's website, the original patents through the USPTO, or Dale Harder's comparable offerings based on the original Walsh A and F designs.