Originally Posted by niterida
I just tried bipolar in place of my direct firing surrounds.
Note that my surrounds are about 10deg in front of MLP so the seat closest is about 30deg off-axis which I found helps to remove hot-spotting anyway.
Your surround speakers are "in front of" your MLP? That's slightly unusual. They're normally directly to the side (typical of 7.1) or 10-20 degrees behind the MLP (typical of 5.1), although the room plays a big part in the decision. There are some famous speaker designers that prefer them in front of instead of behind, though.
Originally Posted by niterida
I put the bipolar at 90deg and same height as the direct firing surrounds. I didn't try them at different azimuth since I imagine you would lose the bipole effect.
I tested them with Kraftwerk Atmos bluray and you clearly lost track of the pinpoint sound darting around the room in track 3.
I think part of the problem may be in how they are being used. Dipoles were commonly used with the null area directly to the sides to create more ambience (hard to locate speakers effect). Bipoles used that way with no drivers facing towards the seating do it to a lesser degree and image somewhat more like direct drivers. Used this way, bipoles are kind of a halfway solution between the old Pro Logic recommendations for dipoles and 5.1 imaging that needed more precision and works well in the old 5.1 only surround setups, IMO (My first 5.1 system used this). It's not as dispersed as a dipole, but not as pin-point as a direct firing radiator, which is what I believe you are describing here. It's probably not the best choice for Atmos, however as more precision is needed, particularly with more speakers available with overhead and/or rear surrounds in use).
Bipoles used between rows with partially angled drivers (typically not front/back, but angled 30-40 degrees into the room towards rows in front of or behind the speaker) act like two sets of closely arrayed monopoles (sound similar to direct drivers, but get rid of the bad off-axis response when you only have ONE direct firing speaker which can only face one row of seats. By putting them between rows with two sets of angled drivers, you essentially get perfect on-axis response in both directions. This should sound almost identical to a direct firing speaker used that way. My side heights used as surround height for Auro-3D or DTS:X and "Top Middle" for Atmos are set up like this, placed between rows and directly in the middle of the room between both sets of front/rear height speakers. This sounds similar above as two sets of sides that are arrayed sound below. They image to the side the same as the front/rear heights image from those directions as they are really two arrayed direct radiators aimed like that. The rear wave from either direction acts more like the method below (i.e. a rear wave reverb-like reflection).
The other way to use bipoles (That Definitive Technology pushed along with Mirage and some others) is placing the front of the bipole speaker (drivers forward) in front of the MLP like a regular stereo speaker with the rear drivers facing the front (or rear if used in the back) walls. This requires the drivers be at least 12" from the wall with bipolar (or 3+ feet with dipolar) speakers. Used that way, they create an extra set of reflections that anchor the phantom images in space, creating a more "realistic" sounding phantom image (e.g. with my Carver Dipole Ribbons upstairs, a vocalist sounds like they're really in the room singing as opposed to a stereo "image" of someone singing, if you take my meaning). This is more of an ambient/spatial effect than any type of surround use, however.
In your case, if you orientated the bipoles such that one set of drivers faced directly towards the MLP, you'd get a much sharper imaged effect. But then it also matters whether the bipoles in question are at 180 degrees to each other (front/back like my old Definitive Tech BP2 speakers) or one of these side wall types that have them angled closer to 30/150. The former would work better angled towards you. The latter works better between rows of seats (or as a null directly to the side in old 5.1 systems only). This would be purely to salvage the speakers if you didn't want to buy another direct firing set or whatever.
Frankly, with one row of seating, you're probably better off with direct firing monopoles regardless as there's not much useful to do with the other set of drivers (save perhaps the front/back ambient usage which is hard to do from the side unless you have a very wide room that you can put the side surrounds 12 inches away from the side walls without being too close to the seating). I think the angled bipoles in an Atmos type system are only really appropriate between multiple rows of seating, which really just fix the off-axis response issue of having one speaker between rows facing neither row, although if the speaker has excellent off-axis response that can work instead.