Because you hear the entire direct sound field, though as you move toward your (forward) axis, there is increasingly greater significance placed within that horizontal and vertical axis "range".
Ex. say you have a vertically flat on axis with increasing pressure ABOVE that forward axis - result: it "pulls" the image vertically, placing "images" higher in the soundstage and/or "stretching" those images vertically. Note that diffraction sources can mess with this effect.
Remember, direct sound dominates, and for image placement cues intensity and freq.s from 500-7kHz dominate. There is also a vertical effect region that varies among individuals in the 7 to 9 kHz region.
I should also note that in a theater context your side channels generally provide this vertical effect, even still - Dolby is starting to add vertical effects channels for the L/R channels in newer theaters.
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What I'm trying to say is that the literature I've read in JAES, as I understand it summarizes to this:
With an average listening room and a speaker that has a wide angel of dispersion (take a stand mount small monitor speaker) the general preference is for speakers who's off axis response is similar to the on-axis response, and a gradually increasing directivity.
As the listening room gets more absorbtive and or diffractive, the ability for the speaker to have variations in the off axis response becomes a bit wider, since the resultant reflections won't be as loud and intrusive when they get to the listener. (They've been absorbed and/or diffracted. )
Floyd Toole really has done the most research on this. I would point you to:
“Subjective Measurements of Loudspeaker Sound Quality and Listener
Preferences,” J. Audio Eng. Soc., 33, pp. 2–31.
“Loudspeaker Measurements and Their Relationship to Listener Preferences,”
J. Audio Eng. Soc., 34, pt. 1, pp. 227–235; pt. 2, pp. 323–348.
Keep in mind this work was done long before the Synergy design was even remotely an option. The one point source device they tried was a Tannoy coaxial unit that has issues with resonances in the tweeter and varying directivity over its range.
Scott
Member
Joined 2003
-though I might further refine this for stereo and say that:
Stereo (2-channel loudspeakers in a domestic room with decent placement in-room - notably a meter a more away from room walls),
..should have a dispersion character almost inverse to that of most loudspeakers:
No/Low directivity as freq.s increase and Increasing/High directivity as freq.s decrease,
..and this is despite the fact that the room swamps the freq. response with modes at lower freq.s - seemingly removing directivity at those low freq.s.
I was being facetious when I brought up the 180 degree horn, but now I'm actually kind of considering it.
Specifically, I'm considering a wide baffle of more than 2 feet across placed directly on the wall, but angled. (See attached picture). The speakers would be triangular prisms (with a triangular base). The speaker depth would be small: half the baffle width or less. As a result, the depth would be small compared to the wavelength of frequencies that wrap around the baffle; resulting in minimal ripple from the reflection off the front wall (to the outside of the speakers). I'm really not sure how bad the front wall reflection (to the inside of the speakers) would be with such a narrow angle between the baffle and the wall. I suppose some mid/high frequency treatment might be in order. Don't corner horns use the room walls to extend the horn in a sense? What's been done there?
At any rate, if the vertical arrays null the first floor and ceiling reflections, and if the front wall is managed as described above, that seems like a good starting point for any room treatments and/or EQ. It seems there is almost a consensus that the lateral wall reflections are preferred, anyway, so preserving them might be a benefit of this approach.
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It is difficult to get HF drivers close enough into a corner to survive the jump off unscathed. That is assuming you start with directivity matching the walls, and it is probably best to give it space to let you diffract it cleanly. It is easier at lower frequencies, and easier if you can mount the drivers behind the wall.
Great Thread!
We do not all agree on what directivity is optimal. It seems to be at least partially dependent on a few factors such as genre, room size, room treatment, SPL, listening distance, qty of speakers (surround) etc.
No single speaker design that I know can satisfy everyone. If ideal refers to the best compromise, some will still consider such a speaker as inferior compared to a design targeting different goals optimized for the target sound.
Determine what you prefer, buy it or build it! cheers
We do not all agree on what directivity is optimal. It seems to be at least partially dependent on a few factors such as genre, room size, room treatment, SPL, listening distance, qty of speakers (surround) etc.
No single speaker design that I know can satisfy everyone. If ideal refers to the best compromise, some will still consider such a speaker as inferior compared to a design targeting different goals optimized for the target sound.
Determine what you prefer, buy it or build it! cheers
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