Which is the best Guys,dipole or multiple monopole subs,too much tech jargon ,for us with limited tech knowledge,my opinion is the bass should be at the same loud level and spatial level as the other drivers...
A well set-up multiple monopole system does a very good job of having the same loudness level across the bass region. It also can have very good spatial level, with a little bit more cost and complexity.
But I would not try to tell someone what is "best" without knowing a lot about their situation, because what is best for them depends very much on the situation.
It seems like, based on this conversation if I'm reading it correctly, that the answer is actually a combination of the two. Assuming we're talking about a two-channel stereo setup, the ideal appears to be a pair of stereo subs (ideally cardioid in radiation pattern, although a dipole would seem a desirable second option due to similar pattern control improving issues dealing with room modes) playing down to roughly 40Hz. From there to as far down as one would like to go, the research AJ references suggests a distributed set of monopole subs (like Duke's swarm setup) is the way to go, as sound localization no longer stands as an issue.
My understanding is that, among recordings, there is a continuum that extends from "pure mono bass" (below say 100 Hz or so) to "true stereo bass", and that most recordings are pretty close to the "mono" end of this continuum, with classical music recordings most likely to be the exceptions. In other words, I think that most recordings have essentially mono bass, from a perceptual standpoint if not literally.
Now I don't think there is anything wrong with having a stereo subwoofer system, and about 1/4 to 1/3 of my Swarm customers use two amps, so they can either set them up for stereo, or use the Griesinger phase-quadrature configuration, or both.
I'm not ready to concede that a stereo pair of cardioid subs offers more than a minor spatial advantage over a stereo-configured four-piece Swarm-type system. And if the recording has insignificant stereo separation down low, then a two-amp phase-quadrature Griesinger setup would probably tip the scales in favor of the Swarm, because it would synthesize the sort of spatial impressions we get from good stereo bass. I believe Griesinger's word for it is "immersion".
Now if you are going to use stereo cardioid or dipole subs, then it may very well make sense to add a monopole sub for the very low frequencies. This may or may not correspond to the transition from the modal zone to the pressure zone - it may simply be a matter of not having the amplifier headroom and/or woofer excursion capability called for by the equalization that would be needed to extend the response low enough.
However if we are able to make the transition from dipole/cardioid to monopole in about the same frequency region as the transition from modal to pressure zone, we might be able to get away with just using a single monopole sub.
This combination of subs would theoretically present the smoothest, most even response below a frequency where spatial perception fails people, while maintaining proper stereo separation and imaging between there and up to where whatever chosen main speakers are in the system take over.
I think dipole/cardioid over most of the bass region + monopole (perhaps in multiples) down low would work very well.
The interesting wrinkle in bass management presented so far in this discussion suggests that between 130Hz and 40Hz-ish there is a great need for processing and EQ to make that range work well with the stereo pair of subs, but below that, saturation to even out room response through summed dissimilar sources is key to the exercise, with whatever little processing or EQ one chooses to do being mostly a function of calibrating the swarm of lowest frequency subs to most optimally compensate and correct for each other.
This is an area where multiple monopole subs, with one in reverse polarity, does well: Very good results are not limited to the few with powerful measurement and signal processing capability. One of my Swarm customers has a very powerful Meridian processor that he had had a technician calibrate for his system previously. When he got the Swarm, he set it up according to my guidelines, reset all the filters in the Meridian processor to "flat", and called in the technician to fine-tune the system. The ONLY thing the technician did to the Swarm was, tweak the level - no EQ was needed! Quoting now from his e-mail:
"... The other big change I made was replacing my single [competitor's sub] with your AudioKinesis Swarm asymmetric four-subwoofer array this past summer. Results - unbelievable bass with no suckout anywhere in the room !
"The MRC program can insert up to 60 digital filters between ~10hz and 250 hz to eliminate the dominant room resonant nodes. The previous calibration resulted in 16 filters distributed across 5.1 speakers, (the left and right Vandersteen Quatro Woods, VCC-5 center channel, the two VSM-1 surround speakers, and the [competitor's subwoofer]. The VCC and the two VSM's were crossed over at 80 hz, while the Quatros were set for full range. The speakers are in a 16' wide by 22' deep symmetric room using the ITU 5.1 placement standard). With your Swarm taking the place of the [other sub], the MRC only inserted 2 filters - one for each VSM-1 ! (I think this may due to their proximity to the ceiling corners in the back of the room.) The Quatro Wood 11-band analog equalizers were set flat, and the Meridian processor left them that way.
"The asymmetric Swarm array works so well that the only "calibration" really required is for level. (We were able to get every speaker within 1/2 dB, prior to the processor burst noise sequence and resultant filter build). It has rendered both the MRC and Vandersteen's analog equalizers unnecessary for my room
[emphasis in the original].
After reading Earl Geddes and Fred Toole's papers, I knew it would force the room nodal distribution to be inherently flatter, but I had no idea how much improvement was going to occur.
"The tech., who has performed dozens of these calibrations, said he has never seen anything like this. The room is rendered literally flat in frequency response and spatial energy distribution - sonically the room disappears. We played one of Kal Rubinson's recommended demo discs, the 100th anniversary for the San Francisco Symphony Orchestra using the John Adams piece, "Short Ride on a Fast Machine", and you would swear you were in the hall. You can "feel" the ripple in the tympani skins ! Very impressive."
In other words, zero equalization was needed to achieve results that the technician felt could not be improved on by using the Meridian processor's filters. All he did was correct the gain setting on the Swarm amp. I'm not saying that you can't get equal or better results with a more complicated cardioid/monopole hybrid system, but it's probably going to be a lot harder to get dialed in.
Returning to the spatial issue for a moment - in my opinion there is a LOT more spatial information that can be made good use of north of 100 Hz. But that's another thread for another day.