OHm micro walsh series...

The use of the word "coherent" in this specific sentence may not be the most appropriate word for what they are trying to describe: "The Ohm Walsh Loudspeakers utilize unconventional technology to provide a less expensive speaker which is substantially more efficient and less critical of room placement, but still coherent over a wide listening area. By that, what i'm trying to say is the sound produced by such a design is NOT coherent so much as it is "equally diffuse".

While some may wonder how the sound radiating out of the rear of a mid-woofer combined with a forward firing tweeter could be "equally diffuse", that is simple. All of the sound that one hears is "leaked" through all of the holes in the metal canister and the material that lines the inside of that "cage". As such, the "beaminess" of the tweeter at higher frequencies is nullified due to all of the diffraction / internal reflections taking place. The end result is that one hears the sound eminating through the holes in the canister, not from any single driver. There is no direct radiation, hence everything is "equally diffuse", which is the opposite of providing a point source of radiation that exhibits a "coherent" wave-front. Sean
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Some years back, i took the cans off a pair of 4XO's and i could not hear a differance when i slipped then off and on again; i did this several times. There must have been a differance, but my ears could not hear it. You know...they used to think the bumblebee could not fly.

You have to search their site to see the current ones are not omnis, as this thread indicates. They physically damp the rear radiation from the Walsh driver in all the main models, and use a conventional tweeter starting around 8 or 10k. These tweeters are seriously toed in by default.

If you talk to them they specifically disavow omni-directional radiation.

Ok well, the Micros were originally omni up to a little past 1 Khz, I was working at Ohm for a while and I began designing the Micros while John (the president and main resident speaker designer) was away on vacation. After returning from his vacation he was surprised and pleased with the results from the initial prototypes so we set about completing the design in earnest, working together. I guess they've made some changes to reduce the omni ratiation pattern to lower frequencies. Once you get to a low enough frequency, they are of course, still omnidirectional.
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Critofur (Christopher)

After reading through these messages I feel compelled to dispel much of the misinformation contained herein, excepting Chris who actually worked on the design prototypes and as such is authoritative.

1. The Walsh micros, and the full range Walsh 5 and it's smaller breathren, utilize the Walsh bending wave principle wherein cone breakup is controlled through wave termination at the surround. Thus, the apex of the cone produces the highest frequencies - the sound heard is in fact coming from the front of the cone (the "back" of the woofer as it were). The high frequency extension is naturally limited by the mass and inductance of the voice coil.
2. The great advantage of the Walsh mechanism is that the full range from the lowest bass to the upper midrange frequencies and treble (to circa 8 khz) are produced by a single driver without a phase-shifting crossover. The omni-dispersion of the Walsh driver provides for perfect overlap of frequency response and power response (total radiated acoustic energy on and off axis) and seamless crossover to the tweeter, which is substantially omnidirectional (at the crossover frequency) due to it's small radiating area.
3. As bending waves travel down the cone faster than the speed of sound in air (supersonic wave transmission line), and as the cone is angled so that the total distance of wave propogation traversal is a multiple of the driver horizontal radius, it is possible to produce a perfect wave from from low bass to the upper cutoff frequency (i.e. 8 khz): there is no phase shift or time delay. The Walsh driver can pass a square wave. Conventional loudspeakers cannot produce a square wave except perhaps at one specific point in space.
4. The Walsh driver as implemented by Ohm has been modified to attenuate the rear radiation field and result in a high dispersion frontal radiator - the modern Ohms are not "omnis" as the Ohm F was. This design choice makes for easier room placement, minimizes room interactions, results in a warmer tonal balance, and improves the stereo image specificity, without sacrificing the spaciousness of the sound field produced.
4. The Ohm Walsh design provides for controlled directivity, vis-a-via the upper operating range of of the main full-range Walsh driver, and the tweeter. The tweeter is baffled in such a way as to provide for smoothly increasing directivity. The tweeter is directional above 10khz by design because in the highest octane reside the directional cues which provide for localization (imaging). There is no great advantage to an omdirectional radiation above 10 khz - in fact, it generally results in an over-bright fatiguing sound with compromised imaging and requiring acoustic damping of the room walls to counteract it by eliminating early reflections.
5. The perforated can is acoustically transparent - it's only function is to physically cover and protect the driver construct. It is not a diffuser.

The advantage of producing a coherent wave from low bass all the way up to far above the region of maximal human auditory acuity (circa 2-5 khz) is the resulting sound quality: natural, clear, detailed without the phase-shift, lobing and power-frequency response mismatching that plagues all conventional multidriver loudspeakers and rob the music of natural detail resolution, add coloration, and render a contrived quality to the sound. Also, the Walsh driver affords a very large radiating area for the production of the critical midrange, and it's geometry provides for perfect dispersion in the horizontal plane. The former characteristic results in extremely low distortion as excession cone motion is eliminated - the latter eliminates the beaming and cone-breakup that palgue all front-firing woofer cones, even exotic materials. The Walsh driver can hence be run full-range up to it's bandwidth limit, this eliminating the need for a signal mangling crossover with its energy-storing capacitors and inductors.

To really grasp the design advantages of the Walsh driver listed above, one need only listen to an Ohm Walsh loudspeaker in a proper setup to appreciate it's superior depiction of acoustic space and musical performance vis-a-vis conventional loudspeakers.