Originally Posted by tuxedocivic
It is helpful James. As are all your posts. Wish you wouldn't lurk so much and would post your wisdom more
Sounds really nice when put that way. But here's another spin on it. The lister sits in a giant suck out only to hear reflected sounds to create an artificial spaciousness over and above the recorded spaciousness. The speaker suffers from reduced sensitivity and design complexity.
I've really only dusted off the surface of the concept, so maybe I'm out to lunch. But couldn't NicksHitachi take a two-way design with wide dispersion, build two angeld 45 degress. Wire one out of phase. And bam, he's got a dipole surround (not exactly a true dipole like a Nao Note or similar, but would have the dipole null facing out towards the listeners.)
Thanks for the kind words.
There are two issues here to address:
Ultimately, you are correct about the artificial spaciousness of a dipole.
When I was a younger man, I was at a Frank Zappa concert and someone yelled at the Police guard that they were Gestapo sheep, all wearing the same uniform. Zappa looked out at the crowd of us quasi-hippies and said, “Don’t fool yourselves, you are all wearing uniforms”.
Analogously, I would have to say, we are all creating artificial spaciousness, above or below that of the original first venue sound field, both quantitatively and qualitatively.
We do not yet have a recording capture and playback standard that works, so we each make the decision as to how best to make our systems achieve a presentation that is as uncolored and neutral as possible. And then, in the realization that it still cannot fool a 5-year old into believing they are listening to a live event, we must determine how much, and what type of enhancement we wish to add to create a sonic event that at least somewhat allows us to best experience a suspension of disbelief.
To paraphrase Frank, we need to not fool ourselves, in that we are all incorporating complimentary distortions of the original signal to attempt a compelling facsimile of the live event in our room.” Often those wonderful audio components that we find so striking, are not necessarily reaching into the program source and drawing out reality, but instead are distorting the signal in a manner that better fools us into believing.
Dipole surrounds, provide that same enhancement, but does so in a such a way that at least the ear/brain is not drawn to the sound source in an manner that points to a sound source. Again, it is the simplest source that can achieve what it does. In fact, one can even use a single dipole, centered directly behind the listener and achieve envelopment and/or ambience that is more convincing than a use of one or two monopoles.
I did a lot of work with dipoles in the 1970’s and 80’s and patented dipole configurations for use in surround sound, and licensed it to LucasFilm/THX.
You were asking why they were ever created in the first place. They were originally developed to use with delayed signal surround systems in the early ambience and 4-channel days, but were specifically chosen for the THX specified systems to maximize envelopment and scale in an attempt to recreate the surround sound systems in the theaters that use many side and rear loudspeaker sources to create the surround sound effects. While my original reference systems for domestic use were based on using 6 to 8 surround speakers in a 2-2-2 or 4-2-4 LS-R-RS format, and this is still the most impressive for home use, it was not acceptable for most domestic environments. So, the dipole surround was applied to the home theater specification of the time as a multi-speaker emulator, with the preferred addition of a decorrelation processing function. This provided the most faithful in-home replication of the sound in the dubbing stages that were used for mixing movie soundtracks.
Dipoles are often criticized because they are not configured properly to reach their full potential… as it is with most things audio.
Which leads to your second question, which if I understand correctly, asks about the use of two wide dispersion speakers, each angled at 45-degrees, and operated out-of-phase as a dipole system. While this approach can realize a dipole surround effect, a problem exists with achieving adequate low frequency extension. If the device is too small, and/or the opposite polarity drivers positioned too close together, without an intervening baffle, the high-pass characteristic of the dipole will start at too high of a frequency for the system to maintain reference level response in the lower midrange.
Bill Waslo’s mention of two constant directivity 90-degree waveguides, angled at 45-degrees to each other, as I believe you are also suggesting, can work very well, in-phase, as a bi-pole, as a natural null is created orthogonal to the mounting wall without requiring the out-of-phase cancellation of a dipole… but, that is only maintained down to the lowest frequency of waveguide pattern control, which is too high of a frequency unless very large waveguides are used.
There are a couple of other configurations that achieve dipole cancellation but for a single source device per room side, the other devices that are commonly known that work reasonably well are a floor to ceiling line source or a CBT based system, but these still should be used in multiples of at least two per wall if envelopment and lack of source detection are desired (There strength is that they are excellent at maintaining even SPL level across the listening area, left to right). Combining a line source and dipole can make for a best of both worlds device.
I apologize if I rambled more than what was requested with the question, but these few paragraphs just scratch the surface of the topic which has many factors to consider to approach the ideal result.