1. I actually did that with the home theater tech when I moved in and there was no furniture in the room yet. There was almost no echo. The pine walls don't seem to reflect sound a lot. The rooms with drywall had a lot more echo. With furniture and a rug on the floor, it's a very good sounding room.
2. My understanding is that bipole speakers are often used in theaters on the sides to fill in non-directional sound to extend the sound field. The point in mentioning bipole speakers as opposed to horn loaded speakers is that directional sound creates a quite different impression on the listener than diffuse sound. It's more than just horn resonances. It's like the difference between a spotlight and diffused lighting. When we turn our head, we can sense the directionality, the same way we see sharp shadows caused by a spotlight. I guess I would describe the difference as "presence".
3. When I read about speakers, it seems the goal is an even dispersed coverage of the soundstage with all the speakers matching. But with a multiple speaker / multiple channel system, every speaker in the system doesn't have to have the same sort of sound dispersion pattern. That's an interesting thing to experiment with. I've tried to create two soundstages on top of each other... one dispersed for even coverage, and one directional to strengthen the stereo separation at the far right and left, and dialogue/vocal channel in the middle.
4. I'm interested to hear if any other systems have interesting theories about contrasting directional and diffuse sound. 5. (Open baffle speakers are definitely interesting to me.)
1. The amount of "echo" (actually reverberation) is not related to the difference in drywall vs wood. Both have roughly the same coefficient of absorption. But drywall walls tend to be very flat, and rooms are often closed boxes and rectangles. Parallel surfaces tend to reflect sound back and forth a lot, and the reverb time in those spaces is longer. Until you add the same carpet and furniture, at which point regardless of wood or drywall you'd end up at the same result if the surfaces are the same. You didn't hear echos because any secondary arrival from a reflection within the first 30ms is integrated by human hearing into the direct sound (Haas or Precedence Effect). But those reflections also mess with the ability of a system to create high quality phantom images.
2. Bipole speakers are not used in commercial theaters. Dipole surround speakers were part of the original Home THX specification, now THX Ultra2 (and now includes Tripoles). The goal was to present a diffuse surround field in a smaller home theater that closely approximates the multiple surround speakers in a commercial cinema, which may us up to 20, but likely at least 10. Multiple speakers in a big space create a diffused surround field that is deliberately not intended to precisely localize. This was a problem in the home because typically there are only two speakers, which are obviously localized. Using a dipole with the null pointed at the LP presents a difficult to localize soundfield in a small space from only two speakers. Additionally the THX spec requires flat off-axis power response of those dipoles. In later developments it was found that the null could be slightly filled in with a third HF driver creating a "tri-pole" configuration which created a somewhat less ambiguous, more easily localized surround speaker. Some tripoles have a switch for dipole/tripole. The bipole is a bit of an anomaly, and was likely created to mimic a dipole without violating patents.
Yes, the presentation from a dipole is very different from all direct radiating speakers, but that is the intention driven by the application.
3. In the ideal configuration the LCR speakers should match in every way, including dispersion. Equally important, the acoustic space around and near to the speakers should also be as identical as possible.
There are two generalized applications of surround sound, film and music. All 5.1 film mixes assume a diffuse multi-speaker surround system, which dipoles mimic in small rooms. Within music there are mixes intended for direct radiating speakers, and mixes intended for diffused field/dipole speakers. Both can work, but the "in the band" perspective works best with direct radiating surround speakers, and they should ideally be identical the the LCRs in that application. But that's a very specific surround mix configuration, the "band on stage" surround perspective mix works just fine with all types of surround speakers, best on dipoles.
4. There have been many speaker designs that were bipolar and dipolar, as will as omnidirectional (or at least toroidal), most had the intention of creating a very large sounding feel by using all surfaces in the room as reflectors. They do sound big! Everything becomes spacious and very ambiguous. But they also are terrible at creating a palpable phantom image. The requirements to do that are directly opposite of those speaker designs. What works for good imaging are direct radiating speakers either designed to control dispersion and keep reflections off walls, ceilings and floors, or less directive speakers (with better sound, most likely) placed in spaces that have had reflections treated.
An interesting thing happens in a treated space. You might expect it to be dry, two-dimensional and a bit flat. The exact opposite occurs, you get a bigger presentation, solid phantom images, and other phantom directional cues like height and depth begin to appear. Current understanding seems to indicate not a completely dry treated room, but one with some reflections, just not a lot of strong early ones.
