[Letitroll98]

Well, it basically evolves from the work of Toole (see his book) and Geddes.  The idea is that the sound one hears is a lot more than just the directly radiated sound.  The spectrum of all the reflections greatly influences the tonal balance. 

It is not enough to have flat on axis response and actually that is less important.  Its about the power response, or frequency response over the entire radiating angle of the speaker that matters since that is what is influencing all the in room sound.

One way to go about an even power response is omni-directional speakers.  However, Toole and Geddes both argue against such.  The reason is all the early reflections are destructive to the way we hear.  Our hearing is quite apt at seperating late reflections from direct sound but not so well at seperating direct from early reflections.  So the idea is to narrow the radiating angle and keep the power response smooth in that angle.

Well I understand the theory for one listening position (or maybe I don't), how does CD work for the multiple seating positions of HT setups?  Regardless of the errors with in room frequency response that are fixed with CD speakers, doesn't imaging for multiple listeners suffer? 
(And please, it's a question that I want a answer to, not baiting or anything.  Sometimes one must make this clear when you can't hear the inflection in my voice)

[satfrat]

My plan is to set up a 2.x HT system (x because its either 3 or 4 subs, depends on what works) using the Abbeys and then add surrounds.   My priority is concert DVDs, as I still feel surround for movies is more of a gee-whiz factor, but it comes as a freebie. 

Any other good ideas that I should look at?  What are the rest of you guys using, particularly the ones with Geddes or similar concept mains?

Josh, I don't know what you have as a cable source but DirecTv has more and more concerts that are broadcast in Dolby Digital. Palladia also routinely has Dolby Digital concerts also. IMHO, the only way to truely appreciate these concerts is with a 5.x system. Compromising the Dolby Digital surround field just doesn't sound right if any of the 5 speakers are missing, like say using a "phantom" center, hense my basic disagreement with your gee-whizz comment as far as Dolby Digital concert reproduction is concerned (movies, I hear your point  ). I'm also a believer of the standard surround practice that all 5 speakers should be the same so the tonal balance isn't compromised.
 
Other than that, I got nuthin'.    Be well & prosper.
 
Cheers,
Robin

[JoshK]

Well I understand the theory for one listening position (or maybe I don't), how does CD work for the multiple seating positions of HT setups?  Regardless of the errors with in room frequency response that are fixed with CD speakers, doesn't imaging for multiple listeners suffer? 

Well again, I don't profess to be an expert.  I haven't read Toole's book yet, nor Geddes'.  That said...

Because radiation is even over a larger angle than a typical speaker, high frequencies are more balanced in amplitude as the listener moves side to side.  Sketching a diagraphm on paper might help you see why.  This makes imaging more balanced from outside of the sweet spot. 

There is actually two things going on here based on the geometry of two speakers and a listener moving side to side.  One is the distance the listener is from each speaker.  The listener's ears detect the differences in magnitude based on relative distances to determine where the source is located.  This works for either type of speakers.  The other thing is as the listener moves off axis he is changing the off axis listening angle of each speaker.  If the speaker is not CD then the magnitude of each speaker changes relative to one another and destorts the imaging off axis.  With CD speakers, this is largely mitigated. 

[Letitroll98]

Thanks Josh, I've been reading up on some comments from Geddes work, not the original paper but his comments on it, and found the major thing I was missing.  I had been following the "45 degree" toe in comments and assumed they meant pointed directly at the listener's position, which would cause major changes in imaging when moving out of the sweet spot.  Now I see the positioning is intended to cross several feet in front of the main listening position, this is a technique I've been familiar with for many years in HT setups to compensate for not having a center channel.  I assume the surrounds follow the same positioning rules. 

Still quite a departure from the dipole, bipole, and multi sided surrounds we've been using for years.  Now that I've got the main speakers down, perhaps someone can explain the advantages of CD surrounds over the aforementioned options.  I think I've got the theory down now, how do CD surrounds sound compared to the omnidirectional options, what are the real world advantages.

As an aside, hopefully not to hijack the thread, I'll repost a new thread if it goes anywhere, but wouldn't flat panel planar speakers like Maggies be the ultimate CD speaker?  I mean no wave guide is needed, they beam all of their frequencies, top to bottom.  Maybe I should post a new thread, but where?  Here or the planar circle, (quandaries, quandaries).

[JoshK]

As an aside, hopefully not to hijack the thread, I'll repost a new thread if it goes anywhere, but wouldn't flat panel planar speakers like Maggies be the ultimate CD speaker?  I mean no wave guide is needed, they beam all of their frequencies, top to bottom.  Maybe I should post a new thread, but where?  Here or the planar circle, (quandaries, quandaries).

I think you are starting to get it.   No planars are actually not CD at all.  They beam more and more at higher frequencies (not at all frequencies they just start beaming earlier) just like traditional non CD speakers.  Its wavelength dependent just like normal speakers. 

Use of CD surrounds in principal is about keeping the same spectral balance in the reflections as in the direct radiation, same as with the mains.  I haven't really pondered it much but the off axis amplitude consistency would also be a benefit I guess. 

[JoshK]

P.S. its no problem with hijacking the thread as the original topic was answered to my satisfaction as I ordered parts to build econowave 10e's. 

[youngho]

Unfortunately, planar speakers are not truly dipoles at all frequencies and instead tend to have very ragged off-axis response. You can see this in the Stereophile measurements of some Magnepan and Quad speakers.

I would imagine that CD surrounds could be a little tricky, depending on the room. You would want them angled to cross behind the central listening position. The potential real-world advantage would be the same as for the front speakers, which would be the fall-off in response as one moves closer to the proximal speaker but further off-axis. The problem with conventional surrounds is that the closer speaker is louder than the farther one. Toole discusses the use of full (not truncated) arrays as another potential alternative allowing for reduced fall-off with distance.

Josh, as I recall, it's actually a combination of on-axis response, sound power, and bass extension that seems to matter, though more complicated than that when comparing speakers of similar bass response.