# Aurasound NS15 reference subwoofers, ported or sealed?



## thadman (Mar 1, 2006)

I'm compiling a reference system (sound quality, spl) involving the RAAL 140-15D ribbon tweeter, AE TD6.5M, and AE TD15M. They will need to be augmented by subwoofers on the bottom end to ease excursion demands on the midbass.

I purchased four Aurasound NS15s a while back and plan on taking advantage of their capabilities They will be used for Music, Video Games, and Movies...they will really have to assume the role of Jack of all trades.

Output goals:
bass: 130dB transient, 120dB continuous. I do not want to fear blowing these drivers.
full-range: 120dB transient, 110dB continuous

Crossover:
LPF 80hz
HPF 20hz

Room: Medium

Any recommendations? Remember this is a reference system and they will have to keep up all the way down to 20hz with a TD15M crossed at 80hz.


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## norcalsfinest (Aug 30, 2008)

thadman said:


> I'm compiling a reference system (sound quality, spl) involving the RAAL 140-15D ribbon tweeter, AE TD6.5M, and AE TD15M. They will need to be augmented by subwoofers on the bottom end to ease excursion demands on the midbass.
> 
> I purchased four Aurasound NS15s a while back and plan on taking advantage of their capabilities They will be used for Music, Video Games, and Movies...they will really have to assume the role of Jack of all trades.
> 
> ...



you don't play around. $2,800+ on subs? 

Based on the T/S parameters, I'd go ported. the recommended box of 4.5 cubic feet sounds about right to me. Hey, it's only 18 cubic feet


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## DS-21 (Apr 16, 2005)

Another Aura guy, excellent! I love my NS12-794-4A's.

I would go with four 120L sealed enclosures, for a Qtc right around 0.577. 

I think with such a setup you'll easily meet your output goals, especially if you seriously rethink your crossover scheme. There's no reason for a high-pass at all on the TD15M's. Just seal them and let them roll off naturally. If my comparatively little 12" Tannoy Dual Concentrics don't strain when thus used, I doubt the much better Lambda woofer would. (I wish Nick and John would do a coax based on the TD15. I'd be all over those like a Scottish cashmere sweater.) Likewise, I would up the lowpass on the NS15's to maybe 120Hz, and spread them around the room Geddes-style: one in a corner, one or two along the walls far away from the corner, one out a little bit, and one of the wall ones above the centerline of the room. And obviously, with that much cone area and sealed boxes, no need at all for a highpass on the subs.

How much power do you plan on putting into the subs? If you don't already have amps, I would think four Crown XTi2000's (one per driver) would be perfect. You'd also then be able to take advantage of their DSP to tailor the LF response exactly how you want it.


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## thadman (Mar 1, 2006)

DS-21 said:


> Another Aura guy, excellent! I love my NS12-794-4A's.
> 
> I would go with four 120L sealed enclosures, for a Qtc right around 0.577.
> 
> How much power do you plan on putting into the subs? If you don't already have amps, I would think four Crown XTi2000's (one per driver) would be perfect. You'd also then be able to take advantage of their DSP to tailor the LF response exactly how you want it.


I have two Crown XLS602Ds already available, 600 watts would be available per driver at 4ohms. I'm not sure if the drivers could thermally handle anything over 600 watts, so I'm a little hesitant to use anything much larger.

Integration could be determined experimentally. Since I'll be going active it's just a matter of moving the subwoofers around.


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## 60ndown (Feb 8, 2007)

V.B.A any way you do it.


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## thadman (Mar 1, 2006)

I've decided on experimenting with the Geddes model for LF. I'm familiar with the theory behind the Geddes model, use as many sources as possible to more evenly disperse the LF energy in a way that positively excites the modal resonances within the room. But not the details of the model, where to place the subwoofers (Harmon Kardon recommends placing one at the center of each wall)...the desired rolloff...the desired level of each driver...etc I've done research and haven't been able to find the answers to these questions. The thinking assumed for mid to high frequency drivers (placing drivers within 1/4WL to avoid power response aberrations related to phase, although not always achievable this would be optimal) does not necessarily apply to LF drivers as waves behave very differently in the modal region than they do higher in the spectrum where sound behaves closer to the ray model. Could anybody offer any insight into this?


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## thadman (Mar 1, 2006)

Some thoughts. placing subwoofers near the positions of the nodes of the axial modes (no excitement for that particular mode) would be easy to predict, but the tangential modes would be much more difficult and would require a very dense grid of subwoofers. The larger subwoofers designed for the lowest frequency would intuitively be placed at the positions of the lowest nodes and would gradually rolloff higher in frequency. The lower displacement drivers (ie visually less obtrusive) would be located at higher frequency nodes and would gradually rolloff below the point where the node functions.


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## DS-21 (Apr 16, 2005)

thadman said:


> I've decided on experimenting with the Geddes model for LF. I'm familiar with the theory behind the Geddes model, use as many sources as possible to more evenly disperse the LF energy in a way that positively excites the modal resonances within the room. But not the details of the model, where to place the subwoofers (Harmon Kardon recommends placing one at the center of each wall)...the desired rolloff...the desired level of each driver...etc


Markus's writeup is excellent: http://www.mehlau.net/audio/multisub_geddes/

Beyond that, in all honesty, I say basically put 'em where they fit and move 'em around if they don't measure well there. 

FWIW, in my setup as it currently stands (things might change a bit when I have some time to really tweak in mid-late December),
the Maelstrom-X is near the front-right corner;









one of the Aura NS12's is at the other end of that wall (which folds back into a hallway in my condo); and









the second NS12 is along the side of the couch, which if memory serves is something like 40" or 42" from the back wall, so kind of out in space. 









(ignore the ugly old couch; it will be out of the room soon enough)

In my current case, as you can see, none of the subs are above the room's centerline. But the mains all are and because they contribute so much to the upper bass (where the real problems are) it seems to work great in practice.

Dr. Geddes recommends staggered tunings. (He uses, and advocates the use of, 4th order bandpass subs.) In practice, putting identical subs in different places will "tune" them differently. As far as crossovers, that's something to determine experimentally in your room, with the caution to not be afraid of what some would consider excessively high crossover frequencies. I think Dr. Geddes' "broadband" (higher-tuned) subs go up to something like 150Hz. I think in my case the M-X has the mains bass up to 120Hz, the other sub on that side is set to something like 70Hz, and the one alongside the couch is set at 120Hz.

As far as level of each driver, that again is subject to experimentation. For me, I followed Geddes' approach basically, though my Velodyne SMS-1 made it a _much_ quicker process compared to taking measurements of sweeps on my MacBook. (I'm inclined to say that the time savings alone of the SMS-1's built-in measurement rig is worth $600). The important thing is to think of it as a _system_ rather than as discrete subs. Set the foundation (i.e. get the best possible blend between your mains and your corner sub) and then add pieces to it. I didn't even bother to measure the "broadband" subs separately besides a check to make sure they worked and that my port plugs (plates, really) weren't leaking, because all I care about is how they improved the smoothness of the bass around the room.
[EDIT]I also "cheated" a bit by running Audyssey MultEQ XT with just the Maelstrom-X to get the crossover region between that sub and the mains right, and then fiddled with the other two briefly until I got a not-perfect but pretty good response, running MultEQ XT a second time after I was happy with the general response trend to fix the levels.) I'm going to see later this month if I can do better starting from scratch, or think of more creative ways to employ the amazing Audyssey technology. Considering I only spent about an hour setting them up in the first place - which is why you haven't seen any graphs of my current system's bass FR, only that of my older system, with inferior parts but much more careful setup  - I would be shocked if some actual attention does not yield a worthwhile payout.[/EDIT]

Because the demands on the "broadband" subs are so comparatively less, in your case I would experiment with the one corner sub and three randomly-placed ones vs. two co-located NS15's and two randomly placed ones. My gut feeling is that you won't lose much if any smoothness of response with two of the NS15's in a corner and obviously you'll gain a whole lot more low-end headroom. Even thusly employed, that's still a much closer ratio of Vd in the corner sub vs. Vd in the "broadband" subs compared to what I'm doing. I'd still want you to try both approaches, though, if only so the rest of us can learn from your experience.

Did that help a bit?


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