Omni Speaker Options

Amilcar, regarding the suitability of your room to omnis, let me describe some pertinent aspects of how the ear/brain system processes incoming sound. I think this is useful background for people considering omni, dipolar, or bipolar speakers. This will be a brief introduction rather than an in-depth study of the topic.

The ear derives directional cues primarily from the first .68 milliseconds of a sound impules (corresponding to the roughly 9 inch path length around your head from one ear to the other). After this initial .68 milliseconds the ear suppresses directional cues from repetitions of the original signal (reflections), but still accepts loudness and timbre cues from the reflected energy. That being said, a strong, distinct reflection arriving after that initial .68 millisecond window can still skew the imaging.

The subjective effect on sound quality of reflections is related to their arrival time. In general, reflections arriving earlier than 10 milliseconds behind the first-arrival sound (corresponding to a path length difference of 11 feet) tend to be perceived as coloration, and reflections arriving later than 10 milliseconds (assuming their spectral balance is good) tend to be perceived as richness, warmth, ambience, spaciousness, texture, and liveliness. That's why music in a good recital or concert hall sounds so good, and that's why omnis often sound so good.

You've probably noticed that owners of dipole speakers (Maggies, Quads, etc.) like to position them pretty far out into the room. This is because they sound better when the extra reverberant energy from the backwave arrives after as much time delay as is reasonably feasible. The same principle applies to omnis, only their equally strong radiation to the sides makes the first sidewall reflection a concern. Often diffusion in the first sidewall reflection zone is beneficial with omnis. Likewise, diffusion in the first reflection zone behind the speakers is usually beneficial, especially if they must be placed within 5 or 6 feet of that wall.

Since lots of early sidewall reflection energy is inevitable with an omni, you might well get some image imbalance with that big opening along the right-hand side of your room. In my experience even heavy absorption in the corresponding area on the opposite side of the room may not even things out with that type of speaker. In general I don't like to use any more than the bare minimum amount of absorption necessary to prevent slap-echo when using dipoles, bipoles, omnis or polydirectionals, because much of what they do well comes from having a strong, diffuse, spectrally correct, slowly decaying reverberant field.

I'm a big fan of getting the reverberant field right; in my opinion that and dynamic contrast are among the primary differences between live and reproduced sound from a perceptual standpoint.

Duke
dealer/manufacturer

Duke - that was an excellent explanation.

The only catch is that each person has their own set of priorities when it comes to the order they assign to various sonic characteristics. For one person, that sense of spaciousness may trump a loss of image stability. For another, the same characteristic may be completely unacceptable.

These differences of opinion help explain why there are so many different speaker manufacturers and why the debates among audiophiles are often filled with such rancor.

While one can improve the odds of finding a speaker you'll like by reading the opinions of others, there is never a substitute for hearing the speaker for yourself in your own room.

Once again some wise words from Duke. The path length of 11 feet or the 10 msec rule of thumb is something you need to consider whatever speakers you have. The rule also applies where you sit (do not sit near a wall). This is one of the reasons that you find main speakers built directly in to a wall in most high end studio setups (no spurious reflections).

One concern with Omnis is the necessary mounting and shapes of the speaker box - inevitably there are often edge diffractions of the sound from mounting posts and many of these designs use surfaces to deliberately reflect or disperse the sound (Beolab 5 for example). Therein can lie a weakness in this type design. The result can be that certain frequencies may collapse to the speaker (as secondary reflections color the sound) even if the majority of the sound is natural and wide open. It is worth auditioning to carefully check for these issues - cymbals can often hint at this issue due to their broad frequency content. I found the Beolab to sound very open on airy on some sounds and less so on others - I wonder if there is not a 3 to 6 db SPL drop and edge diffraction occurring as certain frequencies reach the edge of the reflective discs. Overall the speaker sounds great but these coloration will be of concern to some listeners.

All speakers are trade-offs, Omnis are wonderful sounding but there are some compromises (as with any speaker).

Amicar...strongly urge you to listen to your choice before you plunk down money. I couldn't live with MBL's if I were paid for it. Someone on this discussion said they had great fireworks, and I do agree. To my trained, professional violinist ears, they are anything but natural sounding. I suppose a lot has to do with the feeding ancillaries...I heard them with MBL electronics. It would be awful to get these set up in your listening room and hate them.

I've heard the big Beolabs at the Beverly Hills B&O store on at least three occasions. They sound very good till the spl goes up - at which point they become a complete mess featuring compression, significant tonal shift and audible break-up. I'm not talking live rock concert level here, either. It could be unique to the sample/set up at that B&O store, but you would hope that the sales/mgmt people address the issue at some point and I heard the same problem on all 3 visits, which spanned more than a year.

Marty