"The number one disadvantage of omnidirectional speakers is also the root of their greatest attribute.
Omnidirectional dispersion maximally interacts with the room. Room interaction and the subsequent reflections are the source of peaks and nulls in listening position frequency response, and time delayed sound which can be viewed as a form of distortion; that which does not exist in the original recording is distortion. How do conventional direct radiating speakers differ from omnis in this regard? As mentioned elsewhere in this site, direct radiators are omnidirectional below a few hundred hertz and become progressively more directional with increasing frequency. Obviously, direct radiators maximally interact with the room only in the lower part of their bandwidth, then progressively less in the upper registers. Yet, the most detrimental interactions are in the lower frequencies where room modes create strong peaks and deep nulls. In the upper mid and high frequencies summing and canceling level out. This is true with any dispersion pattern. But with direct radiators, the time delayed reflections of higher frequencies are reduced due to the narrowing dispersion. So shouldn't this be a good thing? Not really. It leaves most of the reverberant field low passed and lacking in treble energy, i.e., a distorted reverberant field.
The consequence of a low passed soundfield is a more boxy, stuffy, out of balance sound and a diminished perception of the ambience in a recording. Omnis avoid this by delivering full spectrum sound to the whole room, evenly dispersing the entire audible bandwidth and maximally interacting with the room. There is no way around room related issues except an anechoic chamber."
