after looking through the list of econowave completed projects, it appears that most folks are using a traditional forward firing setup. parham, and later geddes as well as many others have suggested that the listening sweet spot can be widened by aiming the speakers to a point in front of a centrally located listener (the traditional sweet spot).
the zilchster brought to our attention jbl's use of asymmetrical horns that achieved a wide sweet spot by radiating more power to the listener sitting on the opposite side of the room, while radiating less power directly forward to the person sitting in front of the speaker. several reviews, including a couple really good ones linked over to the lansing heritage forum, as well as mr. zilchster's own reports are that the effect worked well.
since the benefits of having a wide sweet spot are numerous and include allowing multiple people in the same room to share the full econowave experience at the same time to not needing a center channel in order to locate sound accurately on the center of the screen for home theater, i have put together a few drawings that attempt to provide a setup/understanding guide for folks who might not understand how this works.
we have previously identified three requirements for good imaging. the sound from each speaker must arrive with the same:
1. frequency response
2. spl
3. time arrival
true controlled directivity horns such as the econowave do a pretty good job of minimizing reflections and providing a nice consistent frequency response off-axis from about 1khz up (the frequencies where imaging cues are particularly important) so go a long way toward achieving #1.
small differences in time arrival between the two speakers for a listener who is sitting off-axis may not be an issue because of the haas effect--the effect where sounds that arrive within about 15ms are combined by our brains into a single sound if they are the same in frequency response and to a lesser extent spl.
with the two other effects considered, the imaging game comes down to having the sound from the controlled directivity horns arrive at all listeners at the same spl.
this first diagram shows the radiated sound power from two forward firing econowaves. each oval represents declining sound power and it can be seen that it falls faster off-axis than on-axis.
listener a, the one centrally located, will have equal sound power arriving from each speaker and thus good imaging. listener b however receives a higher level of sound power from the speaker on the right (the one located in front of him). the blue arrow shows that sound power will fall before reaching listener b. thus listener b will not share in econowave's imaging potential.
in the second picture, the speakers are toed in at about 45 degrees. the sound power for listener a and listener b is almost identical, so both listeners will be able to share the full econowave imaging potential.
in the third picture, the speakers are moved a little bit closer to the listeners and toed-in further in order to maximize the sweet spot. the dotted black represents the region where listeners will all receive about identical spl and so will have great imaging. this setup is conceptually close to what jbl did with its asymmetric horns.
finally, another strategy that can be employed in the placement of econowaves can solve situations where speakers must be placed in non-symmetric locations or with a goal in mind of moving the sweet spot around the room to accomodate as many listeners as possible.
the important thing to know is that this strategy only works for speakers, such as the econowave, that have off-axis sound that is spectrally similar to the on-axis sound. with a little bit of experimentation in placement, the sweet spot can be widened or, with asymmetric placement of the speakers, the sweet spot can even be moved forward and backward in the room.
these drawings are not to scale and are meant only to serve as inspiration for experimentation in placement.
My order is placed and I shoud be EconoWave'n next week if all goes well.
