Originally Posted by Bill Shenefelt
I am looking for some advice about how to best incorporate a JBL 18 inch subwoofer driver in an 8 cu ft ported sub with two SB 16 ultras to gain chest compressing punch. I have the two SVS 16 ultras in the front just behind my right and left front speakers(JBL 4343 homebuilts) outboard of my screen. The single JBL 18 inch subwoofer is roughly centered in the rear of the room between two homebuilt JBL L-300 speakers. The sub is ported with a box tune of 26 cps with about 4 dB boost at about 25 cps copied after the JBL 460 subwoofer built in the 1980's. I am tempted to run the 4 big JBLs full range to take advantage of the front and rearr 15 inch drivers and 27 cps box tunes just adding in the big 18 inch sub at the low end to help out.
My goal is to gain some of the "chest punch" at the 40 to 80 cps range from the JBL while the main SVS ultras provide the strong sub 30 cps frequency range. I have the JBL on a bridged Crown XTi 1002 amplifier does provide a bandpass function and some control of parametric eq and cone control below 25 cps.
Any recommendations on the best way to incorporate the JBL? I am just looking to add "punch" to the upper bass range. I have a Y connector sending the "subwoofer out" line level from my Anthem MRX 1120 to one front SVS sub and to the rear JBL sub. The second output (really the same as the first but a duplicate jack on the Anthem) feeds the second SVS. The room is about 27 ft long with seating (just a couch) about 15 ft from the front subs and projector screen and 8 ft from the front of the big JBL sub and two rear JBL surrounds behind the couch and against the rear wall. Front right and left as well as rear right and left speakers are ported and capable of pretty decent response well over 110 dB down slightly below 30 cps with their box tunes of 27 cps. Side surrounds are JBL 12 inch midbass drivers in 4 cu ft ported enclosures good just below 50 cps to about 40 cps. All 7 floor level speakers use the identical JBL midrange compression drivers for decent balance of voicing.
I do have a 6 foot archway beside the seating to a dining room and kitchen raising the total volume of the space to about 4800 cubic ft. Kind of tough to get a lot of compression with that volume without some very large ported drivers but maybe one 18 inch JBL could help. .
Is it best to just follow the Anthem room correction (ARC) with an 80 cps crossover to the subs? With a Radioshack sound level meter I reach in the area of 115 dB with significant floor shake movement at the seating area with loud bass events on blu ray. Just no "chest slap" pressurization.
I have a couple of preliminary thoughts and perhaps someone else can add some others. First, I would not run the front speakers as full-range. Without bass management, I don't believe you will be able to take full advantage of your subs. And, if your Anthem has a double-bass feature, where the front speakers and the subs play the same frequencies, that is likely to be a mess. What I might do, though, is to use the tone control to increase the bass in the front speakers with a 60Hz or 80Hz crossover. That will increase your mid-bass.
If I really wanted to get more chest punch, which is typically in the 50 to 100Hz range, I would probably buy a Behringer B1200D and place it nearfield behind my listening position. The closer the better. Ported subs generate much more tactile energy near their tuning points, and the 1200 has a tuning point of about 60Hz. That will be by far the best way to add chest punch to your system.
I am not very familiar with ARC, so I'm not sure whether you will do better to try to EQ everything together, or just EQ the SB16's; or the 16's and the JBL; and then add the 1200 in after the calibration. If you use a Y-Connector, ARC will never know that you added it and it won't interfere with your EQ. Both Audyssey and Dirac work that way. I would probably use one sub out for the two 16's in front, and the other sub out for the JBL and the Behringer in the rear. That will help with respect to setting distances. The Behringer is small enough that it can fit on top of the JBL if you do end up using all four subs.
Anytime you mix different subs (and especially different types of subs) like that, the results are unpredictable. So, no guarantees with respect to frequency response, but the 1200 will be a good way to get more chest punch, and it's relatively inexpensive. I hope this helps!