Omnidirectional speakers. The future?

Check these out. Decware Radials

El: I commented that most "omni's" like the Ohm's are not true Omni's due to the limited vertical dispersion. Other than that, until you can do a side by side and listen to the differences in presentation between a panel and an "omni", it is all "theory".

Holzhauer: There are speakers that have tried to do the "pulsating sphere" thing. The first one that comes to mind is the Design Acoustics D-12. This was a dodecahedron ( 12 sided ) cabinet with a driver on every panel. In effect, you kind of had a wooden "disco ball" with speakers in it. The thing here was that these used conventional woofers, mids, tweeters, etc... and the sound was crossed over and "sprayed" at random. Never heard these in person or read any "real" test reports on them, but i bet it was a disaster both sonically and electrically. Once again, another example in speakers of "good in theory, horrible in implimentation".

As to Stuart Hegemann, there are some articles about his theories and speaker designs in a recent Audio Xpress. From what i can recall, i think that there will be a follow up article. If you're not familiar with Audio Xpress, it is a DIY type magazine that covers everything from electronics to speakers, both SS and tube. I can get you the info on the specific issue(s) if you want.

As to why i said what i did about 901's and the Shahinian's, the 901's effectively radiate in every direction horizontally due to the layout of their drivers on the front and angled rear panels and the purposely designed amount of reflections that they encounter. In effect, they are "spraying & bouncing" everywhere. In the same respect, the Shahinian's ( specifically the Obelisk ) "spray & bounce" the upper frequencies all over due to the use of multiple drivers and the use of angled panels. Having said that, the Shahinian's have far more vertical dispersion, make use of far better quality drivers and actually have a LOT more thought and research put into them. As such, they are similar yet VERY different designs and that is all that i was implying. Once again, i'll point out that i consider the Shahinian's to be a "good" speaker even though there are things about them that i would do differently. With that in mind, i have recommended these speakers to others and have gotten emails from Agon members that are very happy with them after purchasing them based on my recommendations. One should bare in mind that most of these are not designed to "crank" ( much like my Ohm's ) but at "reasonable" volume levels, they produce "magic".

For that matter, i don't know of any speaker made that i think does everything as well as it should and believe that most designs could be easily improved upon. That is why i've modified most everything that i have. Then again, it is quite easy to pass judgment / criticize / "talk shit" in public if one is strictly a spectator and not really in the game "professionally" so to speak : )

Matchstikman: I could give you a LOT of background of how the "radials" came to be and none of it is very supportive. Let's just say that Steve Deckert had a set of my Ohm's and very nearly destroyed them. After playing with them and experiencing what these could do, even though they weren't working correctly due to his "repairs", Steve started working on the "Radials". For that matter, if one can't look at the "Radials" and then Ohm's "Sound Cylinders" and see an amazing amount of resemblance, there's something wrong with their vision. Sean
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PS... While the Decware site and information that is provided looks impressive, believe me, things are NOTHING like that in the real world. Either at their shop or in the services provided. Obviously, some folks know their way around a computer and can create wonderful websites. How close the information presented compares to reality is another matter. Personally, i've "been there, done that, won't EVER go back".

Thanks Sean. I learned some more about Hegeman on the Asylum "Shahinians Anyone" thread. Shahinians Arc has identical shape as the original Hegeman loudspeaker. Shahinian states that Hegeman and others were his inspiration. Admirably, Shahinian does not take credit for much of his inspiration. He is proud of assimilating the knowledge of some nearly ignored geniuses. Although not a true omni, I like his design because it allows for extreme dyamics and deep bass. The most prevalent complaint I've heard is with respect to blurring of the image with overly diffuse sound. I also expeienced this until deadening the rear and side walls so as to absorb the early reflections. After treatment, the imaging/ instrument placement became better than anything i've heard from a box.

How about breaking it down to the theoretical fundamentals: What would be best if it could be perfectly realized in physical implementation (an impossibility)?

>A completely omnidirectional, evenly radiating pulsating sphere (or point, if you prefer)

>Same as the above, but a monopolar hemisphere only, maybe wall-mounted to simulate an infinite baffle constituting a listening room boundary

>A true monopolar, laser-like (parallel-focused) 'ray of sound' eminating from a point-source (actual or simulated) and aimed directly at one of the listener's ears (what would the difference be between this and a set of headphones?)

>A 360-degree radiating, cylindrical line-source with zero vertical dispersion

>Same as above, but a 180-degree cylindrical half-section only ('monopolar' line-source, analogous to the sphere/hemisphere example above), again maybe wall-mounted to simulate an infinite-baffle

>A dipolar version of of any of the above, such as a Quad ESL is to a simulated pulsating sphere

>None of the above: The ideal radiation pattern should be an exact inverse of the recording microphone's 'acceptance-field' pattern, whatever that may be (in realistic terms, this kind of thinking could only even begin to apply with a very tiny minority of recordings actually made, due to prevalent recording methods)

>None of the above: Given the preceeding, stipulate that you'll never be able to standardize and optimize the recording process to conform to some idealized encode/decode protocol with an equally-conforming playback system, and thus there is no one 'correct' ideal radition pattern possible, so you should just work with whatever sounds good to you in your room

>It doesn't matter, as long as you listen inside a perfect anechoic chamber, maybe in a multi-channel setup

As Sean pointed out, most omni's aren't truly omni, since the drivers usually become directional at high frequencies. But the net effect can be the same as for a true omni - namely, a well energized and tonally correct reverberant field.

Just for the record, the Bose 901 was NOT an omnidirectional system. The array of 8 drivers on the rear of the enclosure was highly directional, in stark contrast with Bose's advertisements which depicted a very wide radiation pattern from the rear-firing array and a narrow pattern from the single front-firing driver. In fact, the opposite was the case! The rear-firing array's radiation pattern would have approximated that of a single driver roughly 8" tall by 16" wide (the 45 degree angle down the center of the rear baffle does help somewhat with horizontal dispersion, so maybe the net effect is more like a single 8" by 12" driver). The 901's forward radiation narrowed to a roughly 90 degree angle at about 4 kHz and continued to narrow progressively above that. The rear radiation narrowed to 90 degress at maybe 1.5 kHz, and of course it just got worse at higher frequencies. The selling point of the 901 was the psychoacoustically pleasing effect of a well-energized reverberant field. Note that assuming the equalizer corrects to give more or less flat power response, the on-axis first-arrival sound from that single front-firing driver will be quite tipped up. Bose got away with it because the reverberant energy was so much louder than that first-arrival signal that it dominated the perceived tonal balance. I'm not going into the other design tradeoffs Bose made at this point - they might sue me (I say that only half jokingly). But the 901 is an ingenious application of psychoacoustics, and I tip my hat to Amar Bose on that score.

The Shahinain Diapason on the other hand gets the tonal balance correct in both the direct and reverberant sound fields. The design uses two woofers, four cone midwoofers, two 3" dome mid-tweeters, two 1.5" dome tweeters, and six 1/2" dome supertweeters (the latter to maintain adequate energy in the reverberant field in the top octave). Designer Dick Shahinian takes into account not only the frequency responses of the drivers, but also their physical orientation and inherent radiation patterns in building a psychoacoustically intelligent loudspeaker.

The Ohm F, German Physics, Huff, MBL Radialstrahler, and Wolcott Omnisphere speakers are perhaps more elegant (though not necessarily better sounding) solutions than the Shahinians, as they use fewer and more exotic drivers, but their radiation patterns tend toward the doughnut-shaped at high frequencies rather than the truly omnidirectional. Bi-polar speakers from Mirage and Definitive Technology also do a good job with the reverberant field. Some planars (namely Beveridges and the big Sound Labs) also generate a tonally correct reverberant field, as do cornerhorns like the Klipschorn and Hartsfield, albeit with less reverberant energy (relatively speaking) than an "omni". But the principle of maintaining correct tonal balance in the reverberant field makes sense to me.

Apparently it also makes sense to Seigfried Linkwitz and Jorma (pronounced "Yorrrrma") Salmi. The latter is the designer of the Gradient Revolution, which is a very well thought-out system in my opinion (yup, I sell 'em). The Revolution uses a dipole bass system and a cardioid mid/tweeter module. At first glance it would seem that these very differently-shaped radiation patterns (the figure-8 dipole and heart-shaped cardioid) would give a very disjointed reverberant field, but the audio gods smiled on Jorma. The ear is very tolerant of arrival time differences in the reverberant field; timing is only critical in the first-arrival signal. And it just so happens that (assuming equal on-axis, first-arrival SPL's) the net energy put out into the reverberant field is the same for a dipole and a cardioid! So using fairly conventional drivers (and only a few of them) in a reasonably-sized enclosure, the Revolution has consistent tonality of both first-arrival and reverberant sound. And this matters because the ears take them both into account; a nice smooth on-axis anechoic frequency response curve is incomplete data, from a psychoacoustic perspective.

In case you can't tell, getting the reverberant field right is probably my favorite obscure loudspeaker design consideration. I find that often perceived loudspeaker characteristics are demystified when the reverberant field is factored in, and the most realistic-sounding systems I've encountered are ones that get the reverberant field right.

Now the one justified criticism of omni's (and their wide-pattern cousins) is their typically non-pinpoint imaging, at least in comparison with a good two-way mini-monitor. I'm afraid that to a certain extent this is an inevitable tradeoff. Even from one concert hall to another, there's a tradeoff between precise localization of sound sources and enveloping ambience. The more energy in the reverberant field, the richer the ambience but the less precise the soundstaging. However, it is the early reflections that are the most detrimental to good imaging. By their very nature wide-pattern speakers have more energetic early reflections, and so with wide-pattern speakers it is especially important to treat the first reflection zones if imaging is a high priority.

Getting back to Stan's original post, I wouldn't say that I'm in favor of omnis just for the sake of omnidirectional radiation. Rather, I'm in favor of getting the reverberant sound to have the same (correct) tonal balance as the first-arrival sound - and an omnidirectional or quasi-omnidirectional system is one very effective way of meeting this criteria. And the test is this - with the music playing a bit louder than normal, walk out of the room. If it still sounds like live music through the open dooreway, then those speakers are getting the reverberant field right - much the same as real instruments do.

Duke