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4 dual opposed SSD 15s - Page 4

post #91 of 199
Quote:
Originally Posted by bossobass View Post

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.

Here are the results of my preliminary test (there have been subsequent tests, but I ain't tellin' just yet):

I picked the worst corner in my 3500 cubes room. I placed a single dual opposed 2x15" module (slightly smaller than gpmbc used to prevent bottoming in a worse-case scenario) in that corner and calibrated. The mic was placed at the LP and not moved throughout the exercise.

Sine sweep from the LP, single module:


I then stacked a 2nd module. They're 8 ohm modules, so the 2 were wired to 4 ohms into the same amp, same calibration.

Sine sweep from the LP, stacked dual module:


I then stacked 2 more modules for a stack of 4 total. About 88" high. I set the bottom module on a circular piece of 3/4" MDF that was just large enough a diameter to catch the feet of the bottom module and leveled it. I did not secure the top plate to anything, so that the column was free-standing.

I wanted to, among the other things I listed, see if dual opposed was all I've cracked it up to be in that, had the stack vibrated at all, it would have easily walked off the MDF base and BAM! Disaster!

Sine sweep, 4 modules, 2-identical amplifiers into identical loads, calibrated the same:


The difference between the 1 module and the 2 module should be +6dB. The difference between the 1 module and the 4 module should be +12dB. Instead, taking into account the difference in frequency response, the average difference was +18dB.

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.

After days of playing bass-heavy movies at the systems limits... the stack did not budge 1 mm from it's original placement. Besides the fact that the test for stack stability was successful, that also means that when the floor rippled with high level ULF soundtrack pulses from the beginning of Star Trek, et al, it was strictly from the pressure wave and not the subs sending extraneous vibrations into the floor.

After placement and sine sweep measurements, I ran Audyssey:


Actually, all that was required was 2 PEQ filters to smooth the response. I personally don't much care for the way my version of Audyssey manipulates the signal, nor the huge boost it imposes on <25 Hz, so that's what I did and I shut Aud off.

The SSD drivers are well built overhungs for relatively cheap $$ (although the price has gone up about 15% since I bought them), the module size is quite small, the stack looks pretty cool and the results were very much as predicted for a pretty small penny.

here's a shot taken during the tests. The front panels were faced into the corner so we could have easy access to the terminals for wiring. [You can see the MDF base with one of the bottom modules feet right at the edge]:



Bosso

Were you running full range or with a crossover? I have had great success with stacking in the front corners, even better than 4 corner placement. My ceilings are short so I can only stack so many.
post #92 of 199
Thread Starter 
Thanks for that informative response Bosso. Before I went all in with this build, your floor to ceiling array and the smoothing of response was of huge interest. All I know is it can only get better so no regrets with the route I took
post #93 of 199
Quote:
Originally Posted by MKtheater View Post

Were you running full range or with a crossover? I have had great success with stacking in the front corners, even better than 4 corner placement. My ceilings are short so I can only stack so many.

All sweeps full range, with mains, crossed at 90 Hz.

Bosso
post #94 of 199
Thread Starter 
Bosso, will I benefit from putting a top on the woofer that's facing up to free air in my stack?
post #95 of 199
Quote:
Originally Posted by gpmbc View Post

Bosso, will I benefit from putting a top on the woofer that's facing up to free air in my stack?

In my experience, yes. But, it's one you have to experiment with. The benefits are not huge, but I squeeze every clean dB I can get out of a system and the top plate is a cheap step.

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.

Not a big in your case, but something fun to do down the road.

Bosso
post #96 of 199
Thread Starter 
Cool thx
post #97 of 199
Quote:
Originally Posted by bossobass View Post

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.

Bosso

Interesting, ... always contemplated the asymmetry, however anyone addressing it like that I'd never considered.




Quote:
Originally Posted by bossobass View Post

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

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 best



btw 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

Thanks
post #98 of 199
Thread Starter 
post #99 of 199
Quote:
Originally Posted by gpmbc View Post


Looking sharp!
post #100 of 199
Thread Starter 
Finally got around to painting and put on a 1/4" thick rubber gasket, plus an extra 16Oz of polyfil per enclosure. Thx Husker!
post #101 of 199
Very nice!!! Got any high-res pics??
post #102 of 199
Very good.

Now.... MOAR!!!
post #103 of 199
Thread Starter 
Quote:
Originally Posted by edoggrc51 View Post

Very nice!!! Got any high-res pics??

Don't wanna zoom in too close then you see the flaws lol. I'll see what I can do later when I get off work.
post #104 of 199
Thread Starter 
Quote:
Originally Posted by Scott Simonian View Post

Very good.

Now.... MOAR!!!

I thought about it, but even as is when I cranked them a few dbs above the front subs it sounds outta wack as in easier to localize. I think my fix would be to beef up the front subs but no lateral moves. Gotta at least double in displacement and need small enclosures. Right now I have 4 chase 18s up front. I haven't found the limits currently so more just for overhead.
post #105 of 199
Sorry. When I said, "MOAR!!!" I meant... I'd like to hear more about these. Your thoughts on the sound. SPL. Extension. Was it worth it? Are you happy?

The usual stuff that comes with a new build.

Do you plan on picking up one of Dave's EQ units or use something else for general shaping?
post #106 of 199
Thread Starter 
Gotcha! More on that note to come. I plan on picking up one of his signal shapers but he has been hard to get ahold of these days.
post #107 of 199
Thread Starter 
Legs on the cheap, simple and effective. Finally stacked up and back in place.

Attachment 244119



Attachment 244120



Attachment 244121



Attachment 244122
LL
LL
LL
LL
post #108 of 199
Looking Great gpmbc; hope you are pleased with your efforts here!

Larry
post #109 of 199
Is there any kind of rule of thumb about spacing between the drivers cone?

Excellent build BTW! I have followed this for a while. I wish I had room to do something like this.
post #110 of 199
Thread Starter 
Quote:
Originally Posted by 04FLHRCI View Post

Looking Great gpmbc; hope you are pleased with your efforts here!

Larry

Thx much appreciated!
post #111 of 199
Thread Starter 
Quote:
Originally Posted by filtor1 View Post

Is there any kind of rule of thumb about spacing between the drivers cone?

Excellent build BTW! I have followed this for a while. I wish I had room to do something like this.

I'm sure there is one but my first concern was just to make sure the cones don't hit each other. The spacing is about 3.25". It took me a lot longer than anticipated but now that all the kinks have been worked out it would be so much easier if I were doing it again.
post #112 of 199
Looks great now! Are those legs merely small sections of pipe or something? How are they secured, if at all?
post #113 of 199
Thread Starter 
Thx! They are couplers used for plumbing. They were supposed to be just a quick fix cause I needed my theater up and running today - hosting UFC. They are not secured at all, and now that they are in place I have no desire for something more elaborate. In place, they look better than I expected and they serve the purpose without issue.
post #114 of 199
That's cool, and a good, cheap solution. I imagine they're a bit slick, so to just give a little extra piece of mind, have you thought about coating the ends with some type of non-volatile rubberizing compound so a bump won't slide them out of place and cause a stack collapse?
post #115 of 199
Thread Starter 
I haven't but I just might, thx.
post #116 of 199
Those are 4" schedule 40 pvc plumbing couplings, right? Those things will hold a _lot_ of weight - in the 800-1000lbs range for four.
post #117 of 199
Thread Starter 
3" and they definitely feel sturdy. Weight on top helps for sure.
post #118 of 199
Sorry but did Dave mention the price on the signal shaper?
post #119 of 199
Regarding the gap information between drivers, drivers and plates,..... I remember seeing this info at The Cult. I'm unsure how accurate, and equally unsure of the ill effects, however Collo's gap calculations call for this per driver;

gap = nominal diameter / 4 for most drivers
gap = nominal diameter / 3 for high excursion drivers



10"-----normal driver, 2.5"-----high excursion driver, 3.4"
12"-----normal driver, 3.0"-----high excursion driver, 4.0"
15"-----normal driver, 3.8"-----high excursion driver, 5.0"
18"-----normal driver, 4.5"-----high excursion driver, 6.0"
21"-----normal driver, 5.3"-----high excursion driver, 7.0"

This is found here, in the FAQ

If someone could elaborate and verify this info, I would find it interesting.

Hope this helps
post #120 of 199
Quote:
Originally Posted by gpmbc View Post

Gotcha! More on that note to come. I plan on picking up one of his signal shapers but he has been hard to get ahold of these days.

Lookin' good, my friend. That's a serious tower.

Your SEQSS is finished and sitting here. Best way to get me is ping me via e-mail:

bossobass.com@mac.com

Quote:
Originally Posted by chrapladm View Post

Sorry but did Dave mention the price on the signal shaper?

$375 was the initial offering. Dunno how long I'll honor that.

Quote:
Originally Posted by FOH View Post

Regarding the gap information between drivers, drivers and plates,..... I remember seeing this info at The Cult. I'm unsure how accurate, and equally unsure of the ill effects, however Collo's gap calculations call for this per driver;

gap = nominal diameter / 4 for most drivers
gap = nominal diameter / 3 for high excursion drivers



10"-----normal driver, 2.5"-----high excursion driver, 3.4"
12"-----normal driver, 3.0"-----high excursion driver, 4.0"
15"-----normal driver, 3.8"-----high excursion driver, 5.0"
18"-----normal driver, 4.5"-----high excursion driver, 6.0"
21"-----normal driver, 5.3"-----high excursion driver, 7.0"

This is found here, in the FAQ

If someone could elaborate and verify this info, I would find it interesting.

Hope this helps

That's a formula that bases the distance to the plate/floor on matching the area of the driver, probably at the middle of the surround.

It has no significance, IMO. You base the calculations on the displacement of the driver in its specific box/app. Mine is a secret.

When drivers are face-to-face... whole nuther ball game.

Bottom line is that there is a bit of loading and air spring distortion-induced asymmetrical throw correction magic in stacking. These are things I threw out there years back and none of it stuck, so I pursued it myself in the Black Ops Sub Shop.

I've been off the radar designing a couple of drivers, since none of the build houses here or in Asia seem interested in building a good HT driver for the DIY gang. First batch is in and tested. 2nd Gen are spec'd and being built as I type.

If they pan out as they probably will, I plan to offer an 18" version to the DIY folk and am seriously considering offering Blackbird and the new Raptor Systems at retail because they're that good.

It suddenly hit me while reading yet another "which is better, ported or sealed?" thread that there really hasn't been a G2G that compares the 2 alignments. The sealed commercial stuff mostly has HPF protection and both ported and sealed commercial stuff have serious limiting and a series of DC blocking caps in line that belie the errant claim; "Our sealed subs roll off 2nd order, no HPF...".

After searching every forum in every language, as far as I've seen, I have the only systems that provide documented reference level playback to 3-5 Hz on the planet. It's not because the driver is better. That's only a part of the equation.

If you look at the blind listening G2G (as I have intently done), you see the perfect example of the "ported vs sealed" fallacy. Looking at the LP FRs, you see that there is basically no distinction between the subs:



Compare them to a true (2nd order) sealed sub, has a curve for every room that's flat to 2 Hz, is juiced by an amp that's flat to 2 Hz and is scalable to the desired room/playback level:



That's the difference between a sealed system and any other alignment. There's not a ported sub available that will match it and there is a striking difference in presentation.

It's just that when folks compare commercially available subs, most of the sealed versions (JL Audio, Paradigm, Velo, Epik, etc.) have steep roll offs below EQ "tune" and so do ported subs, all "tune points" being around 15-20 Hz. They have the same basic bandwidth.

The evidence is in the subjective comments: "Most guessed wrong when it came to ported or sealed", "A good ported sub can sound as good as a good sealed sub", "They sounded very close", etc.

In the comparison shown in the SpecLab graphs, there was no mistaking one from the other, knowledge and experience notwithstanding.

Bosso
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