After reading numerous posts of people wanting info on the PRX718s, I thought I would post my opinions on this model.
Our church recently purchased one, along with a pair of QSC HPR122i's for our portable kit. These speakers replaced a pair of EV 15" two-way speakers that we had used for the last eleven to twelve years. The HPR's are phenomenal for the size, but that's a different review and everyone already knows what they can do.
The PRX718s is a recent model, and I won't bother repeating the specs that are reasily available. I will stick to my experience with this sub and will post my opinions.
We picked this sub up just over a month ago, just in time for a Youth fund-raiser event. The event was in our gym and the sub was placed on the floor next to the stage risers and about 15 feet away from the side wall and 20 feet away from the back wall. The event was set up so the stage was at one end of the gym and the audience faced it extending along the remainder of the gym floor area (length-wise). Due to time limitations, I barely had time to set up everything and make sure it would make noise before the event started. I didn't have time to tune it or adjust anything more than a rough balance between the sub and the tops.
The sub performed adequately, but I was far from impressed. While it did give a nice musical bottom end, it just didn't have that powerful sound that I was expecting and looking for. It was markedly better and more even sounding than the JRX118 that is in our youth room, but wasn't anywhere close to the performance of our JBL ASB6118's that we have flown in our main auditorium. I left the event wondering if I had made a bad purchase decision.
For the record, I used a TT24 running an AES signal into a DCX2496 which sent the sub an analog signal with an HPF filter of 24dB at 30Hz and an LPF of 24dB at 100Hz.
The second time I used the sub was for a week long church camp that we attended this last week. We set up on Sunday evening and ran it at various times through Friday morning. This venue was an open sided shed with the sub placed at the front of the stage under the right main speaker (HPR122i) and approximately 80' from the rear wall and the FOH position. The chapel/shed seats approximately 300-350. It has a concrete floor and aluminum roof over a steel support structure. We also had a full band this week.
This time, I had a little time to adjust on the crossover settings and EQ before we used it. I used the same system, but adjusted the crossover so the HPF was at 35Hz and the LPF was at 90Hz. I gave a slight bump to the 31-band graphic at 40Hz (maybe 2-3 dB).
This time, the sub performed as I had hoped it would. It gave very loud, clear, and even bass throughout the venue and even provided a mild "kick in the chest" even at 80 feet back at FOH. Never once did it sound "boomy" or "boxy" but always gave a nice smooth, tight sound.
The kick drum (Audix D6) sounded very loud and clear without breaking up, and the bass guitar resonated well and could be felt as well as heard. There were a few times when I did hear the sub start to break up, but that was when I was pushing it harder than it wanted to go. Backing the volume down restored the nice clean tight sound. I estimate that we were regularly running SPL in the mid 90's at FOH, though I didn't have an SPL meter to back that up. SPL in the front rows was easily over 100dB and likely near 110. The only times that I didn't have enough "rig for the gig" was when the crowd (a bunch of teenagers) was really, really noisy and I was trying to overcome their screaming.
Based on the performance of the PRX718s at the camp, I would have to say that it would easily perform on par with an SRX718 if not a little better; and would be pretty close to a VRX918sp.
One thing I did notice is the amp on the back gets hot...really hot. After pushing the sub for a while, you'll need to let it cool down before touching the amp. It could burn you. I am not exaggerating either. I touched it one day to see how hot it was and jerked my arm back out of reflex. I won't be doing that again. Regardless, the sub never shut down from overheating and I never saw the clip/limit light come on, even when pushing it really hard. The sub can take a pretty good beating and still come out sounding great.
Further, the sub is really light. Even though it supposedly weighs over 10 pounds more than our HPR122's, it feels lighter. It feels so light that it almost feels "delicate"...as if you don't want to abuse it too much for fear it might collapse. I'm sure that wouldn't happen, but I don't think it would stand up well to touring of any sort. The occasional transport for a portable church or a weekend musician would be fine, but I'd be looking for something more substantial for regular road use.
In summary, I am very pleased with this sub and I don't think that there is anything else that performs nearly as well in the same price range. Of course, these are my opinions and your mileage may vary.