History on ohm A's and F's.

As a huge OHM F fan/owner I really enjoy the Q"s an A"s on this forum. I"m not sure who rebuilt my pair of F"s, but my eyes/ears tell me they were done correctly. The sound is just awesome in my 20x13x7 (audio room) which opens to a wet bar and half bath through a 7ft opening. My pair of F"s have a top end with plenty of detail/shimmer that is neither hot nor too recessed, leading into that glorious mid range. Female vocals are in room, singing to me. Bottom end has a natural foundation with good attack, enough thump as to not need a subwoofer.

I agree, OHM F"s are NOT for headbangers who think they need 110db to enjoy music. My pair sounds quite nice around 90-95db, from a Belles 55 preamp (subsonic filter engaged) to a VSP gold power amp (totally recapped) thanks again (audionut66@comcast.net) beautiful job!

In closing ... if your OHM F"s don"t sound correct, then they were repaired incorrectly. My all-time Favorite!

Just a question from a naive reader: wouldn't the transition from a wave-bending mode to a pistonic mode in a single driver result in an audible "crossover" effect, although perhaps much less audible than a well-managed crossover between two separate drivers?

Lewis,

There is a transition from wave bending at higher frequencies to pistonic at lower, I believe.

Not sure I'd call it a "crossover" necessarily. Not sure to what extent that transition is audible or discernible to the human ear. Maybe others might know more?

The F driver had three separate sections covering different frequencies with different materials comprising each section. I believe I've heard reference to the 2 cut-over points between sections referred to as the physical equivalent of an electronic crossover, similar function, totally different technology/approach.

Also it is not clear to me the exact specifications in regards to at what frequencies and to what extent at each the driver operates pistonically versus bending wave.

I think it would be accurate to say that the modern Walsh drivers used by OHM operate more in the pistonic mode than wave bending in that wave bending is associated with higher frequencies I believe and the modern OHM CLS Walsh drivers use a supplementary tweeter. German Physics DDD drivers on the other hand operate at the high end of the frequency spectrum supplemented for the most part by conventional woofers, I believe, which is an opposite approach.

Getting a single Walsh driver to do it all or as much as possible without destroying itself at high SPLs would seem to be the name of the game in general.

Lewis,

Without presuming too much technical knowledge of my own, I suspect that the opposite happens. Since the dispersion pattern of the Ohms is always (nearly) omnidirectional, there is a sense of "continuousness" to the speakers. Whatever discontinuity that might be a result of your observation seems to be subsumed by this effect. At least to my ear.

Also, I would guess that the transition may be gradual, with some frequencies being partially reproduced by both bending and pistonic motion. Such an arrangement would be akin to very low order (presumably well less than first order) crossover. Such schemes usually mask transitional issues, although they can certainly introduce other artifacts. By the time response is primarily pistonic, you may well be at a frequency low enough that most listener's sensitivity is reduced. Similarly, BTW, the cross to the tweeter is so high in frequency that -IME- most listeners will be relatively insensitive to that hand-off.

Maybe John S can comment further.

YEs, I'd really love to understand the pistonic/wave bending thing in more detail in regards to the CLS Walsh driver.

OHM CLS must be doing some wave bending in the mid range and up, though clearly not at the very top end where the super tweet works. The cls high end response extends beyond 16-17Khz which I think is approximately where the F ended.

I'm assuming wave bending is at least part of what propagates sound outward horizontally from the rear of the downward firing cone as opposed to up/down (pistonic) using the cabinet to tune the low end, but I do not know for sure, just how smooth, dynamic and "coherent" the resulting sound is, particularly in the mid-range. The very generalized diagrams I've seen on the OHM site showing how the CLS driver works seem to indicate this.