Speaker Asylum

RE: Omni-directional Speakers

4.242.141.104

In Reply to: RE: Omni-directional Speakers posted by Drew Eckhardt on January 10, 2008 at 11:26:33

I concur with everything Drew said, but would add some points.

Speakers which radiate omnidirectionally all the way up into the high treble may suffer from lack of image specificity. The soundstage is huge, but individual instruments and voices can sound bloated and bigger than life (in contrast to many forward-firing minimontiors which image very precisely, but the images are unnaturally small and narrow).

The best compromise, as seen in the Linkwitz Plutos and a few other available kits and models, is to cross the upward-firing mid to a forward-firing wide-dispersion tweeter on a very small baffle. This allows the response to gradually taper from omnidirectional to monopolar, at a much higher frequency than is possible with even a small front-firing box. The advantage of this is more precise imaging combined with the wide, deep soundstage provided by the omnidirectional mid-frequency radiation.

The Pluto mounts the tweeter on a periscope above the midbass driver. Some designs from Dick Olsher and GR Research mount it on the front panel of the cabinet, right near the top edge. The two approaches present different phase issues which must be addressed in the crossover, but can produce equally good results if the 90 degree off-axis roll-off of the mid is smoothly integrated with the HF roll-in of the tweeter.

I have built two experimental omni systems so far, one with each of the above approaches, with inexpensive drivers. Both sound far better than they have any right to, and big 3-D soundstaging with excellent separation of instruments is their forte. They work best out in the room, a good 5 feet or more from the nearest walls. The room is normally furnished with a mixture of diffractive and absorbtive surfaces.

I'd recommend looking into one of the good kits before blowing big bucks on an assembled system (unless you want something really exotic, like MBLs). Hire a good local cabinet maker if you can't make the boxes, and you'll still save money and end up with something that sounds great.

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