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Corners and frequencies [message #78646] Fri, 13 December 2013 11:17 Go to next message
Skip Pack is currently offline  Skip Pack
Messages: 46
Registered: May 2009
Location: Hollister, California
Baron
Wayne,

I'm slowly but steadily building a home theater room (with an emphasis on music quality) in a metal building, and I'm within 1-3 months from completion. The corners will be available, so your work comes immediately to mind. If you were to put 2Pi speakers all the way back into a corner, could you count on 90 degree lateral control. The midwoof would naturally start to narrow, but how much of that would be ameliorated if you extended the front baffle to the corner walls?

Thanks,

Skip
Re: Corners and frequencies [message #78648 is a reply to message #78646] Fri, 13 December 2013 11:41 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17659
Registered: January 2001
Illuminati (33rd Degree)

Honestly, I'd not use a two π loudspeaker in a corner, because it wasn't designed for that and won't take advantage of it. I'd use a constant directivity cornerhorn instead. So my suggestion is to consider a six π, seven π or eight π loudspeaker, because being constant directivity cornerhorns, they make the best use of corner placement.

The eight π speaker uses the same woofer as the two π model, so that might be a cool option for you. Or step up to the fully upgraded six π or seven π cornerhorns, which offer smoother response and lower distortion by using better drivers. Lots of choices there, but do take advantage of the π constant directivity cornerhorn design, since you have the corners.

Re: Corners and frequencies [message #78649 is a reply to message #78648] Fri, 13 December 2013 14:23 Go to previous messageGo to next message
Skip Pack is currently offline  Skip Pack
Messages: 46
Registered: May 2009
Location: Hollister, California
Baron
Pretty much what I had expected, but I was curious about the degree to which a corner could widen the directivity of a midwoofer (facing outwards) when the frequency rises to that range where it starts to narrow in a (non-horn) enclosure out in the room. My use of the 2Pi example was more to pose the question than an expectation that it might sort-of work.

A second relevant issue is that I would think you would want to have the mid and high range sound coming out of the corner at mid-screen height. If you were to raise the entire 6Pi or 7Pi unit several feet, you would change the 3-surface corner loading of the low frequencies. Would it make sense to build two low-frequency boxes for each corner with one on the floor, driver in the low position, and the other in normal configuration elevated so the midhorn is at, say 60-70 inches?

Thanks,

Skip
Re: Corners and frequencies [message #78652 is a reply to message #78649] Fri, 13 December 2013 21:25 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 17659
Registered: January 2001
Illuminati (33rd Degree)

I've designed constant directivity cornerhorns for over three decades, and the current configuration is the best I've come up with. There are a handful of competing priorities, some that you've mentioned like listener height and others too, like acoustic distance from the boundaries. That's probably the biggest issue - The source must be acoustically close to the apex of the corner or it becomes a reflector.

If the source is directional, it can help mitigate nearest boundary reflections because the amplitude of sound radiated towards them is reduced. But at low frequencies, a horn cannot reasonably be made large enough to provide directional control. This is where the constant directivity cornerhorn approach gets its strength - the walls of the corner provide directional control all the way down to the Schroeder frequency. They're like a ground plane, and being acoustically close, the low and lower midrange frequencies are contained without suffering self-interference.

The best thing is to be acoustically close to the tridedral junction at the apex of the corner, of course. The next best thing, if not apex of all three boundaries, is to be at least acoustically close to the dihedral junction of the two adjacent walls. And finally, if acoustically distant, then having a source that's directional helps a great deal at limiting the reflections from nearest boundaries.

The design philosophy of the π constant directivity cornerhorn balances these priorities. The lowest frequencies up through the lower midrange are acoustically close to the apex of the corner. In order to keep the important midrange and treble frequencies at listener ear height, the midhorn and tweeter are raised above the lower corner apex, and so as wavelengths grow shorter (as frequency rises) the lower midrange transitions from being acoustically close to the apex to only being acoustically close to the two adjacent walls. But the woofer and midrange overlap in this region, so they smooth any vertical modes similarly to the way flanking subs work, as a truncated array. And being acoustically close to the two adjacent walls prevents anomalies from self-interference from them, which is the most important thing anyway.

As frequency rises further, into the upper midrange and treble, the horns provide ample directivity control to keep the beam within the wall angle. This doesn't prevent all energy from radiating towards the walls, of course, but what remains is highly attenuated. It is also at a grazing angle which does not reflect towards the listening area, and pretty much stays along the wall. So only people sitting very near the wall would be able to hear that reflection. This makes the whole room be "the sweet spot" except right up against the walls.

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