In front of or behind the speaker if we are talking side wall? What do we do with the ceiling?
Heights recommended? Bare? Diffuse? Doubt absorption unless you have a very low ceiling height. Most ceilings are 8 ft as it will be at RMAF. Mine are 10.5-11 ft.
Without disclosing the specific drivers, can you tell us size and arrangement? Is it a quad array?
I'm reading that the efficiency into 2.83V is variable with a passive level control in the signal path between high 80's and low 90's. Bandwidth and impedance variation over what bandwidth? I figure impedance will have to be consistently high for this to work electrically.
Good questions!
We definitely want the Space Generators behind the main speakers.
As long as the ceiling isn't deliberately absorptive, we should be in good shape with the range of tonal adjustability the speaker has.
I don't yet know whether diffusion or reflection works best, as I haven't tried them in a room with good diffusion on the nearby room surfaces. Ceilings up to 16 feet tall work fine, and I haven't tried it low-ceiling rooms, but should still work as the 10 milliseconds Earl likes between the direct and reflected sound isn't a hard boundary but rather a fuzzy transition zone. [That's not meant to imply that Earl would agree with what I'm doing - I'm pretty sure he wouldn't - but he is one of my sources of information.]
The driver is a 10" coaxial. That seemed the way to shoehorn the most radiation pattern control into the target 12" square footprint.
Bandwidth is 60 Hz to about 18 kHz. The attenuation is purely in the form of series resistance, so I had to keep the impedance curve smooth so the frequency response isn't modulated by the level control. It tracks quite well as we go from 88 down to 78 dB voltage sensitivity (you want the Space Generators to be several decibels down in volume relative to the mains). I'm using an acoustic filter inside the box to deal with the impedance peak at system resonance. It's not unlike something one might use for targeting a pervasive bass peak in a room, but on a smaller scale.
You certainly have your work cut out for you overturning the conventional wisdom of the less in the signal path is better mentality. Sounds to me like one of those headphone switches to add reverb to the sound stage for loudspeakers. Like what Headroom used to manufacture. Good luck!
Originally I delved into polydirectional speakers (bipolars) as a means of getting the basics right - specifically, tonal balance. The relatively poor spectral balance of most speakers' off-axis energy is arguably detrimental to their typically rather good direct sound. So if we can significantly improve the spectral balance of the off-axis energy by pulling it in the right direction, we're probably going to improve the speaker. That's where the rather wide range of tonal adjustability of the Space Generators can come in handy - a slightly tipped-up balance can be dialed in to compensate for the rolled-off top end of most speakers' off-axis response.
Anyway in the course of working with the Late Ceiling Splash concept, the increase in apparent room size stood out as perhaps more beneficial than the improvement in timbre. So that's what I'm putting the spotlight on.
I don't think what I'm doing with the Space Generators would appeal to the engineer in a recording studio, but it might appeal to a fair number of music lovers. I may send a pair out on "tour" for people to try in their systems.
When I remembered to ask people whether they felt like they were hearing "more of the recording" or "more of the hotel room" with the Space Generators engaged, everyone who responded said "more of the recording". That's not a scientific survey, but agrees with Toole's findings that the ear/brain system can better decipher complex sounds when it gets multiple "looks" via spectrally-correct reflections.
But you are right that it will be an uphill battle. All of the worthwhile ones are!
Kind of reminds me of Winslow Burhoe's Silent Speakers, and a couple of his EPI designs.
http://directacoustics.com
...Same base principal but in a unique application.
Is it "purist?" Maybe not. But no one lives in an anechoic chamber. I like seeing creative solutions to the room problem. I can see where something like this could be better or more enjoyable on many levels than dealing with (intrusively large and often ugly) room treatments.
The difference is, the Space Generators are meant solely for use as secondary speakers. They sound decent as main speakers, but more like for background listening, as their first-arrival sound is weak and not well differentiated from the subsequent reflections in that role.
When acousticians studied what the difference is between a good seat and a poor seat in a concert hall, here is what they found: A good seal has a clear first-arrival sound, and then after some delay, a good reverberant sound. In a poor seat, the two run together too much. My theory is that most speakers can be positioned to give a good first arrival sound, with a reasonably long delay before the reflections come in strong, but that the reverberant field is inadequate in most rooms, in quality if not in quantity. We lose liveliness when the two are not well differentiated, and by making the onset of reflections a more pronounced event in many systems, I think the Space Generators will improve liveliness.
Now we don't want too much reverberant energy either, there's a "goldilocks zone" that will vary with the specifics of speakers, room, speaker locations, and listener locations. But such variables are already in play, and I think the Space Generators are a tool that can move the reverberant field in the right direction for most systems.
