Unsound, 7p62mm described the newer "Walsh" series. My only comment to what was stated is that it does not use what is historically known as a "Walsh Driver". Instead, the newer designs use a conventional woofer that is loaded face-first into the top of the box. What you hear coming out of the "can" is the backwave of the driver i.e. the sound leaking out of the holes in the drivers' basket. The front wave of the downward firing woofer is vented from within the box. Since there is limited cone exposed through the drivers' basket and upper mids and treble are highly directional, they augment the woofers high frequency output with a tweeter.
In comparison, the original Walsh driven Ohm A's and later version called the Ohm F's use very different drivers from the newer versions. While both use one full range driver ( no tweeter or crossover network ) that radiates 360* horizontally and looks like a "pylon" or "road cone" mounted on top of a sealed box, the designs are quite different from each other.
The A's used a greater flare rate near the end of the cone and somewhat resemble the old horns on Victrola's. The cones were made up of two sections ( top and bottom ), each one making use of different metalic materials that were internally damped. The suspension was rubber based. As such, the surrounds do not decay and would not need "refoaming" unless ripped, etc... Efficiency on the A's was said to be in the very high 70 dB range. I'm guessing somewhere around 78 db's or so from what i've read about them. Impedance was spec'd at 8 ohms but later models were much, much lower impedance. As such, it was a phenomenally tough load to drive, especially with the amps that they had available back then. As far as i know, there are VERY few pairs of these remaining.
The F's were basically an attempt to refine the A's. The cones on the F's have a more linear taper and make use of three different materials and arranged in a top, middle and bottom section. Each material was selected for specific attributes within specific frequency ranges. There are even "slashes" that were strategically cut into the bottom section to help break up standing waves along the length of the cone. While the impedance is rated at 4 ohms nominal and 3 minimum by the factory, they actually average closer to 2.5 ohms and dip below 2 at low frequencies. Efficiency was factory rated at about 87 dB's but my experience says something closer to about 82-83 dB's or so. Once again, these were tough loads for most amps back then ( and even today ) to deal with. I have run into problems with some very well respected amps trying to drive these.
Both of these speakers take a tremendous amount of power to function at their best. I remember an old review of the F that stated "anything less than 60 wpc is just not suitable". Personally, i think that an amp that can do at least 300 wpc at 2 ohms without a fuss would be the minimal requirement. Even with that in mind, i have had amps that were rated for 400 wpc @ 4 ohms begging for mercy with these speakers. Obviously, this pushes a LOT of amps out of the equation and proves that not all amps are created equally, regardless of specs.
As to sound, both the A's and F's ( when running right and in good condition ) are known for tremendous low frequency output. I recently had a set doing FIVE Hz ( !!! ) at high output levels. It sounded like a helicopter was inside the house : )
Soundstage is phenomenally wide and deep with a very natural presentation. Notes tend to effortlessly float in the air. This is probably related to the dispersion pattern and fact that you have one driver producing all the sounds in phase with each other.
Midrange sounds very cohesive and seamless, as all the primary notes & harmonic overtones from both instruments and voice are reproduced with no crossover points or multiple drivers to disturb the signal. Highs are very crisp and clear with bell like qualities. Most of that may be attributable to the metalic section of the cone. To minimize "metalic ring" like you get with metal domes, they applied a thin layer of glue and foam inside the driver itself. Not only does this help to absorb high frequency reflections and standing waves inside the driver and box, it also damps the metal membrane.
There were quite a few revisions during the production run of these speakers. Some obvious ones were the design characteristics of the frame used for the driver. I have two sets of these and they are visibly quite different from each other. Other things not noticeable from the outside were the types and quantities of internal damping materials.
These speakers are limited in terms of SPL and dynamic range. They work best for listening at low to medium levels. They can play at higher levels, but attempting to do so for an extended amount of time will almost surely result in either the amplifier or speakers coughing up smoke. Keep in mind that i like "LOUD", so my "medium" listening level might not be the same as yours. Either way, when used within their limitations, they do some things that most other speakers can only dream about. That is why i own TWO sets of them : )
The last Ohm's that i know of that made use of what i would call a "Walsh driver" would be the Ohm G's. These were a short lived model that did things very differently from the earlier "Walsh" speakers. Not only was the height and radiating surface of the driver reduced, the materials used were quite different. Besides that, the Ohm G made use of a passive radiator design rather than a sealed box. This was obviously done to augment low frequency output but also maintain a small amount of damping for the driver. I guess that they were trying to use a smaller, lower mass Walsh to achieve greater high frequency capabilities. By doing so, they ended up losing both mass and surface area in the attempt. Both of these are major factors when it comes time to reproducing deep bass. Anything after the G is simply a "Walsh" in name for advertising purposes.
Obviously, this is just my point of view. Take it for what it is worth. If anyone is interested in further info on "vintage" Ohm's, drop me a line. Sean
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