Upgrading sub to get a live feel.

upgrade the Speaker brand.
 don't take that the wrong way  

Clio09,  

Enjoy the 911.  The 84-89 911s were special.  Personally, the 964s always have held my heart.  

Noble100,

It is obvious in your mind there is only one solution to a problem, yours.  Thank goodness people like James B. Lansing, Paul Klipsch, Henry Kloss, Paul Walker, Roy Allison, and Jim Winey didn't decide that the best speakers of their day were as good as could be.  

For virtually every issue in life and science, there are multiple solutions, each with its own trade offs.  Those that get so myopically focused as to believe there is only, or decide they already know it all, never learn and never develop further.   There is no best speaker design, dynamic drivers, horns, electrostatic, ribbon, or quasi ribbon, they all have trade offs.  

You can fool yourself that the only important thing with subwoofers is a smooth frequency response, regardless of output capability, transient response, room decay, phasing, and a plethora of other issues that we are still learning and defining in the setup of sound. 

You can also continue to believe that your 2.7s extend with any authority to 35 hz, they start to roll off in the 50hz range and will quickly slap the panels when trying to reproduce any type of deep bass.  If you would high pass the 2.7s they will sound less dark and sound cleaner after being relieved of trying to handle the deep bass.  Did I mention I owned a pair of 2.7s for more than a decade which were run both full range and with an active crossover?

Just for shits and giggles, I ran a quick MLSSA at my listening position in my main systems this morning.  There are two graphs, the one with bass flat to 20hz is my 3.5s with a single Rythmik 15, crossover set at 80hz between the two, and NO EQUALIZATION.  The second with the rolloff is the 3.5s running full range.  

https://photos.app.goo.gl/rDxsgpnU5xVsz1UWA

@mcreyn --

...

There is something magical that happens when you have that free dynamic headroom. Most home subs suffer from dynamic compression and distortion when turned up. It starts in the 90db range below 30hz for nearly all subs, until you start getting into the big boys. For example, even the Velodyne DD18+, considered a huge, accurate sub, cannot hit more than 110db at 30hz, 105 at 20hz. Same for a Rythmik F18.

When all you have ever heard are subs that are running into dynamic compression and distortion (which is the case with almost all home subs when pushed to even 100db), they sound great, until you hear a setup that doesn’t. When you hear the setup that doesn’t you experience this effortless, fast, tight, bass that seems to come from blackness. It also has a dramatic effect on the sound of the mains, making them sound much cleaner.

At the end of the day, it is not about hitting huge SPL levels, it is about getting the best sound, which requires using subs that can stay clean and not run into dynamic compression. 4 10" subs can’t do this in a reasonably sized room. It is why my progression of home subs has taken me from Velodyne F series, through ULD’s, to HGS, and finally Rythmik. At each step, it has seemed to be amazing (and better than anything I ever heard at a dealer), but the next step revealed more.

Finally, you can rag on those guys at the AVS forums, but unlike many, they spend a lot of time correlating objective data with subjective sound to get improvements.

Sweet music to my ears - well put indeed. While I would gladly recommend a 4-sub approach I’d differ on the oft-promoted stance here on using ~10" woofers for that purpose mostly (that’d be a typical selection of lower fs hifi drivers with a sensitivity no higher than 90dB’s, if that high), direct radiating units at that, and instead - to significantly gain headroom - throw in a bunch of bigger diameter pro-style units - preferably via tapped or front loaded horns or other partially or wholly hidden driver approach from the likes of some 6th order bandpass iterations.

Subs like that though are big, certainly with drivers of at least 15" diameter, so having a quad arrangement of those is a stretch in many if not most domestic environments. Therefore I’d strongly recommend going with a pair of subs, and I’d urge making it a pair instead of only one (i.e.: smoother coverage, and more headroom), although a single sub can be made to integrate very well from a rather narrow seating position, as has been already suggested.

The operative word posed by the OP seems to be that of a sought after "live feeling," and to get that and meet properly with the likely future acquisition of the JBL 4367 mains you have to get the midbass right as well, and for this I wouldn’t go too low in tune (no lower than some 20Hz, but OTOH no higher than 28-30Hz to still qualify as subs), have lots of effective air radiation area, and generally keep sensitivity fairly high (no lower than some 90-95dB’s). This naturally lends one a fair amount of headroom as well, which is an absolutely necessity here when smooth, clean, effortless bass reproduction is required.

Now this is just my preference, one that I actually live by with my choice of subs, and it largely dictates going with a DIY-approach (though I’m aware there are other, pre-assembled solutions to be had that could fulfill the same overall goal as well). A single 15"-loaded tapped horn I’m using, taking up 20 cubic feet per cabinet, will hit ~120dB’s at about 22Hz with approx. 200 watts, and I got a pair of them.. The specific B&C pro driver takes 1000 watts Nominal Power Handling (2-hour pink noise signal), so even pushed to ~600 watts where it reaches Xmech in this Tapped Horn (prior to thermal ditto), dynamic compression will be held at bay at have a pair of those TH’s reach honest 125dB’s over its entire usable bandwidth (20-100Hz) with zero issues, also being that the heavily ventilated driver motor is placed in free air in not inside a more or less closed box, so to be able to shed heat more freely. This bodes well for ample headroom of at least 20dB’s if 105dB’s is the typical upper ceiling for SPL.

And yes, my tapped horns derive from the Avsforum, more specifically a developer who goes by the user-name of "lilmike," and those guys over there are oftentimes rather hardcore with their approach, knowledge and actual sub-implementations.

From a slightly different angle. Depending on the condition and value of the car, with 911s you do not want to deviate so far as to not be able to return the car to stock. Use drivers that fit in the factory locations. Do not cut into or drill any metal. Otherwise have fun. Most 911 guys will tell you that you already have the best sound system going, 6 cylinders screaming away behind the rear axle:)

phusis,

Tapped horns are awesome, make mine a DTS-10.

I am not a big fan of 6th order enclosures, they lean towards a narrow frequency range and have to built perfectly to specification or it all falls apart. For high output with limited space, 6th order enclosures have a place. There is a reason the SPL car guys use them. I did build and use a 4th order bandbass for a car for several years, but that was when power was limited and it gave good output for the space.