Originally Posted by bossobass
I posted several years back measurements with and without a top plate. It showed +1dB average across the BW more output and less 2HD by somewhat lessening the asymmetry from the air spring of a small box. Multiplied by 4 boxes (at the time), it was a healthy improvement.
Interesting, ... always contemplated the asymmetry, however anyone addressing it like that I'd never considered.
Originally Posted by bossobass
This idea I got about 2-1/2 years ago of going vertical was to accomplish several goals that are out of the scope of multiple placements on the floor.
1) To eliminate the typical peak/null (depending on where you sit in the room) caused by the floor-to-ceiling standing wave, 2) to explore the results of facing 2 identical and identically powered drivers, 3) to be able to place serious fire power in a tiny footprint and, 4) to see if the theory of adding a 4th virtual point source (the ceiling) had any veracity.
The null at 73 Hz, which perfectly matches my floor-to-ceiling dimension times 2, goes from -30dB to perfectly flat. The overalll FR from 1 module to 4 modules goes from (+/-) 21dB to (+/-) 8dB, all in a footprint of 2.75 square feet.
Bosso, good stuff and it's odd more attention/comments aren't paid to such a post. I've been performing a lot of acoustic experiments as of late and it really surprises me a contribution like that doesn't elicit a stronger response.
I'd like to elaborate on what you've shared, as I understand it,...and perhaps more will pile on and others will share their experiences.
Clearly, what you've shared with us plainly shows the benefits spreading subs across a particular axis of a room. More specifically, by placing LF sources on either side of a pressure minima, significantly helps to mitigate potential issues with axial modes in the direction of choice. When considering room modes, axial modes are the most significant. Addressing these issues by utilizing careful sub spacing, etc., can pay big dividends toward response smoothing and potentially restoring any lost impact due to the associated nulls.
In a typical room, by simply placing a single sub on each side, left and right,
addresses response issues that direction. A front and back placement minimizes problems that may exist in that axis. And in this case, Bosso shows how to restore a frequency null, a fundamental null that could easily contain the all important "punch, impact, slam",...or whatever audio adjective dujour that you're prefer.
Sound has size. A room's acoustic energy behaves entirely differently dependent on the sound's wavelength size relative to the room. Above the transition frequency the acoustic energy and reflections function and can be modeled like light rays. However below the transition frequency, the sound propagates as a pressure wave. Thus in Bosso's example of vertical spaced subs, the pressurization exists simultaneously
, however spaced on each side of the pressure minima (null), and in opposite polarity
. This is key and instrumental to all the fundamentals that are oft cited in various white-papers etc, on minimizing response issues with a multi-sub approach of various types.
Imagine a median line, bisecting all three axis in the typical rectangular room. Halfway between the floor and ceiling, halfway between each sidewall, and finally one separating the space front to back. By employing subwoofer sources energizing each side of the median line, with an opposite polarity source, the null will not be energized because of their opposite polarity.
Regardless whether this exercise is done with subs vertically oriented, laterally across the room, or even two up front and two in the rear, the same effect occurs in typical rectangular rooms. At any given instant, the acoustic pressure on opposite sides of a standing wave null are opposite in polarity.
Bosso's single dual opposed
on the floor would excite all the height modes in the room. Simply placing another such sub in a symmetrical position on the other side of whichever median line he wishes, in this case the vertical, helps in eliminating nulls in that axial direction. The subs are are operating in phase with one another other, but the first and third order modes possess opposite polarities at the individual sub locations. This facilitates the subs to couple in a destructively with the odd-order modes, so those modal nulls just don't occur. Just the top and bottom subs function this way, and thus leave only one mode floor to ceiling. The icing on the cake is by employing the subs as he's done, with all the individual driver sources all spread across that axis, nicely resulting in a significant reduction of height modes.
Additionally, the simple elegance of the acoustic coupling of the sources is just fantastic. The dual opposed, round "Sono" style approach (I know a gross over simplification), allowing all the drive units so closely spaced and reinforced off the adjacent boundaries, has got to squeeze out every possible dB of energy due to lack of destructive SBIR interaction. Obviously not an issue in the bottom octaves, but I'd suspect as much physical phase coherence/signal alignment as possible certainly helps in this regard. I don't have them in front of me, but I do recall your ripple tank work exploring some of these issues IIRC.
Anyway, I appreciate you sharing and I hope there's more to come.
All the bestbtw pressurization polarity;
Typical floor sub;
sub on floor
Bosso's example;sub at ceiling (red)- +
sub on floor (black)
pretty sucky diagram, anyone interested further, there exists tons of good reading on various elements of this, let me know which aspect, I'll post up the pertinent work,...as I've got 'em all