Omnidirectional speakers. The future?
Hi AudioKinesis - IMHO the reverberant energy in a hall is either a fortunate or unfortunate attribute of that hall - depending on one's tastes and location. I would call it distortion, as compared to the piano in an anechoic chamber. Except that, to get philosophical about it, certain genres, forms, and specific pieces of music were developed/composed with certain assumptions about the acoustical properties of the places or media where they were likely to be heard - especially with regards to classical music, e.g. Russian church choral music wouldn't sound right in a jazz club. But my point is that the best a speaker can do is re-create what you would have heard at the point where you were sitting - and a microphone has ALREADY picked up all those reflections, time-delayed, and out-of-phase sounds. As far as the ear's diaphragm is concerned, there are never "sounds arriving at different times in different ways" - there is only one complex waveform which already IS the net sum of all those primary and secondary elements hitting you at any point in time. (That's why there is only one groove necessary in a record). This is what the microphone records, and is all that needs to be re-amplified. Adding omni-directional characteristics to speakers is simply like changing the acoustics of the hall that the piano was recorded in. Some will like it, others won't - but it's not what was there in the first place. I'm not a purist in the sense of maintaining the original if something else is more pleasing or fun, but personally, I'd rather have a Yamaha DSP that gives all sorts of acoustic playback options - including the option of turning it off. And I'm a big fan of the DBX 5bx dynamic range expander (which actually DOES restore the signal to more like the original.) I just think that if you want to alter the signal that's on that CD or LP, having your speakers bouncing sound off the walls and ceiling is really not the best way do it. |
Opalchip, interesting points you bring up. I can't help but have a question come to mind: When you listen to a grand piano in a recital hall, the vast majority of the sound power that reaches your ears from the piano is reverberant energy, not direct energy. Would you consider this reverberant energy (which cannot possibly be time and phase coherent with the original signal) to also be "distortion"? You see, the ear treats sounds arriving at different times in different ways. Different cues are extracted from reflections than are extracted from the first-arrival sounds. I believe the correct approach is to see them as two separate events, and to try to get them both right. Twilo, I didn't hear the Hsu bipolar setup, but believe your description. However, note that the back-to-back speaker pair will probably have a deep notch in the response centered on the frequency where the path length difference from the two sets of drivers to the listening position is equal to 1/2 wavelength. Assuming the back-to-back speakers were each 8" wide and 6" deep the on-axis path length difference is 6 + 6 + (8/2) = 16 inches, so at approximately 420 Hz you'd have severe cancellation, along with partial cancellation at nearby frequencies. So back-to-back speakers may not be the ideal solution. If I recall correctly, Mirage used a single bass driver on the front of a wide cabinet, and a rear-firing midrange and tweeter on the back of the cabinet crossed over higher than that 1/2 wavelength notch frequency. Definitive Technology patented a technique for using side-firing woofers along with forward and rearward facing mid/tweet arrays, once again to avoid that 1/2 wavelength cancellation notch. |
The microphone "samples" one point of a planar wavefront generated during the performance. A planar loudspeaker recreates the planar wavefront, and what happens after that, regardless of what kind of loudspeaker is used, is at the mercy of room acoustics. Can you give some examples of point sources? Every instrument I can think of, with the exception of a human vocalist, has a sounding board larger than the typical cone driver. |
The amount of misleading "science" thrown around by "audiophiles" sometimes drives me nuts! Some people obviously like the "sound" of omni-directional speakers - but what they are liking is a form of increased phase and time alignment distortion from having the original signal bouncing around the listening area. There used to be all sorts of electronic "spatializers", or "spacial enhancement" boxes in the 70's and 80's that did exactly what omni's do - introduce controlled phase and time distortion. Why? - because some people found it pleasant or fun. "Distortion", which is simply a deviation from the original source's output, isn't necessarily unpleasant but let's be real about what it is. 1. Your ears are not able to discern the broad "shape" of the "front" of a soundwave. A change in the air pressure in your ear canal moves your eardrum either in or out, which in turn vibrates some bones, which then vibrate fluid in your inner ear, and finally - at the back of your inner ear that is converted to an electrical impulse. In addition, the "cleanest" wave you can incite will come from a smooth "point" source. 2. The idea that somehow bouncing recorded output around at random is more accurate than directing back, from a "point source", what stereo microphones have already picked up is nonsense and/or marketing hype. You only have two ears - and they do exactly the same thing as microphones. You don't need 6 or 8 ears to receive spatial information. The most accurate thing a speaker can do is create in reverse EXACTLY what occured at the diaphragm of the microphone. It's extremely delicate information, and the more it bounces around the room, the more of it is lost, period! Of course it's not perfect reproduction - everything ELSE a speaker does may sound good to some people and bad to others, but it's "distortion". The spatial information of the original sounds' environment is ALREADY IN THE SIGNAL - you don't need to somehow alter or re-recreate it to make it more "real". 3. I have owned many types and brands of speakers, sometimes 8 or 10 pairs at once, and have a very nice A/B testing set-up where I can swap from one pair to another using only a foot switch. I personally prefer minimum baffle speakers***. But for example, even in A/B testing the Dahlquist DQ20i (minimum baffle) against the Alon V (which is an extremely similar design but has a 90% OPEN baffle mid and tweet) it is becomes apparent how much distortion the rear waves from the Alon's sets up. By itself, it sounds "open" and "spacious" - in A/B it sounds open, spacious, and MUDDY! *** Of course, minimum baffle design is also a trade-off of where you like your distortion, too. Instead of output reflecting immediately off the baffle, there'll be more "escaping" to reflect from surrounding walls, etc. Apparently, my ears prefer that. |
I am reminded by this subject, that while at Rutgers U., in the late '50's, I had the pleasure of visiting Hegeman's home and auditioning a stereo pair of his unusual design. The enclosures were large transmission-line loaded, with the woofer/mid mounted on top at a visible angle to the listener, and fitted with his own take on the venerable "whizzer" cone. They were driven by a pair of Dynaco amps, fed from a stereo reel-to-reel tape (RCA Menotti: Sebastian), and the sound was *fabulous*! I will never forget it. John |
We all have extra amps and speakers from upgrading - you can connect 2 amps by RCA "Tape out" to "Tape in" on another amp. Now you have 4 channels to hook up your speakers - 4 good ones, unlike most surround receivers. Place 2 speakers back to back - one firing backwards and now you will enjoy deeper soundstage along with other benefits. You can add a third set and make it more omni-directional. This improves most speakers - I was in search of a deep realistic soundstage, and I got it by doing this. The depth was what I was going for, and now I am happy to find it with the equipments I already own. |
Twilo: I agree with you that the Mirage bipolars, while very popular in their day, were not completely satisfying speakers. A couple of things you could potentially experiment with in an opposed/twinned set-up would be slightly shelving down the volume level being directed to the rearward-facing pair, or mirroring a small toe-in angle front-to-back, both in order to fine-tune the imaging/soundstaging. |
Zaikesman, HSU set up the system. What I can tell you, when I had the Mirage M1 speakers, they were definitely laid back with an airy sound. But they were to warm sounding and lacked detail. When you use the back to back setup, you get that 360 degree sound with nice detail. It definitely sounded much better then the Mirage Bipolar speakers I had. But I'm convinced the back to back setup is the best way to get the omni directional sound with detail and a good bass response. |
Twilo: The "RA" in RA Labs stood for Roy Allison - see my post at the top. I don't know if it was Dr. Allison himself who displayed those speakers in that back-to-back set up, but in any case, he didn't invent the configuration, as many hobbyists have played around with it through the years, often using similarly inexpensive small speakers. The opposed-twinned set up is not a cure-all, but it does let one investigate bipolar sound without needing special speakers. |
Hi, I saw your post about Omnidirectional speakers. I had to tell you one thing. I found the holy grail of how to get omni directional sound with detail. I originally had the Mirage M1 speakers in 1993. They were the big bipolar speakers. They definitely had a 3 dimentional sound. But I felt they were to warm sounding and lacked detail. I then got the Carver Al 3 speakers. These were dipole ribbon speakers with a 10 inch woofer. I really liked these speakers. They had an open sound and the bass was really good. Then at the Stereophile show in 1996. I walk in the HSU room. All of a sudden I hear the most airest sounding speakers with a great bass response. I look to see what speakers HSU was using. He was using these cheap bookshelf speakers called RA Labs. He did something interesting, that I would have never thought of. He was using 4 bookshelf speakers. Each bookshelf speaker had a 6 1/2 midbase and the tweeter. He was using 4 of these bookshelf speakers. The 4 bookshelf speakers were basically back to back. 2 of them were facing the wall. The other 2 were facing foward. He was using a Yamaha 4 channel amp. He was using a HSU sub on the 4 bookshelf speakers. I think this is a genius idea. You had to hear the sound. It had that 360 degree sound with nice detail. The bass was really good. Now you cant do this with deep speakers. But with bookshelf speakers or tower speakers that are not to deep, you can do this. Check out these tower Fried speakers. You couldn't use 4 of these speakers. There to deep. Here's a pic. http://www.enjoythemusic.com/ces2004/saturday/ But with these Tyler 7U tower speakers. You can use 4 of them. Here's a pic. http://tyleracoustics.home.mindspring.com/taylo.html I'm telling you, this idea gives you that 360 degree sound with detail and great bass. Thats what i'm doing with my system. I'm using 4 Dynaudio 1.3 speakers. These are bookshelf speakers with a 6 1/2 Dynaudio midbase and tweeter. I'm using 2 Meridian 557 amps, Adcom 750 preamp and Tara Labs cables. I'm using a Velodyne HGS 12 sub. You got to hear the sound. 360 degree sound with detail and nice bass. |
DB: Making such a post would both be useless and deceiving. I've haven't heard 10% of all the speakers out there, so my comments would be quite limited in scope and a dis-service to many manufacturers and readers of this forum. Suffice it to say that there are very few commercially designed speakers in stock form that i think are built as well as they should be or perform as well as they could. The fact that not one pair of speakers that i own ( and i have over a dozen pairs ) are stock should tell you something. Sean > |
Sean, can you please tell us what you think are the top 5 best speakers on the market today and why you think each speaker on your list is exceptional. This is not meant as a flame, it's just a matter of intrigue. It's obvious you have a lot of knowledge in this area and your recommendations could be of value to myself and others on this board. Thanks, DB |
I am so intrigued with this concept that, I am going to try out the hybrid omni directional Ohm Micro Walsh's with the matching center channel for my apartment. Admittedly, I am a little nervous getting them site unseen. They will be my first entry into nicer audiophile speakers and if they donÂ’t work out, well then IÂ’ll just return them. I listened to several less than 1000.00 floorstanders from some respectable manufacturers. B&W JMLAB, Paradigm, Monitor Audio Acoustic Energy, Dali, and only the Dali Suite series seemed to come close to really moving me regarding imaging. That is where I think they will excel. I also seems like everyone that has owned an Ohm Walsh speaker in the past reflects on them with positive memories. |
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. |
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 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 |
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 |
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 |
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. |
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 > 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". |
Check these out. Decware Radials |
Sean- I think Richard Shahinian would have constructed a pulsating sphere type loudspeaker if he had the technology. I agree that the greatest problem with current omni drivers are the lack of high spl ability and limited dynamic range. Shahinian chose to deal with this shortcoming by using conventional dynamic drivers arranged so as to mimic the sphere. I have not detected the lobing problems you mentioned. I don't understand why you think the Bose 901's are as much omnis as the Shahinians. Doesn't the 901 radiate sound forward and back only? Eldartford- I don't think of musical instuments as being a point source for sound. A vibrating guitar string has sound waves emminating from the entire length. At any given point along the string, the sound would radiate in all directions from that point wouldn't it. Richard said he adopted the theories of Stuart Hegeman. Does anyone know exactly what those are? I would like to read more about this if I could. Jrd351- agreed |
Fine posts, all. I designed my first speaker system as an omni (vertical-radiating planar?) back as a teen in the late 60s, using a Utah triaxial driver sitting upfiring into a plaster-filled kitchen funnel mounted in a wooden "basket", the whole thing sitting atop a 90 lb clay suwerpipe! Yikes. Antiresonant, anyway. A couple of visits to Tweeter, Etc. caught me hearing the new small Mirage Omni-whatevers. My gosh what horrible sound. The sales staff at both locations hate 'em too. Sigh.... I proposed to a good friend/master acoustician the idea of collaborating on an omni-design someday, and he asked why? as they don't work right in normal living rooms. Can't remember his primary concerns (maybe indeed the "primary" early arrival/reflections summation stuff). Happy Holidays all. |
As I see it progressing we'll be able to construct whole rooms that can transmit sound from any location to any location and only to that location. That way multiple listeners from any point in the room will hear the same as any other. Supermarkets are already working on part of the technology. What they do is have one speaker with very limited dispersion beam sound only to a specific location and only someone at that location can hear it like in front of the taco section and you hear an ad. Not sure I'm explaining it sufficiently to do it justice. But imagine what a movie might sound like with a whole room that is the speaker(s). |
sean...To be precise, the wavefront generated by the original Ohm speakers is cylindrical, rather than spherical. Lack of vertical dispersion is a good thing when the speaker is used in a room with ceiling and floor to make reflections, and is a characteristic of line arrays, and of the ubiquitous MTM driver configuration. Even so called "planar" speakers resemble line arrays because (Quads excepted) they are taller than they are wide. More on point sources...the musical instruments are not points, but the microphones that make the recording are. I regard the microphones as "sampling" the planar wavefront of the original sound. Now, when you play back the recording using a point source loudspeaker, the loudspeaker sound radiates outward again forming a spherical (planar) wavefront. However, with a point source speaker the radiation process starts over again from a point, with SPL falling off rapidly with distance, whereas a planar speaker generates the wavefront as it exists at a distance from the source where it has already expanded, and so there is only slight variation of SPL with distance from the speaker. Speakers of all descriptions can sound good in certain situations (even horns and ported boxes). In fact I have even heard the original Bose speakers sound pretty good with the right setup and kind of music. There is more than one way to skin a cat, which we all agree is a good thing. |
omnidirectional is without a doubt the best kept secret in home audio. shahinian,allison,gradient,and ohm and a handful of others are still the closest thing to the real thing from bottom to top. they will always be a cult item because they are out of step(and hard to design)with what most hi enders want. |
I have always grooved to the sound of wide-dispersion speakers. I grew up in a household where my father's final listening room speakers were a pair of classic Allison: One towers, with their V-shaped front baffles that sported a dual compliment of their ultra-wide dispersion dome midranges and nipple-shaped tweeters angled 45 degrees apart, and whose flat backs were designed for on-front-wall placement to achieve a virtual infinite-baffle loading of the speaker/room interface. Although they didn't compete with today's speakers in terms of resolution and precision, their presentation was a kind of aural widescreen that energized the whole room to a degree (and even at low volumes) which you just don't hear from most speakers. I'd love to hear the new iteration of this landmark 70's design that was brought out a couple of years ago with renewed involvement from Roy Allison... I find the sound of dipolar panels like Maggies, Soundlabs, etc. very attractive, until you try setting them up in a realistically-sized listening room ; conventional box-style monopolar radiators are just plain easier to place and extract optimum sound from in many instances. Bipolars can be another story becaue you don't run into as many phase-related difficulties, but I've never been overly impressed with most of the designs I've heard that achieve this radiation pattern through the use of separate, opposed drivers. Maybe something more along the lines of designs like the MBL Radialstahler, Ohm Walsh, or that forthcoming B&O superspeaker, which radiate through 360 degrees from single drivers lacking vertical baffles. BTW, although I can like the sound of bi-, di-, and omni-polar speakers, I don't necessarily agree with the 'live music' argument against monopolar speakers in theory. Yes, live music is radiated in all directions (although not equally), but I don't view this as being directly analogous to the home playback situation. I am philosophically of the 'you are there' school, as opposed to the 'they are here' school. To be 'there', it is a good idea to minimize the reverberant contribution of the listening room to the reproduced acoustic, which means controlled-dispersion speakers. I see the job of the loudspeakers as being not the inverse of the original musical instruments and performers, but as the inverse of the microphones which recorded them. The end result is that there often seems to be a sonic dichotomy between the sense of envelopment and presence, whether 'correct' or 'artificial', that you can get from speakers which directly radiate to more than just the frontal direction, and the sense of precise focus and scaled perspective you can get from monopoles. Both have their virtues, but in my listening rooms monopoles have always been the practical dictate. My present choice of Thiel speakers represents a monopolar design having wide dispersion for the breed with very even off-axis response tapering (at least in the horizontal plane - improving the vertical plane uniformity would seem to be one advantage of Thiel's newer coaxial designs) and a low-diffraction cabinet. Actually, I'm not sure that my idealized speaker design wouldn't be a monopolar line- or point-source, the former of which is represented by the Wisdom closed-back narrow planars, and the latter by the Cabasse tri-axial 'eyeballs', neither of which I've had an opportunity to hear, to my sorrow (not that I could really afford 'em anyway). Of course, one could always try installing a pair of Quad ESL's into a wall that's been cut-out to form a simulated infinite-baffle between two relatively small listening rooms... |
Drubin: The design that B&O has is severely flawed, regardless of what you read about it in "Hi-Fi glossies". It is similar in concept to what BIC did 20 years ago and Mirage is trying to do today but with a lot more research and technology involved. It will still suffer from nearfield reflections and the associated standing waves that come with such designs. If you want this to work "right", you have to use a single point source driver. If you don't, you'll run into multiple arrival times from each driver due to the different path lengths that each driver has to take to get to your ears. Not only will you hear the sound directly radiated horizontally out of the driver, but also the sound reflected off of the driver above it. If you look at what they are trying to do with these, you'll be able to see that it is nothing more than a way to duplicate the Ohm A and Ohm F that make use of Walsh drivers with multiple conventional drivers instead. In this aspect, Walsh took the various arrival times into account in this one driver, hence the taper of the cone and what German Physik's calls "bending wave theory". As the top of the speaker is closer to ear height, it is further away from your ear. As the bottom of the cone is physically closer to your ear due to diameter, it is further away from the ear in terms height. Both arrival times should be near identical if the taper of the cone were designed correctly and your seated listening height is taken into account. El: I have both "panel" type speakers and Omni's. If i could combine the speed and low mass of the planar design with the radiation characteristics of the Omni's and then add SPL capacity to all of that, i would have it all. As it is, the wavefront from a point source Omni is FAR more natural with a deeper, wider and more spacious presentation than any planar ( or speaker for that matter ) that i've ever heard. None the less, Omni's have their problems too. Since i like specific attributes of each design, i have dedicated systems set-up to run both : ) |
While the Shahinian's are nice speakers, they really aren't "Omni's" so much as they are multiple radiators arrayed to produce a diffuse pattern. Any time you use multiple drivers, you run into lobing problems due to cancellation, etc... While i hate to bring up a bad word and make yet another comparison to this company, Bose 901's are as much "Omni's" as Shahinians are. This is NOT to compare Shahinian's to Bose, as i have a lot of respect for the Shahinian's and very little for Bose. Having said that, "true" Omni's* that radiate from a point source ( single driver ) have some very specific problems with them. Most all are spl limited and lack dynamic range. If you can live with that, they can do some truly incredible things at low to medium listening levels. On top of this, their placement will be different from what is optimal for most front firing designs, so this should be factored in before shelling out the cash. The only "point source Omni's" that i know of are the speakers from Ohm Acoustics. I'm specifically referring to the Ohm A, Ohm F, Ohm G with the G kind of "half in / half out" of that category. This is due to using a passive radiator to reinforce the low frequency response, producing two distinct points of radiation. Since it is not an active driver though and primarily only contributing sounds at low frequencies as it is passively excited, we'll let it "slip by". The other "Walsh series" speakers that Ohm uses do not use "real" Walsh drivers in the classic sense and are not really omni-directional in nature. These would fall more into the "diffuse radiator" category like the Shahinians. Having said that, they use a very different approach from both the Shahinian's and their namesakes, the A, F and G. The others that i would consider "Omni's" are the MBL Radialstrahler's, the German Physik's speakers and the Huff's, which use German Physik's drivers in their own proprietary designs. The difference between these "Omni's" and the Ohm's are that the Ohm's are a point source ( single source of sound radiation ) and cover the full frequency range by themselves. The others mentioned above make use of some type of active assistance ( woofers, sub-woofers, etc.. ) in conjunction with the Omni drivers being used for the mids and treble. As such, they have two very distinct and different types of radiation with the associated differences in presentation taking place. Obviously, this is only my opinion, so take it for what it is worth. As i mentioned in another thread, i really like my F's. I liked the first pair enough after becoming familiar with them to drive to Boston to pick up a second pair. Part of the problem with these and / or any other "esoteric" driver is the lack of support for them and the potential for damage when shipping. Due to the exposed radiating surfaces of these drivers, any type of puncture to the shipping carton can be fatal. On top of that, when the Ohm's ( in specific ) suffer from foam rot due to age, the mass of the cone is hanging strictly from the spider ( the corrugated orange, yellow , tan looking thing behind the cone and in front of the magnet ). Since it is unlikely that you'll find someone locally to repair these ( unless you live in a big city ), you'll have to ship them. With the lack of support from the foam being eaten away, the driver is now slapping the voice coil around inside the magnet as it is moved, producing further possible damage. On top of this, the spider becomes even more stretched out, causing a reduced amount of control of the driver due to a weaker suspension. As such, if you are planning on buying something like this ( or any other exotic speaker ), you better make sure that you can transport them safely AND know where to go should you need to have them repaired. I could go on and on here, but i've already got one thread where i've said too much going right now : ) Sean > *Omni's are not really "Omni's" in the fact that most all of them suffer from limited vertical dispersion characteristics. Obviously, "omni" means sound distribution to all directions in an even manner, but due to the limited vertical and horizontal radiation of most other designs, even these "limited vertical radiators" are FAR more "Omni" than most. Omni's should not be confused with Dipole's ( E'stat's, Planar's, Ribbon's ) or Bipole's ( speakers with extra drivers firing out of the rear of the cabinet ) as they are quite different in radiation characteristics. The rear wave coming out of a dipole is out of phase with the front wave whereas a speaker like those mentioned above radiate the signal in all directions horizontally in phase. Bipolar speakers, i.e. those with rear mounted tweeters, mids, woofers, etc... have the front wave and rear wave in phase with each other, but because there is nothing joining the signal as it wraps around the box, these too will produce cancellation when the waves "collide". Due to the continuous radiation of an "omni" driver on all sides, the sound from the driver itself is produced in phase, so there is no cancellation. The only cancellations that do take place are from room reflections, which become even more of a problem. Since you have sound going in EVERY direction in a rather uniform manner, you've got a lot more points to reflect off of. That is why i mentioned different placement within rooms, etc... |
The "point source" thing doesn't really make sense if you think about it. Most instruments are pretty big points. Furthermore, even if the instrument were a solo kazoo, its sound would propogate as a spherical wavefront, and after traveling 30 or 40 feet, this wavefront would be nearly flat. A planar speaker can best regenerate this wavefront. |
