Omnidirectional speakers. The future?

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

I love my German Physiks. I have the borderland's they are the acorn congac hi polish finish. They are getting the new ddd's and crossovers. I didnt know how much I miss them until they were out of my room.

They are just very fine. I like to get loud alot of times and I do push my gp's. Works well with a m&k 350 sub ( and also the jbl 4918?

I do prefer horns for loud rock but for some slow jazz or nice classical or just pretty music nothing can beat these speakers. I have friends over that dont have alot of audio knowledge but are usually musicians and they comment on how pretty the music sounds from the german physiks.

The best I have heard was at ces with the loralies(spelling?) with 4 or 6 ddd's and 4 gp subs on each side. You had to get use to the sound but when you did you kept comming back for more. THe other room I really liked was the edgar horn room ( the avantgarde room had a line)

I am interested in the shahinian, for what better dynamics, thats what makes my heart beat fast (anymore)

Kelton

Duke, I really enjoy your discussions on reverberant fields. I especially like the listen from the next room test. It's funny that you mentioned that. I was just poking around on the net and found some info on a fellow who had reviewed the Hegeman loudspeaker (one of if not the earliest omni). Apparently rather than post the frequency response of the loudspeaker, he described how the woman in his apartment building complained about the person playing the piano late at night. It was a recording of Sir Elton John.
I'm convinced that the reverberant field is very very important also. There are those who espouse the importance of flat frequency response. I personally do not consider the frequency response to be more important than reverberant field. (Yes this is a subjective observation) I have heard several loudspeakers with flatter response than my omni emmulators that did not sound as real.
As you mentioned, all the designs have trade offs. When someone finally designs a loudpeaker with the clarity of an electrostat and the dynamics of a cone speaker and gets the reverberant field correct, I'll be there with my check book ready to buy and invest.
Maybe someday our loudpeakers will be balloons filled with excitable molecules that expand and contract as directed by remote lasers. Ok I'll stop now before I go any farther off the deep end.

I do like the idea of omni direction speaekers and the way they sound. They sound pleasant and open - after hearing one, a conventional speaker sound veild somewhat in comparison.

I have Sonus Faber with four tweeters on top, and sounds good. Radio Shack has a lineum tweeter that is pretty nice too (somewhat transparent), for DIY speaker builders.

Energy towers have sounds coming out of many places, and sounds nice and open.

If you are DIY, one could make one without too much difficulty for under a grand using premium parts.