Wondering what distance you guys have decided on as far as distance between speakers in relation to distance to main listening position ? I have played with this for literally hours and hours. I have come to find for me at least a spot on equilateral triangle with toe in 6 inches outside either shoulder is where everything comes alive with seamless enveloping soundstage. I have used my laser pointer to achieve this, would be so much harder with a tape measure.
Here is a very interesting FAQ response to ideal dipole setup from the Linkwitz website:
Q31 - Is there an optimum room placement for a dipole?
A31 - Yes, there is, from a sound reflection and also from a standing wave point of view. Both are a consequence of the figure-of-eight or cos(angle) free-space polar response of a dipole with its opposite phase front and rear radiation and very low output at 90 degrees off-axis.
Assume the dipole speaker is placed at the same distance from the front wall as the listener has to the wall behind him. The negative polarity sound from the dipole's backside is reflected off the wall behind it towards the listener. The sound from the front side of the dipole travels directly to the listener and also to the wall behind him where it is reflected back towards him. The rear wall reflection reaches the listener at the same time as the reflection off the wall behind the speaker. The two reflected sounds have traveled the same total distance for this particular speaker and listener setup. The two reflections cancel each other, because they are of opposite polarity. (Jorma Salmi, "Dipole source placement in a room", 92nd AES Convention, 1992, Preprint 3327)
A diagram helps to clarify the case. It shows the plan view of a rectangular room with dipole D and listener L. The four hard room boundaries can be removed and replaced by four image sources D1 through D4. The special setup, where a = b, does not help with reflections 3 and 4 off the side walls. Moving the speaker away from the side wall reduces the strength of the reflection, because the radiation goes to an angle where the dipole output is attenuated relative to the on-axis level. In practice it may be difficult to move the speakers far enough into the room to satisfy a = b, but keeping them at least 1 m (3 ft) from the rear wall is recommended.
Occasionally a cardioid free-space radiation pattern is suggested for a speaker, because it would radiate, like a dipole, 4.8 dB less power than a monopole for the same on-axis SPL. Unlike a dipole, the cardioid radiates weakly towards the rear. Thus, there is little reflection off the wall behind it. But, there is no cancellation when a = b. In addition there will be stronger reflections off side walls, floor and ceiling.
It is important to understand that the discussion up to this point has only dealt with the first reflection off a single room boundary. The next order of reflections involves both front and rear walls and the image model would have to be expanded with additional sources. Successive reflections always occur and they lead to the gradual build up of stored energy in the form of room resonances or modes. Thus the cardioid speaker, even though it does not radiate towards the rear, excites a strong longitudinal mode between front and rear walls, similar to the dipole. The dipole, though, excites side-to-side and floor-to-ceiling modes only weakly, because they propagate along the null-axis of its radiation pattern. Furthermore, by angling the dipole its coupling to specific modes can be changed, whereas cardioid rotation has considerably less effect.
The cardioid radiation pattern is the sum of a dipole and a monopole and its in-room behavior lies between the two constituent types of sources. It has the reduced total power output of the dipole into the reverberant field above the Schroeder frequency. It lacks in adjustability of coupling in the discrete mode frequency range where it behaves more similar to the monopole. The low frequency response rolls off at 6 dB/oct like for a dipole and has to be equalized. Unlike monopole and dipole the cardioid produces no first order reflection from the wall behind it.
The dipole has minimum room mode excitation when it is placed near a pressure maximum (= velocity minimum) of a mode and when its axis of radiation is not aligned with the direction in which the mode travels. Pressure maxima are at the room boundaries and room corners. A dipole woofer should be placed near the side walls, provided the distance from woofer to listener is nearly the same as that from the midrange. Again, most likely practical limitations will have to guide best dipole speaker placement for room modes as well as for first reflections off room boundaries.
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